In the depths of the Pacific, strikingly blue mud contains evidence of life in conditions previously considered uninhabitable. This alkaline substance, brought up by mud volcanoes near the Mariana Trench, indicates biological activity in one of the most hostile environments on our planet.
Exploring these extreme ecosystems represents a major scientific challenge for understanding the limits of life. An international team, led by the University of Bremen, has successfully documented the presence of microbial communities in sediments with exceptionally high pH. Their work, published in
Communications Earth & Environment, relies on the analysis of lipid biomarkers to reconstruct the survival strategies employed by these organisms.
Blue mud from a recently discovered mud volcano in a drill core. Samples were studied by a team to decipher the survival strategies of microorganisms.
Photo: SO292/2, Scientific expedition team An exceptional ecosystem
The samples come from two mud volcanoes recently discovered in the Mariana forearc, at a depth of nearly 3000 meters (about 9,800 feet). Their unique geological composition creates a hyperalkaline environment with a pH reaching 12, comparable to that of limewater. This extreme alkalinity results from serpentinization processes, where certain rocks react with seawater to form specific minerals.
In this environment poor in organic nutrients and characterized by high salinity, detecting microbial DNA often proves unsuccessful due to low cell density. Researchers therefore adopted an alternative approach by targeting membrane lipids, which are more stable and persistent over time. These fatty molecules serve as reliable witnesses to past and present biological activity.
Detailed analysis of these biomarkers revealed the simultaneous presence of several microbial communities adapted to these drastic conditions. The distinction between intact lipids, indicating a recent community, and fossil molecules, testifying to fossil ecosystems, makes it possible to trace the evolutionary history of these extreme habitats over geological timescales.
Microbial survival strategies
The identified microorganisms exhibit unique metabolisms, fundamentally different from those observed in conventional marine ecosystems. Rather than depending on organic matter from the ocean surface, these communities draw their energy directly from the rocks and gases they contain. This nutritional autonomy allows them to thrive completely independently of photosynthesis.
The study demonstrates that these specialized microbes metabolize sulfate and produce methane from the carbon dioxide and hydrogen available in their immediate environment. These biochemical processes, although less efficient than classical metabolic pathways, are sufficient to maintain a functional ecosystem under limited resource conditions. Methane production also represents an important aspect of the global carbon cycle.
The presence of these microbial communities in such a challenging habitat confirms the resilience capacity of life. Their persistence despite the near-total absence of available organic carbon indicates that similar processes could support extraterrestrial life under comparable environmental conditions.
Article author: Cédric DEPOND