Abstract
The Sonora Margin cold seeps present a seafloor mosaic pattern consisting of different faunal assemblages and microbial mats. To better understand if sedimentary microbial communities reflect this patchy distribution, all major habitats were investigated using four complementary approaches: 16S rRNA 454 pyrosequencing, quantitative polymerase chain reaction, fluorescence in situ hybridization and geochemistry analyses. This study reveals that sediments populated by different surface assemblages show distinct porewater geochemistry features and are associated with distinct microbial communities. In the sediments underlying the microbial mat and the surrounding macrofauna, microbial communities were dominated by anaerobic methane oxidizers (archaeal anaerobic methanotroph ANME) and sulfate-reducing Deltaproteobacteria. In contrast, sediment-associated microbial communities underlying the megafauna habitats (vesicomyids and siboglinids) were characterized by a lower biomass and important proportions of the Marine Benthic Group D (MBG-D), Chloroflexi as well as filamentous Gammaproteobacteria and Deltaproteobacteria. Together, geochemical and microbial surveys indicate that porewater methane concentrations play an important role in the microbial community structure and subsequently in the establishment of the surface colonizers. Furthermore, presence and activity of the surface colonizers influence the underlying microbial communities probably because of modification of energy source availabilities.
Highlights
Seafloor emissions of hydrocarbon low-temperature fluids are a characteristic feature of cold seep ecosystems
This process appears to be mainly mediated by anaerobic methanotrophic Archaea (ANMEs), which are frequently observed in structured aggregates with sulfate-reducing bacteria mostly affiliated to Deltaproteobacteria
Microorganisms occurring in the non-seep area (e.g., MGI, Marine Benthic Group E (MBG-E), Marine Benthic Group A (MBG-A), specific lineages of Gammaproteobateria) were different from the microbial community identified in the cold seep sediments (e.g., ANME, Marine Benthic Group D (MBG-D), candidate division JS-1) (Figures S2, S3)
Summary
Seafloor emissions of hydrocarbon low-temperature fluids are a characteristic feature of cold seep ecosystems. This process, as well as the activity of abundant sulfate-reducing bacteria, generates high concentrations of sulfide produced in porewater sediments which provides high fluxes of sulfide to the seafloor (Boetius et al, 2000; Orphan et al, 2001; Hinrichs and Boetius, 2002; Jørgensen and Boetius, 2007) These uprising sulfide-enriched fluids fuelled various surface assemblages such as mat-forming giant bacteria (Lloyd et al, 2010; Grünke et al, 2011; Mckay et al, 2012) or symbiont-bearing invertebrates (Sibuet and Olu, 1998; Dubilier et al, 2008; Cambon-Bonavita et al, 2009). These different types of communities are associated with specific seeps (characterized by different rates of fluid flow velocity and composition) depending on their ability to grow on available energy sources and to tolerate oxygen limitations and toxic sulfide concentrations (Barry et al, 1997; Sibuet and Olu, 1998; Sahling et al, 2002; Niemann et al, 2006; Lichtschlag et al, 2010; Pop Ristova et al, 2012; Ruff et al, 2013)
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