[Biosynthesis of polyhydroxyalkanoates and its metabolic pathway in Comamonas sp. strain CNB-1]

Comamonas sp. strain CNB-1 degrades chloronitrbenzene and nitrobenzene for carbon and nitrogen sources. In this study, accumulation of polyhydroxyalkanoic acids (PHAs) within strain CNB-1 cells was investigated under various conditions. Results indicated that strain CNB-1 was able to synthesize PHA from various short-chain fatty acid and alcohols, and 57 w% of the dry cell weight (DCW) PHA was obtained when valerate and 1,4-butanediol were co-fed. Supplements of short-chain alcohols stimulated the accumulation of PHAs, and this stimulatory effect was attributed to the more amount of reductant generated from alcohol dehydrogenation. The genes encoding for PHA polymerase (phaC), for acetoacetyl-CoA thiolase (phaA), and acetoacetyl-CoA reductase (phaB) were cloned in Escherichia coli, and the recombinant E. coli synthesized PHA and showed enzymatic activities of PHA polymerase, acetoacetyl-CoA thiolase, and acetoacetyl-CoA reductase. The three genes occurred as a cluster of pha(C-A-B). To optimize their expression, the three genes were cloned to the pET vector and expressed respectively. Mass of expressed protein was detected and the enzyme activities increased greatly in contrast to wild CNB-1 strain, which is about 4.1, 71, and 2882 folds of activities of CNB-1.