Production of an extracellular copper-binding compound by the heterotrophic marine bacterium Vibrio alginolyticus

The heterotrophic marine bacterium Vibrio alginolyticus was shown to produce extracellular copper-binding compound (s) when exposed to copper in a seawater medium. Fractionation and analysis of copper, and methionine incorporation in culture supernatant fractions showed that the copper-binding compound coeluted with material which was radiolabeled with ³⁵S methionine. This suggests that the copper-binding compound may be proteinaceous. Analysis of label incorporation from ¹⁴C glucose into the fraction containing the copper-binding compound indicated that it was produced actively by the cells during recovery from copper toxicity, and was not present because of non-specific release by lysed bacterial cells. Concentrated supernatants from control and copper-challenged cultures contained two compounds which could be marginally resolved by size exclusion HPLC (26 kD and 28 kD), and which were produced at about a ten-fold higher level in copper-challenged cultures than in controls. These data indicate that the bacteria respond to toxic copper levels by excretion of a ca. 28 kD compound (s), which serves to detoxify copper in the medium by formation of organic copper complexes.The data suggest a potential role for macromolecules excreted by heterotrophic bacteria in control of copper ion activity in seawater. The production of copper-complexing compounds in response to copper represents a mechanism through which bacteria may directly influence the speciation of metal ions in seawater.