Susceptibility to heavy metals and cadmium accumulation in aerobic and anaerobic thermophilic microorganisms isolated from deep-sea hydrothermal vents

Thirty thermophilic strains isolated from heavy metal-rich hydrothermal ven t sites at Lau Basin were tested for their susceptibility to cadmium, zinc, cobalt, and nickel. The 14 aerobic spore formers belonging to the genus Ba cillus, 6 anaerobic fermenters from the order Thermotogales, and 10 anaerob ic sulfur reducers from the order Thermococcales could be clearly distingui shed according to their metal susceptibilities. The Thermococcales were fou nd to exhibit the highest resistance to cadmium and zinc, whereas Thermotog ales were highly sensitive to these metals. In contrast, the Thermotogales displayed the highest resistance to cobalt ions. No clear distinction could be established between the metal susceptibilities of these strains and sev en reference organisms used for comparative studies. Cadmium resistance, sl ightly inducible in some cadmium-resistant bacilli, was not plasmid mediate d. The amount of cadmium immobilized by the Thermotogales was related to th eir level of resistance to this metal.