Microbial Geochemistry: At the Intersection of Disciplines

Abstract

Subsurface environments support active microbial communities that interact with the geological framework, carrying out redox reactions, assimilating nutrients, excreting waste and extracellular substances. These reactions perturb the extracellular environment, altering mineral -water equilibria, reaction rates and pathways, and are often the chemical basis for low -temperature mineral diagenesis. These complex biologicalmineral interactions represent a coupled system where the microbe takes advantage of specifi c minerals, and the mineral -water reactions depend on a particular microbial population and the activities of the microbial community.We review here the chemistry of microbial interactions with minerals and subsurface environments from the perspective of the microbial metabolism and subsurface microbial ecology. Using example microbe -mineral interactions we examine the driving forces for microbial geochemical interactions and outcomes, with a central theme of asking why a microbe would expend energy to perturb mineral -water equilibria and to drive geochemical reactions. In most cases we fi nd that microorganisms drive geochemical reactions, but that they often gain something from the interaction; access to a nutrient, buffering of extreme habitat conditions, or perhaps protection from predation. Answering the question of why often leads to a richer understanding of how, how fast and how important the microbial geochemical interaction is.

AstRoMap European Astrobiology Roadmap

“…In this context, study of the oldest traces of life underline the inherent difficulties in distinguishing biogenicity and syngenicity of potential biosignatures. Nevertheless, in the geological and biological communities, understanding of the nature of biosignatures has been growing steadily over the last decades as a result of better knowledge of the preservation of signatures of life through experimentation and observation (Orange et al , 2009 ; Westall and Cavalazzi, 2011 ; Benzerara et al , 2014 ; Oehler and Cady, 2014 ), for example, of the effects of microbial activity on its immediate mineralogical environment (Bennet and Omelon, 2011 ; Röling et al , 2015 ) and, not least, because of the availability of instrumentation with increasing powers of resolution (Miot et al , 2014 ). The applications of this increased understanding are widely applied to the search for the oldest traces of life on Earth and for potential extraterrestrial biosignatures on Mars (Noffke, 2015 ).…”