ZOMBIE MINES AND BRAIN BIOFILMS: ACID MINE DRAINAGE IMPACT AND IMPLICATIONS FOR THE ARCHEAN-PALEOPROTEROZOIC TRANSITION

Streams impacted by acid mine drainage (AMD) represent local environmental and ecological disasters; however they may also present an opportunity to study microbial communities in environments analogous to past conditions. Following the emergence of oxygenic photosynthesis, atmospheric O₂ generated by Cyanobacteria came into contact with streams and rivers on continental surfaces replete with detrital pyrite, producing ideal conditions for pyrite oxidation similar to that found at modern AMD-impacted sites. We sampled sites that exhibited a range of AMD-impact (e.g., pH from 2.1 to 7.9, Fe²⁺ from 5.2 mmol/L to below detection limits, SO₄^2- from 0.3 to 52.4 mmol/L) and found i) nearly all analytes correlated to sulfate concentration, ii) all sites exhibited the presence (and even predominance) of a single microbial taxon most closely related to Ferrovum myxofaciens which is capable of nitrogen fixation and chemoautotrophy via Fe²⁺ oxidation, iii) signs of potential inorganic carbon limitation and nitrogen cycling. From these findings, we present a conceptual model of continental surfaces during the Paleoproterozoic. Our model suggests a connection between O₂ production in the ocean to AMD-type pyrite oxidation on continental surfaces through a negative feedback loop. Sulfate production through oxidative weathering of terrestrial surfaces would be delivered to near-shore environments which in turn drove euxinia through the action of sulfate reducing organisms. Thus, the result of the model is a potential negative feedback loop/throttle for O₂ production during the Paleoproterozoic.