CHARACTERIZING MICROBIAL POPULATIONS IN BASALT FROM THE OCEAN CRUST

Microbes present in the upper part of the oceanic crust have been shown to participate in the alteration of basalt (Thorseth et al. 1995; Torsvik et al. 1998), but little is so far known about the nature of these microbes. The aim of this study is to characterize microbial diversity in the ocean crust, with special regard to microorganisms participating in the dissolution and alteration of basaltic glass. Basalt was sampled from the Mohn and Knipovich Ridges in the Norwegian-Greenland Sea by dredging the ocean floor. The samples were collected from depths between 2000 and 3500 meter. In addition to basalt samples, samples of sea water and sediment were collected for comparison. Microbial populations were characterized by growth experiments and DNA analysis. Enrichment cultures of microbes from basalt, sediment and sea water were set up on various carbon and energy sources. Microbes participating in the cycling of S, Fe/Mn and H2/CO2/CH4 were targeted. DNA analysis was performed with DNA extracted directly from rock, sediment and sea water and from enrichment cultures. Results from enrichment cultures, chemical analysis of metabolic products, PCR, DGGE, and 16S rDNA sequencing show that iron and manganese oxidizing and reducing bacteria, methanotrophic bacteria, and methanogenic Archaea are present in the basalt samples. Sulfate reducing bacteria were not abundant in the basalt samples, but were common in the sea water and sediment samples.

References: 1. Thorseth, I.H., Torsvik, T., Furnes, H. and Muehlenbachs, K. (1995). Microbes play an important role in the alteration of oceanic crust. Chem. Geol. 126: 137-146, (special issue. Proc. of «the Mantle- Ocean Connection». workshop, Amsterdam 1995). 2. Torsvik, T., Furnes, H., Muehlenbachs, K., Thorseth, I.H. and Tumyr, O. (1998). Evidence for microbial activity at the glass-alteration interface in oceanic basalts. Earth and Planetary Science Letters 162: 165-176.