Proteomic Analysis Reveals Resistancemechanism Against Hexane In Synechocystis Sp. PCC6803

Recent studies have demonstrated that photosynthetic cyanobacteria could be an excellent cell factory to produce renewable biofuels and chemicals due to their capability to utilize solar energy and CO2as the sole energy and carbon sources. Biosynthesis of carbon-neutral biofuel alkanes with good chemical and physical properties has been proposed. However, to make the process economically feasible, one major hurdle to improve the low cell tolerance to alkanes needed to be overcome.Towards the goal to develop robust and high-alkane-tolerant hosts, in this study, the responses of model cyanobacterial Synechocystis PCC6803to hexane, a representative of alkane, were investigated using a quantitative proteomics approach with iTRAQ-LC-MS/MS technologies. In total,1,492unique proteins were identified, representing about42%of all predicted protein in the Synechocystis genome. Among all proteins identified, a total of164and77proteins were found up-and down-regulated, respectively. Functional annotation and KEGG pathway enrichment analyses showed that common stress responses were induced by hexane in Synechocystis. Notably, a large number of transporters and membrane-bound proteins, proteins against oxidative stress and proteins related to sulfur relay system and photosynthesis were induced, suggesting that they are possibly the major protection mechanisms against hexane toxicity.The reliability of proteomics results was verified by mutant analyses. Six mutants△slr0298,△sll0779,△slr1490,△slr2131,△slr1205,△slr1828whose coding genes were up-regulated, were constructed. Growth of mutants and wild type strain was assessed under BG11normal medium or medium supplemented with0.8%hexane. No obvious difference was found between mutants and wild type strain, suggesting the complexcity of the hexane response network, change in a single gene can not fully change the tolerance of Synechocystis.The study provided the first comprehensive view of the complicated molecular mechanism employed by cyanobacterial model species, Synechocystis to defend against hexane stress. The study also provided a list of potential targets to engineer Synechocystis against hexane stress.