Research Of Physiological Function Of NudB In Escherichia Coli And S.Typhimurium

Enteric organisms, such as Escherichia coli, survive acidic environment for some hours. Induction of each acid resistence system alters under a variety of conditions, such as growth media/growth phase, acidic media. Depending on complicated acid resistance systems, Escherichia coli successfully breaks through the acidic barrier(stomach)before reaching the intestinal tract where pathogenesis occurs. A more comprehensive in-depth understanding of bacterial acid resistance is significant for prevention and clinical treatment of intestinal disease.In our previous studies, we found that the expression level of the acid stress response related genes were remarkable decreased in E.coli W3110 ? nudB-pCA24 N. Based on the results we have obtained, our works foucs on the effect of nudB deletion on acid resistance systerm.In this sudy, we obtained conclusions as follow:(1)During acid challenge, survival rates of wild E.coli W3110 strains containing pCA24 N vector were slightly reduced, which were grown in growth media with high concentration of chloramphenicol(50 ?g/m L).(2)Compared with wild type strains, survival rates of E.coli W3110 ? nudB-pCA24 N strains grown in LB with high concentration of chloramphenicol(50 ?g/m L), were dramaticlly reduced in acid media. E.coli W3110 ? nudB ? folM-pCA24 N strains can totally restored decreased AR which was caused by nudB deletion. The guarantee of decreased AR of wild E.coli W3110 must possess two condition: growth media with high concentration of chloramphenicol(50 ?g/m L) and deletion of nudB.(3)The overexpression of GadX in E.coli W3110 ? nudB-pCA24 N strains in LB with high concentration of chloramphenicol(50 ?g/m L) can totally restored decreased AR which was caused by nudB deletion. Thus,we concluded that the process RpoS promotes gadX expression was disturbed by high concentration of chloramphenicol(50 ?g/mL) and excess production of tetrahydromoapterin because of deletion of nudB in the E.coli W3110 ? nudB-pCA24 N strains. As for the specific mechanism how these two factors affect AR, we need to further research.In our previous work, we found that, deletion of nudB in E. coli leads to increased sensitivity to both SMX and TMP. We examined whether this phenotype also occurs in S. Typhimurium. Deletion of nudB in S. Typhimurium is slightly more sensitive to TMP and SXT treatment. MIC of SMX for ? nudB strains were not decreased. For this reason, we supposed that S. Typhimurium LT2 have multiple copies of dihydr-roneopterin triphosphate pyrophosphatase besides NudB.