Co-existence of Metal Transporter Genes and Heavy Metal Bioremediation Potential of Bacterial Strains from the Effluent Water

Abstract

Heavy metal contamination and accumulation pose a major threat to all life forms in the environment due to its toxic nature, non-biodegradable properties and accumulative behavior. The present study aims to investigate the metals resistance mechanisms, removal capacity and bioremediation potential of the high metal-resistant indigenous bacterial species Bacillus thuringiensis strain BHR1, Bacillus cereus strain BHR2, Enterobacter cloacae strain BHR4, Bacillus pumilus strain BHR5, Bacillus altitudinis strain BHR6 and Klebsiella pneumonia strain BHR8 isolated from the effluent water. Moreover, the presence of specific metal transporter genes such as chrA, chrB, pbrA and nccA in these isolates indicated their role in metal resistance and removal. Based on minimum inhibitory concentration, bacterial isolates namely, BHR1 and BHR5 exhibited high metal tolerance against Cr (510 and 550 ppm), Pb (250 and 300 ppm), Ni (300 and 150 ppm) and As (200 and 120 ppm), respectively. The bioremediation potential of these bacterial isolates (BHR1 and BHR5) was evaluated under batch-scale conditions. Our results revealed that the addition of nutrients, as well as modification of pH to 6.0, enhances the bioremediation potential of BHR1 enabling the reduction of Pb, Cr, Ni and Zn by 60.9%, 31%, 22.7% and 22%, respectively. These findings suggested the potential application of these metal resistant bacterial isolates for the bioremediation of heavy metal contaminated effluents.