PRODUCTION OF POLY(BETA-HYDROXYBUTYRATE-BETA-HYDROXYVALERATE) COPOLYMER FROM SUGARS BY AZOTOBACTER-SALINESTRIS

Azotobacter salinestris, a sodium-dependent. microaerophilic N-2-fixin g soil bacterium, formed polyhydroxyalkanoate copolymers comprised of beta-hydroxybutyric acid and 9-12 mol% beta-hydroxyvaleric acid (HV) d uring growth on sugars. Increased HV content was achieved by feeding v aleric acid to the culture growing on glucose, but propionic acid coul d be directed to HV formation only when it served as the sole C source . Polymer production in nitrogen-fixing cells was increased at higher aeration, provided that a complex organic nitrogen source was also pre sent, but there was no HV in the polymer. HV production was increased to 28 mol% in nitrogen-fixing cells when aeration was lower and acetat e was provided with glucose in the medium. Enzymes leading to the prod uction of polyhydroxyalkanoate copolymers were found to be similar in A. salinestris and Azotobacter vinelandii, but A. vinelandii is unable to form HV from propionate or from sugars without valeric acid additi on. A biochemical scheme is proposed for the production of HV in A. sa linestris, whereby the glyoxylate bypass assimilates acetate to genera te succinate, which may be converted into propionyl-CoA for HV synthes is. The results suggest that it may be possible to control the molar y ield of HV formed from sugars by A. salinestris.