Networked Speaker Series #28

Microbial metabolisms preferentially utilize substrate molecules containing lighter isotopes of elements. As a result of this preferential usage, from mineralized metabolites, we can place constraints on environmental conditions that influence metabolism over long periods of time. However, these constraints assume that a given microbial functional transformation has imparted the same quantitative isotopic partitioning in response to environment over time. The work presented here describes a series of experiments designed to test the hypothesis that microbial isotope fractionation is independent of microbial adaptation to environmental changes. Specifically I use experimental evolution to interrogate the effects of electron acceptor depletion, electron donor depletion, and a change from planktonic growth to biofilm-like growth. These challenges were selected to mimic those experienced by microbes deposited on the surface of marine sediments, and progressively buried as a result of sedimentation; or in the case of planktonic versus particle associated growth, to emulate global changes in seawater chemistry. The results of these studies suggest that microbial fractionation of isotopes is not independent of adaptation, and that the biosignatures that have been utilized in paleo reconstructions may also bear a signal of microbial adaptation.