Extracytoplasmic function (ECF) sigma factor σF is involved in Caulobacter crescentus response to heavy metal stress

BMC Microbiology

Suely L Gomes¹  Gabriela M Avelar¹  Rogério F Lourenço¹  Christian Kohler² 

[1] Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-000, São Paulo, SP, Brazil;Present address: Friedrich Loeffler Institut for Medical Microbiology, Greifswald, Germany

关键词: Caulobacter crescentus;    Cadmium;    Chromium;    ECF sigma factor σ^F;    Stress response;   

Others  :  1221753
DOI  :  10.1186/1471-2180-12-210

 received in 2012-07-04, accepted in 2012-09-10,  发布年份 2012

【 摘 要 】

Background

The α-proteobacterium Caulobacter crescentus inhabits low-nutrient environments and can tolerate certain levels of heavy metals in these sites. It has been reported that C. crescentus responds to exposure to various heavy metals by altering the expression of a large number of genes.

Results

In this work, we show that the ECF sigma factor σ^F is one of the regulatory proteins involved in the control of the transcriptional response to chromium and cadmium. Microarray experiments indicate that σ^F controls eight genes during chromium stress, most of which were previously described as induced by heavy metals. Surprisingly, σ^F itself is not strongly auto-regulated under metal stress conditions. Interestingly, σ^F-dependent genes are not induced in the presence of agents that generate reactive oxygen species. Promoter analyses revealed that a conserved σ^F-dependent sequence is located upstream of all genes of the σ^F regulon. In addition, we show that the second gene in the sigF operon acts as a negative regulator of σ^F function, and the encoded protein has been named NrsF (Negative regulator of sigma F). Substitution of two conserved cysteine residues (C131 and C181) in NrsF affects its ability to maintain the expression of σ^F-dependent genes at basal levels. Furthermore, we show that σ^F is released into the cytoplasm during chromium stress and in cells carrying point mutations in both conserved cysteines of the protein NrsF.

Conclusion

A possible mechanism for induction of the σ^F-dependent genes by chromium and cadmium is the inactivation of the putative anti-sigma factor NrsF, leading to the release of σ^F to bind RNA polymerase core and drive transcription of its regulon.

【 授权许可】

   
2012 Kohler et al.; licensee BioMed Central Ltd.

【 图 表 】

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