A highly resistant to toxic oxyanions, Halomonas sp. strain MAM.


Among the 22 strains of moderately halophilic bacteria isolated from saltern soils, the isolate MAM tolerated salt and grew well in nutrient broth containing 0.5-32% salt. Preliminary experiments revealed that the strain was highly resistant to oxianions. Agar dilution method was used to measure tolerance of the strain to metal (KCrO4, NaCrO4) and metalloid (Na2SeO4, Na2SeO3, Na2HAsO4, NaHSeO3, K2TeO3) oxianions. All tests were performed in nutrient agar plates with 5, 10, and 15% salt and incubated at 32 ?C. The results obtained, showed that the isolate can tolerate the oxianions tested up to the following concentrations: Arsenate 450 mM, selenate 400 mM, selenite 450 mM, biselenite 150 mM, chromate 25 mM, tellurite 1 mM. The data obtained proved that sodium plays an important role in bacterial growth, and also in tolerance to the oxianions tested. The strain MAM was able to grow in the presence of 25 mM sodium chromate but could not grow in potassium chromate in concentrations higher than 20 mM. . It is worth to emphasis that the strain tolerated tellurite and selenite and reduced the oxyanions also, producing black and dark red colonies due to the intracellular accumulation of the elemental tellurium and selenium. When potassium tellurite was used in combination with sodium selenite, the strain could tolerate up to 20 mM concentration of tellurite ions.