Evolution of microbial "streamer" growths in an acidic, metal-contaminated stream draining an abandoned underground copper mine.

A nine year study was carried out on the evolution of macroscopic "acid streamer" growths in acidic, metal-rich mine water from the point of construction of a new channel to drain an abandoned underground copper mine. The new channel became rapidly colonized by acidophilic bacteria: two species of autotrophic iron-oxidizers (Acidithiobacillus ferrivorans and "Ferrovum myxofaciens") and a heterotrophic iron-oxidizer (a novel genus/species with the proposed name "Acidithrix ferrooxidans"). The same bacteria dominated the acid streamer communities for the entire nine year period, with the autotrophic species accounting for ~80% of the micro-organisms in the streamer growths (as determined by terminal restriction enzyme fragment length polymorphism (T-RFLP) analysis). Biodiversity of the acid streamers became somewhat greater in time, and included species of heterotrophic acidophiles that reduce ferric iron (Acidiphilium, Acidobacterium, Acidocella and gammaproteobacterium WJ2) and other autotrophic iron-oxidizers (Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans). The diversity of archaea in the acid streamers was far more limited; relatively few clones were obtained, all of which were very distantly related to known species of euryarchaeotes. Some differences were apparent between the acid streamer community and planktonic-phase bacteria. This study has provided unique insights into the evolution of an extremophilic microbial community, and identified several novel species of acidophilic prokaryotes.

Evidence that the potential for dissimilatory ferric iron reduction is widespread among acidophilic heterotrophic bacteria.

Nineteen characterized strains and isolates of acidophilic heterotrophic bacteria were screened for their abilities to catalyse the reductive dissolution of the ferric iron mineral schwertmannite, under oxygen-limiting conditions. Acidocella facilis, Acidobacterium capsulatum, and all of the Acidiphilium, Acidocella and Acidobacterium-like isolates that grew in liquid cultures were able to reduce iron. In contrast, neither Acidisphaera rubrifaciens nor three Acidisphaera-like isolates tested were found to have the capacity for dissimilatory iron reduction. One of two iron-oxidizing Frateuria-like isolates also reduced iron under oxygen-limiting conditions. Microbial dissolution of schwertmannite was paralleled with increased concentrations of soluble ferrous iron and sulfate in microbial cultures, together with increased pH values and decreased redox potentials. While dissimilatory ferric iron reduction has been described previously for Acidiphilium spp., this is this first report of this capacity in Acidocella and the moderate acidophile Acidobacterium. The finding has significant implications for understanding of the biogeochemistry of acidic environments.

Macroscopic streamer growths in acidic, metal-rich mine waters in north wales consist of novel and remarkably simple bacterial communities.

The microbial composition of acid streamers (macroscopic biofilms) in acidic, metal-rich waters in two locations (an abandoned copper mine and a chalybeate spa) in north Wales was studied using cultivation-based and biomolecular techniques. Known chemolithotrophic and heterotrophic acidophiles were readily isolated from disrupted streamers, but they accounted for only <1 to 7% of the total microorganisms present. Fluorescent in situ hybridization (FISH) revealed that 80 to 90% of the microbes in both types of streamers were beta-Proteobacteria. Terminal restriction fragment length polymorphism analysis of the streamers suggested that a single bacterial species was dominant in the copper mine streamers, while two distinct bacteria (one of which was identical to the bacterium found in the copper mine streamers) accounted for about 90% of the streamers in the spa water. 16S rRNA gene clone libraries showed that the beta-proteobacterium found in both locations was closely related to a clone detected previously in acid mine drainage in California and that its closest characterized relatives were neutrophilic ammonium oxidizers. Using a modified isolation technique, this bacterium was isolated from the copper mine streamers and shown to be a novel acidophilic autotrophic iron oxidizer. The beta-proteobacterium found only in the spa streamers was closely related to the neutrophilic iron oxidizer Gallionella ferruginea. FISH analysis using oligonucleotide probes that targeted the two beta-proteobacteria confirmed that the biodiversity of the streamers in both locations was very limited. The microbial compositions of the acid streamers found at the two north Wales sites are very different from the microbial compositions of the previously described acid streamers found at Iron Mountain, California, and the Rio Tinto, Spain.

Oxidation of arsenite by Thiomonas strains and characterization of Thiomonas arsenivorans sp. nov.

A novel bacterium, strain b6(T) (T=type strain), was isolated from a disused mine site by growth using arsenite [As(III)] as energy source in a simple mineral medium. Cells of strain b6(T) were rod-shaped, Gram-negative, non-sporulating and motile. Optimum growth occurred at temperatures between 20 and 30 degrees C, and at pH between 4.0 and 7.5. Strain b6(T) grew chemoautotrophically on As(III), sulphur and thiosulphate, and also heterotrophically on yeast extract and a variety of defined organic compounds. Several other Thiomonas strains, including the type species Thiomonas (Tm.) intermedia, were able to oxidize As(III), though only strain b6(T) and strain NO115 could grow using As(III) as sole energy source in the absence of any organic compound. The G+C content of the DNA of strain b6(T) was 65.1 mol %. Comparative small subunit (SSU) ribosomal RNA (rRNA) analysis indicated that strain b6(T) belongs to the genus Thiomonas in the beta-subdivision of the Proteobacteria. It was closely related to an unnamed Thiomonas strain (NO115) isolated from a Norwegian mining site, though sequence identities between strain b6(T) and characterized Thiomonas species were less than 95%. DNA-DNA hybridization between strain b6(T) and the type species of the genus Tm. intermedia showed less than 50% homology. On the basis of phylogenetic and phenotypic characteristics, strain b6(T) (DSM 16361(T), LMG 22795(T)) is proposed as the type strain of the new species Thiomonas arsenivorans, sp. nov.