Phosphoribulokinase mediates nitrogenase-induced carbon dioxide fixation gene repression in Rhodobacter sphaeroides.

In many organisms there is a balance between carbon and nitrogen metabolism. These observations extend to the nitrogen-fixing, nonsulfur purple bacteria, which have the classic family of P(II) regulators that coordinate signals of carbon and nitrogen status to regulate nitrogen metabolism. Curiously, these organisms also possess a reverse mechanism to regulate carbon metabolism based on cellular nitrogen status.

Altered residues in key proteins influence the expression and activity of the nitrogenase complex in an adaptive CO2 fixation-deficient mutant strain of Rhodobacter sphaeroides.

Previously, the RubisCO-compromised spontaneous adaptive Rhodobacter sphaeroides mutant, strain 16PHC, was shown to derepress the expression of genes that encode the nitrogenase complex under normal repressive conditions. As a result of this adaptation, the active nitrogenase complex restored redox balance, thus allowing strain 16PHC to grow under photoheterotrophic conditions in the absence of an exogenous electron acceptor. A combination of whole genome pyrosequencing and whole genome microarray analyses was employed to identify possible loci responsible for the observed phenotype.