RESISTANCE OF ENVIRONMENTAL BACTERIA TO HEAVY-METALS

Bacteria were isolated from different naturally polluted environments. Metal-resistant bacteria were selected and minimal inhibitory concent rations of heavy metals (MICs) for each isolate were determined. In ad dition the mobility of the most important metallic cations (Cu, Zn, Cr , Cd, Co, Hg) was evaluated by comparing results obtained by two tests of toxicity in solid and liquid media. Results of the test of toxicit y in solid media agreed with those in liquid, however; inhibitory conc entrations in solid media were much higher than those in liquid. The r ange of metal concentrations tolerated in solid and liquid media yield ed information on the capacity of adsorption and complexation of rite metals. Mercury, and to a lesser degree copper, seemed to have a good capacity for adsorption and complexation and, consequently had a limit ed diffusion in different naturally polluted environments. The presenc e of metals in the growth medium allowed us to maintain the tolerance of bacteria at a comparable level with that observed in naturally poll uted environments. Cu and Cr were the best tolerated metals. Hg was th e most toxic component for all bacteria, followed by Co and Cd. Pseudo monas aeruginosa (strain S6), with a relatively high MIC for metals an d a large spectrum of-antibiotic resistance appears to be a bacterial model for eco-toxicological studies. (C) 1998 Published by Elsevier Sc ience Ltd. All rights reserved.