Sll1725, an ABC transporter in Synechocystis sp. PCC 6803 for the detoxification of cadmium ion stress

Cadmium threatens eco-environmental security and human health, but the interaction between cadmium and microalgae cells remains unknown. This research examined the molecular detoxification mechanism of Synechocystis sp. to cadmium. The results indicated that cadmium stress significantly inhibited chlorophyll a content and maximum photochemical quantum yield (Fv/Fm), with EC₅₀ of 0.50 mg L^-1. The differentially expressed genes/proteins (DEGs/DEPs) were significantly enriched in pathways of two-component system, translation, nucleotide metabolism, ribosome, photosynthesis and chlorophyll synthesis. 1073 DEGs and 338 DEPs were identified, and 84 DEGs/DEPs with consistent expression trends were obtained. Foldchange of Sll1725 ranked fourth in DEGs/DEPs but its function was unexplored. Phylogenetic analysis and 3D structure identified Sll1725 as an ABC transporter and molecular simulation determined its cadmium-efflux function. Under 0.50 mg L^-1 cadmium stress, Δsll1725 had lower growth and Fv/Fm values than the wild-type. Meanwhile, the intracellular cadmium in Δsll1725 was higher, indicating that Sll1725 mitigated cadmium toxicity by efflux. The duckweed with overexpressed sll1725 exhibited cadmium tolerance. It could be deduced that Sll1725, belonged to ABC transporters, which played an important detoxification mechanism. These mutants might possess the potential for bioremediation. This study provides a basis for applying algal genetic resources in cadmium pollution treatment.