Transcriptome response to nitrosative stress in Rhodobacter sphaeroides 2.4.1.

The facultative photosynthetic bacterium Rhodobacter sphaeroides 2.4.1 has a nitric oxide-response transcriptional regulator, NnrR, and nitric oxide reductase (NOR), although it is incapable of denitrification. To investigate at the genomic level the physiological response to nitrosative stress of R. sphaeroides, the transcriptome profiles of strain 2.4.1 and its NnrR mutant were analyzed before and after exposure to nitrosating agents, S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP), under microaerobic conditions. GSNO and SNP affected the expression of different but overlapping sets of genes. Only a limited number of these genes, including the genes for NOR, were under the control of NnrR, and those genes were significantly upregulated by GSNO and by SNP. The oxygen-responsive regulator FnrL and a predicted iron-sensing regulator were perhaps also involved in the transcriptome response to reactive nitrogen species. Some genes, including hemN for heme biosynthesis, were subject to dual regulation by NnrR and FnrL.