XC_0531 encodes a c-type cytochrome biogenesis protein and is required for pathogenesis in Xanthomonas campestris pv. campestris.

BACKGROUND: The phytopathogenic Xanthomonas campestris pv.campestris is a gram-negative bacterium and the causal agent of black-rot disease of cruciferous crops. Many gram-negative bacteria possess a family of proteins, called Dsbs, which are involved in disulfide bond formation in certain periplasmic proteins. In our preliminary screening of the virulence to the plants we identified that gene XC_0531 which annotated gene dsbD of Xanthomonas campestris pv. campestris (Xcc) is related to the virulence to the host plants.

RESULTS: Here, we found XC_0531 encoded a DsbD like protein. Its deletion is sensitive to DTT and copper, decreased accumulation of free thiols in periplasm. Its deletion also affected heme synthesis, position of Soret band and the production of peak c550. This suggests that XC_0531 is related to c-type cytochromes biogenesis. XC_0531 mutation decreased the utilization of different carbon sources (such as galactose, xylose, maltose, saccharose and glucose), reduced extracellular polysaccharide (EPS) production, decreased extracellular enzyme activities (protease, cellulose and amylase), slowed down growth rate of Xcc and weakened virulence to the plants. These results suggest that these phenotypes caused by XC_0531 mutation is possibly due to deficient biosynthesis of c-type cytochromes in respiration chain and the formation of disulfide bonds. Our work confirmed the function of XC_0531 and provide theory basis for scientists working on molecular mechanisms of cytochrome c biogenesis, pathogenesis of Xcc, development of EPS commercial values and protecting plant from black rot.

CONCLUSION: We confirmed the function of gene XC_0531, which encodes a DsbD like protein, a protein correlated with c-type cytochrome biogenesis. This gene is related to the virulence to plants by affecting funtion of cytochromes c and probably disulfide bonds modification of proteins in type II secretion system (T2SS).