Copper-induced inhibition of growth of Desulfovibrio desulfuricans G20: Assessment of its toxicity and correlation with those of zinc and lead

The toxicity of copper [Cu(II)] to sulfate-reducing bacteria (SRB) was stud ied by using Desulfovibrio desulfuricans G20 in a medium (MTM) developed sp ecifically to test metal toxicity to SRB (R. K. Sani, G. Geesey, and B. M. Peyton, Adv. Environ. Res. 5:269-276, 2001). The effects of Cu(II) toxicity were observed in terms of inhibition in total cell protein, longer lag tim es, lower specific growth rates, and in some cases no measurable growth. At only 6 muM, Cu(II) reduced the maximum specific growth rate by 25% and the final cell protein concentration by 18% compared to the copper-free contro l. Inhibition by Cu(II) of cell yield and maximum specific growth rate incr eased with increasing concentrations. The Cu(II) concentration causing 50% inhibition in final cell protein was evaluated to be 16 muM. A Cu(II) conce ntration of 13.3 muM showed 50% inhibition in maximum specific growth rate. These results clearly show significant Cu(II) toxicity to SRB at concentra tions that are 100 times lower than previously reported. No measurable grow th was observed at 30 muM Cu(II) even after a prolonged incubation of 384 h . In contrast, Zn(II) and Pb(II), at 16 and 5 muM, increased lag times by 4 8 and 72 h, respectively, but yielded final cell protein concentrations equ ivalent to those of the zinc- and lead-free controls. Live/dead staining, b ased on membrane integrity, indicated that while Cu(II), Zn(II), and Pb(II) inhibited growth, these metals did not cause a loss of D. desulfuricans me mbrane integrity. The results show that D. desulfuricans in the presence of Cu(II) follows a growth pattern clearly different from the pattern followe d in the presence of Zn(II) or Pb(II). It is therefore likely that Cu(II) t oxicity proceeds by a mechanism different from that of Zn(II) or Pb(II) tox icity.