We used molecular techniques to analyze basalts of varying ages that were collected from the East Pacific Rise, 9 oN, 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 twelve different phyla and sub-phyla associated with basalts. These include the Gemmatimonadetes, Nitrospirae, the candidate phylum SBR1093 in the c, 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 gamma-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.

Prokaryotic diversity, distribution, and insights into their role in biogeochemical cycling in marine basalts

Microbial communities inhabiting subseafloor ocean crust were analyzed using culture-dependent and -independent techniques of volcanic basement drill-cores from various locations in the Pacific Ocean. Our results suggest that a low-diversity community of bacteria belonging to the Betaproteobacteria, Alphaproteobacteria, and Bacteroidetes exists in this rocky habitat. Drilling-related contamination was observed, however, identification of these phylotypes was (and will continue to be) beneficial for distinguishing indigenous from contamination-related communities. Due to difficulties in accessing the subseafloor crustal environment, this study further highlights the necessity for innovative approaches in future drilling-based microbiological studies conducted in ocean crust.

Tapping the Subsurface Ocean Crust Biosphere: Low Biomass and Drilling-Related Contamination Calls for Improved Quality Controls

The interaction of a single bacterial species (Burkholderia fungorum) with basaltic rocks from the ICDP HSDP2 drill core and synthetic basaltic glasses was investigated in batch laboratory experiments to better understand the role of microbial activity on rock alteration and Fe mobilization. Incubation experiments were performed with drill core basaltic rock samples to investigate differences in the solution chemistry during biotic and abiotic alteration. Additionally, colonization experiments with synthetic basaltic glasses of different Fe redox states and residual stresses were performed to evaluate their influence on microbial activity and surface attachment of cells. In biotic incubation experiments bacterial growth was observed and the release of Fe and other major elements from drill core basaltic rocks to solution exceeded that of abiotic controls only when the rock sample assay was nutrient depleted. The concentration of dissolved major elements in solution in biotic colonization experiments with synthetic basaltic glasses increased with increasing residual stress and Fe(II) content. Furthermore, the concentration of dissolved Fe and Al increased similarly in biotic colonization experiments indicating that their dissolution might be triggered by microbial activity. Surface morphology imaging by SEM revealed that cells on basaltic rocks in incubation experiments were most abundant on the glass and surfaces with high roughness and almost absent on minerals. In colonization experiments, basaltic glasses with residual stress and high Fe(II) content were intensely covered with a cellular biofilm. In contrast, glasses with high Fe(III) content and no residual stress were sparsely colonized. We therefore conclude that structurally bound Fe is most probably used by B. fungorum as a nutrient. Furthermore, we assume that microbial activity overall increased rock dissolution as soon as the environment becomes nutrient depleted. Our results show that besides compositional effects, other factors such as redox state and residual stress can control microbial alteration of basaltic glasses.

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Experimental Microbial Alteration and Fe Mobilization From Basaltic Rocks of the ICDP HSDP2 Drill Core, Hilo, Hawaii.

Microbial bioerosion of volcanic glass produces conspicuous ichnofossils in oceanic crusts that are a valuable tracer of sub-surface microorganisms Two morphologically distinct granular and tubular ichnofossils are produced The ‘Granular form’ consists of individual or coalescing, spherical bodies with average diameters of ~04 μm The ‘Tubular form’ are straight, sometimes ranched, to curving and spiralled tubes with average diameters of 1-2 μm and lengths of up to ~200μm A biogenic origin for these structures is confirmed by: the concentration of DNA that binds to biological stains in recent examples; enrichments in C, N and P along their margins in both recent and ancient examples; and systematic C isotope shifts measured upon disseminated carbonate in the surrounding glass The constructing microorganisms are thought to include heterotrophs and chemolithoautotrophs that may utilise Fe and Mn from basaltic glass as electron donors and derive carbon sources and electron acceptors from circulating fluids These microbial ichnofossils are found at depths of up to 550 metres in the oceanic crust in the glassy rims of pillow basalts and interpillow breccias A diverse spectrum of ichnofabrics is created by overlapping phases of granular and tubular bioerosion; banded abiotic dissolution; and the precipitation of phyllosilicates, zeolites and iron-oxy-hydroxides The resulting ichnofabrics have been documented from in situ oceanic crust spanning the youngest to the oldest oceanic basins (0 to 170 Ma) Their geological record extends to include meta-volcanic glass in oceanic crustal fragments from Phanerozoic to Proterozoic ophiolites Examples infilled by the mineral titanite (CaTiSiO4) have also been found in Palaeo- to Mesoarchaean pillow basalts from the Barberton Greenstone Belt of South Africa and the East Pilbara Terrane of Western Australia Direct 206Pb / 238U radiometric dating of the Australia examples has confirmed their Archaean age and thus they represent the oldest candidate ichnofossils on Earth

Micro-bioerosion in volcanic glass: extending the ichnofossil record to Archaean basaltic crust

An experimental model approach of biologically-assisted silicate dissolution with olivine and Escherichia coli - Impact on chemical weathering of mafic rocks and atmospheric CO2 drawdown

. Microorganisms have been reported to be associated with the alteration of the glassy margin of seafloor pillow basalts (Thorseth et al., 2001, 2003; Lysnes et al., 2004). The amount of iron and other biological important elements present in basalts and the vast abundance of basaltic glass in the earth's crust, make glass alteration an important process in global element cycling. To gain further insight into microbial communities associated with glass alteration, five microcosm experiments mimicking seafloor conditions were inoculated with seafloor basalt and incubated for one year. Mineral precipitations, microbial attachment to the glass and glass alteration were visualized by scanning electron microscopy (SEM), and the bacterial community composition was fingerprinted by PCR and denaturing gradient gel electrophoresis (DGGE) in combination with sequencing. SEM analysis revealed a microbial community with low morphological diversity of mainly biofilm associated and prosthecate microorganisms. Approximately 30 nm thick alteration rims developed on the glass in all microcosms after one year of incubation; this however was also seen in non inoculated controls. Calcium carbonate precipitates showed parallel, columnar and filamentous crystallization habits in the microcosms as well as in the sterile controls. DGGE analysis showed an alteration in bacterial community profiles in the five different microcosms, as a response to the different energy and redox regimes and time. In all microcosms a reduction in number of DGGE bands, in combination with an increase in cell abundance were recorded during the experiment. Sequence analysis showed that the microcosms were dominated by four groups of organisms with phylogenetic affiliation to four taxa: The Rhodospirillaceae, a family containing phototrophic marine organisms, in which some members are capable of heterotrophic growth in darkness and N2 fixation; the family Hyphomicrobiaceae, a group of prosthecate oligotrophic organisms; the genus Rhizobium, N2 fixating heterotrophs; and the genus Sphingomonas, which are known as bio-film producing oligotrophs. Although no bioalteration of glass could be confirmed from our experiments, oligotrophic surface adhering bacteria such as the Sphingomonas sp. and Hyphomicrobium sp. may nevertheless be important for bioalteration in nature, due to their firm attachment to glass surfaces, and their potential for biofilm production.

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Microbial colonization and alteration of basaltic glass

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Microbial colonization and alteration of basaltic glass