Wide Distribution among Halophilic Archaea of a Novel Polyhydroxyalkanoate Synthase Subtype with Homology to Bacterial Type III Synthases

• DOI: 10.1128/aem.01117-10
• Publication Date: 2010-10-02T02:45:23Z
• Authors: Jing Han; Jing Hou; Hailong Liu; Shuangfeng Cai; Bo Feng; Jian Zhou; Hua Xiang
• Keywords: 0301 basic medicine; Haloarcula marismortui; Halobacteriaceae; Polyesters; Blotting, Western; Molecular Sequence Data; Hydroxybutyrates; Sequence Homology; Sequence Analysis, DNA; 03 medical and health sciences; DNA, Archaeal; Fermentation; Cluster Analysis; Acyltransferases; Phylogeny

ABSTRACTPolyhydroxyalkanoates (PHAs) are accumulated as intracellular carbon and energy storage polymers by various bacteria and a few haloarchaea. In this study, 28 strains belonging to 15 genera in the familyHalobacteriaceaewere investigated with respect to their ability to synthesize PHAs and the types of their PHA synthases. Fermentation results showed that 18 strains from 12 genera could synthesize polyhydroxybutyrate (PHB) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). For most of these haloarchaea, selected regions of thephaEandphaCgenes encoding PHA synthases (type III) were cloned via PCR with consensus-degenerate hybrid oligonucleotide primers (CODEHOPs) and were sequenced. The PHA synthases were also examined by Western blotting using haloarchaealHaloarcula marismortuiPhaC (PhaCHm) antisera. Phylogenetic analysis showed that the type III PHA synthases from species of theHalobacteriaceaeand theBacteriadomain clustered separately. Comparison of their amino acid sequences revealed that haloarchaeal PHA synthases differed greatly in both molecular weight and certain conserved motifs. The longer C terminus of haloarchaeal PhaC was found to be indispensable for its enzymatic activity, and two additional amino acid residues (C143 and C190) of PhaCHmwere proved to be important for itsin vivofunction. Thus, we conclude that a novel subtype (IIIA) of type III PHA synthase with unique features that distinguish it from the bacterial subtype (IIIB) is widely distributed in haloarchaea and appears to be involved in PHA biosynthesis.