Abstract
Summary Microbial and functional diversity were assessed, from a serpentinization‐driven subterrestrial alkaline aquifer – C abeço de V ide A quifer ( CVA ) in P ortugal. DGGE analyses revealed the presence of a stable microbial community. By 16 S rRNA gene libraries and pyrosequencing analyses, a diverse bacterial composition was determined, contrasting with low archaeal diversity. Within B acteria the majority of the populations were related to organisms or sequences affiliated to class C lostridia , but members of classes A cidobacteria , A ctinobacteria , A lphaproteobacteria , B etaproteobacteria , D einococci , G ammaproteobacteria and of the phyla B acteroidetes, C hloroflexi and N itrospira were also detected. Domain A rchaea encompassed mainly sequences affiliated to E uryarchaeota . Only form I RuBisCO – cbb L was detected. Autotrophic carbon fixation via the rTCA , 3‐ HP and 3‐ HP /4 H ‐ B cycles could not be confirmed. The detected APS reductase alpha subunit – aprA sequences were phylogenetically related to sequences of sulfate‐reducing bacteria belonging to C lostridia , and also to sequences of chemolithoautothrophic sulfur‐oxidizing bacteria belonging to B etaproteobacteria . Sequences of methyl coenzyme M reductase – mcrA were phylogenetically affiliated to sequences belonging to A naerobic M ethanotroph group 1 ( ANME ‐1). The populations found and the functional key markers detected in CVA suggest that metabolisms related to H 2 , methane and/or sulfur may be the major driving forces in this environment.