ANALYSIS OF IRON UPTAKE AND OXYGENIC PHOTOSYNTHESIS BY A BENEFICIAL ACIDOPHILIC ALGA IN ACID MINE DRAINAGE

Euglena mutabilis, an acidophilic, photosynthetic alga living in coal-related acid mine drainage (AMD), forms reddish intracellular granules, similar in color to iron oxides, and contributes high levels of dissolved oxygen (up to 200% saturation with the atmosphere) to the acidic effluent. This study analyzes the elemental composition of the granules and characterizes oxygen output in a laboratory setting based on a day-night cycle. An environmental scanning electron microscope (ESEM) with an X-ray spectrometer was used to examine the granules and to analyze their chemical composition. ESEM backscatter data reveal that the granules are stored in vacuoles and vesicles in the cytoplasm. Semi-quantitative X-ray analysis of the cytoplasm shows a general composition of K+S±O±P±Si±Al±Mg±Cl. A similar composition is also observed in the granules; however, they differ from the rest of the cell by having elevated iron content. The iron-based composition of the granules suggests that E. mutabilis has the ability to sequester iron from the AMD system.

E. mutabilis communities were reared in artificial AMD media and in filtered AMD. A well defined day-night cycle was observed, in which oxygen was produced during day hours at a rate directly related to light availability, and was consumed during night hours. The maximum levels of dissolved oxygen measured during day hours in the artificial media and filtered AMD were 150% and 110%, respectively. Whereas, dissolved oxygen during night hours in the artificial media and filtered AMD dropped to 86% and 29%, respectively. Field measurements in AMD devoid of photosynthesizers generally range from 40-50% dissolved oxygen.

Both the intracellular sequestration of iron and the production of elevated concentrations of dissolved oxygen (which drives precipitation of reduced metal species commonly present in AMD) effectively remove iron and possibly other metals from AMD. Further work is necessary to quantify the amount of contaminant removal by E. mutabilis in AMD systems.