Potassium regulates cadmium toxicity in Microcystis aeruginosa

Microcystis aeruginosa (M. aeruginosa) was found to be capable of cadmium (Cd²⁺) assimilation. Potassium (K⁺), an essential factor in transmembrane transport, can possibly manipulate the interaction between Cd²⁺ and M. aeruginosa. In this study, the effect of available K⁺ levels on Cd²⁺ toxicity in M. aeruginosa is examined. The results showed that the K⁺ level was positively linked with toxicity of Cd²⁺ to M. aeruginosa. And with respect to the M. aeruginosa incubated in K⁺ = 460 μM treatment, the release of extracellular polymeric substance was augmented, which benefited the retention of Cd²⁺ on the M. aeruginosa surface. In addition, the assimilation of Cd²⁺ showed a 3.42-fold increase in comparison to that without K⁺ supplement. Moreover, the enhanced K⁺ level caused the up-regulation of the Cd²⁺ transporting protein and down-regulation of the Cd²⁺ efflux protein, associated with the positive energy metabolism response. These results documented that the K⁺ availability could influence the toxicity of Cd²⁺ to M. aeruginosa jointly through the manipulation of Cd²⁺ assimilation, excretion, and the biological response. These findings may attach importance to the effects of K⁺ level on Cd²⁺ assimilation by M. aeruginosa and shed a degree of light on the enhanced Cd²⁺ removal using algal-based technology.