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

CydR is an Fnr-like protein in the obligatory aerobic nitrogen-fixing bacte rium Azotobacter vinelandii. The cydR mutant overproduces the cytochrome bd terminal oxidase. Using two-dimensional polyacrylamide gel electrophoresis . we showed that beta -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 beta -ketothiolase and acetoacetyl-CoA reduct ase activities in this mutant. The cydR mutant accumulated poly-beta -hydro xybutyrate throughout the exponential growth phase. unlike the wild-type st rain that only accumulated poly-beta -hydroxybutyrate during stationary pha se. The results: demonstrate that CydR controls poly-beta -hydroxybutyrate synthesis in A., vinelandii. (C) 2001 Federation of European Microbiologica l Societies. published by Elsevier Science B.V. All rights reserved.