مراحم آشنگرف

Tellurium compounds can be found in high concentrations in land and water near sites of waste discharge of industrial manufacturing processes (1). Salts of oxyanions tellurite (TeO3-2) are toxic to many microorganisms at concentrations as low as 1 µgml-1 (4 µM). It has been suggested that this toxicity is due to the strong oxidizing ability of tellurite (2). Tolerance of bacteria to tellurite has been studied in previous works, but little is known about tolerance to the oxyanions in halophilc microorganisms (2). In the current study, isolation of halophiles from the salty environments was attempted. We isolated 90 strains of bacteria from different environments (saline soils, hyper saline waters and waste water of toxic dyes) in Iran. Among them, 49 strains were moderately halophiles and 41 strains were halotolerant. Agar dilution method was used to determine the bacterial tolerance to tellurite. Minimmum Inhibitory Concentration (MIC) for each oxyanion was determined. The MIC was defined as the minimum concentration of inhibitor preventing growth 34º C, pH 7.3, 10% (w/v) NaCl and one week incubation. Among strains, strain CHW1 (a halotolerant bacterium) and strains QW5 and QW6 (Halophile bacteria) could showed high-level resistance to tellurite. The strain CHW1 could tolerate the tellurite anion up to 20 mM, while strains QW5 and QW6 showed tolerate to potassium tellurite up to 10 and 12 mM, respectively. The influence of salinity (1, 5 and 10% NaCl) and various concentrations of selenooxyanions (5, 25, 50, 75 and 100 mM) on the toxicity of tellurite were determined. In halophilic strains, QW5 and QW6, enhancing the salinity from 1 to 10% (w/v), increased the tolerance from 4 to 10 and 6 to 12 mM, respectively, while in halotolerant strain (CHW1) by highering the concentrations of NaCl from 1 to 10% (w/v), reduced the MIC of tellurite from 22 to 16 mM. When potassium tellurite was used in combination with sodium selenite, tolerance to tellurite was increased in hal