Biosynthesis of poly-β-hydroxybutyrate (PHB) is controlled by CydR (Fnr) in the obligate aerobe Azotobacter vinelandii

Abstract CydR is an Fnr-like protein in the obligatory aerobic nitrogen-fixing bacterium Azotobacter vinelandii. The cydR mutant overproduces the cytochrome bd terminal oxidase. Using two-dimensional polyacrylamide gel electrophoresis, we showed that β-ketothiolase and acetoacetyl-CoA reductase were also overexpressed in the cydR mutant. Fumarase C and a coenzyme A transferase, possibly succinyl-SCoA transferase, were decreased in this mutant. Enzyme assays confirmed the elevated β-ketothiolase and acetoacetyl-CoA reductase activities in this mutant. The cydR mutant accumulated poly-β-hydroxybutyrate throughout the exponential growth phase, unlike the wild-type strain that only accumulated poly-β-hydroxybutyrate during stationary phase. The results demonstrate that CydR controls poly-β-hydroxybutyrate synthesis in A. vinelandii.