CAREER: Do extraordinarily long enzyme lifetimes drive microbial community assembly in deep subsurface sediments?

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Microbes that live deep in ocean sediments help drive Earth's elemental cycles, influencing key aspects of habitability on the planet, such as the amount of oxygen in the atmosphere. Microbes in the deep subsurface have a remarkable lifestyle. They turn over their biomass on timescales of decades, centuries, or even millennia, while microbes in most other environments do so every few hours or days. The driving hypothesis for this project is the unusually high stability of the deep subsurface microbes' enzymes is key to these microbes' survival. The scientific results of this project will help understand the function of a vast and mysterious ecosystem at the bottom of the ocean and may lead to new discoveries about enzyme structure and function that could have valuable applications in the food or pharmaceutical industries. The project supports the training of undergraduate and graduate students in research and teaching. In addition, K12 students participating in a summer school program called East Tennessee Freedom Schools help generate data and design experiments, giving them early input into the scientific process. The educational program allows a set of young scientists to gain experience with authentic scientific research. The central hypothesis that unusually stable enzymes help subsurface microbes to persist over long timescales is tested via a field program to collect subsurface sediments in the Gulf of Alaska, experimental manipulations of those sediments, laboratory experiments in simplified model systems, and bioinformatic analyses. Metagenomic sequencing of surface and subsurface sediments, followed by construction of metagenome-assembled genomes and computational analysis of enzyme stability, are employed to yield predictions on the stability of enzymes in subsurface sediments and the degree to which enzyme stability affects community assembly. Experimental manipulations of subsurface sediments are then used to test those predictions. The research team is also expressing, purifying, and experimentally determining the structure of a selected set of subsurface enzymes to allow independent testing of the bioinformatic predictions and simplified laboratory experiments. Together, these experiments will reveal the role of enzyme stability in driving microbial community assembly in subsurface sediments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.