Probing regulon of ArcA in Shewanella oneidensis MR-I by integrated genomic analyses

Background: The Arc two- component system is a global regulator controlling many genes involved in aerobic/ anaerobic respiration and fermentative metabolism in Escherichia coli. Shewanella oneidensis MR-I contains a gene encoding a putative ArcA homolog with similar to 81% amino acid sequence identity to the E. coli ArcA protein but not a full- length arcB gene. Results: To understand the role of ArcA in S. oneidensis, an arcA deletion strain was constructed and subjected to both physiological characterization and microarray analysis. Compared to the wild- type MR-I, the mutant exhibited impaired aerobic growth and a defect in utilizing DMSO in the absence of O-2. Microarray analyses on cells grown aerobically and anaerobically on fumarate revealed that expression of 1009 genes was significantly affected ( p < 0.05) by the mutation. In contrast to E. coli ArcA, the protein appears to be dispensable in regulation of the TCA cycle in S. oneidensis. To further determine genes regulated by the Arc system, an ArcA recognition weight matrix from DNA- binding data and bioinformatics analysis was generated and used to produce an ArcA sequence affinity map. By combining both techniques, we identified an ArcA regulon of at least 50 operons, of which only 6 were found to be directly controlled by ArcA in E. coli. Conclusion: These results indicate that the Arc system in S. oneidensis differs from that in E. coli substantially in terms of its physiological function and regulon while their binding motif are strikingly similar.