isolation and identification of heavy metal resistant bacteria from industrial wastewaters in guilan province

heavy metal pollution by natural factors is a world-wide phenomenon. release of large quantities of heavy metals without handling proper processes that could decrease the concentration of such a material is a hassle that makes strains resistant to these heavy metals apart from entering into human food chain. in this research, wastewater of four firms in guilan province such as foolad, risandegi, chooka and ganje tannery were analyzed according to standard methods. these methods were included culturing the strains on the specified media such as luria-bertani agar and kings’ b. in the wastewater of these factories, there were kinds of heavy metals such as chromium, nickel, cobalt, mercury and etc. however existence of these heavy metals is fatal to keep the life progressive, but a kind of creatures like some bacteria could adapt themselves to the condition. here we mentioned two genera of bacteria, bacillus sp. and pseudomonas sp., which were more renowned in the category of resistance to heavy metals. first of all, we used nutrient agar medium in order to distinction of gram positive bacteria from gram negative ones. after that, by dilution preparation from sample and inoculation the bacterial suspension into medium, the range of resistance to heavy metal concentration for bacillus sp. in luria-bertani agar and for pseudomonas sp. in kings’ b medium were determined. this estimation was validated by adding salt of heavy metal by the concentration from 0 µg/ml through 100 µg/ml and ph from 5 to 9. results showed that both of two isolates had the most accumulation rate in ph=7 and concentration of 50 µg/ml heavy metal.