Isolation and Characterization of Thiobacillus ferrooxidans from Coal Acid Mine Drainage

Coal mine drainage refers to the acidic drainage caused by surface mining, deep mining or coal refuse piles. Being highly acidic with elevated levels of dissolved metals, it is otherwise known as “Acid Mine Drainage (AMD)”. Formation of AMD is due to a series of geochemical and microbiological processes involving acidophilic chemolithotrophs such as Thiobacillus, Thiomispora, Leptospirillum etc. Presence and growth of these bacteria in coal mine drainage further decreases pH, making the drainage more acidic. Such highly acidic drainage when mixes with other water bodies disrupt the normal aquatic food web. In the present study, a chemolithotrophic, acidophilic, ironoxidizing, gram-negative, stricked shaped bacteria i.e Thiobacillus ferrooxidans preferring temperature range 20-35°C was isolated and microbiological characterization was performed. The study revealed that it is an aerobic, mesophilic, acidophilic bacteria having variable pH tolerance range (2-8). Detailed growth analysis revealed its chemoautotrophic, mixotrophic and heterotrophic mode of growth. Heterotrophic and mixotrophic growth of bacteria with added carbon substrate led to the improvement of pH of the culture medium indicating the cessation of chemolithotrophic activity. The study therefore suggested that supplementation of coal mine drainage with organic carbonaceous substrate can be one of the effective environmental management strategy for minimizing acid production by the chemolithotrophs.