Modern microbe-metal-mineral interactions: testing for biosignatures in ancient rocks

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A variety of morphological, mineralogical, and geochemical characteristics in ancient sedimentary rocks have been used to decipher the history of life and environment in which it evolved here on Earth, and perhaps on other planets. These potential "biosignatures" include, but are not restricted to: the relative abundances and isotopic compositions of trace and redox-sensitive elements in banded iron formations (BIFs) and microfossils preserved in chert. It is this regard that my research programme will integrate geochemical, microbiological and genetic experimental studies with field-based research at modern hydrothermal springs and Fe-rich lakes to identify features in the sediments that are indicative of microbial activity. There are three specific components to my research. First, I will study the surface reactivity of various bacterial species, from both laboratory cultures and natural microbial mats, as a means to evaluate specific trace element partitioning onto biomass. A better understanding of biological factors influencing metal sequestration will not only enable more efficient strategies for bioremediation of contaminated sites and biorecovery of ore metals (both of which are of utmost importance to Canadian industry and our environment), but trace element distributions in microbial-influenced sediment may also prove to be reliable and robust biosignatures for ancient Earth. Second, I will measure isotope and trace element compositions in experimentally-produced iron minerals and BIF core. It is anticipated that through these comparative analyses new insights will be gained into how microbial activity and mineral adsorption reactions partitioned elements from the Precambrian ocean waters to the bottom sediment, thus facilitating reconstruction of global elemental cycling and evolution of the biosphere through deep time. Third, I will evaluate the relative contribution of microbes to silicification in nature, and how some microbes respond to mineral encrustation. The ultimate goal is to better understand how microbes fossilize, whether there exists preservational biases, and thus identify which microbes likely constituted our earliest physical record of life.