Graduate Thesis Or Dissertation
 

Prokaryotes associated with marine crust

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/c247dw192

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  • Oceanic crust covers nearly 70% of the Earth's surface, of which, the upper, sediment layer is estimated to harbor substantial microbial biomass. Marine crust; however, extends several kilometers beyond this surficial layer, and includes the basalt and gabbro layers. In particular, the basalt layer has high permeabilities which allows for infiltration and circulation of large volumes of seawater. Seawater interacts with the host rocks and can result in abiotic hydrogen, methane, and other low molecular weight carbon compounds. Endoliths residing in this environment are; therefore, uniquely poised to take advantage of the by-products of this reaction. Whether the resident prokaryotic communities in lithic crust utilize abiotically produced volatiles, such as methane, is unknown. Further, little is known about the global distribution of basalt endoliths. To date, gabbroic microflora have not yet been examined. The gabbroic layer may; therefore, harbor great microbial and metabolic diversity. To this end molecular and bioinformatics techniques were used to examine the microbial communities associated with basalt and gabbro. Cloning and sequencing of 16S rDNA from basalt and gabbro samples revealed that a disparate microbial communities resides in these two environments. Basalt samples harbor a surprising diversity of seemingly cosmopolitan microorganisms, some of which appear to be basalt specialists. Conversely, gabbros have a low diversity of endoliths, none of which appear to be specifically adapted to the gabbroic environment. Despite the differences in the microbial communities in basalt and gabbro, analysis of functional genes using a microarray revealed overlapping metabolic processes. Genes coding for carbon fixation, methane generation and oxidation, nitrogen fixation, and denitrification were present in both rock types. None of these metabolic processes have been reported previously in basalt or gabbro hosted environments. Taken together, these findings provide significant insight into the possible biogeochemical cycling occurring in marine crust.
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