Sinorhizobium meliloti rpoE2is necessary for H₂O₂stress resistance during the stationary growth phase

Abstract

RpoE2 is an extracytoplasmic sigma factor produced by Sinorhizobium meliloti during stationary growth phase. Its inactivation affected the synthesis of the superoxide dismutase, SodC, and catalase, KatC. The absence of SodC within the cell did not result in an increased sensitivity to extracellular superoxides. In contrast, the absence of KatC affected the resistance of S. meliloti to H(2)O(2) during the stationary growth phase. A katC strain behaved as an rpoE2 strain during an H(2)O(2) challenge, suggesting that the H(2)O(2) sensitivity of the rpoE2 strain resulted only from the lack of KatC in this strain.

RpoE2 of Sinorhizobium meliloti is necessary for trehalose synthesis and growth in hyperosmotic media

“…2); these results were in accordance with previous observations (Flechard et al, 2009;Sauviac et al, 2007). When cells were inoculated into 0.5 M NaCl GAS medium, b-glucuronidase activity increased immediately from 5±1 mmol min 21 (mg protein)…”

“…The regulation of rpoE2 was analysed in the R635 strain carrying a wild-type copy of rpoE2 and a rpoE2-uidA fusion in the chromosome (Flechard et al, 2009 (Fig. 2); these results were in accordance with previous observations (Flechard et al, 2009;Sauviac et al, 2007).…”

“…In both S. meliloti and E. coli, and in all growth conditions, trehalose synthesis is controlled by an alternative sigma factor (RpoS for enterobacteria and RpoE2 for S. meliloti). These sigma factors have a more general role in stress regulation, since they control genes involved in adaptation to other stresses (Flechard et al, 2009;HenggeAronis, 2002;Sauviac et al, 2007). In this respect, RpoE2 has a role that is very similar to that of E. coli RpoS.…”

Dual Control of Sinorhizobium meliloti RpoE2 Sigma Factor Activity by Two PhyR-Type Two-Component Response Regulators

“…Accordingly, we have shown that one of these sigma factors, RpoE2, is activated under various conditions, including heat shock, salt stress, and entry into stationary phase following nitrogen or carbon starvation (33), and is probably activated in planta as well (3; unpublished data). RpoE2 controls the transcription of a large regulon comprising at least 45 target genes, some of which encode stress-related functions, like katC, rpoH2, and sodC (10,33). S. meliloti rpoE2 mutants were recently described as more sensitive than the wild-type strain to desiccation (23) as well as to high H 2 O 2 concentrations in stationary phase (10), confirming the involvement of RpoE2 in stress responses.…”

“…RpoE2 controls the transcription of a large regulon comprising at least 45 target genes, some of which encode stress-related functions, like katC, rpoH2, and sodC (10,33). S. meliloti rpoE2 mutants were recently described as more sensitive than the wild-type strain to desiccation (23) as well as to high H 2 O 2 concentrations in stationary phase (10), confirming the involvement of RpoE2 in stress responses. Interestingly, this sigma factor is largely conserved among alphaproteobacteria (33), and RpoE2 orthologues have been involved in stress resistance and/or host colonization in several species, including Brucella melitensis (7), Caulobacter crescentus (1), and more recently Rhizobium etli (28) and Bradyrhizobium japonicum (17).…”