Copper and cadmium: responses in Pseudomonas putida KT2440

Aims: To compare responses of a soil bacterium to Cu and Cd. Methods and Results: In minimal medium, Cd caused a dose-dependent growth stasis of logarithmic phase cells of Pseudomonas putida, strain KT2440, whereas Cu did not compromise growth up to 10 mg l-1. Proteomics showed changes in accumulation of both membrane and soluble proteins by 6 h of treatment; increased Krebs cycle enzymes were apparent. Transcript analysis showed Cd- and Cu-induced different genes. Cd-induced genes encoding the transcriptional regulator CzrR2; an outer membrane protein associated with lipopolysaccharide stability, H1; two oxidative stress protective proteins and the P-type ATPase, CadA2, associated with Cd2+ efflux. The genes most responsive to Cu encoded the regulator CopR1 and the outer membrane resistance protein regulated by CopR1, CopB1; a putative porin, PorD and the Cu-binding protein, PacZ or CopZ, and CopA2. Conclusions: These findings support that a soil pseudomonad restricts internalization of the metals by using different sets of binding proteins and efflux pumps. Activation of mechanisms to protect against oxidative stress also was evident especially with Cd exposure. Significance and Impact of the Study: The differential cellular responses to Cd and Cu suggest that risk assessment for Cd and Cu should be different.