An investigation was carried out to determine the sensitivity of diffe
rent soil microbes (Rhizobium, Bradyrhizobium and Pseudomonas) to vari
ous metals (Cu2+, Zn2+, Co2+, Mn2+, Mo2+ and Fe2+) in vitro. Sulphate
and chloride forms of these microelements were used (except Mo2+ as Na
2MoO4) in 0.1, 1.0 and 10 mu g/ml concentrations in modified YEM and n
utrient broth. Growth (optical density, OD550 and OD640) of bacterium
inoculated (approx. 10(6) CFU/ml) tubes, was measured spectrophotometr
ically after 48 h of incubation at 28 degrees C in a rotary shaker (15
0 rpm). Data of triplicate samples are shown as percent of control tub
es (inoculated, free from treatments) and after an analysis of varianc
e SE was calculated. Strains of Rhizobium leguminosarum proved to be t
he most sensitive to Cu2+, Zn2+ and Co2+. The slow growing Bradyrhizob
ium and plant growth pronating (PGPR) Pseudomonas isolates, however, w
ere affected only at the highest (10 mu g/ml) dose of these elements.
In contrast Mn2+, Mo2+ and Fe2+ microelements were stimulatory for the
growth of all investigated soil microbes. Sulphate forms of the most
harmful Cu2+ and Zn2+ cations were more toxic than the chloride forms.
An especially high diversity was found among the R. leguminosarum bv.
viceae isolates. Monitoring the sensitivity of these microbes has a p
rimary importance for selection of ecologically diverse isolates, as p
otential inocula in heavy-metal affected soils.