Sensitivity of thermophilic methanogenic bacteria to heavy metals

Abstract

The effects of Cd, Cu, and Ni on pure cultures of thermophilic methanogenic bacteria were studied. The bacteria used wereMethanobacterium thermoautotrophicum and TAM, a thermophilic, acetate-decarboxylating, methanogenic bacterium. Much lower concentrations of heavy metals were needed to cause initial inhibition of TAM (1 mg/liter Cu and Cd; 5 mg/liter Ni) compared withM. thermoautotrophicum (10 mg/liter Cu and Cd; and 100 mg/liter Ni). No growth of TAM occurred at 5 mg/liter Cu and 25 mg/liter Ni, while the corresponding values forM. thermoautotrophicum were 50 mg/liter Cu and 200 mg/liter Ni. Cd (50 mg/liter) was totally inhibitory toM. thermoautotrophicum but allowed minimal growth of TAM. Ni stimulated both organisms at an optimal concentration of 5 mg/liter forM. thermoautotrophicum and 1 mg/liter for TAM. The toxicity of Cd and Cu was found to depend upon the presence of Ni in the medium.