Uptake and efflux of 64Cu by the marine cyanobacterium Synechococcus (WH7803)

The uptake and efflux of 64Cu was studied in the marine cyanobacterium Synechoccous strain WH7803 (DC2). Uptake followed classical Michaelis∐Menten type kinetics in metal∐buffered seawater. The maximum uptake rate, Vmax, was 0.236 ± 0.016 × 10−18 mol Cu cell−1 h−1, with the half∐saturation constant, KS, of 10−10.81±0.11 mol L−1. An efflux mechanism was also observed in WH7803, whose growth was inhibited by high internal Cu concentrations. Efflux of Cu enabled WH7803 to maintain homeostasis for Cu at typical seawater ambient free copper concentrations ([Cu]f). The sensitivity of WH7803 growth to Cu was related to a simple inability to regulate internal Cu concentrations when external concentrations were >10−11 mol L−1.