title: Poly beta-hydroxybutyrate depolymerase (PhaZ) in Azospirillum brasilense and characterization of a phaZ mutant.
abstract: Like many other prokaryotes, rhizobacteria of the genus Azospirillum produce high levels of poly-beta-hydroxybutyrate (PHB) under sub-optimal growth conditions. Utilization of PHB by bacteria under stress has been proposed as a mechanism that favors their compatible establishment in competitive environments. PHB depolymerase (PhaZ) is an essential enzyme in PHB degradation. The phaZ gene was identified in Azospirillum brasilense, cloned, sequenced, and shown to be located on the chromosome. Insertion of a kanamycin-resistant cassette within phaZ of A. brasilense resulted in a phaZ mutant that was unable to degrade PHB; however, carbon source utilization was similar in both the wild-type and the mutant strain. The ability of the wild-type to endure starvation conditions, ultraviolet irradiation, heat, and osmotic shock, and to grow in the presence of hydrogen peroxide was higher than that of the mutant strain. By contrast, the ability of the phaZ mutant strain to endure desiccation was higher than that of the wild-type strain. No differences between the strains were seen in their ability to endure sonication, or to survive in carrier materials used for soil inoculants. In addition, motility was the same between the two strains, whereas cell aggregation and exopolysaccharide production were higher in the wild-type than in the phaZ mutant strain.
authors.affiliation: Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agricultural Food and Environmental Quality Sciences, 76100 Rehovot, Israel.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kadouri
authors.forename: Edouard
authors.initials: E
authors.lastname: Jurkevitch
authors.forename: Yaacov
authors.initials: Y
authors.lastname: Okon
mesh_terms: D000595:Amino Acid Sequence; D015806:Azospirillum brasilense / Q000201:enzymology* / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure; D002244:Carbon / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification; D003890:Desiccation; D005798:Genes, Bacterial; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006885:Hydroxybutyrates / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009997:Osmotic Pressure; D011091:Polyesters / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011135:Polysaccharides, Bacterial / Q000032:analysis; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012988:Soil Microbiology; D013010:Sonication; D014466:Ultraviolet Rays; D000094122:Polyhydroxybutyrates
chemical_list: D002244:Carbon; D002265:Carboxylic Ester Hydrolases; D004269:DNA, Bacterial; D006861:Hydrogen Peroxide; D006885:Hydroxybutyrates; D011091:Polyesters; D011135:Polysaccharides, Bacterial; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates; C022417:poly-beta-hydroxybutyrate depolymerase