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Frida Lise Daae, University of Bergen (Norway)
Ingeborg Elisabet Okland, University of Bergen (Norway)
Lise Ovreas, University of Bergen (Norway)
Torbjorg Bjelland, University of Bergen (Norway)
Ingunn Thorseth, University of Bergen (Norway)
Rolf Birger Pedersen, University of Bergen (Norway)
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Hydrothermal alteration of ultramafic rocks (serpentinization) is known to produce hydrogen and hydrocarbons. These compounds can be utilized as energy and carbon sources by microorganisms, and may sustain a deep oceanic subsurface biosphere.
The ophiolite hosted, serpentinized ulramafic rocks on the island Leka, Mid-Norway give a unique opportunity to study geochemical and microbial processes in a stable low-temperature environment. The microbial diversity associated with the weathering of ophiolite-hosted, serpentinized ultramafic rocks on Leka has been studied by microscopy, molecular analyses and culturing methods.
Analysis of the percolating groundwater and fracture-fillings of secondary minerals (magnesite MgCO3, brucite Mg (OH)2) and chrysotile (Mg3Si2O5(OH)4) demonstrates that this highly alkaline environment supports a rich endolitic microbial life. Groundwater collected from a 50 m deep borehole had higher pH, higher TOC, and lower cellnumber compared to groundwater from surface seepages. Molecular and cultivation analyses from the surface seeps showed bacteria affiliating with Bacteriodetes, alpha-, beta-, and gamma-Proteobacteria. In groundwater from the borehole only sequences that affiliated with beta- and gamma-Proteobacteria were detected. The results obtained from the fracture minerals show that the endolithic community is not reflected in the groundwater.
Molecular analyses of relatively thick (>3 mm) fracture fillings from 15-20 cm below the rock surface revealed a rich microbial community, where sequences from microorganisms related to Acidobacteria, Actinobacteria, Bacteriodetes, Cyanobacteria, Deinococcus, Planctomycetes, alpha-, beta-, gamma-Proteobacteria, Crenarchaeotae, Ascomycota including lichens, and Chlorophyta were detected. Isolates from these fractures were closest related to members of Actinobacteria, Firmicutes, alpha and beta-Proteobacteria and Ascomycota.
In thin (<2 mm) fracture fillings from 20-160 cm below the rock surface, only sequences which related to prokaryotic organisms were detected. Many of these sequences displayed very low similarity when compared to known 16S rRNA gene sequences in the database.
Based on community analysis we suggest that the energy yielding metabolic processes in the wide, surface-near fractures can be driven by both photosynthesis and low-temperature water-rock interactions. In the thinner and deeper fractures bacterial sequences affiliating to hydrogen-, iron- and manganese-oxidizing bacteria indicates that molecular hydrogen and reduced manganese and ferrous iron produced by low-temperature water-rock reactions can be oxidized by these bacteria in energy yielding chemosynthetic processes. In addition many sequences have high similarity to C1- and hydrocarbon -degrading bacteria, which indicates the existence of an unidentified source of organic material.
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