Microbiological sampling and analysis of the Outokumpu Deep Borehole biosphere in 2007-2008

Three sampling campaigns were performed during the years 2007-2009 to develop microbiological sampling techniques and to study the deep biosphere in the Outokumpu Deep Drill Hole R2500, drilled into a Palaeoproterozoic sequence of rocks consisting of metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granite. The results revealed the presence of microbial communities in the saline fluids sampled from the open borehole and fracture systems in the low-porosity crystalline bedrock in Outokumpu. According to the microbiological analyses, the microbial cell density varies from 105 cells ml-1 at the surface to 103 ml-1 at 2350 m depth. The composition of microbial communities in the borehole was found to vary with sampling depth, and the changes appear to be connected to both geological and geochemical factors as well as to fracture zones in the bedrock. Sulphate reducing bacteria and methanogenic archaea are present throughout the borehole water column.