Antagonistic regulation of motility and other cellular functions by RpoN and RpoS in Escherichia coli

Bacteria generally possess multiple factors that, based on structural and functional similarity, divide into two families: D and N. Among the seven factors in Escherichia coli, six belongs to the D family. Each factor recognizes a group of promoters, providing effective control of differential gene expression. Many studies have shown that factors of the D family compete with each other for function. In contrast, the competition between N and D families has yet to be fully explored. Here we report a global antagonistic effect on gene expression between two alternative factors, N (RpoN) and S (RpoS), a D family protein. Mutations in rpoS and rpoN inversely affected a number of cellular traits, such as expression of flagellar genes, N-controlled growth on poor nitrogen sources, and S-directed expression of acid phosphatase AppA. Transcriptome analysis reveals that 40% of genes in the RpoN regulon were under reciprocal RpoS control. Furthermore, loss of RpoN led to increased levels of RpoS, while RpoN levels were unaffected by rpoS mutations. Expression of the flagellar F factor (FliA), another D family protein, was controlled positively by RpoN but negatively by RpoS. These findings unveil a complex regulatory interaction among N, S and F, and underscore the need to employ systems biology approaches to assess the effect of such interaction of factors on cellular functions, including motility, nutrient utilization, and stress response.

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Dong T, Yu R, Schellhorn H