Encystment and alkylresorcinol production by Azotobacter vinelandii strains impaired in poly-β-hydroxybutyrate synthesis

Abstract

The lipids poly-beta-hydroxybutyrate (PHB) and alkylresorcinols are the major metabolic products of Azotobacter vinelandii cysts. Cysts are formed in less than 0.01% of late stationary phase cells grown on sucrose. Culturing vegetative cells in n-butanol or beta-hydroxybutyrate induces encystment. After induction of encystment, PHB rapidly accumulates in large granules. Then, the cells begin the synthesis of alkylresorcinols that replace the phospholipids in the membranes and are components of the exine, the outer layer of the cyst envelope. Vegetative cells do not synthesize alkylresorcinols. We report here the effect of mutations in the phbBAC operon, coding for the enzymes of the PHB biosynthetic pathway, on the synthesis of alkylresorcinols and cyst formation. The phb mutations did not impair the capacity to form mature cysts. However, the cysts formed by these strains posses a thicker exine layer and a higher content of alkylresorcinols than the cysts formed by the wild-type strain. A blockage of PHB synthesis caused by phb mutations resulted in the synthesis of alkylresorcinols and encystment even under non-inducing conditions. We propose that, as a consequence of the blockage in the PHB biosynthetic pathway, the acetyl-CoA and reducing power pools are increased causing the shift to lipid metabolism required for the synthesis of alkylresorcinols and cyst formation.

Sigma Factor RpoS Controls Alkylresorcinol Synthesis through ArpR, a LysR-Type Regulatory Protein, during Encystment of Azotobacter vinelandii

“…␤-Hydroxybutyrate or related metabolites induce this differentiation process (33). Also, a mutant impaired in PHB biosynthesis showed a phenotype of increased encystment and production of ARs, even under vegetative growth conditions (23). Here we show that acetoacetyl-CoA increases the affinity of ArpR for the promoter region of arsA in vitro.…”

“…The production of ARs was measured as previously described (23). Briefly, the lipids were extracted with acetone for 20 min at room temperature.…”

Exploring biodegradable polymer production from marine microbes

“…PHAs are biopolymers that are beneficial to bacteria and environment; they are utilized as nutrient under stressful condition in rhizosphere, soil, and phyllosphere [175,179,[180][181][182][183], distribution of carbon sources [184][185][186][187], enhancing survival factors in stress condition; osmotic shock, solvent stress, UV irradiation, heat and cold, ethanol, H2O2, and desiccation [188][189][190][191][192][193]183,[194][195][196] and control exopolysaccharide production [197,198,191,192,199] play a vital role in different energy consuming pathways, chemotaxis, nitrogen fixation, cell motility and aerotaxis [200,51,183,201,202], formation of cyst, germination, and sporulation [203]. Despite the PAHs producing significant advances, bacterial inoculants currently received much attention in plant growth promotion or plant production [204].…”

Transcriptional activation of the Azotobacter vinelandii polyhydroxybutyrate biosynthetic genes phbBAC by PhbR and RpoS

“…Synthesis of PHB in A. vinelandii occurs entering the stationary phase (Martínez et al, 1997), and is carried out in three enzymic steps: a b-ketothiolase catalyses the condensation of two molecules of acetyl-CoA to produce acetoacetylCoA, which is reduced by the NADPH-dependent acetoacetyl-CoA reductase to form b-hydroxybutyrylCoA, which is polymerized by the PHB synthase. The genes encoding the b-ketothiolase phbA, acetocetyl-CoA reductase phbB and PHB synthase phbC are organized in the phbBAC operon (Segura et al, 2003). The phbR gene, located upstream and in the opposite direction to phbB, encodes a transcriptional activator of the AraC family, and a mutation in phbR reduces accumulation of PHB (PeraltaGil et al, 2002).…”