1. Field of the Invention
The present invention relates to a polyhydroxyalkanoate containing a novel unit and a producing method therefor utilizing microorganisms.
2. Related Background Art
“Biodegradable Plastics Handbook”, edited by Biodegradable Plastics Association, N.T.S.Co., p 178–197 (1995) reports that various microorganisms produce poly-3-hydroxybutyric acid (PHB) or other polyhydroxyalkanoates (PHA) and accumulate such products therein. Such microorganism-produced polymers, for example PHA, can be utilized for producing various products, for example, by fusion, like the conventional plastics. Also, the microorganism-produced polymer, such as PHA, is biodegradable, and has an advantage in that it can be completely decomposed by the microorganisms. Therefore, polyhydroxyalkanoate produced by the microorganisms, when discarded, unlike the various conventional synthesized polymers, does not contaminate the environment. The polyhydroxyalkanoate produced by the microorganisms generally shows satisfactory compatibility with living tissues and is expected to be useful for medical applications as a soft material.
Such microorganism-produced PHA is known to assume various compositions or structures depending on the kind of microorganism, composition of the culture medium and culturing conditions employed for production. Various researches have been conducted to control such composition and structure, principally for improving the physical properties of PHA.
In one type of such researches, a microorganism production of a polyhydroxyalkanoate having an aromatic ring in the unit has been actively investigated in recent years.
(a) PHA containing phenyl group or a partially substituted group thereof:
Makromol. Chem. 191, 1957–1965 (1990) and Macromolecules, 24, 5256–5260 (1991) report that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-phenylvaleric acid as a unit, from 5-phenylvaleric acid as substrate.
Also Macromolecules, 29, 1762–1766 (1996) reports that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-(p-tolyl)valeric acid as a unit, from 5-(p-tolyl)valeric acid as substrate.
Also Macromolecules, 32, 2889–2895 (1999) reports that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-(2,4-dinitrophenyl)valeric acid and 3-hydroxy-5-(p-nitrophenyl)valeric acid as units, from 5-(2,4-dinitrophenyl)valeric acid as substrate.
(b) PHA containing phenoxy group or partially substituted group thereof:
Macromol. Chem. Phys., 195, 1665–1672 (1994) reports that Pseudomonas oleovorans produces a polyhydroxyalkanoate copolymer containing 3-hydroxy-5-hydroxyvaleric acid and 3-hydroxy-9-phenoxynonaic acid as the units, from 11-phenoxyundecanoic acid as substrate.
Also, Japanese Patent No. 2989175 discloses inventions relating to a homopolymer formed by a 3-hydroxy-5-(monofluorophenoxy)pentanoate (3H5(MFP)P) unit or a 3-hydroxy-5-(difluorophenoxy)pentanoate (3H5(DFP)P) unit; a copolymer containing at least a 3H5(MFP)P unit or a 3H5(DFP)P unit; a novel strain of Pseudomonas putida capable of producing these polymers; and a method for producing the aforementioned polymers utilizing the Pseudomonas genus. This patent specification teaches, as the effects of such inventions, that PHA polymer having a phenoxy group substituted with 1 or 2 fluorine atoms at the end of the side chain can be biosynthesized from a long-chain fatty acid having a substituent and that such a polymer has a high melting point and is capable of providing stereoregularity and water repellency while maintaining satisfactory working properties.
In addition to the fluorine-substituted PHA having a fluorine substitution on an aromatic ring in a unit, there is also investigated a polyhydroxyalkanoate in which an aromatic in the unit is substituted with a cyano or nitro group.
Can. J. Microbiol., 41, 32–43 (1995) and Polymer International, 39, 205–213 (1996) report production of a polyhydroxyalkanoate containing 3-hydroxy-6-(p-cyanophenoxy) hexanoic acid or 3-hydroxy-6-(p-nitrophenoxy) hexanoic acid as the monomer unit by Pseudomonas oleovorans ATCC 29347 strain and Pseudomonas putida KT2442 stain, from octanoic acid and 6-(p-cyanophenoxy) hexanoic acid or 6-(p-nitrophenoxy) hexanoic acid as substrate.
A polyhydroxyalkanoate including a unit having an aromatic ring provided with a substituent constitutes a polyhydroxyalkanoate of multiple functions, including novel functions resulting from the substituent present on the aromatic ring, while retaining polymer properties of a high glass transition point and a satisfactory working property, resulting from the aromatic ring.
On the other hand, active investigations are conducted to obtain a polyhydroxyalkanoate of multiple functions, based on polyhydroxyalkanoate having a bromo group in the unit and introducing an arbitrary functional group into a side chain of the produced polymer, by a chemical conversion utilizing such a bromo group.
Macromol. Rapid Commun., 20, p. 91–94 (1999) reports producing polyhydroxyalkanoate having a bromo group in a side chain by Pseudomonas oleovorans and modifying the side chain with a thiolated product of acetylated maltose, thereby synthesizing a polyhydroxyalkanoate different in solubility or hydrophilicity.
As described in the foregoing references, a bromo group has a high reactivity in an addition reaction or the like, and can be used for introducing various functional groups or for chemical conversion. It can also constitute a cross-linking point, which is a starting point of a cross-linking reaction of the polymer. Consequently, the presence of a bromo group in a unit constituting a polyhydroxyalkanoate can be considered very useful in conceiving applications of the polymer as a functional material.
Such a polyhydroxyalkanoate having a bromo group in the unit has been biosynthesized from ω-bromoalkanoic acid only as the raw material, or in co-existence of a straight-chain alkanoic acid.
Macromolecules, 25, p. 1852–1857 (1992), reports that the Pseudomonas oleovorans strain produces a polyhydroxyalkanoate containing a 3-hydroxy-ω-alkanoic acid, unit in the co-existence of an ω-bromoalkanoic acid such as 11-bromoundecanoic acid, 8-bromooctanoic acid or 6-bromohexanoic acid and n-nonanoic acid.
In addition to the foregoing, Japanese Patent Application Laid-Open No. 2001-288256 is cited in the present application.
However, thus obtained polyhydroxyalkanoate having a bromo group in the unit is usually a copolymer including a straight-chain 3-hydroxyalkanoic acid unit. Such PHA has a glass transition temperature of −20° C. to −30° C., so that the application as a polymer is limited. Because of this limitation, a polyhydroxyalkanoate having a bromo group in the unit, which is thermally so stable as to expand the field of application as a polymer and which also allows to arbitrarily control physical properties, and a producing method therefor are desired.