Dr. James Bradley - Widespread energy limitation in global marine sediments


Dr. James Bradley (University of Southern California)

Jeudi 14 février 2019 à 12h00 - Thursday, February 14, 2019 at 12:00pm

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

Résumé / Abstract:

Marine sediments harbor vast consortia of microorganisms that have been shown to survive for millennia, calling into question the limit for life. The energy turnover, i.e. power, of subseafloor microorganisms sets a limit on gene expression, mutation rates, and the survival of rare and novel taxa. Furthermore, microbial activity in subseafloor sediments drives global biogeochemical processes including the degradation of Earth’s largest pool of organic carbon. However outside of measurements from specific sites or laboratory experiments, the power of subsurface life is virtually unknown. Here, we apply a new modelling approach to determine cell-specific power utilization in all Quaternary sediments by simultaneously quantifying the distribution, rate and thermodynamic properties of particulate organic carbon (POC) degradation, as well as the global distribution of cells, and electron acceptors. We report extreme and widespread energy-limitation in subseafloor sediments. The vast majority of all cells subsist at powers that are less than the lowest energy flux calculated for any microbial habitat (1.9×10-19 W cell-1, LaRowe & Amend, 2015). Furthermore, we find that stepwise decreases in microbial power largely follow the redox state of the sediment. Although we rule out the possibility of cellular growth among most subseafloor organisms, our results demonstrate how microbial populations are capable of surviving at energy fluxes far lower than what has previously been considered to sustain life, and maintain a vast reservoir of biodiversity through ecological coexistence. We assert that sediments should be considered as critical to understanding the cell-specific minimum power requirement for survival, as well as to predict the habitable boundaries of life on Earth.

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Widespread energy limitation in global marine sediments