2.6. Bioremediation of heavy metal
Five milliliters ofthe overnight pre-culture were inoculated into
45 mL of YA broth contained in 250 mL conical flasks. The YA broth
contained 5 mM urea and 25 mM CaCl2, which were filter sterilized
using a 0.22 m filter, and was supplemented with 2 mM of heavy
metal mixture. The flasks were incubated in a shaking incubator
(200 rpm) at 30 ◦C for 48 h. Control sets without any added bacterial
cells were also included in all experiments.After incubation,the
cultures were centrifuged at 8000 × g for 15 min. The heavy metal
bioremediation by single cultures and bacterial mixtures (A3) were
calculated as the percentage difference between the initial and final
concentrations of heavy metals present in the supernatants. Concentrations
of heavy metals were measured using a Perkin-Elmer
OPTIMA-7300DV inductively coupled plasma optical spectrometer
(ICP-OES, PerkinElmer, Inc., USA).