New perspectives in acid mine drainage microbiology

Acid mine drainage varies significantly from site to site, and spans a wide range of pH, temperature and oxygen content. Such variations inevitably mean that a variety of acidophilic microorganisms with varying physiological properties can be found in AMD. With our increased understanding of the microbiology of AMD, better experimental design will lead to a greater understanding of the biogeochemistry of these environments. For example, even though it is readily accepted that at pH 4 and below abiotic oxidation of iron does not occur, it has been concluded that oxidation of iron in mine drainage of ∼ pH 3.5 was not due to microbial activity. This conclusion was based on the fact that no oxidation of iron occurred in culture medium typically used for A. ferrooxidans with a pH of 2, thereby excluding the growth of the moderate acidophiles that probably inhabited that mine drainage.In addition, the detection of acidophiles with varying physiological capabilities allows for the further development of strategies for the remediation of this important pollution problem, and ultimately to the continued exploitation of minerals. Such emerging strategies include the use of acidophiles with varying pH optima for oxidation and precipitation of iron from AMD of varying water chemistry. Also, the exploitation of key phenotypes such as arsenite oxidation capacity of Thiomonas spp. allows for the removal of key pollutants in AMD. Similar approaches can also be taken for other toxic metals such as chromate. Lastly, the isolation and further understanding of anaerobic acidophiles has led to the proposal of methodology to selectively precipitate toxic metals from AMD, turning a pollution problem into a potential source of metals.

Research highlights► Acid mine drainage varies from site to site with respect to geochemical parameters. ► The geochemical variation is reflected by differing populations of acidophiles that inhabit AMD. ► Acidophilic microorganisms vary significantly in physiological and metabolic characteristics. ► The metabolic variations of acidophiles can be exploited in a variety of AMD remediation strategies.