Bacterial diversity and tolerance to heavy metals in acid mine drainage at Davis Mine - Massachusetts.

摘要

Davis Mine, an abandoned pyrite mine in western Massachusetts, was my study model for acid mine drainage (AMD). Acidic waters from AMD cause the dissolution of other resident minerals increasing the concentration of heavy metals in these environments. Therefore, bacteria isolated from AMD exhibit high levels of tolerance to heavy metals.; The objective of this work was to isolate and characterize acidophilic, aerobic, chemoorganotrophic bacteria from AMD that are tolerant to high concentrations of heavy metal divalent cations. First, I analyzed the microbial community present at aerobic sediments obtained at the opening of the former main shaft at Davis Mine. This sediment was used as inoculum for enrichments of bacteria in a mixture of heavy metals. Enrichments and isolated bacteria were characterized by tolerance to heavy metals, presence of extrachromosomal DNA, and presence of known metal tolerance-related genes.; In addition, community structure and phylogenetic identities were determined. The diversity analysis of the sediment revealed that the microbial diversity at Davis Mine at the level of Bacterial classes is comparable to other aerobic sediments from AMD sites. The majority of the sequences were related to yet uncultured bacteria obtained from other mine sites or acidic soils making it difficult to describe accurately the microbial community structure.; Chemoorganotrophic, heavy metal tolerant bacteria were successfully isolated from Davis Mine. The majority of the strains were closely related to the acidophilic genera Acidocella and Thiomonas. In addition, I isolated bacteria related to Burkholderia which was not previously isolated from AMD. The heavy metal tolerance profiles of 21 strains revealed that high tolerance was correlated to the addition of heavy metals to the pre-cultivation medium as well as the presence of a 480 kb plasmid. I suggest that the heavy metal resistances observed are the result of more than on type of mechanism that are induced by the presence of heavy metals in the culture medium.