Dr. William Leavitt - The isotopic 'fingerprints' of microbes contributing to surface ocean methane, and other geochemical signatures of microbial activity from past life

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Dr. Will Leavitt (Dartmouth College)

Vendredi 15 mars 2019 à 11h00 - Friday, March 15, 2019 at 11:00 am

Gill Room, FDA 232, 3450 rue Université, Université McGill

Résumé / Abstract:

We live on a microbial planet. From the air we breathe to the regulation of critical greenhouse gases, microorganisms that inhabits the oceans, lakes, sediments and soils play an integral role in most elemental cycles.

The supersaturated concentrations of methane observed in many of the world’s surface oceans can is likely due to certain aerobic bacteria when they experience phosphate-starvation. These microbes are able to acquire P by breaking down organic matter bound alkyl phosphonates, such as methylphosphonate (MPn). Through the metabolic decomposition of MPn and related compounds, methane is released as a by-product. The release of this potent greenhouse gas in P-starved surface oceans may significantly contribute to the atmospheric methane budget. To track this methane we are developing a comprehensive set of isotopic ‘fingerprints’, determining the stable isotopic fractionations upon MPn degradation to methane. Using pure cultures of representative marine and freshwater microorganisms, we determined the bulk C and H, as well as two clumped isotopic metrics. The methane produced during MPn degradation shows little to no fractionation from the substrate in bulk C-isotope values and some depletion from medium water H-isotope values. The clumped isotope values suggest that this production mechanism likely produces methane that is distinct from canonical anaerobic methanogenesis pathways, but also significantly departed from isotopic equilibrium. Through further experiments with isotopically enriched or depleted waters, we are further able to constrain the mechanism of isotopic fractionation.

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The isotopic 'fingerprints' of microbes contributing to surface ocean methane, and other geochemical signatures of microbial activity from past life