Metal uptake potential of four methylotrophic bacterial strains from coal mine spoil, exploring a new possible agent for bioremediation

The abundance of total metal tolerant culturable bacteria and methylotrophic bacteria was numerated in the barren mine spoil. Metal resistant methylotrophic bacteria were isolated and identified through biochemical testing and 16SrRNA gene sequence analysis. The metal uptake potential of the isolates was determined. The size of the methylotrophic bacteria was significantly low (104) compared to total bacterial population (108). The methylotrophic population was less tolerant to the tested metals viz., Cd, Cu, Cr, Ni and Zn. The metal resistant isolates showed close similarity with Pseudomonas, Methylophilus and Methylobacterium sp. Lower concentration (5-10 μM) of al the tested metals was growth stimulatory. MIC values were lowest for Cd and highest for Zn. At the same time, MIC value was highest for Pseudomonas strain and lowest for Methylobacterium. Highest metal uptake was observed for Cd and lowest for Cr. Metal uptake potential varied with strain as well as metal species. There was no relation between the intracellular metal accumulation and metal adsorbed to the bacterial cell wall. Lowest adsorption capacity was exhibited by the Pseudomonas strain. Highest adsorption was for Cu and lowest for Ni. Metal uptake was rapid during first 4 h, and then after rate of uptake declined. It suggests that methylotrophic bacteria can be used as potential accumulator of Cd.