MICROFABRICS OF MACROFABRICS OF BIOLAMINATES PRODUCED BY EUKARYOTE-DOMINATED BIOFILMS FROM AN ACID MINE DRAINAGE SYSTEM: IMPLICATIONS FOR EVIDENCE OF LIFE ON EXTRATERRESTRIAL PLANETARY BODIES

Eukaryotic microorganisms—Euglena mutabilis, Nitzschia (diatom), and Klebsormidium (filamentous alga)—are the primary architects of Fe-rich stromatolites in acid mine drainage (AMD) environments at West Terre Haute, IN. The intricate, repeated, paired layers of highly porous microlaminae with massive microlaminae that alternate with thicker (up to 50 mm), porous, sponge-like layers of stromatolite textures reflect interactions between the biofilm consortium and physicochemical characteristics of the environment. Our purpose was to link microbial behavior with microfabrics that comprise macrofabrics of Fe-rich stromatolites produced in AMD channels using microvideography and SEM-EDS analysis. Microvideography showed a back-and-forth (i.e., sweeping) motion of E. mutabilis cells when a particle slurry was applied, involving the posterior end attached to the surface with the anterior part sweeping up slurry particles. The cells then used mucilage to drag the cluster of particles using euglenoid locomotion to a larger mass of assembled particles being reworked by cells concentrated within that mass. Over time, areas of the glass slide were cleared of solid material with simultaneous growth of accumulated particle masses. This shows that E. mutabilis directly mediates their environment by binding chemical sediments with mucilage, clearing the space around them, and building an intricate, repeated, structure of micron-scale layering of highly porous microlaminae (E. mutabilis-dominated biofilm) that alternates with significantly less porous, massive microlaminae (no biofilm growth). The paired sequence is repeated multiple times to create macroscopic thinly laminated wavy layers. The wavy layers alternate with thicker, porous, sponge-like layers produced by Nitzchia- and Klebsormidium-dominated biofilms, which do not show active mediation. The porous layers are composed of encrusted material on cell surfaces. Semiquantitative EDS analysis of all layers indicates a composition of Fe, O, and S, consistent with schwertmannite. Identification of similar biosignatures in the rock record of extraterrestrial planetary bodies can be used as proxies to identify microbial consortia, based on our understanding of those features produced by microbial activity in Earth environments.