title: Polyhydroxybutyrate biosynthesis in Caulobacter crescentus: molecular characterization of the polyhydroxybutyrate synthase.
abstract: Caulobacter crescentus was investigated with respect to polyhydroxybutyrate (PHB) biosynthesis. Polyhydroxyalkanoate (PHA) accumulation contributing to approximately 18% of the cell dry weight was obtained in the presence of glucose. Gas chromatography-mass spectrometry and gel permeation chromatography of the purified PHA showed that this polyester was solely composed of 3-hydroxybutyrate and had a weight average molar mass of 5.5 x 10(5) g mol(-1) and a polydispersity of 1.6. An ORF encoding a conserved, hypothetical protein which shared approximately 47% identity with the PHB synthase from Azorhizobium caulinodans was identified within the complete C. crescentus genomic sequence. This putative C. crescentus PHB synthase gene, phaC, consisted of a 2019 nt stretch of DNA (encoding 673 aa residues), which encoded a PHB synthase with a molecular mass of approximately 73 kDa. This is currently the largest PHA synthase identified. The phaC coding region was subcloned into vector pBBR1-JO2 under lac promoter control. The resulting plasmid, pQQ4, mediated PHB accumulation in the mutant Ralstonia eutropha PHB(-)4 and recombinant Escherichia coli JM109(pBHR69), which produced the beta-ketothiolase and acetoacetyl-CoA reductase from R. eutropha, contributing to approximately 62% and 6% of cell dry weight, respectively. Functional expression of the coding region of phaC was confirmed by immunoblotting and in vitro PHB synthase activity.
authors.affiliation: Institut für Mikrobiologie der Westfälischen Wilhelms-Universität Münster, Corrensstrasse 3, 48149 Münster, Germany.
authors.forename: Q
authors.initials: Q
authors.lastname: Qi
authors.forename: B H
authors.initials: BH
authors.lastname: Rehm
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D016935:Caulobacter crescentus / Q000201:enzymology* / Q000235:genetics; D020118:Cupriavidus necator / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005798:Genes, Bacterial; D006885:Hydroxybutyrates / Q000378:metabolism*; D008969:Molecular Sequence Data; D011091:Polyesters / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D000094122:Polyhydroxybutyrates
chemical_list: D000217:Acyltransferases; D006885:Hydroxybutyrates; D011091:Polyesters; D011994:Recombinant Proteins; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates; C060970:poly-beta-hydroxybutyrate polymerase