Regulation Of Acid Tolerance By A Response Regulator Slr1909 In Synechocystis Sp.PCC 6803

Low pH is recognized as a major environmental stress to cyanobacteria that play a pivotal role in the global carbon cycling. Although several cellular mechanisms in response to acid stress were proposed, the regulatory mechanism related to acid stress has not been fully elucidated. In this study, by screening gene knockout mutants for all 44 putative response regulator(RR) encoding genes of Synechocystis sp. PCC 6803 grown under acid stress, a mutant of slr1909 gene encoding an orphan RR was identified to grow poorly in BG11 medium at pH 6.1-6.5 when compared with the wild type. Using a quantitative iTRAQ-LC-MS/MS proteomics approach coupled with GC-MS based metabolomics and quantitative real-time reverse transcription-PCR(RT-qPCR), the possible acid response network mediated by Slr1909 was further determined. The results showed that the signal transduction pathway mediated by Slr1909 may be independent from that mediated by SphS-SphR previously discovered, as none of the proteins and their coding genes regulated by SphS-SphR were differentially regulated in the ?slr1909 mutant grown under acid stress. 24 and 10 proteins were up- and down-regulated in the ?slr1909 mutant when compared with the wild type under acid stress condition, respectively. Notably, three proteins, Slr1259, Slr1260 and Slr1261 whose encoding genes seem located in an operon, were down-regulated upon the knockout of the slr1909 gene, suggesting their roles in acid tolerance. In addition, metabolomic analysis allowed identification of a dozen metabolites important for the discrimination of the ?slr1909 mutant and the wild type under acid stress, including several monosaccharide and fatty acids. The study provided a proteomic and metabolomic characterization of the acid-response network mediated by an orphan regulator Slr1909 in Synechocystis.