ArcBArcA

ArcBArcA is a bacterial two-component regulatory system that helps cells adapt to changes in oxygen availability and redox state. It is best characterized in Escherichia coli and related gamma-proteobacteria, where it coordinates metabolism and energy generation by adjusting gene expression in response to the cellular redox environment.

ArcB is a sensor histidine kinase that detects the redox state of the quinone pool in the membrane. Under low-oxygen or reduced conditions, ArcB autophosphorylates on a histidine residue and transfers the phosphate to ArcA, the response regulator. Phosphorylated ArcA (ArcA-P) binds DNA and acts as a transcription factor to reprogram the cell’s metabolic pathways.

Under more oxidizing, high-oxygen conditions, ArcB exhibits phosphatase activity that removes the phosphate from ArcA-P, thereby reducing ArcA-mediated transcriptional changes. In addition, non-canonical phosphodonors such as acetyl phosphate can phosphorylate ArcA in the absence of ArcB activity, providing a secondary route to ArcA regulation.

Functionally, ArcA-P generally represses genes involved in aerobic respiration and the TCA cycle while activating genes that support anaerobic respiration and fermentation. This regulatory shift helps the cell optimize energy production when oxygen is scarce and prevents futile expression of incompatible metabolic programs.

The ArcB–ArcA system operates alongside other global regulators and is conserved across many Gram-negative bacteria, contributing to flexible adaptation to fluctuating redox conditions. Its study enhances understanding of microbial energy metabolism, environmental persistence, and pathogenic potential in some species.