Abstract EANA2025-99

Methane is a potent greenhouse gas that is a key component of Earth's atmosphere, which largely originates from anaerobic archaea called methanogens. Methanogens undergo methanogenesis, a biochemical pathway that converts various substrates (e.g., acetate, methanol, carbon dioxide) into methane. Methanogens are some of the most ancient organisms on our planet, many of which predate the Great Oxidation Event (GOE). The GOE saw a significant rise of oxygen in the Earth's atmosphere, bringing many organisms to extinction. How anaerobes like methanogens survived such a transition remains an open question.

One potential answer lies in the redox versatility of the transition metal manganese (Mn), the fifth most abundant element in the Earth’s crust. Mn is a key antioxidant in many biological systems that protect cells from oxidative stress (e.g., superoxide dismutase). During the GOE, anaerobes would have been wiped out by the dramatic rise of oxygen without a strong antioxidant. Mn served as an electron source in photosynthesis before the GOE, so life may have survived the GOE because they already implemented Mn into their metabolism. Here, we investigate the role that Mn(II) has on the physiology and oxidative stress response of the marine methanogen Methanosarcina acetivorans.

We cultured M. acetivorans in oxygen-free synthetic seawater under strictly anoxic conditions with methanol as the carbon source. To assess cell growth, we grew cells in the presence of various Mn concentrations. We quantified the protein content of the cultures at different time points and monitored production of carbon dioxide and methane via gas chromatography. These results were preliminary to assessing the role of Mn as an antioxidant in methanogens. Ongoing experiments are testing whether Mn protects the cells from oxidative stress during oxygen exposure.

Results indicate that the Mn concentration affects total growth and growth rate. Methanol-grown cells showed reduced biomass at elevated Mn concentrations compared to controls. Quantification of headspace gases corroborated these findings, where both carbon dioxide and methane production decreased at higher Mn concentrations. These results establish a baseline to determine if these Mn concentrations influence the survivability of M. acetivorans in the presence of oxygen.