Abstract
The aim of this research was to examine how a marine bacterium Vibrio alginolyticus modifies the form of a particular trace metal, copper, in seawater. The study included examinations of both the effect of copper on the bacterium as well as the effect of the bacterium on copper.Calorimetric, radiochemical and plate counting techniques were used to determine the effect of copper on metabolism and survival of cultures of the bacterium. Toxicity was determined to be the primary interaction of copper with the bacterium at natural concentrations of cells and copper. Copper, added as Cu(II), was more toxic to the cells in anaerobic culture (IC50, 1.6nM) than in aerobic culture (IC50, 0.5nM). The additional toxicity seen in anaerobic culture was due to a cytostatic effect that resulted in a decrease in the rate of metabolism of the surviving cells. The cytostatic effect was attributed to the inhibition of the metabolism of pyruvate via mixed acid fermentation.The culture was able to overcome the toxicity after a lag period by releasing a chelator similar to metallothioneins produced by other organisms. Studies with aerobic cultures of the bacterium found that cells (1 x 10('8) cells/ml) removed 6 (mu)M copper from the solution independent of the concentration of copper in solution and growth phase at the time of exposure. This limited copper removal by the cells was attributed to the saturation of surface cell sites.The effect of speciation on the toxicity of copper was examined by calorimetry. Both inorganic and organic complexing was investigated. The differences in protection of the bacteria from copper by complexation with the various ligands were attributed to kinetic effects, which are not considered in the calculation of copper speciation by thermodynamic models.A similiar study with a mixed culture of bacteria from seawater also demonstrated limited removal of copper from solution and complexation of soluble copper by a chelator. These results along with those from the V. alginolyticus demonstrate that bacteria affect the form of copper in seawater by removal and complexation. This effect is due to the response of the bacteria to the toxicity of copper.