Isolation and identification of heavy metal tolerant bacteria from industrial effluent metal dumping sites and wastewater of Solan region

Abstract

newline Abstract newlineThe present study aimed at identifying heavy metal tolerant bacteria in soil samples obtained from three different sites in and around Solan city of Himachal Pradesh. The samples included industrial effluents from manufacturing unit of batteries and invertors at Oachhghat, metal dumping site at Chambaghat (Salogra) and domestic waste contaminated site at Solan city. From each location, 8, 8 and 6 soil samples respectively were collected. The collection sites were located 5-10 metres apart at each location. For recovery of bacteria from the soil samples, each sample was serially diluted tenfold; the highest dilution (10-6) of each sample was inoculated onto nutrient agar plates and incubated at 37°C for 24 hrs. Colonies with different morphological features from the mixed cultures were subcultured in order to obtain pure colonies. These colonies were then grown on nutrient agar containing different molarities of salts of heavy metals (Zn, Cd, Pb and Co). The highest concentration of each heavy metal at which the growth was observed were as follows: Zn-8mM, Cd-4mM, Pb-6mM and Co-4mM. The bacteria having multiple tolerances were identified as Comamonas testosteroni (3), Pseudomonas spp. (3), Staphylococcus nepalensis (3), Bacillus licheniformis (3), B. cereus (3), B. subtilis (3) and Micrococcus spp. (2) on the basis of colony morphology, microscopic examination and biochemical tests. One sample each of Comamonas testestroni, Staphylococcus nepalensis and Bacillus licheniformis were identified on the basis of partial nucleotide sequencing of amplicons of their 16S rRNAs. The tolerant isolates were further subjected to in vitro antibiotic cultural sensitivity assay and were found resistant to multiple antibiotics. The emergence of such resistant bacteria may be a serious public health problem since the study indicates that these bacteria may be of human and animal origin. The treatment of such bacteria would be really very difficult. The studies may further be extended to determine the correlation between heavy metal and antibiotic resistance in the tolerant isolates. The study is of significance in that such bacteria can be utilized for bioremediation of heavy metals in the environment particularly in the treatment of sewage water and industrial effluents.