RpoH2 sigma factor controls the photooxidative stress response in a non-photosynthetic rhizobacterium, Azospirillum brasilense Sp7.

Abstract

Bacteria belonging to the Alphaproteobacteria normally harbour multiple copies of the heat shock sigma factor (known as σ(32), σ(H) or RpoH). Azospirillum brasilense, a non-photosynthetic rhizobacterium, harbours five copies of rpoH genes, one of which is an rpoH2 homologue. The genes around the rpoH2 locus in A. brasilense show synteny with that found in rhizobia. The rpoH2 of A. brasilense was able to complement the temperature-sensitive phenotype of the Escherichia coli rpoH mutant. Inactivation of rpoH2 in A. brasilense results in increased sensitivity to methylene blue and to triphenyl tetrazolium chloride (TTC). Exposure of A. brasilense to TTC and the singlet oxygen-generating agent methylene blue induced several-fold higher expression of rpoH2. Comparison of the proteome of A. brasilense with its rpoH2 deletion mutant and with an A. brasilense strain overexpressing rpoH2 revealed chaperone GroEL, elongation factors (Ef-Tu and EF-G), peptidyl prolyl isomerase, and peptide methionine sulfoxide reductase as the major proteins whose expression was controlled by RpoH2. Here, we show that the RpoH2 sigma factor-controlled photooxidative stress response in A. brasilense is similar to that in the photosynthetic bacterium Rhodobacter sphaeroides, but that RpoH2 is not involved in the detoxification of methylglyoxal in A. brasilense.

• Authors: Santosh Kumar, Ashutosh Kumar Rai, Mukti Nath Mishra, Mansi Shukla, Pradhyumna Kumar Singh, Anil Kumar Tripathi
• Journal: Microbiology (Reading, England) (Microbiology (Reading)) Vol. 158 Issue Pt 12 Pg. 2891-2902 (Dec 2012) ISSN: 1465-2080 [Electronic] England
• PMID: 23023973 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Heat-Shock Proteins
• Oxidants
• Proteome
• Sigma Factor
• Tetrazolium Salts
• heat-shock sigma factor 32
• triphenyltetrazolium
• Methylene Blue

Topics

• Azospirillum brasilense (drug effects, genetics, physiology)
• Escherichia coli (genetics)
• Gene Deletion
• Gene Expression Regulation, Bacterial
• Genetic Complementation Test
• Heat-Shock Proteins (genetics, metabolism)
• Methylene Blue (metabolism)
• Oxidants (metabolism)
• Oxidative Stress
• Proteome (analysis)
• Rhodobacter sphaeroides (physiology)
• Sigma Factor (genetics, metabolism)
• Stress, Physiological
• Tetrazolium Salts (metabolism)