Molecular Research of Acid-Generating Microbial Communities in Abandoned Ores in the Waste Dump of an Iron Mine in Anhui Province

Abstract

The waste dump of an iron mine in Anhui Province has been abandoned for several decades. Pyrite in the exposed waste ores is oxidized by acidophiles and large amounts of metal ions and H2SO4 are released, resulting in the formation of an acid mine drainage (AMD) lake since 1970s. Besides the lake, there are also some small-scale AMD adjacent to the newly deposited waste ore. In order to study the acid generation potential of the waste ore and the related microbial communities, soil samples were taken from beside the AMD lake (1LL) and small-scale AMD (5J, 5Y, 6-1, 6-2, 6-3) and the physicochemical properties and microbial community of these samples were analyzed. The results reveal that all of samples were highly acidic and the pH of the 1LL sample was 2.77, while the other samples were even more acidic, at less than 2.6. The electrical conductivity (EC) (0.32 mS·cm-1) of the 1LL sample was obviously lower than the other samples (2.25-7.08 mS·cm-1), which indicates that the newly deposited waste ore contains higher ion concentrations. The Fe2+ concentration of the 1LL sample was only 0.80 mg·kg-1 but the other five samples were as high as 2.91-33.40 mg·kg-1. This suggests that most of the Fe2+ in the 1LL sample has been converted to Fe3+ after long-term oxidization. High-throughput sequencing results showed that most acidophiles in 1LL sample were Actinobacteria, Acidobacteria and Chloroflexi but the microbes in the remaining five samples were γ-Proteobacteria, Firmicutes and Nitrospira. The iron-sulfur oxidizing bacteria, such as Sulfobacillus, Leptospirillum, Acidithiobacillus, were scarce in the 1LL sample, while they highly abundant in the other five samples, which proves that the acid-generation process of the newly deposited waste ore is strong. However, the reduced iron and sulfur in the 1LL sample has nearly been depleted. Statistical analysis shows that the microbial composition of the 1LL sample is significantly different to that of the five newly deposited samples, illustrating that microbial community composition is remarkably influenced by physicochemical conditions.