[Synthesis of copolyesters consisting of 3-hydroxybutyrate and 3-hydroxyhexanoate by Aeromonas hydrophila WQ and its molecular basis].

Aeromonas hydrophila WQ isolated from lake water was found to be able to synthesize polyhydroxyalkanoates (PHA) copolymer consisting of 3-hydroxybutyrate (HB) and 3-hydroxyhexanoate (HHx) (PHBHHx). Lauric acid was found to be the most suitable carbon source for cell growth and PHBHHx accumulation. The bacteria accumulated 49% PHBHHx containing 6% HHx in terms of cell dry weight when grown on lauric acid for 72 h. 42% PHBHHx consisting of 14% HHx was obtained with 5 g/L glucose and 10 g/L lauric acid as co-substrate. Higher glucose concentration greatly reduced the cell concentration and PHA content. The PHA biosynthesis genes from A. hydrophila WQ was successfully cloned using a two-step PCR cloning strategy based on PHA biosynthesis genes organization of Aeromonas caviae. A. hydrophila WQ and A. caviae shared high identities in the PHA gene loci, namely, ORF1, phaC and phaJ had 100%, 97% and 97.5% identities respectively. PHA synthases of A. caviae and A. hydrophila were proposed to contain type IV PHA synthases which are different compared with type I PHA synthases on the substrate specificity and location arrangement of PHA metabolic genes.