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ppGpp in Sinorhizobium meliloti : biosynthesis in response to sudden nutritional downshifts and modulation of the transcriptome
Author(s) -
Krol Elizaveta,
Becker Anke
Publication year - 2011
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2011.07752.x
Subject(s) - sinorhizobium meliloti , biology , transcriptome , microbiology and biotechnology , gene , bacteria , genetics , gene expression , symbiosis
Summary Sinorhizobium meliloti Rm2011 responds to sudden shifts to nitrogen or carbon starvation conditions by an accumulation of the stringent response alarmone ppGpp and remodelling of the transcriptome. The gene product of relA , Rel Sm , responsible for synthesis of ppGpp, shows functional similarities to E. coli SpoT. Using promoter– egfp gene fusions, we showed that in Rm2011 relA is expressed at a low rate, as a readthrough from the rpoZ promoter and from its own weak promoter. The low level of relA expression is physiologically relevant, since overexpression of Rel Sm inhibits ppGpp accumulation. The N‐terminal portion of Rel Sm is required for ppGpp degradation in nutrient‐sufficient cells and might be involved in regulation of the ppGpp synthase and hydrolase activities of the protein. Expression profiling of S. meliloti subjected to sudden nitrogen or carbon downshifts revealed that repression of ‘house‐keeping’ genes is largely dependent on relA whereas activation of gene targets of the stress sigma factor RpoE2 occurred independently of relA . The regulatory genes nifA , ntrB , aniA and sinR , as well as genes related to modulation of protein biosynthesis and nucleotide catabolism, were induced in a relA ‐dependent manner. dksA was required for the majority of the relA ‐dependent regulations.