Abstract
In the Guaymas Basin, the presence at a few tens of kilometers of cold seeps and hydrothermal vents coupled with comparable sedimentary settings and depths offer a unique opportunity to assess and compare the microbial community composition of these deep-sea ecosystems. The microbial diversity in sediments from three cold seep and two hydrothermal vent assemblages were investigated using high-throughput 16S rRNA-sequencing. Numerous bacterial and archaeal lineages were detected in both cold seep and hydrothermal vent sediments. Various potential organic matter degraders (e.g. Chloroflexi, Atribacteria, MBG-D) and methane and sulfur cycling related microorganisms (e.g. ANME and methanogenic lineages, sulfate-reducing lineages) were detected in both ecosystems. This suggests that analogous metabolic processes such as organic matter degradation and anaerobic methane oxidation coupled to sulfate reduction, were probably occurring in these two contrasted ecosystems. These highlighted core microbiome of the Guaymas Basin chemosynthetic ecosystems might therefore result from the combined presence of up-rising fluid emissions and high sedimentary rates of organic matter in the Basin. These results, coupled with the detailed ribotype analysis of major archaeal lineages (ANME-1, ANME-2 and MBG-D), also suggest a potential connectivity among deep-sea ecosystems of the Guaymas Basin likely due to the sedimentary context and the absence of physical border. However, thermophilic and hyperthermophilic lineages (e.g. : Thermodesulfobacteria, Desulfurococcales, etc.) were exclusively identified in hydrothermally impacted sediments highlighting the strong influence of temperature gradients and other hydrothermally-related factors such as thermogenic sulfate reduction and sulfide formation on microbial community composition.
Highlights
Deep-sea hydrothermal vents and cold seeps are characterized by elevated microbial biomass and various faunal and microbial assemblages (Van Dover et al, 2002; Jørgensen and Boetius, 2007)
Methane concentrations were lower in vesicomyid cold seep habitats with 0.013 mM and 0.003 mM at the Ayala and Vasconcelos BIG13 sites, respectively (Figures 2A,B), whereas up to 0.18 mM of methane were detected at 15 cmbsf in sediment core of Morelos vesicomyid vent site
Sulfide porewater concentrations were below the technical detection limit [10 μM] in cold seep sediments colonized by vesicomyids (Ayala and Vasconcelos BIG13, Figures 2A,B)
Summary
Deep-sea hydrothermal vents and cold seeps are characterized by elevated microbial biomass and various faunal and microbial assemblages (Van Dover et al, 2002; Jørgensen and Boetius, 2007). Hydrothermal vents are characterized by the presence of geothermally heated fluids that spring through openings in the seafloor, especially along active mid-ocean ridges (Van Dover et al, 2002). Afterwards, by- and end-products of these activities can be metabolized in turn by secondary producers (Jørgensen and Boetius, 2007), leading to the establishment of rich benthic communities at the seafloor (Sibuet and Olu, 1998; Dubilier et al, 2008; CambonBonavita et al, 2009; Lloyd et al, 2010; Grünke et al, 2011; McKay et al, 2012)
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