The biogeographic pattern of microbial communities inhabiting terrestrial mud volcanoes across the Eurasian continent

Abstract

Terrestrial mud volcanoes (MVs) represent the surface expression of conduits tapping fluid and gas reservoirs in the deep subsurface. Such plumbing channels provide a direct, effective means to extract deep microbial communities fueled by geologically produced gases and fluids. The drivers accounting for the diversity and composition of these MV microbial communities, which are distributed over a wide geographic range, remain elusive. This study characterized the variation in microbial communities in 15 terrestrial MVs across a distance of ∼ 10 000 km on the Eurasian continent to test the validity of distance control and physiochemical factors in explaining biogeographic patterns. Our analyses yielded diverse community compositions with a total of 28 928 amplicon sequence variances (ASVs) taxonomically assigned to 73 phyla. While no true cosmopolitan member was found, ∼ 85 % of ASVs were confined within a single MV. Community variance between MVs appeared to be higher and more stochastically controlled than within MVs, generating a slope of the distance–decay relationship exceeding those for marine seeps and MVs as well as seawater columns. For comparison, physiochemical parameters explained 12 % of community variance, with the chloride concentration being the most influential factor. Overall, the apparent lack of fluid exchange renders terrestrial MVs a patchy habitat, with microbiomes diverging stochastically with distance and consisting of dispersal-limited colonists that are highly adapted to the local environmental context.