METAL SENSITIVITY OF SOME SYMBIOTIC N-2-FIXING BACTERIA AND PSEUDOMONAS STRAINS

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.