Contribution of Hfq to photooxidative stress resistance and global regulation in Rhodobacter sphaeroides

Abstract

The photosynthetic alphaproteobacterium Rhodobacter sphaeroides has to cope with photooxidative stress that is caused by the bacteriochlorophyll a-mediated formation of singlet oxygen ( 1O 2). Exposure to 1O 2 induces the alternative sigma factors RpoE and RpoH II which then promote transcription of photooxidative stress-related genes, including small RNAs (sRNAs). The ubiquitous RNA chaperone Hfq is well established to interact with and facilitate the base-pairing of sRNAs and target mRNAs to influence mRNA stability and/or translation. Here we report on the pleiotropic phenotype of a Δhfq mutant of R. sphaeroides, which is less pigmented, produces minicells and is more sensitive to 1O 2. The higher 1O 2 sensitivity of the Δhfq mutant is paralleled by a reduced RpoE activity and a disordered induction of RpoH II-dependent genes. We used co-immunoprecipitation of FLAG-tagged Hfq combined with RNA-seq to identify association of at least 25 sRNAs and of mRNAs encoding cell division proteins and ribosomal proteins with Hfq. Remarkably, >70% of the Hfq-bound sRNAs are 1O 2-affected. Proteomics analysis of the Hfq-deficient strain revealed an impact of Hfq on amino acid transport and metabolic functions. Our data demonstrate for the first time an involvement of Hfq in regulation of photosynthesis genes and in the photooxidative stress response. © 2011 Blackwell Publishing Ltd.