Proteomic And Metabolomic Analysis Reveals The Mechanism Of Cd²⁺ And Ethanol Tolerance In Synechocystis Sp.PCC 6803

Photosynthetic cyanobacteria can not only adapt to the extreme environment, but also produce valuable biological products, such as biofuels, through genetic modification. This study is divided into two directions, which are to analyze the tolerance mechanism of metal cadmium(Cd²⁺) and biofuel ethanol in Synechocystis sp. PCC 6803, respectively.Cadmium is a significant environmental pollutant, and has toxicity to both prokaryote and eukaryote organisms, so it is important to understand the regulatory mechanism of Cd²⁺ tolerance. Although some studies have described the metabolic responses against Cd²⁺ exposure, the related regulatory mechanism is still not clear in Synechocystis. In this study, we discovered a response regulator?RR?-encoding gene sll0649 in Synechocystis, which was involved in Cd²⁺ tolerance. Further phenotypic analysis reflected that ?sll0649 were more sensitive to Cu²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ stress as well. Using a quantitative iTRAQ-LC–MS/MS proteomics approach coupled with EMSAs, we found that, in addition to its positive regulation on genes directly related to Cd²⁺ utilization, Sll0649 can also function either directly or indirectly on expression of multiple genes related to transport several other metal ions as a key positive regulator. This study provided a proteomic description of the Cd²⁺ response network mediated by Sll0649, and revealed novel insights on the metal-tolerance mechanism in Synechocystis.Low ethanol tolerance is a crucial factor that restricts the bioethanol producting in renewable cyanobacterial systems. Our previous studies showed that several transcriptional regulators were involved in ethanol tolerance in Synechocystis. In this study, we identified that three transcriptional regulator-encoding genes sll1392, sll1712 and slr1860, whose mutants were more sensitive to ethanol stress, suggesting that the genes may be involved in the regulation of ethanol tolerance. To decipher the regulatory mechanism, using untargeted GC-MS approaches coupled with PCA and WGCNA analyses, we determined the responsive metabolites and metabolic modules related to ethanol tolerance in the three mutants. Interestingly, the results showed that there was a significant overlapping of the responsive metabolites and metabolic modules between three regulatory proteins, suggesting that a possible crosstalk between various regulatory proteins may be involved in combating against ethanol toxicity in Synechocystis. The study provided new insights into ethanol-tolerance regulation and knowledge important to rational tolerance engineering in Synechocystis.