Researchers have discovered thriving microbial communities in one of Earth's harshest underwater environments, with a pH of 12 in the Mariana forearc region. Using lipid biomarkers, the team revealed how these microbes metabolize methane and sulfate to survive. The findings suggest such extreme conditions may mirror sites where primordial life originated.
In a study published in Communications Earth, scientists led by Palash Kumawat from the University of Bremen's Geosciences Department analyzed sediment cores from mud volcanoes in the Mariana forearc. These samples were collected in 2022 during Expedition SO 292/2 aboard the Research Vessel Sonne, which uncovered previously unknown underwater volcanoes.
The environment's pH of 12 makes it exceptionally alkaline and hostile, with low biomass and nutrient deficiency rendering DNA detection nearly impossible. Instead, the team relied on lipid biomarkers—specialized fat molecules—to identify biological activity. "But we were able to detect fats," Kumawat, a PhD candidate, explained. "With the help of these biomarkers we were able to obtain insights into the survival strategies of methane- and sulfate-metabolizing microbes in this extreme environment."
These microbes form a self-contained ecosystem, drawing energy from minerals in rocks and gases like carbon dioxide and hydrogen to produce methane, a key greenhouse gas. The biomarkers, combined with isotope data, distinguish active or recent microbial populations from ancient remnants. "This distinction helps us when working in areas with extremely low biomass and nutrient deficiency," Kumawat noted.
Co-author Dr. Florence Schubotz, an organic geochemist at MARUM—Center for Marine Environmental Sciences at the University of Bremen—highlighted the discovery's significance. "What is fascinating about these findings is that life under these extreme conditions, such as high pH and low organic carbon concentrations, is even possible," she said. "Until now, the presence of methane-producing microorganisms in this system has been presumed, but could not be directly confirmed. Furthermore, it is simply exciting to obtain insights into such a microbial habitat because we suspect that primordial life could have originated at precisely such sites."
The research is part of the Cluster of Excellence "The Ocean Floor—Earth's Uncharted Interface." Future plans include cultivating these microbes in controlled incubators to study their nutrient acquisition in such inhospitable settings. This work underscores the role of deep-sea microbes in global carbon cycling and expands understanding of life's limits.