Novel acidophiles isolated from moderately acidic mine drainage waters

The microbiology of water draining two abandoned mines in the UK and of a pilot-scale-constructed wetland site at one of the mine sites has been studied. The oxidation of ferrous iron in the acid mine drainage (AMD) of both mines is controlled by indigenous microbes and oxygen concentration, and is limited by the availability of nutrients, especially phosphate. A group of isolates that catalyse the oxidation of ferrous iron at pH >3 ("moderate acidophiles") were obtained from these samples, these outnumbered the more familiar extremely acidophilic iron oxidisers such as Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans. As in the feed AMD, moderate acidophiles outnumbered the more familiar extremely acidophilic iron-oxidising microbes in the surface water and sediment samples of the aerobic wetlands. Novel heterotrophic microorganisms were also isolated from the wetlands. Phylogenetic analysis based on 16S rRNA gene sequence showed that the moderately acidophilic iron oxidisers are unrelated to other more extremely acidophilic iron oxidisers, and revealed that the most dominant heterotrophic microorganisms include a novel Acidobacterium species and Propionibacterium acnes. These results suggest an important role for previously unknown moderately acidophilic iron-oxidising bacteria in the bioremediation of acidic mine drainage waters. (C) 2003 Elsevier B.V. All rights reserved.