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.