Butanol Tolerance Regulated by a Two-component Response Regulator Slr1037 in Photosynthetic Synechocystis Sp. PCC 6803

Background: Butanol production directly from CO2 in photosynthetic cyanobacteria is restricted by the high toxicity of butanol to the hosts. In previous studies, we have found that a few two-component signal transduction systems (TCSTSs) were differentially regulated in Synechocystis sp. PCC 6803 after butanol treatment.

Results: To explore regulatory mechanisms of butanol tolerance, in this work, by constructing gene knockout mutants of the butanol-responsive TCSTS genes and conducting tolerance analysis, we uncovered that an orphan slr1037 gene encoding a novel response regulator was involved in butanol tolerance in Synechocystis. Interestingly, the ∆slr1037 mutant grew similarly to the wild type under several other stress conditions tested, which suggests that its regulation on butanol tolerance is specific. Using a quantitative iTRAQ LC-MS/MS proteomics approach coupled with real-time reverse transcription PCR, we further determined the possible butanol-tolerance regulon regulated by Slr1037. The results showed that, after slr1037 deletion, proteins involved in photosynthesis and glycolysis/gluconeogenesis of central metabolic processes, and glutaredoxin, peptide methionine sulfoxide reductase and glucosylglycerol-phosphate synthase with stress-responsive functions were down-regulated, suggesting that Slr1037 may exhibit regulation to a wide range of cellular functions in combating butanol stress.

Conclusions: The study provided a proteomic description of the putative butanol-tolerance regulon regulated by the slr1037 gene. As the first signal transduction protein identified directly related to butanol tolerance, response regulator Slr1037 could be a natural candidate for transcriptional engineering to improve butanol tolerance in Synechocystis.