RSI Research Seminar

Join us every other Monday at noon for lunch and a 30-minute research talk, presented by Resnick Sustainability Institute Graduate Fellows and Caltech researchers funded by the Resnick Sustainability Institute. To see the full schedule of speakers, visit the RSI Research Seminar web page. Seminars currently take place in a hybrid format, both in-person (Jorgensen building first-floor conference room) and via Zoom. For more information and to get the Zoom login info, please reach out to [email protected]

Developing isotopic tools to study carbon flow in cow rumen upon inhibition of methane-producing microbes

Methane is a potent greenhouse gas responsible for ~one-third of global warming. Ruminant animals (e.g. cows) are a major source of methane, but they are also a tractable target for climate solutions. Multiple strategies have been developed to lower methane emissions from ruminants, including feed additives that inhibit the resident population of methanogenic microbes. Regardless of the strategy used, eliminating methanogenesis will have cascading effects on the rest of the microbial community present in the rumen, including the bacteria that degrade and ferment ingested plant material. These fermenting bacteria generate volatile fatty acids (VFAs) for the animal host to use as its primary source of carbon and energy. As such, fermentation is an essential process to maintain in the rumen. Typically, fermenting organisms live in symbiotic relationships with methanogenic microbes that consume the H2 byproduct of fermentation. Upon the addition of feed additives, this symbiosis is broken and fermenting bacteria are likely to respond. However, we currently lack the tools to quantify how carbon flow through fermentation is altered under these new conditions. In this talk, we will describe a new method for measuring the natural abundance stable isotope ratios (13C/12C and 2H/1H) of VFAs in the rumen and using that information to quantify fermentative pathways. We tested this technique on incubations of rumen fluid with and without the additive Asparagopsis taxiforms, a red macroalgae that inhibits methanogens. We found that the isotope composition of VFAs changed between these conditions, reflecting a metabolic shift in the fermentation of plant material. We are currently developing metabolic models to constrain which adaptations are most likely to have caused the observed trends. Our results could inform the long-term sustainability of methane mitigation strategies in terms of animal health and productivity.