AN ECOSYSTEM ENGINEER IN ACID MINE DRAINAGE SYSTEMS, WESTERN INDIANA: EUGLENA MUTABILIS, AN OXYGENIC, PHOTOSYTHESIZING, STROMATOLITE-BUILDING PROTOZOAN MAKING LIFE POSSIBLE FOR OTHERS

Ecosystem engineers are organisms that directly or indirectly modify the availability of resources to other species by causing physical changes in abiotic or biotic materials. Autogenic engineers change the environment through their own physical structures, whereas allogenic engineers change the environment by transforming abiotic or biotic materials from one physical state to another via several ways (Jones et al. 1994). We believe that the activities of Euglena mutabilis, the dominant, highly oxygenic, photosynthetic protozoan (Brake et al. 2001), fall under both autogenic and allogenic ecosystem engineering. This protozoan provides a suitable substrate environment and substrates for other organisms, such as filamentous algae, yeasts, and gram positive and negative bacteria, to inhabit the extreme environment of acid mine drainage (AMD) systems. Biofilms almost completely composed of E. mutabilis modify their local environment in several ways. (1) They generate an excess of 200% oxygen dissolved in water through photosynthesis in effluent normal below saturation of O2 with respect to the atmosphere. (2) The protozoan directly and indirectly affects the precipitation of Fe and other metals from effluent with extreme concentrations of total dissolved solids. Intracellular sequestration of Fe and the oxygenation of the water by E. mutabilis biofilms cause precipitation of the metals, combined with the aerotactic and phototactic behavior of the biofilm, to produce iron-rich stromatolites. These features provide firm substrates for other microbes to inhabit. (3) The oxygenic, photosynthesis of E. mutabilis may also be responsible for slightly raising the pH of AMD discharge, though this has to be further tested. (4) The stromatolite-building activity of this protozoan also modifies the substrate via terrace construction that smoothes stream roughness from the original rip-rap lined, artificial channels.