Alcoholytic Cleavage of Polyhydroxyalkanoate Chains by Class IV Synthases Induced by Endogenous and Exogenous Ethanol

Polyhydroxyalkanoate (PHA)-producingBacillus strains express class IV PHA synthase, which is composed of the subunits PhaR and PhaC. RecombinantEscherichia coli expressing PHA synthase fromBacillus cereus strain YB-4 (PhaRCYB-4 ) showed an unusual reduction of the molecular weight of PHA produced during the stationary phase of growth. Nuclear magnetic resonance analysis of the low-molecular-weight PHA revealed that its carboxy end structure was capped by ethanol, suggesting that the molecular weight reduction was the result of alcoholytic cleavage of PHA chains by PhaRCYB-4 induced by endogenous ethanol. This scission reaction was also induced by exogenous ethanol in bothin vivo andin vitro assays. In addition, PhaRCYB-4 was observed to have alcoholysis activity for PHA chains synthesized by other synthases. The PHA synthase fromBacillus megaterium (PhaRCBm ) from another subgroup of class IV synthases was also assayed and was shown to have weak alcoholysis activity for PHA chains. These results suggest that class IV synthases may commonly share alcoholysis activity as an inherent feature.