Production of PHA and its copolyesters by methanol-utilizing bacteria

Abstract

Methanol-utilizing bacteria, Methylobacterium organophilum and Methylobacterium sp. KCTC 0048 isolated from soil, were tested for the production of PHA and its copolyesters. These methylotrophs could synthesize a variety of copolyesters when the secondary carbon substrates were added to the nutrient-limited cultures containing methanol as major carbon and energy source.. Methylobacterium organophilum could produce PHB from methanol and P3HB-3HV from valeric acid. A strain, SH 1332, which was identified as Methylobacterium sp. KCTC 0048, was selected for further studies on PHA production considering its high PHA productivity, among several strains. This methylotroph could accumulate PHB, P3HB-3HV, P3HB-4HB and P3HB-3HP from methanol and the secondary carbon substrates. Methylobacterium sp. KCTC 0048 which was confirmed as a facultative methylotroph, could accumulate PHB by using methanol, ethanol, glycerol, and fructose as precursors, respectively. The copolyester of 3-hydroxybutyrate and 3-hydroxyvalerate, P3HB-3HV was accumulated when valeric acid, pentanol or heptanoic acid was added to the nitrogen-limited medium containing methanol. The copolyester of 3-hydroxybutyrate and 4-hydroxybutyrate, P3HB-4HB was synthesized from 4-hydroxybutyrate, 1,4-butanediol, or $\gamma$-butyrolactone, and the copolyester of 3-hydroxybutyrate and 3-hydroxypropionate(P3HB-3HP), from 3-hydroxypropionate as the secondary carbon substrates, respectively. In case of P3HB-3HV production by Methylobacterium sp. KCTC 0048, the composition of copolyester varied from 10\% to 99.9\% of 3HV fraction. For the production of PHA and its copolyester in industrial scale, it is necessary to control preciesely PHAs composition which is important for the physical properties of PHAs polyesters. With respect to the change of P3HB-3HV composition, it was found that mole fraction of 3HV was dependent on initial nitrogen concentration. It seemed that 3HV synthesis from valeric acid by Methylobacterium ...