Molecular analysis of benthic biofilms from acidic coal mine drainage, Pennsylvania USA
Open Access
- Author:
- Mills, Daniel Brady
- Area of Honors:
- Geosciences
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Jennifer Macalady, Thesis Supervisor
Jennifer Macalady, Thesis Supervisor
Dr. Peter J Heaney, Thesis Honors Advisor - Keywords:
- acid mine drainage
geomicrobiology
biogeochemistry
bioremediation - Abstract:
- Acid mine drainage (AMD) is a common environmental problem in Pennsylvania that results from the oxidation of sulfide minerals exposed at abandoned coalmines. In these systems, acidophilic microorganisms catalyze the oxidation of ferrous (Fe2+) to ferric iron (Fe3+), which precipitates as iron-hydroxide minerals. To develop and improve low-pH bioremediation strategies, characterization of the microbiology of AMD systems is essential. An acidic (pH 2-4) AMD spring known as ‘Lower Red Eyes’ in Gallitzan State Forest, PA, is fed by anoxic groundwater with ferrous iron concentrations above 550 mg/L. More than half of the total iron is removed after the springwater flows downstream over 80 m of stagnant pools and iron-oxide terraces. We used fluorescence in situ hybridization (FISH) and 16S rDNA cloning to characterize the microbial communities from orange sediments and green benthic biofilms. 16S rDNA sequences were extracted from a green biofilm found in a pH 3.5 pool 10 m downstream of the emergence. Based on chloroplast 16S rDNA sequences and morphological characteristics, we found that Euglena mutabilis was the dominant eukaryotic organism from this location. Euglena mutabilis is a photosynthetic protozoan common in acidic and heavy metal affected environments and likely contributes to the precipitation of iron oxides through the production of molecular oxygen. Bacterial 16S rDNA sequences were cloned from iron-oxide sediments with orange cauliflower morphology 27 m downstream from the spring emergence. More than 60% of bacterial sequences retrieved from the orange sediment sample are related to the iron-oxidizing Betaproteobacterium Ferrovum myxofaciens. Other bacterial sequences include relatives of iron-oxidizing genera in the Gammaproteobacteria, Betaproteobacteria, and Actinobacteria. FISH analyses show that Betaproteobacteria-dominated communities are associated with Euglena in multiple upstream locations where pH is above 3.0. Using light microscopy, we quantified Euglena in several Lower Red Eyes samples and found that it was abundant in upstream pool sediments, but was extremely rare in terrace sediments. Future research will investigate how different environmental variables—including light intensity, flow rate, pH, iron, and other chemical species—control the distribution of Euglena and associated bacterial taxa in AMD streams. Likewise, understanding the effects these coexisting eukaryotic and prokaryotic microbial taxa exert on each other and on their environment may reveal the extent to which these microorganisms control and shape acidic systems, as well as their own evolution.