BIOSYNTHESIS OF POLY(3-HYDROXYALKANOIC ACID) COPOLYMER FROM CO2 IN PSEUDOMONAS-ACIDOPHILA THROUGH INTRODUCTION OF THE DNA FRAGMENT RESPONSIBLE FOR CHEMOLITHOAUTOTROPHIC GROWTH OF ALCALIGENES-HYDROGENOPHILUS

Pseudomonas acidophila is a bacterial strain producing a poly(3-hydrox yalkanoic acid) (PHA) copolymer from low-molecular-weight organic comp ounds such as formate and acetate. The genes responsible for PKA produ ction were cloned in cosmid pIK7 containing a 14.8-kb HindIII fragment of P. acidophila DNA. With the aim of developing a means of producing a PHA copolymer from CO2, cosmid pIK7 was introduced into a polymer-n egative mutant of the chemolithoautotrophic bacterium Alcaligenes eutr ophus PHB(-)4. However, the recombinant strain produced a homopolymer of 3-hydroxybutyric acid (polyhydroxybutyric acid) from CO2. Since it was thought that the composition of the accumulated polymer might depe nd not on the PHA biosynthetic genes but on the metabolism of the host strain, a recombinant plasmid, pFUS, containing the genes for chemoli thoautotrophic growth of the hydrogen-oxidizing bacterium A. hydrogeno philus was introduced into P. acidophila by conjugation. The recombina nt plasmid pFUS was stably maintained in P. acidophila in the absence of chemolithoautotrophic or antibiotic selection. This pFUS-harboring strain possessed the ability to grow under a gas mixture of H-2, O-2, and CO2 in a mineral salts medium, and PHA copolymer accumulation was confirmed by nuclear magnetic resonance spectral analysis, A gas chrom atogram obtained by gas chromatography-mass spectrometry showed the co mposition of the polymer to be 52.8% 3-hydroxybutyrate, 41.1% 3-hydrox yoctanoate, and 6.1% 3-hydroxydecanoate. This is the first report of t he production of a PHA copolymer from CO2 as sole carbon source.