ارزيابي مقاومت به اكسي آنيون هاي سمي در باسيل هاي اسپوردار نمك دوست نسبي بومي ايران و اثر شوري بر روي اين مقاومت

Survey of Toxic Oxyanions Tolerance in Native Moderately Halophilic Spore Forming Bacilli and Effect of Salinity on this Tolerance

Halophilic microorganisms play an important role in biotransformation or bioremediation of toxic ox anions. Recognizing the tolerance to higher concentration of toxic oxyaniones in these bacteria will assist to determination of their potential for biorernediation. We have isolated ten moderately halophilic spore forming bacilli from various saline soils in Iran and identified their intrinsic high-level-resistance to chromate, arsenate and 4 other toxic oxianions (potassium tellurite, sodium selenite, sodium selenate and sodium biselenite) by agar dilution method. Minimum inhibitory concentration (MIC) for each oxianion was determined, as the lowest concentration of inhibitor that preventing of growth at 34 °C after 72h incubation. All bacteria tested (10 isolates) were resistant to higher concentrations of arsenate. The strains B2 and C2 could tolerate arsenate up to 250 mM. Unusual resistance was observed toward chromate oxianions. Some isolates, the strains A2, Bl and C2 could tolerate sodium chromate up to 75 mM, while strain C2 showed tolerate to potassium chromate up to 70 mM and other strains (A I, A2, BICI, C4) could showed resistance to chromate up to 60 mM. The resistance level of the isolates to selenooxianions was between 10-40 mM. The maximum tolerance was showed with selenite and the minimum tolerance was found with biselenite oxianions. The highest toxicity was found with tellurite (up to 3 mM). The influence of salinity on the toxicity of oxianions was also studied. Increasing the salinity from 5% (w/v) to 15% (w/v), in general, enhanced sensitivity to toxic oxianions.