Mechanisms for copper tolerance in Amphora coffeaeformis-internal and external binding

Growth of the ship-fouling diatom Amphora coffeaeformis and accumulation of copper in the cells were evaluated for cultures exposed to copper. Comparisons with literature reports for other species revealed that A. coffeaeformis shows no ability to maintain normal growth rates in the presence of high cellular copper levels. This suggests that internal binding is not the principal copper tolerance mechanism for this species. In addition, the copper complexing capacity of A. coffeaeformis exudates was evaluated. Significant complexing by these exudates was demonstrated by DPASV analysis. When added to the culture medium of another species (Thalassiosira profunda), A. coffeaeformis exudates were also able to reduce copper toxicity and accumulation in the cells of that species. However, the copper tolerance of A. coffeaeformis was greater than that acquired by T. profunda grown with A. coffeaeformis exudates; thus exudate production was deemed not to be a primary tolerance mechanism. Comparison of copper accumulations inside and outside cells of A. coeffeaeformis suggests that binding at the cell surface or to mucilage may be an important factor in the tolerance of this species to copper.