Identification and Isolation of Genes Involved in Poly(β-Hydroxybutyrate) Biosynthesis in Azospirillum brasilense and Characterization of a phbC Mutant

Abstract

Like many other prokaryotes, rhizobacteria of the genus Azospirillum produce high levels of poly(␤-hydroxybutyrate) (PHB) under suboptimal growth conditions. Utilization of PHB by bacteria under stress has been proposed as a mechanism that favors their compatible establishment in competitive environments, thus showing great potential for the improvement of bacterial inoculants for plants and soils. The three genes that are considered to be essential in the PHB biosynthetic pathway, phbA (␤-ketothiolase), phbB (acetoacetyl coenzyme A reductase), and phbC (PHB synthase), were identified in Azospirillum brasilense strain Sp7, cloned, and sequenced. The phbA, -B, and -C genes were found to be linked together and located on the chromosome. An A. brasilense phbC mutant was obtained by insertion of a kanamycin resistance cassette within the phbC gene. No PHB production was detected in this mutant. The capability of the wild-type strain to endure starvation conditions was higher than that of the mutant strain. However, motility, cell aggregation, root adhesion, and exopolysaccharide (EPS) and capsular polysaccharide (CPS) production were higher in the phbC mutant strain than in the wild type.

BIOSYNTHESIS OF POLY--HYDROXYBUTYRATE AND DISTRIBUTION OF phbC GENE IN LACTOBACILLUS PLANTARUM.

“…The values of C=O were observed between 1626.05-1637.62 cm -1. The values of C=O are slightly lower than the standard value 1712 and this may be due to polymerization of the molecules (Kadouri et al, 2002). The absorption band at and around 3450 cm -1 corresponds to the terminal OH group (Fig.…”

“…The bands in the region of 585bp revealed the presence of phbCgene (Kadouri et al, 2002) and the ability of the strains to produce PHB. The amplified DNA products also revealed the minor diversification among the strains.…”

Production, optimization and characterization of polyhydroxybutyrate, a biodegradable plastic by Bacillus spp.

“…Though there exist many different genetic mechanisms of PHB production, most of the PHB production in bacteria is mediated through phb gene cluster as reported in Rhodobacter sphaeroides, 37) Azotobacter sp., 38) and Azospirillum brasilense. 39) phbB mutants have also been reported for poor growth and less PHB accumulation in many bacteria, suggesting its usefulness during PHB synthesis process. 40) Additionally, many previous studies have amplified phbB gene in the isolates to deduce the molecular nature of PHB production in them.…”

Review on the current status of polymer degradation: a microbial approach

“…are utilized in the production of degradable plastics (Ohura et al 1999;Shimao 2001;Premraj and Doble 2005). Kadouri et al (2002) reported three genes in Azospirillum brasilense strain Sp7 that are involved in PHB synthesis, i.e., phbA, phbB and phbC genes for β-ketothiolase, acetoacetyl coenzyme A reductase and PHB synthase, respectively. Biodegradation of PHA is accomplished by microbiological mineralization and generates CO 2 and H 2 O (Bonartsev et al 2007;Leja and Lewandowicz 2010a, b).…”