Quantitative evaluation of heavy metal bioaccumulation by microbes

Bacterial isolates- AAD1, AAD2, AAD3, AAD4 and AAD5 -were isolated from garden soil, industrial waste waters and textile effluent samples, showing heavy metal tolerance against four heavy metals- Hg, As, Pb and Cd. The isolates were identified using various biochemical tests and 16S rRNA sequencing method. The Minimum Inhibitory Concentration (MIC) for these isolates was determined and it was found to be in the range of 58.93 - 294.60 ppm (Hg), 319.32 - 1596.60 ppm (As), 323.70 - 625.80 ppm (Pb) and 100 - 3322 ppm (Cd). Bioaccumulation of heavy metals was studied in the presence of NaCl concentration variation, pH variation, temperature variation and time dependent accumulation and detected using ICP-AES analysis. The isolates were found to show bioaccumulation capacities at high heavy metal concentrations, neutral pH and high salt concentrations. It was seen that as the time increased, the amount of bioaccumulation efficiency also increased. The cells were immobilised using calcium alginate beads and the bioaccumulation studies showed that immobilized cells were more effective than free cells. These immobilized cells were further used for treatment of effluent samples and were found to be efficient in removal of heavy metals from effluents. These heavy metal resistant organisms could be potential agents for bioremediation of heavy metals polluted environment. Key words: Heavy metal, metal bioaccumulation, ICP-AES analysis, Minimum Inhibitory Concentrations, Immobilization, Effluent treatment.