Subseafloor microbial communities in hydrogen‐rich vent fluids from hydrothermal systems along the Mid‐Cayman Rise

Abstract

SummaryWarm fluids emanating from hydrothermal vents can be used as windows into the rocky subseafloor habitat and its resident microbial community. Two new vent systems on the Mid‐Cayman Rise each exhibits novel geologic settings and distinctively hydrogen‐rich vent fluid compositions. We have determined and compared the chemistry, potential energy yielding reactions, abundance, community composition, diversity, and function of microbes in venting fluids from both sites: Piccard, the world's deepest vent site, hosted in mafic rocks; and Von Damm, an adjacent, ultramafic‐influenced system. Von Damm hosted a wider diversity of lineages and metabolisms in comparison to Piccard, consistent with thermodynamic models that predict more numerous energy sources at ultramafic systems. There was little overlap in the phylotypes found at each site, although similar and dominant hydrogen‐utilizing genera were present at both. Despite the differences in community structure, depth, geology, and fluid chemistry, energetic modelling and metagenomic analysis indicate near functional equivalence between Von Damm and Piccard, likely driven by the high hydrogen concentrations and elevated temperatures at both sites. Results are compared with hydrothermal sites worldwide to provide a global perspective on the distinctiveness of these newly discovered sites and the interplay among rocks, fluid composition and life in the subseafloor.

Spatially distinct, temporally stable microbial populations mediate biogeochemical cycling at and below the seafloor in hydrothermal vent fluids

“…Reveillaud et al . () showed that subseafloor communities in diffuse fluids at two chemically and geologically distinct vent fields were broadly functionally similar, consistent with thermodynamic predictions. In addition, a study within a single vent field at Axial Seamount showed differences in gene expression patterns between both diffuse vents as well as within the intra‐field waters between vent sites (Olins et al ., ).…”

“…In a regional‐scale study comparing the communities in diffuse fluids from two vent fields with distinct geology and chemistry located within 20 km of one another on the Mid‐Cayman Rise, Reveillaud et al . () showed that there were fine‐scale phylogenetic differences in microbial community structure between the two vent fields, with fluid communities at each vent field more closely related to one another than communities found in fluids from the other vent field. In addition, smaller scale spatial studies of multiple diffuse vents within one vent field (Huber et al ., ; Opatkiewicz et al ., ; Perner et al ., ; Akerman et al ., ; Meier et al ., ; Olins et al ., ) show that the microbial community composition is shaped by both the geochemistry as well as the distance between individual diffuse vents.…”

Genome‐resolved metagenomics and metatranscriptomics reveal niche differentiation in functionally redundant microbial communities at deep‐sea hydrothermal vents

“…However, metagenomic analyses of one sample from each site showed that although a wider diversity of metabolisms was observed at Von Damm, including anaerobic methane oxidation, the microbial communities at the two vent fields had near functional equivalence, with metabolisms related to methane, hydrogen, and sulphur cycling. The authors hypothesized that these similarities in functional repertoire likely result from the high concentrations of both hydrogen and sulphide available at both sites (McDermott et al ., , ; Reveillaud et al ., ).…”

“…Using 16S rRNA gene sequencing and metagenomics, Reveillaud et al . () examined diffuse fluids from both Von Damm and Piccard and showed that each vent field hosts phylogenetically distinct microbial communities. However, metagenomic analyses of one sample from each site showed that although a wider diversity of metabolisms was observed at Von Damm, including anaerobic methane oxidation, the microbial communities at the two vent fields had near functional equivalence, with metabolisms related to methane, hydrogen, and sulphur cycling.…”

H2 clumped isotope measurements at natural isotopic abundances

“…H 2 has a strong link with microbial life; for example, it is produced in soils and in the ocean in the process of bacterial N 2 fixation, and in microbial fermentation processes. It is an important subsistence source of energy for soil microbes, which makes soil uptake the most important sink for atmospheric H 2 ; it is also an important source of energy for other (chemoautotrophs, extremophiles) microbes . It is involved in anoxic methane formation, for example in wetlands.…”