The tolerance experiments were carried out in 250 mL conical flasks, each containing 45 mL of YA broth. Approximately equal numbers of cells from the four isolated strains were used and the bacterial mixtures with an initial cell density of 1 × 108 cells/mL for each of the isolated strains. All cultures were incubated at 30 ◦C and agitated at 200 rpm. To study the influence of heavy metals on bacterial growth, bacterial mixtures were exposed to a mix of heavy metals with individual concentrations ranging from 0 to 10 mM.