[Poly- β -Hydroxybutyrate Accumulation by Rhodobacter sphaeroides Phase Variants]

Area of Science:

• Microbiology
• Biochemistry
• Biotechnology

Context:

• The purple photosynthetic bacterium Rhodobacter sphaeroides 2R accumulates poly-β-hydroxybutyrate (PHB) when grown on acetate.
• PHB accumulation occurs under both anaerobic (light) and aerobic (dark) conditions.
• The M variant exhibits higher PHB content (70% of dry biomass) compared to the R variant (40%) under aerobic, dark conditions with C/N imbalance.

Purpose:

• To investigate the mechanisms behind enhanced poly-β-hydroxybutyrate (PHB) synthesis in Rhodobacter sphaeroides.
• To identify key enzymatic factors contributing to increased PHB accumulation in the M variant.
• To evaluate the potential of Rhodobacter sphaeroides M variant for large-scale PHB production.

Summary:

• Rhodobacter sphaeroides M variant demonstrates significant PHB accumulation, particularly under aerobic, dark conditions with a C/N imbalance.
• Decreased activity of citrate synthase, a key enzyme in the tricarboxylic acid (TCA) cycle, is linked to enhanced PHB synthesis.
• Reduced activity of NADH oxidase, involved in NADH oxidation during acetate metabolism, further contributes to PHB accumulation via alternative pathways.

Impact:

• Identifies Rhodobacter sphaeroides M variant as a promising candidate for industrial-scale poly-β-hydroxybutyrate (PHB) production.
• Elucidates the biochemical basis for enhanced PHB synthesis, involving TCA cycle and NADH oxidase regulation.
• Provides insights into acetate assimilation pathways leading to biopolymer accumulation in bacteria.