Bacillus cereus-type polyhydroxyalkanoate biosynthetic gene cluster contains R-specific enoyl-CoA hydratase gene.

Bacillus cereus and Bacillus megaterium both accumulate polyhydroxyalkanoate (PHA) but their PHA biosynthetic gene (pha) clusters that code for proteins involved in PHA biosynthesis are different. Namely, a gene encoding MaoC-like protein exists in the B. cereus-type pha cluster but not in the B. megaterium-type pha cluster. MaoC-like protein has an R-specific enoyl-CoA hydratase (R-hydratase) activity and is referred to as PhaJ when involved in PHA metabolism. In this study, the pha cluster of B. cereus YB-4 was characterized in terms of PhaJ's function. In an in vitro assay, PhaJ from B. cereus YB-4 (PhaJ) exhibited hydration activity toward crotonyl-CoA. In an in vivo assay using Escherichia coli as a host for PHA accumulation, the recombinant strain expressing PhaJ and PHA synthase led to increased PHA accumulation, suggesting that PhaJ functioned as a monomer supplier. The monomer composition of the accumulated PHA reflected the substrate specificity of PhaJ, which appeared to prefer short chain-length substrates. The pha cluster from B. cereus YB-4 functioned to accumulate PHA in E. coli; however, it did not function when the phaJ gene was deleted. The B. cereus-type pha cluster represents a new example of a pha cluster that contains the gene encoding PhaJ.