Abstract
Despite years of research into microbial activity at diffuse flow hydrothermal vents, the extent of microbial niche diversity in these settings is not known. To better understand the relationship between microbial activity and the associated physical and geochemical conditions, we obtained co-registered metatranscriptomic and geochemical data from a variety of different fluid regimes within the ASHES vent field on the Juan de Fuca Ridge. Microbial activity in the majority of the cool and warm fluids sampled was dominated by a population of Gammaproteobacteria (likely sulfur oxidizers) that appear to thrive in a variety of chemically distinct fluids. Only the warmest, most hydrothermally-influenced flows were dominated by active populations of canonically vent-endemic Epsilonproteobacteria. These data suggest that the Gammaproteobacteria collected during this study may be generalists, capable of thriving over a broader range of geochemical conditions than the Epsilonproteobacteria. Notably, the apparent metabolic activity of the Gammaproteobacteria—particularly carbon fixation—in the seawater found between discrete fluid flows (the intra-field water) suggests that this area within the Axial caldera is a highly productive, and previously overlooked, habitat. By extension, our findings suggest that analogous, diffuse flow fields may be similarly productive and thus constitute a very important and underappreciated aspect of deep-sea biogeochemical cycling that is occurring at the global scale.
Highlights
Free-living microorganisms at hydrothermal vents play a fundamental role in supporting highly productive vent ecosystems and influence local, if not global, geochemistry (Resing et al, 2015)
We considered the resulting metatranscriptomic and geochemical data from three perspectives: (1) a dataset-wide investigation of the most abundant transcripts that provide a broad view of the active community and their gene expression profiles in different habitat types; (2) a targeted analysis of gene expression relevant to chemosynthesis and elemental cycling; and (3) differential expression analysis of samples collected using the D-ESP to identify the most differentially-expressed genes between our most hydrothermally-influenced diffuse flow site and the intra-field fluids
Our findings demonstrate that low temperature diffuse flow vents in a single vent field can have dramatically different profiles of microbial activity dominated by vent-associated Epsilonproteobacteria
Summary
Free-living microorganisms at hydrothermal vents play a fundamental role in supporting highly productive vent ecosystems and influence local, if not global, geochemistry (Resing et al, 2015). Hydrothermal Vent Microbial Metatranscriptomics and Geochemistry in supporting the associated animal communities, either as freeliving microbes upon which animals graze or as symbionts. Most of the studies on free-living microbes have focused on communities associated with the prominent high temperature chimneys (200–400◦C) and their fluid plumes, which can be tens of meters and hundreds of meters tall, respectively (e.g., Klinkhammer and Hudson, 1986; Cowen et al, 1990; Kadko et al, 1995). The lower temperatures and mixing of oxygen-rich seawater with chemically-reduced hydrothermal fluids should yield a diversity of niches for microbes, and support higher rates of primary productivity than high temperature vents (Perner et al, 2011; Olins et al, 2013)
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