[Effect of intestinal nitrate on growth of and its regulatory mechanism].

Objective: To explore the effect of intestinal nitrates on the growth of and its regulatory mechanisms.

Methods: strains with nitrate reductase and single or double gene knockout or with NarXL gene knockout were constructed and observed for both aerobic and anaerobic growth in the presence of KNO using an automated bacterial growth analyzer and a spectrophotometer, respectively. The mRNA expressions of and in in anaerobic cultures in the presence of KNO and the effect of the binary regulatory system NarXL on their expresisons were detected using qRT-PCR. Electrophoretic mobility shift assays (EMSA) and MST analysis were performed to explore the specific regulatory mechanisms of NarXL in sensing and utilizing nitrates. Competitive experiments were conducted to examine anaerobic growth advantages of and gene knockout strains of in the presence of KNO.

Results: The presence of KNO in anaerobic conditions, but not in aerobic conditions, promoted bacterial growth more effectively in the wild-type strain than in the gene knockout strain. In anaerobic conditions, the gene knockout strain showed significantly lowered mRNA expressions of and ( < 0.0001). EMSA and MST experiments demonstrated that the NarXL regulator could directly bind to and promoter regions. The wild-type strain in anaerobic cultures showed significantly increased expressions of and mRNAs in the presence of KNO ( < 0.01), and gene knockout resulted in significantly attenuated anaerobic growth and competitive growth abilities of in the presence of KNO ( < 0.01).

Conclusion: The binary regulatory system NarXL of can sense changes in intestinal nitrate concentration and directly regulate the expression of nitrate reductase genes and to promote bacterial growth.