Abstract
The surficial hydrothermal sediments of Guaymas Basin harbor complex microbial communities where oxidative and reductive nitrogen, sulfur, and carbon-cycling populations and processes overlap and coexist. Here, we resolve microbial community profiles in hydrothermal sediment cores of Guaymas Basin on a scale of 2 millimeters, using Denaturing Gradient Gel Electrophoresis (DGGE) to visualize the rapid downcore changes among dominant bacteria and archaea. DGGE analysis of bacterial 16S rRNA gene amplicons identified free-living and syntrophic deltaproteobacterial sulfate-reducing bacteria, fermentative Cytophagales, members of the Chloroflexi (Thermoflexia), Aminicenantes, and uncultured sediment clades. The DGGE pattern indicates a gradually changing downcore community structure where small changes on a 2-millimeter scale accumulate to significantly changing populations within the top 4 cm sediment layer. Functional gene DGGE analyses identified anaerobic methane-oxidizing archaea (ANME) based on methyl-coenzyme M reductase genes, and members of the Betaproteobacteria and Thaumarchaeota based on bacterial and archaeal ammonia monooxygenase genes, respectively. The co-existence and overlapping habitat range of aerobic, nitrifying, sulfate-reducing and fermentative bacteria and archaea, including thermophiles, in the surficial sediments is consistent with dynamic redox and thermal gradients that sustain highly complex microbial communities in the hydrothermal sediments of Guaymas Basin.
Highlights
Guaymas Basin, a young hydrothermally active spreading center in the central Gulf of California, differs from its open-ocean counterparts by its massive sediment layers that host deeply emplaced, hot volcanic sills
Adjacent to hydrothermal sediment core 4868-7 that was used for Denaturing Gradient Gel Electrophoresis (DGGE) analysis, core 4868-10 was sampled for parallel geochemical characterization of the sampling site by porewater analysis (Table 1)
Ammonia concentrations in the millimolar range, and nitrite and nitrate concentrations in the lower micromolar range are similar to other hydrothermal sediment cores of Guaymas Basin where ammonia-rich hydrothermal fluids are mixing with traces of nitrite and nitrate that most likely originate in seawater or in nitrate-accumulating Beggiatoaceae mats overlying the sediment surface
Summary
Guaymas Basin, a young hydrothermally active spreading center in the central Gulf of California, differs from its open-ocean counterparts by its massive sediment layers that host deeply emplaced, hot volcanic sills. The hydrocarbon-rich hydrothermal fluids reach the surficial sediments of Guaymas Basin, where they supply these subsurface-derived organic carbon sources and DIC to complex microbial communities that use seawaterderived electron acceptors, such as oxygen, nitrate and sulfate, to oxidize these carbon sources and to assimilate them into microbial biomass (Pearson et al, 2005). The overlap of hydrothermal carbon sources and electron donors with seawater-derived electron acceptors and sedimenting organic matter sustains microbial interface communities where bacteria and archaea with divergent or mutually exclusive metabolisms coexist, for example nitratereducing sulfur-oxidizing filamentous bacteria of the family Beggiatoaceae and aerobic ammonia-oxidizing Thaumarchaeota (Winkel et al, 2014)
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