Diverse microbial communities thrive on and in deep-sea hydrothermal vent mineral deposits. However, our understanding of the inter-field variability in these communities is poor, as limited sampling and sequencing efforts have hampered most previous studies. To explore the inter-field variability in these communities, we used barcoded pyrosequencing of the variable region 4 (V4) of the 16S rRNA gene to characterize the archaeal and bacterial communities of over 30 hydrothermal deposit samples from six vent fields located along the Eastern Lau Spreading Center. Overall, the bacterial and archaeal communities of the Eastern Lau Spreading Center are similar to other active vent deposits, with a high diversity of Epsilonproteobacteria and thermophilic Archaea. However, the archaeal and bacterial communities from the southernmost vent field, Mariner, were significantly different from the other vent fields. At Mariner, the epsilonproteobacterial genus Nautilia and the archaeal family Thermococcaceae were prevalent in most samples, while Lebetimonas and Thermofilaceae were more abundant at the other vent fields. These differences appear to be influenced in part by the unique geochemistry of the Mariner fluids resulting from active degassing of a subsurface magma chamber. These results show that microbial communities associated with hydrothermal vent deposits in back-arc basins are taxonomically similar to those from mid-ocean ridge systems, but differences in geologic processes between vent fields in a back-arc basin can influence microbial community structure.
"We expanded on existing microbiological observations from similar geologic settings (e.g. Kato et al., 2010; Flores et al., 2012; Sylvan et al., 2013) to illustrate the dominance of the rTCA pathway in vent primary productivity on active structures that emit H 2S-rich and H2 and CH4-poor fluids. Our data also further offer new detail through a more refined subsampling strategy, suggesting hitherto unobserved variations in δ "
[Show abstract][Hide abstract] ABSTRACT: Sulfide 'chimneys' characteristic of seafloor hydrothermal venting are diverse microbial habitats. (13) C/(12) C ratios of microbial lipids have rarely been used to assess carbon assimilation pathways on these structures, despite complementing gene- and culture-based approaches. Here, we integrate analyses of the diversity of intact polar lipids (IPL) and their side-chain δ(13) C values (δ(13) Clipid ) with 16S rRNA gene-based phylogeny to examine microbial carbon flow on active and inactive sulfide structures from the Manus Basin. Surficial crusts of active structures, dominated by Epsilonproteobacteria, yield bacterial δ(13) Clipid values higher than biomass δ(13) C (total organic carbon), implicating autotrophy via the reverse tricarboxylic acid cycle. Our data also suggest δ(13) Clipid values vary on individual active structures without accompanying microbial diversity changes. Temperature and/or dissolved substrate effects - likely due to variable advective-diffusive fluxes to chimney exteriors - may be responsible for differing (13) C fractionation during assimilation. In an inactive structure, δ(13) Clipid values lower than biomass δ(13) C and a distinctive IPL and 16S rRNA gene diversity suggest a shift to a more diverse community and an alternate carbon assimilation pathway after venting ceases. We discuss here the potential of IPL and δ(13) Clipid analyses to elucidate carbon flow in hydrothermal structures when combined with other molecular tools.
"Our study on the distribution of the Aquificales along the ELSC/VFR shows that the communities differ between distinct geographical locations and are influenced by the host-rock of the vent field and deposit type where they were detected. These trends are similar to those reported by other authors    who showed a north–south shift in microbial diversity patterns in different vent communities concomitant with the north–south geochemical gradient along the ELSC/VFR. Furthermore, our comprehensive survey revealed that the ELSC/VFR contains the largest diversity of Aquificales ever reported in a single geographical area and that this geochemical diverse system may harbor new members of the Aquificales, in particular, some Hydrogenothermaceae that might be 'endemic' to this hydrothermal system. "
[Show abstract][Hide abstract] ABSTRACT: The microbial diversity associated with actively venting deep-sea hydrothermal deposits is tightly connected to the geochemistry of the hydrothermal fluids. Although the dominant members of these deposits drive the structure of the microbial communities, it is less well understood whether the lower abundance groups are as closely connected to the geochemical milieu, or driven perhaps by biotic factors such as microbial community interactions. We used the natural geochemical gradients that exist in the back-arc basin, Eastern Lau Spreading Center and Valu-Fa Ridge (ELSC/VFR) in the Southwestern Pacific, to explore whether the chemolithotrophic Aquificales are influenced by geographical location, host-rock of the vent field or deposit type. Using a combination of cloning, DNA fingerprinting (DGGE) and enrichment culturing approaches, all genera of this order previously described at marine vents were detected, i.e., Desulfurobacterium, Thermovibrio, Aquifex, Hydrogenivirga, Persephonella and Hydrogenothermus. The comparison between clone libraries and DGGE showed similar patterns of distribution of different Aquificales whereas results differed for the enrichment cultures that were retrieved. However, the use of cultivation-based and -independent methods did provide complementary phylogenetic diversity overview of the Aquificales in these systems. Together, this survey revealed that the ELSC/VFR contains some of the largest diversity of Aquificales ever reported at a deep-sea vent area, that the diversity patterns are tied to the geography and geochemistry of the system, and that this geochemical diverse back-arc basin may harbor new members of the Aquificales.
"Geochemical conditions also exert an effect on microbial community composition, especially in extreme low-pH environments (Baker and Banfield, 2003). However, hydrodynamic or geochemical conditions alone often cannot fully explain microbial diversity (Flores et al., 2012). Hydrogeochemical niches can be identified by overlaying hydrodynamic and geochemical conditions, and may improve our ability to understand and predict microbial diversity. "
[Show abstract][Hide abstract] ABSTRACT: Biological low-pH Fe(II)-oxidation creates terraced iron formations (TIFs) that remove Fe(III) from solution. TIFs can be used for remediation of acid mine drainage (AMD), however, as sediment depth increases, Fe(III)-reduction in anoxic subsurface areas may compromise treatment effectiveness. In this study we used near-surface electrical resistivity imaging (ERI) and in situ pore-water samplers to spatially resolve bulk conductivity changes within a TIF formed in a stream emanating from a large abandoned deep clay mine in Cambria County, Pennsylvania, USA. Because of the high fluid electrical conductivity of the emergent AMD (1860μS), fresh water (42μS) was added as a dilution tracer to visualize the spatial and temporal extent of hyporheic exchange and to characterize subsurface flow paths. Distinct hydrogeochemical niches were identified in the shallow subsurface beneath the stream by overlaying relative groundwater velocities (derived from ERI) with pore-water chemistry profiles. Niches were classified based on relatively “fast” versus “slow” rates of hyporheic exchange and oxic versus anoxic conditions. Pore-water concentrations and speciation of iron, pH, and redox potential differed between subsurface flow regimes. The greatest extent of hyporheic exchange was beneath the center of the stream, where a shallower (<10cm) Fe(II)-oxidizing zone was observed. Meanwhile, less hyporheic exchange was observed near the channel banks, concurrent with a more pronounced, deeper (>70cm) Fe(II)-oxidizing zone. At these locations, relatively slower groundwater exchange may promote biotic Fe(II)-oxidation and improve the long-term stability of Fe sequestered in TIFs.
Journal of Hydrology 09/2013; 501:163-174. DOI:10.1016/j.jhydrol.2013.08.007 · 3.05 Impact Factor
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