Integrative control of carbon, nitrogen, hydrogen, and sulfur metabolism: the central role of the Calvin-Benson-Bassham cycle.

Nonsulfur purple (NSP) photosynthetic bacteria use the Calvin-Benson-Bassham (CBB) reductive pentose phosphate pathway for the reduction of CO(2) via ribulose 1,5-bisphosphate (RuBP) carboxylase-oxygenase (RubisCO), as a means to build cell mass during chemoautotrophic or photoautotrophic conditions. In addition, the CBB pathway plays an important role in maintaining redox balance during photoheterotrophic growth conditions. In this communication we describe protein-protein interactions between two transcriptional regulators CbbR and RegA and the possible role of the CbbX protein in regulating the CBB pathway in Rhodobacter sphaeroides. In Rhodopseudomonas palustris, the CbbR and the CbbRRS system (a three-protein, two-component regulatory system) regulate the CBB pathway. Moreover, derepression of the nitrogenase complex, and the production of hydrogen gas, appears to be a common mechanism to balance the redox potential in RubisCO-compromised strains of NSP photosynthetic bacteria.