Rock surface attaching deep biosphere microbes and their functionality (DEEPFUN)

Microbial life occupies deep subsurface to multiple kilometres depths. These microorganisms exist both in the aquatic phase of deep groundwater as free-floating cells, and as sessile biofilms within fractures and pores of rocks, adhering to mineral surfaces. Outokumpu deep drill hole has facilitated research of deep life down to 2.5 km depth. The DEEPFUN project had a special focus on mapping and characterizing the ability of microbes to form biofilms under in-situ conditions in the Outokumpu deep bedrock, as well as in the laboratory conditions in microcosm experiments. These microbial communities were characterized with molecular biological methods such as amplicon sequencing and their functional capabilities were estimated with metagenomic analysis. DEEPFUN noted differences between planktic and biofilm community structures. Biofilm lifestyle emphasized heterotrophy,
various carbon and sulfur related metabolic pathways and recycling of dead biomass. Sulfate reducing bacteria were commonly found over mica schist surfaces. Therefore, we suggest that evaluation of both planktic and sessile communities is crucial for understanding the overall impact of microbes on deep subsurface biogeochemical
cycles.