Polyhydroxybutyrate (PHB) is a common
carbon storage
polymer among heterotrophic bacteria. It is also accumulated in some photoautotrophic cyanobacteria; however, the knowledge of how PHB accumulation is regulated in this group is limited. PHB synthesis in Synechocystis sp. PCC 6803 is initiated once macronutrients like
phosphorus or
nitrogen are limiting. We have previously reported a mutation in the gene sll0783 that impairs PHB accumulation in this cyanobacterium upon
nitrogen starvation. In this study we present data which explain the observed phenotype. We investigated differences in intracellular localization of
PHB synthase, metabolism, and the
NADPH pool between wild type and mutant. Localization of
PHB synthase was not impaired in the sll0783 mutant; however, metabolome analysis revealed a difference in
sorbitol levels, indicating a more oxidizing intracellular environment than in the wild type. We confirmed this by directly measuring the
NADPH/
NADP ratio and by altering the intracellular redox state of wild type and sll0783 mutant. We were able to physiologically
complement the mutant phenotype of diminished
PHB synthase activity by making the intracellular environment more reducing. Our data illustrate that the
NADPH pool is an important factor for regulation of PHB biosynthesis and metabolism, which is also of interest for potential biotechnological applications.