title: Geochemical and Temporal Influences on the Enrichment of Acidophilic Iron-Oxidizing Bacterial Communities.
abstract: Two acid mine drainage (AMD) sites in the Appalachian bituminous coal basin were selected to enrich for Fe(II)-oxidizing microbes and measure rates of low-pH Fe(II) oxidation in chemostatic bioreactors. Microbial communities were enriched for 74 to 128 days in fed-batch mode, then switched to flowthrough mode (additional 52 to 138 d) to measure rates of Fe(II) oxidation as a function of pH (2.1 to 4.2) and influent Fe(II) concentration (80 to 2,400 mg/liter). Biofilm samples were collected throughout these operations, and the microbial community structure was analyzed to evaluate impacts of geochemistry and incubation time. Alpha diversity decreased as the pH decreased and as the Fe(II) concentration increased, coincident with conditions that attained the highest rates of Fe(II) oxidation. The distribution of the seven most abundant bacterial genera could be explained by a combination of pH and Fe(II) concentration. Acidithiobacillus, Ferrovum, Gallionella, Leptospirillum, Ferrimicrobium, Acidiphilium, and Acidocella were all found to be restricted within specific bounds of pH and Fe(II) concentration. Temporal distance, defined as the cumulative number of pore volumes from the start of flowthrough mode, appeared to be as important as geochemical conditions in controlling microbial community structure. Both alpha and beta diversities of microbial communities were significantly correlated to temporal distance in the flowthrough experiments. Even after long-term operation under nearly identical geochemical conditions, microbial communities enriched from the different sites remained distinct. While these microbial communities were enriched from sites that displayed markedly different field rates of Fe(II) oxidation, rates of Fe(II) oxidation measured in laboratory bioreactors were essentially the same. These results suggest that the performance of suspended-growth bioreactors for AMD treatment may not be strongly dependent on the inoculum used for reactor startup.
  
  
  
  This study showed that different microbial communities enriched from two sites maintained distinct microbial community traits inherited from their respective seed materials. Long-term operation (up to 128 days of fed-batch enrichment followed by up to 138 days of flowthrough experiments) of these two systems did not lead to the same, or even more similar, microbial communities. However, these bioreactors did oxidize Fe(II) and remove total iron [Fe(T)] at very similar rates. These results suggest that the performance of suspended-growth bioreactors for AMD treatment may not be strongly dependent on the inoculum used for reactor startup. This would be advantageous, because system performance should be well constrained and predictable for many different sites.
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA.|School of Water Resources and Environment, China University of Geosciences, Beijing, China.
authors.forename: Yizhi
authors.initials: Y
authors.lastname: Sheng
authors.affiliation: Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Kyle
authors.initials: K
authors.lastname: Bibby
authors.affiliation: Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Christen
authors.initials: C
authors.lastname: Grettenberger
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Bradley
authors.initials: B
authors.lastname: Kaley
authors.affiliation: Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Macalady
authors.affiliation: School of Water Resources and Environment, China University of Geosciences, Beijing, China.
authors.forename: Guangcai
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA wdb3@engr.psu.edu.
authors.forename: William D
authors.initials: WD
authors.lastname: Burgos
mesh_terms: D001419:Bacteria / Q000145:classification* / Q000378:metabolism*; D019149:Bioreactors / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D059013:Microbial Consortia; D010084:Oxidation-Reduction; D012988:Soil Microbiology; D013997:Time Factors
chemical_list: D007501:Iron