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Background  Bacteria use alternative sigma factors (σs) to regulate condition-specific gene expression for survival and  Shewanella  harbors multiple ECF ( e xtra c ytoplasmic  f unction) σ genes and cognate anti-sigma factor genes. Here we comparatively analyzed two of the  rpoE -like operons in the strain MR-1:  rpoE-rseA-rseB-rseC  and  rpoE2-chrR .    Results  RpoE was important for bacterial growth at low and high temperatures, in the minimal medium, and high salinity. The  degP/htrA  orthologue, required for growth of  Escherichia coli  and  Pseudomonas aeruginosa  at high temperature, is absent in  Shewanella,  while the  degQ  gene is RpoE-regulated and is required for bacterial growth at high temperature. RpoE2 was essential for the optimal growth in oxidative stress conditions because the  rpoE2  mutant was sensitive to hydrogen peroxide and paraquat. The operon encoding a ferrochelatase paralogue (HemH2) and a periplasmic glutathione peroxidase (PgpD) was identified as RpoE2-dependent. PgpD exhibited higher activities and played a more important role in the oxidative stress responses than the cytoplasmic glutathione peroxidase CgpD under tested conditions. The  rpoE2 - chrR  operon and the identified regulon genes, including  pgpD  and  hemH2 , are coincidently absent in several psychrophilic and/or deep-sea  Shewanella  strains .Conclusion  In  S. oneidensis  MR-1, the RpoE-dependent  degQ  gene is required for optimal growth under high temperature. The  rpoE2  and RpoE2-dependent  pgpD  gene encoding a periplasmic glutathione peroxidase are involved in oxidative stress responses. But  rpoE2  is not required for bacterial growth at low temperature and it even affected bacterial growth under salt stress, indicating that there is a tradeoff between the salt resistance and RpoE2-mediated oxidative stress responses.    Electronic supplementary material  The online version of this article (doi:10.1186/s12866-015-0357-0) contains supplementary material, which is available to authorized users.

bmc microbiology

An extracytoplasmic function sigma factor-dependent periplasmic glutathione peroxidase is involved in oxidative stress response of Shewanella oneidensis