Butanol tolerance regulated by a two-component response regulator Slr1037 in photosynthetic Synechocystis sp. PCC 6803

Abstract

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.

Keywords: Butanol; Proteomics; Response regulator; Synechocystis; Tolerance.

Figure 1

Growth of the wild type and the mutant ∆slr1037 of Synechocystis in BG11 media with or without butanol. BG11 medium was supplemented with 0.25% (v/v) butanol.

Figure 2

Growth time courses of the wild type and the ∆slr1037 mutant of Synechocystis under various stress conditions. A) pH 6.5; B) pH 11.0; C) 8 mM urea; D) 1.75% ethanol; E) 4.0% NaCl.

Figure 3

Schematic representation of central metabolic processes regulated by Slr1037.

Figure 4

Putative regulatory module identified upstream of the genes encoding ∆slr1037-responsive proteins. The motif is represented by a sequence logo generated by the WebLogo software [62].