Mud volcanoes and microbial communities: Unraveling the mysteries of formation, features, and occurrence

Over two thousand mud volcanoes have been documented worldwide, predominantly forming in geologically active regions characterized by rapid sedimentation, recent magmatic activity, and compressional tectonics. These features originate from gravitative instability and fluid overpressure, which induce hydrofracturing of impermeable strata, allowing the release of water, gas, and sediments to the surface. As a result, mud volcanoes occur across a range of tectonic and sedimentary settings, including active margins, accretionary complexes, thrust belts, and deep sedimentary basins. They are generally classified as either submarine or terrestrial mud volcanoes, with the former typically associated with tectonic deformation and the later with sediment accumulation in continental settings. Beyond their geological significance, mud volcanoes contribute substantially to global geochemical and biogeochemical processes, influencing methane production and consumption, nutrient cycling, and organic matter transformation. Additionally, microbial communities are essential in the formation and maintenance of mud volcano structures by contributing to the biomineralization of carbonates and sulfates. The microbial communities found in different mud volcanoes are diverse, and their composition can vary based on location, depth, and geochemical conditions. Moreover, these microbial communities have evolved to utilize diverse sources of energy, including hydrogen, methane, and sulfur, to facilitate metabolic processes. This review summarizes the current insights into the formation, distribution, and environmental constraints of mud volcanoes, while highlighting the ecological relevance and metabolic capabilities of associated microbial communities based on metagenomics data to support interdisciplinary research into geobiological interactions in extreme ecosystems.