Enhancement of bacterial efficiency for metal removal using mutation techniques

The objective of the present study was to obtain by mutation and selection techniques bacterial strains capable of removing heavy metals at high efficiency. Four of the bacteria most promising in metal uptake, Staphylococcus aureus, Bacillus Sphaericus, B. licheniformis and Arthrobacter sp. were selected after isolation from water heavily polluted with heavy metals. Two mutagenic agents were used: U.V. irradiation at 245 nm (physical) and 1\% ethidium bromide (chemical). Optimum conditions for metal removal by most of the tested bacteria were: pH 9, 50 degrees C and 200 rev/min agitation speed. Induction of mutation both physically or chemically resulted in mutants that were superior over their wild types in removing heavy metals under investigation. The highest removal efficiencies (REs) achieved were in the following order: Cd(89.19-100\%); Cr(87.3-99.7\%); Zn(47.7-100\%); Cu(40.8-84.7\%); Pb(40.2-51\%); Fe(17.5-28.7\%); Ni(13.8-23.9\%) and finally Co(17.2-18.4\%). Using mixed cultures of the wild and the selected mutants enhanced the RE(s) of some metals compared to those obtained by individual species, and the time required to achieve the highest RE was reduced.