U.S. patent application number 10/444031 was filed with the patent office on 2004-02-05 for polyhydroxyalkanoate production from polyols.
This patent application is currently assigned to Metabolix, Inc.. Invention is credited to Peoples, Oliver P., Skraly, Frank A..
Application Number | 20040023347 10/444031 |
Document ID | / |
Family ID | 22251426 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040023347 |
Kind Code |
A1 |
Skraly, Frank A. ; et
al. |
February 5, 2004 |
Polyhydroxyalkanoate production from polyols
Abstract
Organisms are provided which express enzymes such as glycerol
dehydratase, diol dehydratase, acyl-CoA transferase, acyl-CoA
synthetase .beta.-ketothiolase, acetoacetyl-CoA reductase, PHA
synthase, glycerol-3-phosphate dehydrogenase and
glycerol-3-phosphatase, which are useful for the production of
PHAs. In some cases one or more of these genes are native to the
host organism and the remainder are provided from transgenes. These
organisms produce poly (3-hydroxyalkanoate) homopolymers or
co-polymers incorporating 3-hydroxypropionate or 3-hydroxyvalerate
monomers wherein the 3-hydroxypropionate and 3-hydroxyvalreate
units are derived from the enzyme catalysed conversion of diols.
Suitable diols that can be used include 1,2-propanediol, 1,3
propanediol and glycerol. Biochemical pathways for obtaining the
glycerol from normal cellular metabolites are also described. The
PHA polymers are readily recovered and industrially useful as
polymers or as starting materials for a range of chemical
intermediates including 1,3-propanediol, 3-hydroxypropionaldehyde,
acrylics, malonic acid, esters and amines.
Inventors: |
Skraly, Frank A.;
(Somerville, MA) ; Peoples, Oliver P.; (Arlington,
MA) |
Correspondence
Address: |
PATREA L. PABST
HOLLAND & KNIGHT LLP
SUITE 2000, ONE ATLANTIC CENTER
1201 WEST PEACHTREE STREET, N.E.
ATLANTA
GA
30309-3400
US
|
Assignee: |
Metabolix, Inc.
|
Family ID: |
22251426 |
Appl. No.: |
10/444031 |
Filed: |
May 21, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10444031 |
May 21, 2003 |
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09944243 |
Aug 30, 2001 |
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6576450 |
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09944243 |
Aug 30, 2001 |
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09366920 |
Aug 4, 1999 |
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6329183 |
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60095329 |
Aug 4, 1998 |
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Current U.S.
Class: |
435/135 ;
435/189; 435/252.3; 435/419; 528/274; 800/288 |
Current CPC
Class: |
C12N 15/52 20130101;
C12P 7/42 20130101; C12P 7/625 20130101; C08G 8/04 20130101 |
Class at
Publication: |
435/135 ;
528/274; 435/252.3; 435/189; 435/419; 800/288 |
International
Class: |
C12P 007/62; C12N
009/02; C08G 063/82; A01H 001/00; C12N 015/82; C12N 005/04; C12N
001/21 |
Claims
We claim:
1. A method for producing polyhydroxyalkanoates comprising
providing genetically engineered organisms which express enzymes
selected from the group consisting of vicinal diol hydratase,
acyl-CoA transferase, acyl-CoA synthetase .beta.-ketothiolase,
acetoacetyl-CoA reductase, PHA synthase, glycerol-3-phosphate
dehydrogenase and glycerol-3-phosphatase, providing diols which can
be converted into 3-hydroxypropionate or 3-hydroxyvalerate monomers
by enzymes expressed by the organisms, and and culturing the
organisms under conditions wherein 3-hydroxypropionate or
3-hydroxyvalerate is converted to monomers which are polymerized to
form polyhydroxyalkanoates.
2. The method of claim 1 wherein the organisms are bacteria.
3. The method of claim 1 wherein the organisms are plants.
4. The method of claim 1 wherein the organisms are genetically
engineered with plasmids encoding one or more of the enzymes.
5. The method of claim 1 wherein the organisms are genetically
engineered to incorporate the genes encoding the enzymes into the
chromosome.
6. The method of claim 1 wherein the diols are selected from the
group ocnsisting of 1,2-propanediol, 1,3 propanediol and
glycerol.
7. The method of claim 1 wherein the dehydratases are selected from
the group consisting of glycerol dehydratase and diol
dehydratase.
8. The method of claim 1 wherein the diols which are converted to
monomers selected from the group consisting of 3-hydroxypropionate
or 3-hydroxyvalerate monomers.
9. The method of claim 1 further comprising providing genes
encoding an enzyme selected from the group consisting of aldehyde
dehydrogenase and 1,3-propanediol oxidoreductase.
10. A system for making polyhydroxyalkanoates comprising an
organism genetically engineered to express enzymes selected from
the group consisting of a vicinal diol dehydratase, acyl-CoA
transferase, acyl-CoA synthetase .beta.-ketothiolase,
acetoacetyl-CoA reductase, PHA synthase, glycerol-3-phosphate
dehydrogenase and glycerol-3-phosphatase, wherein the organism can
convert diols into 3-hydroxypropionate or 3-hydroxyvalerate
monomers which are polymerized to form polyhydroxyalkanoates.
11. The system of claim 10 wherein the organisms are bacteria.
12. The system of claim 10 wherein the organisms are plants.
13. The system of claim 10 wherein the organisms are genetically
engineered with plasmids encoding one or more of the enzymes.
14. The system of claim 10 wherein the organisms are genetically
engineered to incorporate the genes encoding the enzymes into the
chromosome.
15. The system of claim 10 further comprising coenzyme B-12.
16. The system of claim 10 wherein the vicinal diol dehydratase is
selected from the group consisting of glycerol dehydratase and diol
dehydratase.
17. The system of claim 10 further comprising genes encoding an
enzyme selected from the group consisting of aldehyde dehydrogenase
and 1,3-propanediol oxidoreductase.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Priority is claimed to U.S. provisional application Serial
No. 60/095,329 filed Aug. 4, 1998.
BACKGROUND OF THE INVENTION
[0002] This is generally in the field of production of
polyhydroxyalkanoates by genetic engineering of bacterial
enzymes.
[0003] Numerous microorganisms have the ability to accumulate
intracellular reserves of poly [(R)-3-hydroxyalkanoate] (PHA)
polymers. PHAs are biodegradable and biocompatible thermoplastic
materials with a broad range of industrial and biomedical
applications (Williams and Peoples, 1996, CHEMTECH 26: 38-44). PHAs
can be produced using a number of different fermentation process
and recovered using a range of extraction techniques (reviewed by
Braunegg et al. 1998, J. Biotechnol. 65: 127-161; Choi and Lee,
1999). Plant crops are also being genetically engineered to produce
these polymers offering a cost structure in line with the vegetable
oils and direct price competitiveness with petroleum-based polymers
(Williams and Peoples 1996, CHEMTECH 26:38-44; Poirier, Y. 1999,
Plant Biotechnology pp. 181-185). PHAs are formed by the action of
a PHA synthase enzyme. As the polymer chains grow, they form
insoluble granules. The PHAs can then be recovered and then
converted into chemicals or converted into chemicals during the
recovery process (Martin et al. PCT WO 97/15681). Therefore, in
addition to their utility as polymers, the PHAs represent a unique
mechanism for storing new chemistries in both microbial and plant
crop systems.
[0004] PHA copolymers containing 3-hydroxyvalerate (3HV),
especially PHBV, have been described extensively. Many wild type
microorganisms are capable of producing 3HV-containing PHAs. PHBV
has been produced commercially using Ralstonia eutropha (formerly
Alcaligenes eutrophus) from glucose and propionate and from glucose
and isobutyrate (U.S. Pat. No. 4,477,654 to Holmes et al.). A
number of other microorganisms and processes are known to those
skilled in the art (Braunegg et al. 1998, Journal of Biotechnology
65: 127-161). Poly(3HV) homopolymer has been produced using
Chromobacterium violaceum from valerate (Steinbuchel et al., 1993,
Appl. Microbiol. Biotechnol. 39:443-449). PHAs containing 3HV units
have also been synthesized using recombinant microorganisms.
Escherichia coli harboring the R. eutropha PHA biosynthesis genes
has been used to produce PHBV from glucose and either propionate or
valerate (Slater et al., 1992, Appl. Environ. Microbiol.
58:1089-1094) and from glucose and either valine o: threonine
(Eschenlauer et al., 1996, Int. J. Biol. Macromol. 19:121-130).
Klebsiella oxytoca harboring the R. eutropha PHA biosynthesis genes
has been used to produce PHBV from glucose and propionate (Zhang et
al., 1994, Appl. Environ. Microbiol. 60:1198-1205). R. eutropha
harboring the PHA synthase gene of Aeromonas caviae was used to
produce poly(3HV-co-3HB-co-3HHp) from alkanoic acids of odd carbon
numbers (Fukui et al., 1997, Biotechnol. Lett. 19:1093-1097).
[0005] PHA copolymers containing 3-hydroxypropionate units have
also been described. Holmes et al. (U.S. Pat. No. 4,477,654) used
R. eutropha to synthesize poly(3HP-co-3HB-co-3HV) from glucose and
either 3-chloropropionate or acrylate. Doi et al. (1990, in E. A.
Dawes (ed.), Novel Biodegradable Microbial Polymers, Kluwer
Academic Publishers, the Netherlands, pp. 37-48) used R. eutropha
tri synthesize poly(3HP-co-3HB) from 3-hydroxypropionate,
1,5-pentanediol, 1,7-heptanediol, or 1,9-nonanediol. Hiramitsu and
Doi (1993, Polymer 34:4782-4786) used Alcaligenes latus to
synthesize poly(3HP-co-3HB) from sucrose and 3-hydroxypropionate.
Shimamura et al. (1994, Macromolecules 27: 4429-4435) used A. latus
to synthesize poly(3HP-co-3HB) from 3-hydroxypropionate and either
3-hydroxybutyrate or sucrose. The highest level of
3-hydroxypropionate incorporated into these copolymers was 88 mol %
(Shimamura et al., 1994, ibid.). No recombinant 3HP containing PHA
producers have been described in the art.
[0006] It is economically desirable to be able to produce these
polymers in transgenic crop species. Methods for production of
plants have been described in U.S. Pat. No. 5,245,023 and U.S. Pat.
No. 5,250,430; U.S. Pat. No. 5,502,273; U.S. Pat. No. 5,534,432;
U.S. Pat, No. 5,602,321; U.S. Pat, No. 5,610,041; U.S. Pat, No.
5,650,555: U.S. Pat, No. 5,663,063; WO 9100917, WO 9219747, WO
9302187, WO 9302194 and WO 9412014, Poirier et. al., 1992, Science
256; 520-523, Williams and Peoples, 1996. Chemtech 26, 38-44. the
teachings of which are incorporated by reference herein). In order
to achieve this goal, it is necessary to transfer a gene, or genes
in the case of a PHA polymerase with more than one subunit,
encoding a PHA polymerase from a microorganism into plant cells and
obtain the appropriate level of production of the PHA polymerase
enzyme. In addition it may be necessary to provide additional PHA
biosynthetic genes, e.g. a ketoacyl-CoA thiolase, an
acetoacetyl-CoA reductase gene, a 4-hydroxybutyryl-CoA transferase
gene or other genes encoding enzymes required to synthesize the
substrates for the PHA polymerase enzymes. In many cases, it is
desirable to control the expression in different plant tissues or
organelles. Methods for controlling expression in plant tissues or
organelles are known to those skilled in the art (Gasser and
Fraley, 1989, Science 244; 1293-1299; Gene Transfer to Plants,
1995, Potrykus, I. and Spangenberg, G. eds. Springer-Verlag Berlin
Heidelberg N.Y. and "Transgenic Plants: A Production System for
Industrial and Pharmaceutical Proteins", 1996, Owen, M. R. L. and
Pen, J. Eds. John Wiley & Sons Ltd. England, incorporated
herein by reference).
[0007] Although methods for production of a variety of different
copolymers in bacterial fermentation systems are known, and
production of PHAs in plants has been achieved, the range of
copolymers possible in bacterial has not been achieved in plants.
It would be advantageous to be able to produce different copolymers
in transgenic plants, and to have more options with regard to the
substrates to be utilized by the transgenic plants.
[0008] It is therefore an object of the present invention to
provide methods and reagents for production of PHAs in plants.
[0009] It is a further object of the present invention to provide
methods and reagents for production of PHAs using simple sugars and
alcohols as substrates.
[0010] It is still another object of the present invention to
provide methods and reagents for production of copolymers other
than PHB and PHVB.
SUMMARY OF THE INVENTION
[0011] Organisms are provided which express enzymes such as
glycerol dehydratase, diol dehydratase, acyl-CoA transferase,
acyl-CoA synthetase B-ketothiolase, acetoacetyl-CoA reductase, PHA
synthase, glycerol-3-phosphate dehydrogenase and
glycerol-3-phosphatase, which are useful for the production of
PHAs. In some cases one or more of these genes are native to the
host organism and the remainder are provided from transgenes. These
organisms produce poly (3-hydroxyalkanoate) homopolymers or
copolymers incorporating 3-hydroxypropionate or 3-hydroxyvalerate
monomers wherein the 3-hydroxypropionate and 3-hydroxyvalreate
units are derived from the enzyme catalysed conversion of diols.
Suitable diol.; that can be used include 1,2-propanediol, 1,3
propanediol and glycerol. Biochemical pathways for obtaining the
glycerol from normal cellular metabolites are also described. The
PHA polymers are readily recovered and industrially useful as
polymers or as starting materials for a range of chemical
intermediates including 1,3-propanediol, 3-hydroxypropionaldehyde,
acrylics, malonic acid, esters and amines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a flow chart of the production of
3-hydroxyvaleryl-CoA from glycerol3-P.
[0013] FIG. 2 is a schematic of the plasmid construct pFS44C
encoding glycerol dehydratase (dhaB) and 4-hydroxybutyryl-CoA
transferase (hbcT).
[0014] FIG. 3 is a schematic of the plasmid construct pFS45
encoding dhaB, hbcT and phaC.
[0015] FIG. 4 is a schematic of the plasmid construct pFS47A,
encoding dhaT, dhaB, and hbcT.
[0016] FIG. 5 is a schematic of the plasmid construct pFS48B,
encoding dhaT, dhaB, hbcT, and phaC.
[0017] FIG. 6 is a schematic of the plasmid construct pMS 15,
encoding dhaT, DAR1-GPP2 (DAR1, dihydroxyacetone phosphate
dehydrogenase; and GPP2, sn-glycerol-3-phosphate phosphatase),
dhaB, hbcT, and phaC.
[0018] FIG. 7 is a schematic of the plasmid construct pFS51,
encoding GPP2 and DAR1.
DETAILED DESCRIPTION OF THE INVENTION
[0019] New metabolic pathways have been developed for the
production of PHAs containing 3-hydroxyvalerate units from
1,2-propanediol and of PHAs containing 3-hydroxypropionate units
from 1,3 propanediol or glycerol. In the case of glycerol, the
glycerol can either be fed to the microorganism or can be produced
from central metabolic intermediates. The key enzymes components of
these novel metabolic pathways leading to these monomers and their
polymerization are illustrated in FIG. 1. 1,2-propanediol and
glycerol are inexpensive substrates that are non toxic to many
microorganisms even at high concentrations. 1,3-propanediol can be
produced from renewable resources (Anton, D. "Biological production
of 1,3-propanediol", presented at United Engineering Foundation
Metabolic Engineering II conference, Elmau, Germany, Oct. 27,
1998). 1,2-propanediol is present in industrial waste streams from
production of propylene glycol. Glycerol can also be obtained from
metabolism in a number of microbes and plant crops. In many cases,
these are superior feedstocks for fermentation as compared to
organic acids, which generally become toxic at low concentrations
to many microorganisms. 3-Hydroxypropionic acid is not chemically
stable and therefore is not commercially available.
[0020] Organisms to be Engineered
[0021] In one embodiment, genes for the entire pathway illustrated
in FIG. 1 are introduced into the production organism. An organism
that does not naturally produce PHAs, such as Escherichia coli, may
be used. A number of recombinant E. coli PHB production systems
have been described (Madison and Huisman, 1999, Microbiology and
Molecular Biology Reviews, 63: 21-53). The genes encoding a vicinal
diol dehydratase, from an organism that naturally can convert
glycerol to 3-hydroxypropionaldehyde (Klebsiella pneumoniae, e.g.),
are introduced into this host. In the case of 1,2-propanediol, the
vicinal diol dehydratase converts the substrate to propionaldehyde,
which can be converted to propionyl-CoA by the endogenous
metabolism of the microorganism, optionally with the aid of an
exogenous acyl-CoA transferase or acyl-CoA synthetase. It may be
useful to mutagenize and select strains with increased resistance
to propionaldehyde. Propionyl-CoA can then be accepted by the
ketoacyl-CoA thiolase in a condensation with acetyl-CoA, thus
forming 3-hydroxyvaleryl-CoA. The ketoacyl-CoA thiolase will also
condense acetyl-CoA with acetyl-CoA, thus forming
3-hydroxybutyryl-CoA. Both 3-hydroxyvaleryl-CoA and
3-hydroxybutyryl-CoA can be accepted by various PHA synthases such
as the one expressed in the recombinant host, and therefore PHBV is
synthesized by the recombinant host.
[0022] The host described above can also be fed 1,3 propanediol or
glycerol either during growth or after a separate growth phase, and
a 3HP polymer is accumulated within the cells. E. coli does not
synthesize coenzyme B-12 de novo, and therefore coenzyme B-12 or a
precursor that E. coli can convert to coenzyme B-12, such as
vitamin B-12, must also be fed. In the case of glycerol, the
vicinal diol dehydratase converts the substrate to
3-hydroxypropionaldehyde, which can be converted to
3-hydroxypropionyl-CoA by the endogenous metabolism of the
microorganism, optionally with the aid of an exogenous acyl-CoA
transferase or acyl-CoA synthetase. 3-Hydroxypropionyl-CoA may then
be polymerized by PHA synthase to P3HP. Hydroxyacyl-CoA monomer
units in addition to 3HP may also be incorporated into the polymer.
If ketoacyl-CoA thiolase and reductase are expressed, for example,
then a copolymer of 3-hydroxybutyrate and 3-hydroxypropionate can
be formed.
[0023] In order to produce the 3HP polymers directly from
carbohydrate feedstocks, the E. coli is further engineered to
express glycerol-3-phosphate dehydrogenase and
glycerol-3-phosphatase. Such recombinant E. coli strains and
methods for their construction are known in the art (Anton, D.
"Biological production of 1,3-propanediol", presented at United
Engineering Foundation Metabolic Engineering II conference, Elmau,
Germany, Oct. 27, 1998; PCT WO 98/21339).
[0024] In another embodiment, a recombinant organism that naturally
contains a vicinal diol dehydratase can be used. One example of
such an organism is Klebsiella oxytoca, although several others
exist, as discussed above. In this embodiment no exogenous vicinal
diol dehydratase need be imported from another organism. However it
may be useful to mutagenise this organism and select mutants that
express the dehydratase during aerobic growth or it can be
genetically engineered to express the gene under aerobic
conditions. It is generally the case that organisms which contain
one or more coenzyme B-12-dependent vicinal diol dehydratases can
synthesize coenzyme B-12 de novo, and in those cases it is not
necessary to add coenzyme B-12 or closely related precursors
thereof to any part of the cultivation. In this case, a PHA
synthase or an entire PHB biosynthetic pathway and optionally an
exogenous acyl-CoA transferase or acyl-CoA synthetase is introduced
into this organism. Techniques for doing this are well known in the
art (for example, Dennis et al., 1998, Journal of Biotechnology 64:
177-186). In order to produce the 3HP polymers directly from
carbohydrate feedstocks, the strain is further engeneered to
express glycerol-3-phosphate dehydrogenase and
glycerol-3-phosphatase as described above.
[0025] In another embodiment, an organism that naturally produces
PHAs can be used. Examples of such organisms include Ralstonia
eutropha, Alcaligenes latus and Azotobacter but many others are
well-known to those skilled in the art (Braunegg et al. 1998,
Journal of Biotechnology 65: 127-161). The introduction of the diol
dehydratase is accomplished using standard techniques as described
by Peoples and Sinskey (1989, J. Biol. Chem. 164, 15298-15303). In
these cases it may be useful to mutate the organism and select for
increased resistance to 3-hydroxypropionaldehyde. PHA-producing
organisms vary in their ability to synthesize coenzyme B-12 de
novo, and therefore coenzyme B-12 or a precursor which the organism
can convert to coenzyme B-12 would be added as appropriate. PHBV is
then produced by feeding 1,2 propanediol and at least one other
feedstock. PHBP is produced by feeding 1,3 propanediol or glycerol
and one other feedstock, for example, glucose. In order to produce
the 3HP polymers directly from carbohydrate feedstocks, the strain
is further engineered to express glycerol-3-phosphate dehydrogenase
and glycerol-3-phosphatase as described above. It may be useful to
utilize mutations that are beneficial for the production of the
P3HP homopolymers in these organisms. Specific mutations include
inactivating the .beta.-ketothiolase and/or acetoacetyl-CoA
reductase genes. As these genes are generally well known and
available or isolatable, gene disruptions can be readily carried
out as described for example by Slater et. al., 1998 (J.
Bacteriol.) 180(8):1979-87.
[0026] The implementation of the production of
poly(3-hydroxypropionate) and its copolymers is also not limited to
bacteria as described in the examples. The same genes may be
introduced into eukaryotic cells, including but not restricted to,
yeast and plants, which, like bacteria, also produce glycolytic
intermediates such as dihydroxyacetone phosphate, from which
glycerol and ultimately poly(3-hydroxypropionate) may be
derived.
[0027] Genes for Utilization of Substrates
[0028] Genes and techniques for developing recombinant PHA
producers suitable for use as described herein are generally known
to those skilled in the art (Madison and Huisman, 1999,
Microbiology and Molecular Biology Reviews, 63: 21-53; PCT WO
99/14313, which are incorporated herein by reference). Because all
of the genes necessary to implement the production of
poly(3-hydroxypropionate) from central metabolic intermediates via
glycerol have been cloned and are available in genetically
manipulatable form, any combination of plasmid-borne and integrated
genes may be used, and the implementation of this pathway is
therefore not restricted to the schemes outlined herein. Many
different implementations will be apparent to those skilled in the
art.
[0029] Glycerol dehydratase (EC 4.2.1.30) and diol dehydratase (EC
4.2.1.28) are distinct coenzyme B-12-requiring enzymes found in
several species of bacteria. Often glycerol dehydratase is induced
during anaerobic growth on glycerol and diol dehydratase is induced
during anaerobic growth on either glycerol or 1,2-propanediol
(Forage and Foster, 1979, Biochim. Biophys. Acta 569:249-258).
These dehydratases catalyze the formation of
3-hydroxypropionaldehyde from glycerol and propionaldehyde from
1,2-propanediol. These aldehydes are usually converted to the
corresponding alcohols by a dehydrogenase. Organisms that contain
one or both dehydratases typically are able to convert glycerol to
3-hydroxypropionaldehyde or 1,3-propanediol. Bacterial species
noted for this ability include Klebsiella pneumoniae (Streekstra et
al., 1987, Arch. Microbiol. 147: 268-275), Klebsiella oxytoca
(Homann et al., 1990, Appl. Microbiol. Biotechnol. 33: 121-126),
Klebsiella planticola (Homann et al., 1990, ibid.) and Citrobacter
freundii (Boenigk et al., 1993, Appl. Microbiol. Biotechnol. 38:
453-457) although many other examples are generally known. Both
dehydratases are formed of three subunits, each of which is
homologous to its counterpart in the other enzyme.
[0030] The substrate range of the glycerol and diol dehydratases
(which will also be referred to generically from this point on as
"vicinal diol dehydratases") is not limited to glycerol and
1,2-propanediol. Bachovchin et al. (1977, Biochemistry
16:1082-1092), for example, demonstrated that the substrates
accepted by the K. pneumoniae enzyme include glycerol,
(R)-1,2-propanediol, (S)-1,2-propanediol, ethylene glycol,
thioglycerol, 3-chloro-1,2-propanediol, 1,2-butanediol,
2,3-butanediol, isobutylene glycol, and
3,3,3-trifluoro-1,2-propanediol. In all cases, the product of the
reaction is the aldehyde or ketone formed by the effective removal
of a water molecule from the substrate.
[0031] Organisms that naturally produce glycerol from sugars
through phosphoglycerate include Bacillus licheniformis (Neish et
al., 1945, Can. J. Res. 23B: 290-296), Lactobacillus sp. (Nelson
and Werkman, 1935, J. Bacteriol. 30: 547-557), Halobacterium
cutirubrum (Wassef et al., 1970, Can. J. Biochem. 48: 63-67),
Microcoleus chthonoplastes (Moezelaar et al., 1996, Appl. Environ.
Microbiol. 62: 1752-1758), Zymomonas mobilis (Viikari, 1988, CRC
Crit. Rev. Biotechnol. 7:237-261), Phycomyces blakesleeanus (Van
Schaftiger. and Van Laere, 1985, Eur. J. Biochem. 148: 399-405),
Saccharomyces cerevisiae (Tsuboi and Hudson, 1956, Arch. Biochem.
Biophys. 61: 197-210), Saccharomyces carlsbergensis (Tonino and
Steyn-Parve, 1963, Biochim. Biophys. Acta 67: 453-469), Rhizopus
javanicus (Lu et al., 1995, Appl. Biochem. Biotechnol. 51/52:
83-95), Candida magnoliae (Sahoo, D. K., 1991, Ph. D. Thesis,
Indian Institute of Technology, Delhi), Candida utilis (Gancedo et
al., 1968, Eur. J. Biochem. 5: 165-172), Aspergillus niger (Legisa
and Mattey, 1986, Enzyme Microb. Technol. 8: 607-609), Trichomonas
vaginalis (Steinbuchel and Muller, 1986, Molec. Biochem. Parasitol.
20: 45-55), Dunaliella salina (Sussman and Avron, 1981, Biochim.
Biophys. Acta 661: 199-204; Ben-Amotz et al., 1982, Experientia 38:
49-52), Asteromonas gracilis (Ben-Amotz et al., ibid.), Leishmania
mexicana (Cazzulo et al., 1988, FEMS Microbiol. Lett. 51: 187-192),
and Crithidia fasciculata (Cazzulo et al., ibid.). In many of these
organisms, glycerol is known to be derived from dihydroxyacetone
phosphate, an intermediate of the glycolytic pathway. Escherichia
coli does not normally synthesize glycerol in significant amounts
when grown on most sugars (Baldom and Aguilar, J. Bacteriol.
170:416, 1988). However, transgenic E. coli strains that can form
glycerol from common sugars such as glucose have been described,
for example, in PCT WO 97/20292.
[0032] Genetically engineered systems for the production of
glycerol from sugars (WO 98/21339), the production of
1,3-propanediol from glycerol (WO 96/35796, WO 98/21339) and the
production of 1,3-propanediol from sugars have been described. E.
coli expressing the DAR1 (dihydroxyacetone phosphate dehydrogenase)
and GPP2 (sn-glycerol-3-phosphate phosphatase) genes of
Saccharomyces cerevisiae were shown to accumulate high
concentrations of glycerol in the medium when grown on glucose
(Anton, D. "Biological production of 1,3-propanediol", presented at
United Engineering Foundation Metabolic Engineering II conference,
Elmau, Germany, Oct. 27, 1998).
[0033] Regulation of Expression
[0034] In any of the aforementioned embodiments, it is possible to
control the composition of the polymer produced by controlling the
expression of the vicinal diol dehydratase or by controlling the
availability of coenzyme B-12. The higher the dehydratase activity,
the more activated mc nomer will be derived as a result of its
activity, up to the point where another factor such as substrate
availability or an enzyme activity downstream of the dehydratase
becomes limiting. Methods for modulation of gene expression (and
thus enzyme activity) in various organisms are well-known to those
skilled in the art. An additional method for the control of vicinal
diol dehydratase activity is the modulation of the availability of
coenzyme B-12 to the microorganism. Many strains of Escherichia
coli, for example, are unable to synthesize coenzyme B-12 de novo,
and therefore recombinant vicinal diol dehydratase, which depends
upon coenzyme B-12 for activity, is not active in these strains
unless coenzyme B-12 or a suitable precursor such as vitamin B-12
is added to the medium. In Escherichia coli strains which harbor
PHA synthesis genes and a vicinal diol dehydratase, it has been
found that with no coenzyme B-12 addition, only PHB is synthesized
even though 1,2-propanediol is present in the medium. The addition
of 1 .mu.M coenzyme B-12 to a cultivation of the same strain in the
same medium leads to PHBV formation as discussed in the examples.
Skraly et al. (1998, Appl. Environ. Microbiol. 64:98-105) found
that transgenic Escherichia coli synthesized increasing levels of
1,3-propanediol from glycerol as increasing concentrations of
coenzyme B-12 were provided in the medium, up to a concentration of
about 20 nM, after which the 1,3-propanediol yield did not
increase. Therefore, coenzyme B-12 concentrations from 0 to 20 nM
can be used to control the PHBV composition in Escherichia coli
harboring PHA synthesis genes and a vicinal diol dehydratase gene
cultivated in a medium containing 1,2-propanediol. The same basic
premise is true for deriving poly(3-hydroxypropionate) from
glycerol. The cells are able to make a PHA (such as PHB) in the
presence of comonomer when no vicinal diol dehydratase is present.
The use of coenzyme B-12 to control polymer composition can be
accomplished with any microorganism that is unable to synthesize
coenzyme B-12 de novo. Such organisms include those that naturally
lack this ability (such as Escherichia coli) and those that
naturally possess this ability (such as Klebsiella pneumoniae) but
have been mutated by the use of chemical mutagenesis or by genetic
methods such as transposon mutagenesis to lose this ability.
[0035] In the case of some microorganisms, some of the genes can be
integrated into the host chromosome and others provided on a
plasmid. In some cases, compatible plasmid systems can be used, for
example, with several steps on the pathway encoded on one plasmid
and the other steps encoded by a second plasmid. A combination of
the two approaches may also be used.
[0036] Substrates
[0037] As discussed above, substrates that can be used to make PHAs
include glycerol and glucose. A number of other substrates, in
addition to glycerol or glucose, can be used successfully. Examples
of other substrates include starch, sucrose, lactose, fructose,
xylose, galactose, corn oil, soybean oil, tallow, tall oil, fatty
acids or combinations thereof.
[0038] The present invention will be further understood by
reference to the following non-limiting examples.
EXAMPLE 1
PHBV Production from Glucose and 1,2-propanediol
[0039] Escherichia coli strain MBX769 (Huisman et. al. PCT WO
99/14313), which expresses the PHA synthesis genes from Zoogloea
ramigera (acetoacetyl-CoA thiolase, acetoacetyl-CoA reductase, and
PHA synthase) containing plasmid pFS44C was used to synthesize PHBV
from glucose and 1,2-propanediol. Plasmid pFS44C (shown
schematically in FIG. 2) contains the genes encoding Klebsiella
pneumoniae glycerol dehydratase (dhaB), isolated from pTC53 (Skraly
et al., 1998, Appl. Environ. Microbiol. 64:98-105), and the
Clostridium kluyveri 4-hydroxybutyryl-CoA transferase (hbcT),
isolated from pCK3 (Sohling and Gottschalk, 1996, J. Bacteriol.
178:871-880), both in one operon under control of the trc promoter.
pFS44C also contains the lac repressor gene (lacI), an ampicillin
resistance gene (ampR), and an origin of replication (OR1), all
derived from the vector pSE380 (Invitrogen; La Jolla, Calif.).
[0040] The cells were precultured in 100 mL of a medium containing
25 g/L of LB broth powder (Difco; Detroit, Mich.) and 100 mg/L
ampicillin. They were removed from this medium by centrifugation
(2000.times.g, 10 minutes) and resuspended in 100 mL of a medium
containing, per liter: 5 g LB broth powder; 50 mmol potassium
phosphate, pH 7; 10 g 1,2-propanediol; 2 g glucose; 1 .mu.mol
coenzyme B-12; 100 .mu.g ampicillin; and 0.1 mmol
isopropyl-.beta.-D-thiogalactopyranoside (IPTG). The cells were
incubated in this medium with shaking at 225 rpm at 30.degree. C.
for 48 hours. They were then removed by centrifugation as above,
washed once with water, and lyophilized.
[0041] The same experiment was done in parallel, except that no
coenzyme B-12 was added. About 25 mg of lyophilized cell mass from
each flask was subjected to simultaneous extraction and butanolysis
at 110.degree. C. for 3 hours in 2 mL of a mixture containing (by
volume) 90% 1-butanol and 10% concentrated hydrochloric acid, with
2 mg/mL benzoic acid added as an internal standard. The
water-soluble components of the resulting mixture were removed by
extraction with 3 mL water. The organic phase (1 .mu.L at a split
ratio of 1:50 at an overall flow rate of 2 mL/min) was analyzed on
an SPB-1 fused silica capillary GC column (30 m; 0.32 mm ID; 0.25
.mu.m film; Supelco; Bellefonte, Pa.) with the following
temperature profile: 80.degree. C., 2 min; 10 C.degree. per min to
250.degree. C.; 250.degree. C., 2 min. The standard used to test
for the presence of 3-hydroxybutyrate and 3-hydroxyvalerate units
in the polymer was PHBV (Aldrich Chemical Co.; Milwaukee, Wis.).
The polymer in the experiment with coenzyme B-12 added accounted
for 60.9% of the dry cell weight, and it was composed of 97.4%
3-hydroxybutyrate units and 2.6% 3-hydroxyvalerate units.
[0042] The supernatant at the conclusion of this experiment was
found by high-performance liquid chromatographic (HPLC) analysis to
contain 0.41 g/L propanol, indicating that the glycerol dehydratase
was functional. The polymer in the experiment with no coenzyme B-12
added accounted for 56.7% of the dry cell weight, and it was PHB
homopolymer. The supernatant at the conclusion of this experiment
did not contain propanol. HPLC analysis was done with an Aminex
HPX-87H column with sulfuric acid (pH 2) as the mobile phase at a
flow rate of 0.6 mL/min and a column temperature of 50.degree. C.
Detection was by both refractive index and ultraviolet
absorption.
EXAMPLE 2
PHBV and Growth from 1,2-propanediol as Sole Carbon Source
[0043] MBX 184 was selected for growth on 1,2-PD, to yield E. coli
strain MBX 1327. MBXI327 was transduced with the PHB genes ABC5KAN
from MBXI 164 to yield E. coli strain MBX 1329. MBX1164 is
MBX247::ABC5KAN (encoding the thiolase, reductase and PHB synthase
from Z ramigera). MBX247 is LJ5218 (Spratt, et al. 1981 J.
Bacteriol. 146:1166-1169) E. coli genetic stock center CGSC 6966)
mutagenized with 1-methyl-3-nitro-1-nitrosoguanid- ine (NTG) by a
standard procedure (Miller, J., A short course in bacterial
genetics, 1992, Cold Spring Harbor Laboratory Press, Cold Spring
Harbor, N.Y.), and screened for the ability to grow with
1,2-propanediol as sole carbon source. Strains of E. coli with this
ability and methods for generation of such strains have been
described previously (Sridhara et al., 1969, J. Bacteriol. 93:87).
E. coli strain MBX1329 has both the capability to grow with
1,2-propanediol as the sole carbon source and to synthesize PHB
from carbon sources that generate acetyl-CoA.
[0044] MBX1329 harboring plasmid pFS44C (shown in FIG. 2) was grown
in a medium containing, per liter: 6.25 g LB broth powder; 3.5 g
sodium ammonium phosphate; 7.5 g dibasic potassium phosphate
trihydrate; 3.7 g monobasic potassium phosphate; 0.12 g magnesium
sulfate; 2.78 mg iron (II) sulfate heptahydrate; 1.98 mg manganese
(II) chloride tetrahydrate; 2.81 mg cobalt (II) sulfate
heptahydrate; 1.47 mg calcium chloride dihydrate; 0.17 mg copper
(11) chloride dihydrate; 0.29 mg zinc (11) chloride heptahydrate;
10 mg thiamine; 10 g 1,2-propanediol; 50 nmol coenzyme B-12; 100
.mu.g ampicillin; and 0.05 mmol
isopropyl-.beta.-D-thiogalactopyranoside (IPTG). The total volume
was 50 mL in a 250-mL Erlenmeyer flask; the inoculum was 0.5 mL of
an overnight culture in 25 g/L LB broth powder and 100 .mu.g/mL
ampicillin. The cells were incubated in this medium for 3 days at
37.degree. C. with shaking at 200 rpm. They were removed from this
medium by centrifugation (2000.times.g, 10 minutes), washed once
with water, centrifuged again, and lyophilized.
[0045] Intracellular polymer content was analyzed by butanolysis as
in Example 1. The cells grew to an optical density (at 600 nm) of
9.8 and contained PHBV to 6% of the dry cell weight. The polymer
itself was composed of 2.5% 3-hydroxyvalerate units and 97.5%
3-hydroxybutyrate units.
EXAMPLE 3
Poly(3-hydroxypropionate) from 1,3-propanediol and 1,3-propanediol
from Glycerol.
[0046] Escherichia coli strain MBX184, which is deficient in the
fadR gene and expresses the atoC gene constitutively, was used to
synthesize 1,3-propanediol from glycerol and
poly(3-hydroxypropionate) from 1,3-propanediol. In both instances
the cells harbored plasmid pFS45 (shown schematically in FIG. 3)
which contains genes encoding Klebsiella pneumoniae glycerol
dehydratase, Clostridium kluyveri 4-hydroxybutyryl-CoA transferase,
and Ralstonia eutropha PHA synthase, all in one operon under the
control of the trc promoter. The cells were cultivated as described
in Example 1, except that glycerol was present instead of
1,2-propanediol.
[0047] HPLC analysis showed that the cells in the coenzyme-B
12-containing medium synthesized 1.3 g/L of 1,3-propanediol while
the cells in the medium free of coenzyme B-12 did not synthesize
any 1,3-propanediol. The same strain was also cultivated using the
method of Example 1 except that 1,3-propanediol was present instead
of 1,2-propanediol, and no coenzyme B-12 was added.
[0048] Lyophilized cell mass was analyzed by GC as in Example 1,
with an additional standard of beta-propiolactone to quantify
poly(3-hydroxypropionate). These cells were shown by GC analysis to
contain poly(3-hydroxypropionate) homopolymer at 7.8% of the dry
cell weight. The synthesis of poly(3-hydroxypropionate) from
glycerol likely did not occur because of the accumulation of
3-hydroxypropionaldehyde, which is very toxic to many
microorganisms (Dobrogosz et al., 1989, Wenner-Gren Int. Symp. Ser.
52:283-292). This toxicity may be addressed by discouraging the
accumulation of 3-hydroxypropionaldehyde in at least two ways: 1) a
1,3-propanediol oxidoreductase from a 1,3-propanediol-producing
organism such as those mentioned above can also be expressed, and
2) the activity of the unidentified endogenous dehydrogenase from
Escherichia coli that is responsible for the observed formation of
1,3-propanediol when glycerol dehydratase is present can be
increased by screening for Escherichia coli cells expressing
glycerol dehydratase that grow well in the presence of both
glycerol and coenzyme B-12. The second approach can be
accomplished, for example, by transforming mutagenized Escherichia
coli with a plasmid such as pFS45, so that the mutagenesis does not
affect the glycerol dehydratase gene, followed by enrichment in a
medium containing glycerol and coenzyme B-12.
EXAMPLE 4
Poly(3-hydroxypropionate) from Glycerol
[0049] The two pathways in Example 3 (glycerol to 1,3-propanediol
and 1,3-propanediol to poly(3-hydroxypropionate) were activated in
the same recombinant Escherichia coli. E. coli strain MBX820, which
stably expresses the PHA biosynthetic genes phaA, phaB, and phaC
from Zoogloea romigera, was transformed with the plasmid pFS47A
(shown schematically in FIG. 4), which contains, under control of
the trc promoter, the genes encoding 4-hydroxybutyryl-CoA
transferase from Clostridium kluyveri and glycerol dehydratase and
1,3-propanediol oxidoreductase from Klebsiella pneumoniae. PFS47A
was constructed from the plasmid pFS16, a predecessor of pFS47A, as
follows: The Clostridium kluyveri orfZ gene was amplified by PCR
from plasmid pCK3 (Sohling and Gottschalk, 1996, J. Bacteriol. 178:
871-880) using the following oligonucleotide primers:
1 5'-TCCCCTAGGATTCAGGAGGTTTTTATGGAGTGGGAAGAGATATATAAAG-3'
(or.function.Z 5' AvrII) 5'-CCTTAAGTCGACAAATTCTAAAATCTCT-
TTTTAAATTC-3' (or.function.Z 3' SalI)
[0050] The orfZ PCR product was ligated to pTrcN, which had been
digested with XbaI (which is compatible with AvrII) and SalI.
[0051] The cells were precultured in 100 mL of a medium containing
25 g/L of LB broth powder (Difco; Detroit, Mich.) and 100 mg/L
ampicillin. They were removed from this medium by centrifugation
(2000.times.g, 10 minutes) and resuspended in 100 mL of a medium
containing, per liter: 2.5 g LB broth powder; 50 mmol potassium
phosphate, pH 7; 5 g substrate (glycerol; 1,2-propanediol; or
1,3-propanediol); 2 g glucose; 5 nmol coenzyme B-12; 100 .mu.g
ampicillin; and 0.1 mmol isopropyl-.beta.-D-thio- galactopyranoside
(IPTG). The cells were incubated in this medium with shaking at 225
rpm at 30.degree. C. for 48 hours. They were then removed by
centrifugation as above, washed once with water, and
lyophilized.
[0052] The lyophilized cell mass was analyzed by GC analysis as in
Example 1, with an additional standard of beta-propiolactone to
quantify poly(3-hydroxypropionate). The cells cultivated in
glycerol and 1,3-propanediol both contained a copolymer of
3-hydroxybutyrate and 3-hydroxypropionate units, and the cells
cultivated in 1,2-propanediol contained a copolymer of
3-hydroxybutyrate and 3-hydroxyvalerate units. Polymer compositions
and quantities as a percentage of dry cell weight are given in
Table 1. The glycerol-cultivated cells synthesized more polymer
than the 1,3-propanediol-cultivated cells, but the percentage of
3-hydroxypropionate units was smaller in the glycerol-cultivated
cells. These differences may be explained by the fact that
3-hydroxypropionaldehyde is toxic and that it is probably generated
more quickly by 1,3-propanediol oxidoreductase from 1,3-propanediol
than it is by glycerol dehydratase from glycerol. The toxicity of
3-hydroxypropionaldehyde can negatively impact cell health and
therefore overall polymer content, but its formation from glycerol
is necessary for 3-hydroxypropionyl-CoA formation whether the
necessary intermediate is 3-hydroxypropionaldehyde or
1,3-propanediol.
2TABLE 1 Polymers produced by MBX820/pFS47A cultivated in various
substrates. Total polymer 3HB units 3HP units 3HV units Substrate
(% of dcw.sup.a) (% of polymer) (% of polymer) (% of polymer)
glycerol 55.8 98.2 1.8 0.0 1,2-propanediol 41.3 97.1 0.0 2.9
1,3-propanediol 26.7 95.1 4.9 0.0 .sup.apercent of dry cell
weight.
EXAMPLE 5
Control of Polymer Composition by Variation of Coenzyme B-12
Concentration.
[0053] Because the vicinal diol dehydratases depend upon coenzyme
B-12 for activity, and because the formation of
3-hydroxypropionyl-CoA from glycerol or of propionyl-CoA from
1,2-propanediol depends upon dehydratase activity, the composition
of the copolymer in either case can be controlled by variation of
the availability of coenzyme B-12 to the dehydratase. In this
example, this was accomplished by variation of coenzyme B-12
concentration added to the medium in which E. coli strain MBX820
carrying the plasmid pFS47A was producing PHA.
[0054] The cells were precultured in 100 mL of a medium containing
25 g/L of LB broth powder (Difco; Detroit, Mich.) and 100 mg/L
ampicillin. They were removed from this medium by centrifugation
(2000.times.g, 10 minutes) and resuspended in 100 mL of a medium
containing, per liter: 2.5 g LB broth powder; 50 mmol potassium
phosphate, pH 7; 10 g substrate (glycerol or 1,2-propanediol); 2 g
glucose; 100 .mu.g ampicillin; 0.1 mmol
isopropyl-.beta.-D-thiogalactopyranoside (IPTG); and 0, 5, 20, or
50-nmol coenzyme B-12. The cells were incubated in this medium with
shaking at 225 rpm at 30.degree. C. for 72 hours. They were then
removed by centrifugation as above, washed once with water, and
lyophilized. The lyophilized cell mass was analyzed by GC analysis
as in Example 4.
[0055] Table 2 shows the amounts and compositions of the PHAs
produced in this way. The absence of coenzyme B-12, whether the
substrate was glycerol or 1,2-propanediol, resulted in synthesis of
only PHB. Glycerol was more conducive to PHA formation in the
absence of dehydratase activity, as shown by the final optical
density and polymer content, presumably because E. coli can utilize
glycerol as a carbon and energy source under aerobic conditions
(Lin, Ann. Rev. Microbiol. 30:535, 1976), while generally this is
not true of 1,2-propanediol (Baldom and Aguilar, ibid.). When
coenzyme B-12 is added in increasing amounts to cells cultivated
with glycerol, the percentage of 3-hydroxypropionate units in the
polymer increases, while the overall polymer content decreases.
This decrease is probably due to the toxicity of
3-hydroxypropionaldehyde, which results in decreased health of the
cells. When coenzyme B-12 is added in increasing amounts to cells
cultivated with 1,2-propanediol, 3-hydroxyvalerate units are
incorporated into the polymer, but the percentage of
3-hydroxyvalerate in the polymer does not increase to the same
extent as the percentage of 3-hydroxypropionate units did in the
glycerol experiment. This indicates that the concentration of
coenzyme B-12 is not limiting to 3-hydroxyvaleryl-CoA synthesis
when its concentration reaches even a few nanomolar, and that some
other factor becomes limiting.
[0056] This example demonstrates that the composition of PHAs
derived from the use of coenzyme B-12-dependent dehydratases can be
controlled by varying the concentration of coenzyme B-12 made
available to the dehydratase. The extent to which the control can
be executed is dependent on the diol substrate used. This can be
due to the preference of the vicinal diol for certain substrates
over others and on the rest of the host metabolism leading from the
aldehyde derived from the diol to the acyl-CoA which serves as the
activated monomer for PHA formation.
3TABLE 2 Composition of polymers produced by MBX820/pFS47A from
glycerol and 1,2-propanediol in media with various coenzyme B-12
concentrations. [CoB12] OD.sup.a 3HB.sup.b, 3HV.sup.c, 3HP.sup.d,
polymer, Substrate nM (600 nm) % of PHA % of PHA % of PHA % of
dcw.sup.e glycerol 0 19.3 100 0 0 65.4 5 17.7 81.4 0 18.6 56.6 20
10.0 79.6 0 20.4 45.9 50 3.9 54.4 0 45.6 12.0 1,2-propanediol 0 4.4
100 0 0 34.1 5 4.8 98.6 1.4 0 32.4 20 3.9 97.6 2.4 0 19.5 50 4.2
98.5 1.5 0 21.2 .sup.aoptical density .sup.b3-hydroxybutyrate units
.sup.c3-hydroxyvalerate units .sup.d3-hydroxypropionate units
.sup.epercent of dry cell weight
EXAMPLE 6
Production of Poly(3-hydroxypropionate) from Central Matabolic
Intermediates.
[0057] Examples 1-5 demonstrate that it is possible to obtain
poly(3-hydroxypropionate) from glycerol, and as discussed above, it
is possible in both transgenic and nontransgenic organisms to
produce glycerol from central metabolic intermediates. Therefore, a
combination of the two pathways will allow the synthesis of
poly(3-hydroxypropionate) from central metabolic intermediates.
These pathways can be combined either by introducing the
poly(3-hydroxypropionate synthesis genes into a glycerol-producing
host or by introducing glycerol synthesis genes into a host already
capable of poly(3-hydroxypropionate) synthesis from glycerol, such
as described in the above examples.
[0058] In the former case, genes encoding a vicinal diol
dehydratase, a PHA synthase, and optionally an aldehyde
dehydrogenase, 1,3-propanediol oxidoreductase, and hydroxyacyl-CoA
transferase are expressed in a host capable of producing glycerol
from central metabolic intermediates. An example of such a host is
an Escherichia coli that expresses the Saccharomyces cerevisiae
DAR1 (dihydroxyacetone phosphate dehydrogenase) and GPP2
(sn-glycerol-3-phosphate phosphatase) genes (Anton, D. "Biological
production of 1,3-propanediol", presented at United Engineering
Foundation Metabolic Engineering II conference, Elmau, Germany,
Oct. 27, 1998; PCT WO 98/21339), as described above. Many strains
of E. coli naturally express 1,3-propanediol oxidoreductase and
aldehyde dehydrogenase enzymatic activities, but their levels may
optionally be augmented by mutagenesis or purposeful overexpression
of enzymes that carry out these functions. The additional genes
necessary can be introduced on a plasmid such as pFS48B, which
contains, under the control of the trc promoter,
4-hydroxybutyryl-CoA transferase from Clostridium kluyveri; PHA
synthase from Zoogloea ramigera and glycerol dehydratase and
1,3-propanediol oxidoreductase from Klebsiella pneumoniae. Any or
all of these genes may also be introduced by integration into the
chromosome using standard techniques well-known to those skilled in
the art.
[0059] Similarly, the DAR1 and GPP2 genes can be introduced into a
host already capable of poly(3-hydroxypropionate) synthesis, such
as MBX820/pFS47A, described above. The DAR1 and GPP2 genes may be
introduced on a plasmid compatible with pFS47A (a plasmid that can
be maintained simultaneously with pFS47A), or they may be
integrated into the chromosome. MBX820 stably expresses
acetoacetyl-CoA thiolase, 3-hydroxybutyryl-CoA reductase, and PHA
synthase, and therefore it is capable of synthesizing
poly(3-hydroxybutyrate-co-3-hydroxypropionate). If the homopolymer
poly(3-hydroxypropionate) is desired, a strain expressing only PHA
synthase rather than all three PHB biosynthetic genes may be
used.
[0060] In order to demonstrate the pathway for the biosynthesis of
PHP form glucose, plasmid pMS 15 (shown schematically in FIG. 6)
was constructed to express the following genes as an operon from
the trc promoter: PHB synthase from A eutrophus, the
4-hydroxybutyryl-CoA transferase from C. kluyveri, the glycerol
dehydratase from Klebsiella, the DAR1 gene from S. cerevisae, the
GPP2 gene from S. cerevisae and the 1,3-propanediol oxidoreductase
from K. pneumoniae.
[0061] The plasmid pFS51 was constructed by ligating DAR1 and GPP2
PCR products one at a time to pTrcN. The DAR1 gene was amplified by
PCR from S. cerevisiae genomic DNA using the following
oligonucleotide primers:
4 The DAR1 gene was amplified by PCR from S. cerevisae genomic DNA
using the following oligonucleotide primers:
5'-CTTCCGGATCCATTCAGGAGGTTTTTATGTCTGCTGCTGCTGATAGA-3' (S. cer. DAR1
5' BamHI) 5'-CTTCCGCGGCCGCCTAATCTTCATGTAGATCTAATTC-3' (S. cer. DAR1
3' NotI) The GPP2 gene was amplified in the same way using the
following oligonucleotide primers:
5'-CTTCCGCGGCCGCATTCAGGAGGTTTTTATGGGATTGACTACTAAACCTC-3' (S. cer.
GPP2 5' NotI) 5'-CCTTCTCGAGTTACCATTTCAACAGATCGTCC-3' (S. cer. GPP2
3' XhoI)
[0062] PCR for each gene was carried out with Pfu DNA polymerase
(Stratagene; La Jolla, Calif.) in a reaction volume of 50 .mu.L,
which contained: 10 units Pfu polymerase, 1.times. reaction buffer
provided by the manufacturer, 50 pmol of each primer, about 200 ng
S. cerevisiae genomic DNA, and 200 .mu.M of each dNTP. The thermal
profile of the reactions was as follows: 27 cycles of (94.degree.
C., 1 min; 55.degree. C., 2 min; 72.degree. C., 3 min), then 7 min
at 72.degree. C. The Pfu polymerase was not added until the
reaction mixture had reached 94.degree. C.
[0063] The PCR products were purified from a 1% low-melt agarose
gel and digested with the restriction enzymes whose corresponding
sites had been included at the 5' ends of the primers (BamHI and
NotI for DAR1, NotI and XhoI, for GPP2). The vector pTrcN is a
version of pTrc99a (Pharmacia; Uppsala, Sweden) modified such that
it lacks an NcoI site. pTrcN was cut with BamHI, NotI, and calf
intestinal alkaline phosphatase (CIAP; Promega; Madison, Wis.) for
insertion of DAR1 and with NctI, XhoI, and CIAP for insertion of
GPP2. The ligations were carried out with T4 DNA ligase (New
England Biolabs; Beverly, Mass.) according to the instructions
provided by the manufacturer. The products of the ligations were
pFS49 (DAR1) and pFS50 (GPP2). To assemble both genes on one
plasmid, pFS49 was cut with Mul and NotI, and the 2.3-kb fragment
containing the trc promoter and DAR1 was ligated to pFS50 that had
been digested with the same two enzymes and CIAP. The resulting
plasmid, which contained the operon DAR1-GPP2 under control of the
trc promoter, was denoted pFS51.
[0064] E. coli strain MBX 184 containing the plasmid pMS 15 (shown
schematically in FIG. 6) was grown overnight in a 200-mL square
bottle at 37.degree. C. in 50 mL of LB medium which also contained
100 .mu.g/mL ampicillin. The cells were removed from this culture
by centrifugation for 10 minutes at 2000.times.g, and the cells
were resuspended in 50 mL of a glucose medium and incubated for 72
hours at 30.degree. C. with shaking at 200 rpm. The glucose medium
contained, per liter: 6.25 g LB powder; 100 .mu.g ampicillin; 20 g
glucose; 50 mmol potassium phosphate, pH 7; 10 .mu.mol
isopropyl-.beta.-D-thiogalactopyranoside (IPTG); and 0, 10, or 100
nmol coenzyme B-12. After the incubation, the cells were removed
from the medium by centrifugation for 10 minutes at 2000.times.g,
washed once with water and centrifuged again, then lyophilized. Gas
chromatographic (GC) analysis of the lyophilized cell mass showed
that, in the experiment with 10 nM coenzyme B-12, poly(3HP) made up
0.11% of the dry cell weight; in the experiment with 100 nM
coenzyme B-12, poly(3HP) made up 0.13% of the dry cell weight; and
in the experiment with no coenzyme B-12, poly(3HP) was not
detected. No polymer constituents other than 3HP were found in any
case. GC analysis was conducted as follows: 15 to 20 mg of
lyophilized cell mass was subjected to simultaneous extraction and
propanolysis at 100.degree. C. for 3 hours in 2 mL of a mixture
containing (by volume) 50% 1,2-dichloroethane, 40% 1-propanol, and
10% concentrated hydrochloric acid, with 2 mg/mL benzoic acid added
as an internal standard. The water-soluble components of the
resulting mixture were removed by extraction with 3 mL water. The
organic phase (1 .mu.L at a split ratio of 1:50 at an overall flow
rate of 2 mL/min) was analyzed on an SPB-1 fused silica capillary
GC column (30 m; 0.32 mm ID; 0.25 .mu.m film; Supelco; Bellefonte,
Pa.) with the following temperature profile: 80.degree. C. for 2
min; 10 C..degree. per min to 250.degree. C.; 250.degree. C. for 2
min. The standard used to test for the presence of 3HP residues was
.beta.-propiolactone. Both poly(3HP) and .beta.-propiolactone yield
the 1-propyl ester of 3-hydroxypropionate when subjected to
propanolysis.
EXAMPLE 7
[0065] PHBV from Central Metabolic Intermediates
[0066] As demonstrated above, it is possible to obtain PHBV from
1,2-propanediol with the optional addition of other carbon sources
such as glucose, and it is possible in both transgenic and
nontransgenic organisms to produce 1,2-propanediol from central
metabolic intermediates (Cameron et. al., 1998, Biotechnol. Prog.
14 116-125). Therefore, a combination of the two pathways will
allow the synthesis of PHBV from central metabolic intermediates.
These pathways can be combined either by introducing the PHBV
synthesis genes into a 1,2-propanediol-producing host or by
introducing 1,2-propanediol synthesis genes into a host already
capable of PHBV synthesis from 1,2-propanediol, such as described
in the above examples.
[0067] In the former case, genes encoding a vicinal diol
dehydratase, a PHA synthase, a 3-ketoacyl-CoA thiolase and
reductase, and optionally an aldehyde dehydrogenase, 1-propanol
oxidoreductase, and hydroxyacyl-CoA transferase are expressed in a
host capable of producing 1,2-propanediol from central metabolic
intermediates. An example of such a host is an Escherichia coli
that expresses rat lens aldose reductase or overexpresses E. coli
glycerol dehydrogenase, as described above. Many strains of E. coli
naturally express 1-propanol oxidoreductase, aldehyde
dehydrogenase, and propionyl-CoA transferase enzymatic activities,
but their levels may optionally be augmented by mutagenesis or
purposeful overexpression of enzymes that carry out these
functions. The additional genes necessary can be introduced as
plasmid-borne genes or may be integrated into the chromosome, or a
combination of the two approaches may be used. For example, a
plasmid such as pFS48B, which contains, under the control of the
trc promoter, 4-hydroxybutyryl-CoA transferase from Clostridium
kluyveri; PHA synthase from Zoogloea ramigera and glycerol
dehydratase and 11,3-propanediol oxidoreductase from Klebsiella
pneumoniae, may be used in combination with integration of the PHB
synthesis genes into the chromosome using standard techniques
well-known to those skilled in the art.
[0068] Similarly, the rat lens aldose reductase or E. coli glycerol
dehydrogenase genes can be introduced into a host already capable
of PIIBV synthesis, such as MBX769/pFS44C, described above. An
additional improvement may result from the overexpression of a
methylglyoxal synthase gene, as suggested by Cameron et al., 1998
(Biotechnol. Prog. 14 116-125). The rat lens aldose reductase or E.
coli glycerol dehydrogenase gene may be introduced on a plasmid
compatible with pFS44C (a plasmid that can be maintained
simultaneously with pFS44C), or they may be integrated into the
chromosome.
EXAMPLE 8
Identification of 3-bydroxypropionaldehyde Dehydrogenase
Activity.
[0069] The aldH gene sequence from E. coli is available from
GENBANK. This gene was cloned into the Acc65I and NotI sites of the
cloning vector pSE380 following PCR amplification using the
approach described in Example 6 and the following primers:
5 ald-Acc65I 5'-ggtggtaccttaagaggaggtttttatgaattttcatcacctg- gctt
ald-NotI 5'-ggtgcggccgctcaggcctccaggcttatcca
[0070] The resulting recombinant plasmid pALDH was intoduced into
E. coli DH5 alpha and grown in 5 ml LB medium with 100 .mu.g/ml
ampicillin 37.degree. C. The next day a 100 ml containing 100
.mu.g/ml ampicillin was innoculated with 100 .mu.l of the overnight
culture and grown until the absorbance at 600 nm reached 0.5 at
which time the trc promoter was induced with 1 mM IPTG and
incubated a further 3 hours at 37.degree. C. The cells were
harvested, washed and resuspended in 0.1M Tris.HCl pH 8.0 and lysed
by sonication. The cell lysate was assayed for aldehyde
dehydrogenase activity using 3-hydroxypropionaldehyde with both NAD
and NADP as cofactor. Assays were performed using an Hewlett
Packard diode array spectrophotometer. Enzyme reactions were
carried out in 1.5 ml UV cuvettes in a solution containing the
following: 0.1 M Tris .Hcl, pH 8.0, 1 mM NAD or NADP, 6 mM
dithiothreitol and crude cell extract to a final volume of 1 ml.
The mixture was incubated for 20 seconds before initiating the
reaction by adding 1 mM 3-hydroxypropionaldehyde and monitoring the
reaction at 340 nm. The lysate showed significant
3-hydroxypropionaldehyde dehydrogenase activity when NAD was the
cofactor (1.35 .mu.moles/min/mg protein) which was not present in
the control sample prepared using the vector alone. Therefore the
aldH gene can be used to increase the 3-hydroxyproionaldehyde
dehydrogenase activity in the strains described in the previous
examples.
[0071] Modifications and variations of the methods and materials
described herein will be obvious to those skilled in the art and
are intended to come within the scope of the following claims:
Sequence CWU 1
1
8 1 49 DNA Artificial Sequence Description of Artificial Sequence
Oligonucleotide primer 1 tcccctagga ttcaggaggt ttttatggag
tgggaagaga tatataaag 49 2 38 DNA Artificial Sequence Description of
Artificial Sequence Oligonucleotide primer 2 ccttaagtcg acaaattcta
aaatctcttt ttaaattc 38 3 47 DNA Artificial Sequence Description of
Artificial Sequence Oligonucleotide primer 3 cttccggatc cattcaggag
gtttttatgt ctgctgctgc tgataga 47 4 37 DNA Artificial Sequence
Description of Artificial Sequence Oligonucleotide primer 4
cttccgcggc cgcctaatct tcatgtagat ctaattc 37 5 50 DNA Artificial
Sequence Description of Artificial Sequence Oligonucleotide primer
5 cttccgcggc cgcattcagg aggtttttat gggattgact actaaacctc 50 6 32
DNA Artificial Sequence Description of Artificial Sequence
Oligonucleotide primer 6 ccttctcgag ttaccatttc aacagatcgt cc 32 7
47 DNA Artificial Sequence Description of Artificial Sequence
Oligonucleotide primer 7 ggtggtacct taagaggagg tttttatgaa
ttttcatcac ctggctt 47 8 32 DNA Artificial Sequence Description of
Artificial Sequence Oligonucleotide primer 8 ggtgcggccg ctcaggcctc
caggcttatc ca 32
* * * * *