Identification Of A Transporter Slr1216 Involved In Salt Tolerance In Cyanobacterium Synechocystis Sp.PCC 6803

Engineered cyanobacteria have been gradually employed to product multiple biofuels,hence a comprehensive understanding of the entire salt acclimation process would be valuable because future mass cultivation of cyanobacteria will be performed in seawater.In the model cyanobacterium Synechocystis sp.PCC 6803,the details of cellular response networks to high and changing salt concentration are not immediately available.In this study,by screening gene knockout mutants of 58 Synechocystis transporter-encoding genes under salt stress,we found a mutant of slr1216,annotated as the magnesium transporter encoding gene in CyanoBase,was less tolerant to salt than the wild type,meanwhile the tolerance loss can be recovered to the similar level of the wild type by complementing the slr1216 gene to the ?slr1216 mutant,suggesting that slr1216 may be involved in salt tolerance in Synechocystis.Interestingly,we found that the salt effect on growth of the ?slr1216 mutant could be complemented by higher magnesium concentrations in the medium,suggesting that Slr1216 may act as a magnesium transporter in Synechocystis.Through flow cytometric analysis,we found that the content of chlorophyll a of the ?slr1216 mutant was slightly decreased when compared with wild type under salt stress.An integrated LC-MS based-and GC-MS based-metabolomics analysis showed many phosphorylated metabolites and intracellular osmo-protective compounds,including glucosylglycerol(GG)and sucrose were affected in the ?slr1216 mutant grown under salt stress,while the GG content was also recovered to a similar level of the wild type in the complementation strain.In addition,the positive effect of exogenously provided GG on growth of the ?slr1216 mutant under salt stress was also observed.Together,the results showed that Slr1216 might act as a magnesium transporter and be involved in salt tolerance by affecting intracellular compatible solutes and chlorophyll a,which provided new insight into the complex cellular response networks to salt stress in Synechocystis.