Cadmium Tolerance Mechanism And Engineering In Synechocystis Sp.PCC 6803

In recent years,cyanobacteria have attracted widely attention because of serving as an ‘autotrophic microbial factory'.Cyanobacteria,a group of extensively existed photosynthetic prokaryotes,play a pivotal role in the global carbon and nitrogen cycling as well as in some bioremediation applications,such as the removal of toxic heavy metals.One of the most common heavy-metal contaminants is cadmium(Cd2+),which is generally toxic to organisms at low concentrations.It is very important to study the Cd2+ metabolic responses of cyanobacteria.In this study,firstly,the DNA-Affinity-Purified-chip(DAP-chip)assay was applied to identify the direct regulation target sites of Sll0649,the Cd2+ tolerance related regulator,in Synechocystis sp.PCC 6803.As a result,the upstream region of slr0946 was enriched 4 folds as determined by qPCR analysis.Electrophoretic mobility shift assays(EMSAs)also demonstrated that Sll0649 was able to bind directly to the promoter region of slr0946.Secondly,to confirm the involvement of slr0946 in Cd2+ telorance,the ?slr0946 mutant was constructed and phenotype analysis showed that the ?slr0946 mutant was more sensitive to Cd2+ when compared with the wild type strain under 5.0 ?M Cd2+ stress condition,and the growth loss could be recovered by complementing slr0946 in the ?slr0946 mutant with 5.7 ?M Cd2+,suggesting that the slr0946 gene was involved in Cd2+ tolerance in Synechocystis.Finally,overexpression of three Cd2+ tolerance related genes,sll1598,slr0798 and slr0946,respectively in the wild type could obviously improve the Cd2+ tolerance of Synechocystis under 5.7 ?M Cd2+.The study provided a better understanding of the tolerance regulatory mechanism of Cd2+ stress in Synechocystis,and successfully constructed three cadmium-resistant strains in Synechocystis,which could be useful cyanobacterial chassis for further Cd2+ tolerance engineering.