Influence of the Heme Nitric Oxide/Oxygen Binding Protein (H-NOX) on Cell Cycle Regulation in Caulobacter crescentus

The ability of an organism to respond to environmental changes is paramount to survival across a range of conditions. The bacterial heme nitric oxide/oxygen binding proteins (H-NOX) are a family of biofilm-regulating gas sensors that enable bacteria to respond accordingly to the cytotoxic molecule nitric oxide. By interacting with downstream signaling partners, H-NOX regulates the production of the bacterial secondary messenger cyclic diguanylate monophosphate (c-di-GMP) to influence biofilm formation. The aquatic organism Caulobacter crescentus has the propensity to attach to surfaces as part of its transition into the stalked S-phase of its life cycle. This behavior is heavily influenced by intracellular c-di-GMP and thus poses H-NOX as a potential influencer of C. crescentus surface attachment and cell cycle. By generating a strain of C. crescentus lacking hnox, our laboratory has demonstrated that this strain exhibits a considerable growth deficit, an increase in biofilm formation, and an elevation in c-di-GMP. Furthermore, in our comprehensive proteome study of 2779 proteins, 236 proteins were identified that exhibited differential expression in Δhnox C. crescentus, with 132 being downregulated and 104 being upregulated, as determined by a fold change of ≥1.5 or ≤0.66 and a p value ≤0.05. Our systematic analysis unveiled several regulated candidates including GcrA, PopA, RsaA, FtsL, DipM, FlgC, and CpaE that are associated with the regulation of the cellular division process, surface proteins, flagellum, and pili assembly. Further examination of Gene Ontology and pathways indicated that the key differences could be attributed to several metabolic processes. Taken together, our data indicate a role for the HNOX protein in C. crescentus cell cycle progression.