Acid and Heavy Metal Tolerant Bacillus sp. from Rat-Hole Coal Mines of Meghalaya, India

Abstract

Coal is a major natural resource of Northeast India and the indigenous process of coal mining known as rat-hole mining results in the pumped mine water being released to the nearby land and water bodies contaminating the area and destroying life forms due to acid mine drainage. The present study aimed at isolating acid and metal resistant bacteria from the rat-hole coal mines to assess their acid and metal tolerance isolated two Bacillus sp. with good tolerance to iron, cadmium and chromium which grew well at pH 5 and could remain viable up to pH 2 without any apparent growth. Growth experiments at pH 2–4 indicated the failure of the isolates to grow and produce colony though they survived metabolically viable. However the inoculum obtained from broth culture incubated for 72 h at pH 2–4 produced distinct colonies when plated in medium at pH 5. Bacillus subtilis subsp. inaquosorum SK22 showed comparatively higher maximum tolerable concentration (MTC) for iron in comparison to Bacillus cereus SK44. Both had the same MTC for both cadmium and chromium. The minimum inhibitory concentration (MIC) and maximum bactericidal concentration (MBC) was similar for cadmium and chromium for both the Bacillus sp. MIC and MBC for iron was higher in case of Bacillus subtilis subsp. inaquosorum SK22 than that of Bacillus cereus SK44. This higher resistance to acidic pH and high metal concentration indicated their potential to be good candidates for bioremediation of contaminated soil and water bodies affected by rat-hole mining and acid mine drainage.