We used molecular techniques to analyze basalts of varying ages that were collected from the East Pacific Rise, 91 N, from the rift axis of the Juan de Fuca Ridge and from neighboring seamounts. Cluster analysis of 16S rDNA terminal restriction fragment polymorphism data revealed that basalt endoliths are distinct from seawater and that communities clustered, to some degree, based on the age of the host rock. This age-based clustering suggests that alteration processes may affect community structure. Cloning and sequencing of bacterial and archaeal 16S rRNA genes revealed 12 different phyla and subphyla associated with basalts. These include the Gemmatimonadetes, Nitrospirae, the candidate phylum SBR1093 in the bacteria, and in the Archaea Marine Benthic Group B, none of which have been previously reported in basalts. We delineated novel ocean crust clades in the c-Proteobacteria, Planctomycetes and Actinobacteria that are composed entirely of basalt-associated microflora, and may represent basalt ecotypes. Finally, microarray analysis of functional genes in basalt revealed that genes coding for previously unreported processes such as carbon fixation, methane oxidation, methanogenesis and nitrogen fixation are present, suggesting that basalts harbor previously unrecognized metabolic diversity. These novel processes could exert a profound influence on ocean chemistry.

We examined the phylogenetic diversity of microbial communities associated with marine basalts, using over 300 publicly available 16S rDNA sequences and new sequence data from basalt enrichment cultures. Phylogenetic analysis provided support for 11 monophyletic clades originating from ocean crust (sediment, basalt and gabbro). Seven of the ocean crust clades (OCC) are bacterial, while the remaining four OCC are in the Marine Group I (MGI) Crenarchaeota. Most of the OCC were found at diverse geographic sites, suggesting that these microorganisms have cosmopolitan distributions. One OCC in the Crenarchaeota consisted of sequences derived entirely from basalts. The remaining OCC were found in both basalts and sediments. The MGI Crenarchaeota were observed in all studies where archaeal diversity was evaluated. These results demonstrate that basalts are occupied by cosmopolitan clades of microorganisms that are also found in marine sediments but are distinct from microorganisms found in other marine habitats, and that one OCC in the ubiquitous MGI Crenarchaeota clade may be an ecotype specifically adapted to basalt.

No abstract