Dataset Information

A novel microbial habitat in the mid-ocean ridge subseafloor.

ABSTRACT: The subseafloor at the mid-ocean ridge is predicted to be an excellent microbial habitat, because there is abundant space, fluid flow, and geochemical energy in the porous, hydrothermally influenced oceanic crust. These characteristics also make it a good analog for potential subsurface extraterrestrial habitats. Subseafloor environments created by the mixing of hot hydrothermal fluids and seawater are predicted to be particularly energy-rich, and hyperthermophilic microorganisms that broadly reflect such predictions are ejected from these systems in low-temperature ( approximately 15 degrees C), basalt-hosted diffuse effluents. Seven hyperthermophilic heterotrophs isolated from low-temperature diffuse fluids exiting the basaltic crust in and near two hydrothermal vent fields on the Endeavour Segment, Juan de Fuca Ridge, were compared phylogenetically and physiologically to six similarly enriched hyperthermophiles from samples associated with seafloor metal sulfide structures. The 13 organisms fell into four distinct groups: one group of two organisms corresponding to the genus Pyrococcus and three groups corresponding to the genus Thermococcus. Of these three groups, one was composed solely of sulfide-derived organisms, and the other two related groups were composed of subseafloor organisms. There was no evidence of restricted exchange of organisms between sulfide and subseafloor habitats, and therefore this phylogenetic distinction indicates a selective force operating between the two habitats. Hypotheses regarding the habitat differences were generated through comparison of the physiology of the two groups of hyperthermophiles; some potential differences between these habitats include fluid flow stability, metal ion concentrations, and sources of complex organic matter.

SUBMITTER: Summit M

PROVIDER: S-EPMC30109 | biostudies-literature | 2001 Feb

REPOSITORIES: biostudies-literature

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A novel microbial habitat in the mid-ocean ridge subseafloor.

Summit M M Baross J A JA

Proceedings of the National Academy of Sciences of the United States of America 20010201 5

The subseafloor at the mid-ocean ridge is predicted to be an excellent microbial habitat, because there is abundant space, fluid flow, and geochemical energy in the porous, hydrothermally influenced oceanic crust. These characteristics also make it a good analog for potential subsurface extraterrestrial habitats. Subseafloor environments created by the mixing of hot hydrothermal fluids and seawater are predicted to be particularly energy-rich, and hyperthermophilic microorganisms that broadly re ...[more]

PMID: 11226209

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Project description:The temporal variation in archaeal diversity in vent fluids from a midocean ridge subseafloor habitat was examined using PCR-amplified 16S rRNA gene sequence analysis and most-probable-number (MPN) cultivation techniques targeting hyperthermophiles. To determine how variations in temperature and chemical characteristics of subseafloor fluids affect the microbial communities, we performed molecular phylogenetic and chemical analyses on diffuse-flow vent fluids from one site shortly after a volcanic eruption in 1998 and again in 1999 and 2000. The archaeal population was divided into particle-attached (>3-microm-diameter cells) and free-living fractions to test the hypothesis that subseafloor microorganisms associated with active hydrothermal systems are adapted for a lifestyle that involves attachment to solid surfaces and formation of biofilms. To delineate between entrained seawater archaea and the indigenous subseafloor microbial community, a background seawater sample was also examined and found to consist only of Group I Crenarchaeota and Group II Euryarchaeota, both of which were also present in vent fluids. The indigenous subseafloor archaeal community consisted of clones related to both mesophilic and hyperthermophilic Methanococcales, as well as many uncultured Euryarchaeota, some of which have been identified in other vent environments. The particle-attached fraction consistently showed greater diversity than the free-living fraction. The fluid and MPN counts indicate that while culturable hyperthermophiles represent less than 1% of the total microbial community, the subseafloor at new eruption sites does support a hyperthermophilic microbial community. The temperature and chemical indicators of the degree of subseafloor mixing appear to be the most important environmental parameters affecting community diversity, and it is apparent that decreasing fluid temperatures correlated with increased entrainment of seawater, decreased concentrations of hydrothermal chemical species, and increased incidence of seawater archaeal sequences.

Project description:Textures and compositions of minerals can be used to infer the physiochemical conditions present within magmatic systems. Given that plagioclase is an abundant phase in many magmatic systems, understanding the link between texture and process is vital. Here, we present a database of textural and compositional data for?>?1800 plagioclase crystals in mid-ocean ridge basalt from the Gakkel Ridge (Arctic Ocean) to investigate the physiochemical conditions and processes that govern the formation of plagioclase textures and compositions. The Gakkel basalts have high modal crystal contents (up to 50%). The crystal cargo is complex, with both individual plagioclase and glomerocrysts showing large variations in crystal habit, zoning and resorption. The most common types of zoning are reverse and patchy; we attribute patchy zoning to infilling following either skeletal growth or resorption. Resorption is abundant, with multiple resorption events commonly present in a single crystal, and results from both magmatic recharge and decompression. Periods of strong undercooling, distinct to quench crystallisation, are indicated by matured skeletal crystals and thin normally zoned melt inclusion-rich bands following resorption. Individual samples often contain diverse textural and compositional plagioclase groups. Furthermore, most plagioclase is not in equilibrium with its host melt. Finally, the porous open structures of some glomerocrysts suggest that they represent pieces of entrained disaggregated mush. We interpret this to indicate that the crystal cargo is not generally phenocrystic in origin. Instead, plagioclase crystals that formed in different parts of a mush-dominated plumbing system were entrained into ascending melts. The textures of individual crystals are a function of their respective histories of (under)cooling, magma mixing and decompression. The morphologies of melt inclusion trapped in the plagioclase crystals are associated with specific host crystal textures, suggesting a link between plagioclase crystallisation processes and melt inclusion entrapment. The database of plagioclase presented herein may serve as a template for the interpretation of plagioclase textures in magmatic systems elsewhere.

Dataset Information

A novel microbial habitat in the mid-ocean ridge subseafloor.

Publications

A novel microbial habitat in the mid-ocean ridge subseafloor.

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