Effects of heavy metals on growth of species of Micrococcus and Pseudomonas in a crude oil/mineral salts medium

Bioassays were conducted to observe the responses of species of Micrococcus and Pseudomonas to the metals zinc, lead, copper and manganese, added singly or in combination to a crude oil/mineral salts medium. Bacterial density decreased with increasing metal ion concentration. A 50% reduction (LC50) in the bacterial density of Micrococcus sp. occurred on the addition of either 0•46 μg zinc/ml, 1•41 μg lead/ml, 11•25 μg copper/ml or 28•2 μg managanese/ml. For Pseudomonas sp., the corresponding values were 0•43 μg zinc/ml, 2•80 μg lead/ml, 6•30 μg copper/ml or 317•0 μg manganese/ml. Of the metals tested, only zinc was found in higher concentrations in the oil contaminated site than the LC50 value obtained.