Study on the oxidative stress responses of a major periodontopathogenic bacteria

点击翻译按钮获取中文摘要

Inspection of genomic DNA sequence of the oral anaerobe Porphyromonas gingivalis reveals that the microorganism possesses the peroxide-sensing transcription activator OxyR, but not the superoxide-sensing transcription factor SoxR. Oxidative stress-responsive proteins in the microorganism were investigated using two dimensional gel electrophoresis and it was found that two proteins, SOD and AhpC were predominantly upregulated in oxidative conditions. In P. gingivalis oxyR mutant these two proteins were not induced by treatment with hydrogen peroxide under aerobic conditions. P.gingivalis sod and ahpC were positively regulated by OxyR. Putative -35 boxes of these promoters were found immediately adjacent to their putative OxyR binding sequences. Moreover, the promoter regions of sod and ahpC had the ability to bind P.gingivalis OxyR protein. These results demonstrate that P.gingivalis sod is one of the OxyR regulons, suggesting that OxyR functions as an intracellular redox sensor rather than a peroxide sensor in this organism.The new protein (UstA) was also identified in this study. Expression of UstA was upregulated in stationary phase or by exposure to atmospheric oxygen. The UstA-encoding gene (ustA) was located upstream of a homologue of the usp gene. The ustA gene appeared to be transcribed in a monocistronic fashion. The ustA mutant grew slower than the wild type parent strain, resulting in a lower yield in stationary phase. Furthermore, in this mutant, the expression levels of SOD, Tpr, and Trx were markedly higher than those in the wild type. The ustA mutant was more resistant to diamide, a thiol-specific oxidant, than the wild type. In addition, the ustA mutation suppressed hypersensitivities of the oxyR mutant to diamide,. metronidazole, and mitomycin C. These results suggest that UstA may play a significant role in oxidative stress responses in the bacterium.