PRODUCTION OF POLY-3-HYDROXYALKANOATES FROM CO AND H-2 BY A NOVEL PHOTOSYNTHETIC BACTERIUM

A novel process is described to efficiently photoconvert low-grade org anic materials such as waste biomass into natural biological plastics. When heterogeneous forms of dry biomass are thermally gasified, relat ively homogeneous synthesis gas mixtures composed primarily of carbon monoxide and hydrogen are produced. Unique strains of photosynthetic b acteria were isolated that nearly quantitatively photoassimilate the c arbon monoxide and hydrogen components of synthesis gas into new cell mass. Under unbalanced culture conditions when cellular growth is limi ted by shortages of nitrogen, calcium, magnesium, iron, or essential v itamins, up to 28% of the new cell mass is found as granules of poly-3 -hydroxyalkanoate (PHA), a high-molecular-weight thermoplastic that ca n be solvent-extracted. The dominant monomeric unit of PHAs is 3-hydro xybutyrate (3HB), which is polymerized into the homopolymeric poly-3-h ydroxybutyrate (PHB). PHB is marketed as a biodegradable plastic with physical properties similar to polystyrene. When a green alga was cocu ltured with the photosynthetic bacterium in light-dark (day-night) cyc les, the bacteria synthesized a polymer of poly-3-hydroxybutyrate-3-hy droxyvalerate (PHB-V) with a composition of 70% 3HB and 30% 3-hydroxyv alerate (3HV) to an extent of 18% of the new cell mass. PHB-V is comme rcially marketed as Biopol and has physical properties similar to poly propylene or polyethylene. Our results demonstrate that a strain of ph otosynthetic bacteria capable of photoassimilating synthesis gas or pr oducer gas is a potential candidate for large-scale production of biol ogical polyesters.