So close, so different: geothermal flux shapes divergent soil microbial communities at neighbouring sites

Abstract This study is focused on the (micro)biogeochemical features of two close geothermal sites ( FAV 1 and FAV 2), both selected at the main exhalative area of Pantelleria Island, Italy. A previous biogeochemical survey revealed high CH 4 consumption and the presence of a diverse community of methanotrophs at FAV 2 site, whereas the close site FAV 1 was apparently devoid of methanotrophs and recorded no CH 4 consumption. Next‐Generation Sequencing ( NGS ) techniques were applied to describe the bacterial and archaeal communities which have been linked to the physicochemical conditions and the geothermal sources of energy available at the two sites. Both sites are dominated by Bacteria and host a negligible component of ammonia‐oxidizing Archaea (phylum Thaumarchaeota). The FAV 2 bacterial community is characterized by an extraordinary diversity of methanotrophs, with 40% of the sequences assigned to Methylocaldum, Methylobacter (Gammaproteobacteria) and Bejerickia (Alphaproteobacteria); conversely, a community of thermo‐acidophilic chemolithotrophs ( Acidithiobacillus , Nitrosococcus ) or putative chemolithotrophs ( Ktedonobacter ) dominates the FAV 1 community, in the absence of methanotrophs. Since physical andchemical factors of FAV 1, such as temperature and pH , cannot be considered limiting for methanotrophy, it is hypothesized that the main limiting factor for methanotrophs could be high NH 4 + concentration. At the same time, abundant availability of NH 4 + and other high energy electron donors and acceptors determined by the hydrothermal flux in this site create more energetically favourable conditions for chemolithotrophs that outcompete methanotrophs in non‐nitrogen‐limited soils.