Special DLS Lecture – Elliott Mueller (Caltech)

“Organic Acids, the Carbon Currency of Anoxic Environments: Isotopic Tools to Probe and Mitigate Global Methane Emissions”

On both human and geologic timescales, microbial life significantly influences Earth’s climate. It is particularly important in environments without oxygen, where microbes degrade organic carbon, releasing CO2 and methane into the atmosphere. To develop climate solutions that mitigate these emissions, we need to understand the activity and function of anaerobic microbial communities. Despite numerous geochemical and ‘omics techniques, the microbial metabolism that initiates organic degradation – fermentation – remains unaccounted for in biogeochemistry.

In my work, I study fermentation and other anaerobic processes by analyzing organic acids from the environment. These molecules serve as a carbon currency, rapidly exchanging between microbial cells as they decompose organic matter. In this talk, I will discuss the development of novel analytical and computational platforms to measure and interpret the isotope ratios (¹³C/¹²C and ²H/¹H) of organic acids. I will first demonstrate how these tools can constrain the in situ mechanisms and rates of fermentation. I will then present a case study on fracture fluids from the vast continental subsurface of the Canadian Precambrian Shield. My analyses suggest that in certain sites, fermentation of buried organic matter is the primary source of organic acids. Whereas in Kidd Creek Mine, host of the most ancient fracture fluids found to-date (>1 Ga), organic acids may be synthesized and actively cycled via radiolytic reactions. From my constraints on turnover rates, I estimate that radiolytic carbon fixation could be a quantitatively important component of both the continental and marine carbon cycles. Together, these studies demonstrate that by focusing on transient molecular currencies, we can reveal hidden processes linking organic carbon, microbes, and climate.

Contact: djwright@mit.edu