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Hydrothermal plumes are widely distributed throughout the global spreading ridges, yet few of them are microbiologically explored. The ultraslow-spreading ridges, recently recognized as a unique, new class of mid-ocean-ridge system, have provided surprises and new insights in hydrothermal system research. A suite of water column samples including both hydrothermal plume samples and ambient seawater were collected at different depths from the ultraslow-spreading Southwest Indian Ridge (SWIR) in 2010. We use molecular approaches such as clone libraries, denaturing gradient gel electrophoresis (DGGE) and quantitative PCR to determine microbial community compositions and their spatial variability within the hydrothermal plume and seawater. Phylogenetic analysis showed that plume samples were mainly dominated by members ofα-Proteobacteriaandγ-Proteobacteriaand members of marine group I group within theCrenarchaeota. Within the hydrothermal plume, archaeal populations were spatially homogeneous, while bacterial compositions were heterogeneous and remarkably distinct at different depths. Moreover, several lineages, closely related to known Mn(II) oxidizers were found to be abundant and even predominant within the plume bacterial communities. DGGE band patterns showed that there was no significant difference in microbial compositions between the samples of hydrothermal plume and ambient seawater. Taken together, we inferred that microbial communities in the SWIR hydrothermal plumes were sourced from ambient seawater rather than from seafloor vent-derived niches. This is the first report on the characteristics of microbial community structures in hydrothermal plume and ambient seawater in the Southwest Indian Ridge. [ABSTRACT FROM PUBLISHER]

Abstract: Microbial biomineralization in submarine hydrothermal environments provides an insight into the formation of vent microfossils and the interactions between microbes, elements and minerals throughout the geological record. Here, we investigate microbial biomineralization of a deep-sea vent community in the Edmond vent field and provide ultrastructural evidence for the formation of microfossils and biogenic iron-rich minerals related to Archaea and Bacteria. Environmental scanning electron microscopy (ESEM) analysis shows that filamentous and spiral microbes are encrusted by a non-crystalline silica matrix and minor amounts of iron oxides. Examination by transmission electron microscopy (TEM) reveals acicular iron-rich particles and aggregates that occur either intracellularly or extracellularly. A culture-independent molecular phylogenetic analysis demonstrates a diverse range of Bacteria and Archaea, the majority of which are related to sulfur metabolism in the microbial mats. Both Archaea and Bacteria have undergone silicification, in a similar manner to microorganisms in some terrestrial hot springs and indicating that silicification may be driven by silica supersaturation and polymerization. Formation mechanisms of intracellular and extracellular iron oxides associated with microbes are discussed. These results enhance our understanding of microbial mineralization in extreme environments, which may be widespread in the Earth''s modern and ancient hydrothermal vent fields. [Copyright &y& Elsevier]

Microbial mats, several millimeters thick and brown-yellow to white in color, were collected in hollow inside of chimney structure from Edmond hydrothermal field on the Central Indian Ridge. Microbes with shapes of rod and helical stalk-like filaments were observed in the microbial mats, and are commonly characterized by their cells completely encrusted by thick mineralized layers, made up of large amounts of amorphous silica and minor amounts of iron oxides. Transmission Electron Microscope observation has demonstrated that the acicular Fe-bearing matter was not only heterogenously distributed on the surface of the cell wall, but also deposited in the inside of cell, suggesting that bio-precipitation of Fe had occurred both on the surface and in the interior of cell. Microbial silicification was also commonly found in the mats. Silica usually precipitated homogeneously on the surface of the microbes and forms micro-laminated layers, which might be controlled by the inorganic process of precipitation in hydrothermal environment. The biomineralization phenomenon in the microbial mats showed that the precipitation of Fe and Si was closely related to microbes in hydrothermal environment. Considering that hydrothermal activities provided required chemical elements for mineralization, it is suggested that this biomineralization process also might be driven by hydrothermal activities at the sea floor to some extent. [ABSTRACT FROM AUTHOR]

During DY105-17 cruise onboard the RN "Da Yang Yi Hao" in 2005, methane concentrations in the water column above Logachev hydrothermal vent field were measured by applying stripping/trapping-gas chromatographic (GC) and the distinct methane plumes were detected. Results show that the background methane concentration within the Logachev area is from 1.05 nmol/L to 1.68 nmol/L, significantly higher than the background level of the Atlantic abyssal plain of 0.4-0.5 nmol/L, suggesting that hydrothermal venting is a major source of dissolved methane to the ocean. The highest anomalies of methane concentrations in the water column range from 7.14 nmol/L to 113.9 nmol/L and occur just at 180-500 m above the seafloor. The distribution of methane concentration and the structural characteristics of hydrothermal plumes are strongly influenced by the supply of underlying hydrothermal fluids, the mixing process of ocean bottom currents and the microbial oxidation. Furthermore, the differences in distribution of methane plume between the station MAR-CTD3 and the other stations indicate a probable unknown hydrothermal vent site nearby. There occurs high concentration of methane along with temperature and nephelometry anomalies, which strongly confirms that the subtle measurement of methane concentration in water column is one of the effective ways to locate active sites of hydrothermal venting. [ABSTRACT FROM AUTHOR]

The discovery of deep-sea hydrothermal vents in the late 1970s widened the limits of life and habitability. The mixing of oxidizing seawater and reduction of hydrothermal fluids create a chemical disequilibrium that is exploited by chemosynthetic bacteria and archaea to harness energy by converting inorganic carbon into organic biomass. Due to the rich variety of chemical sources and steep physico-chemical gradients, a large array of microorganisms thrive in these extreme environments, which includes but are not restricted to chemolithoautotrophs, heterotrophs, and mixotrophs. Past research has revealed the underlying relationship of these microbial communities with the subsurface geology and hydrothermal geochemistry. Endolithic microbial communities at the ocean floor catalyze a number of redox reactions through various metabolic activities. Hydrothermal chimneys harbor Fe-reducers, sulfur-reducers, sulfide and H2-oxidizers, methanogens, and heterotrophs that continuously interact with the basaltic, carbonate, or ultramafic basement rocks for energy-yielding reactions. Here, we briefly review the global deep-sea hydrothermal systems, microbial diversity, and microbe–mineral interactions therein to obtain in-depth knowledge of the biogeochemistry in such a unique and geologically critical subseafloor environment. [ABSTRACT FROM AUTHOR]

The important geological, environmental, and biological information contained in Fe-oxides (oxyhydroxides) in extreme hydrothermal environments has provided unique opportunities for exploring the microbial-driven mechanism of Fe-oxide formation. However, the interactions between Fe-oxides and organic components and their association with in situ geochemical signatures in hydrothermal systems remain poorly understood. This study analyzed Fe-oxide deposits collected from the Longqi hydrothermal field in the Southwest Indian Ridge and the Edmond and Kairei hydrothermal fields in the Central Indian Ridge using the manned submersible " ShenhaiYongshi ". Mineralogical and geochemical characteristics of hydrothermal iron oxide deposits indicated that microbial activity may influence trace element distribution. Analysis with laser confocal Raman spectroscopy (LR) revealed biomineralized structures with significant absorption peaks of Fe-oxyhydroxides. This was further confirmed by two typical L-shaped and Y-shaped structures directly measured using a novel scanning probe technique called infrared photo induced force microscopy (IR-PiFM). The strong peak in the range of 1500 to 1680 cm−1 corresponded to the bending vibration of Fe-O-H. X-ray photoelectron spectroscopy (XPS) showed that the oxidation state and coordination of iron strongly correspond to a biogenic origin. Fe-bearing phases in the biomineralized structures occurred mainly as FeOOH. The combined results of in situ LR, IR-PiFM, and XPS showed that organic compounds identified in mineralized structures could be polysaccharides, lipids, and proteins. The results suggested that bioorganic molecules may play a key role in the formation of Fe(III)-deposited nucleation sites, which promoted the development of biomineralized iron structures. These observations may provide new insights for understanding the biomineralization mechanism of Fe in extreme hydrothermal environments. • The mineralogical and geochemical characteristics of hydrothermal iron oxides can be influenced by microbial activity. • Fe-bearing phases in the biomineralized structures are associated with the diagenetic environment. • Organic compounds related to Fe(III)-deposited sites may facilitate the development of biomineralized structures. [ABSTRACT FROM AUTHOR]