Editorial: Hydrothermal Microbial Ecosystems

The papers in the "Hydrothermal Vent" research topic cover a range of microbiological research in deep and shallow hydrothermal environments, from high temperature "black smokers, " to diffuse flow habitats and episodically discharging subsurface fluids, to the hydrothermal plumes.Together they provide a snapshot of current research interests in a field that has evolved rapidly since the discovery of hydrothermal vents in 1977.The topic opens with a review by Dick et al. (2013) on hydrothermal plumes and their microbial communities in the deep sea.The review synthesizes recent advances in the microbial ecology, physiology, and genomics of the mostly chemosynthetic bacteria that have adapted to the supply of carbon and energy sources in the turbulently mixed vent plume.These pelagic communities are distinct from those in hydrothermal chimneys, sediments and the subsurface, yet they show some taxonomic and physiological linkages.This review is followed by four papers that shed new light on microbial ecosystems in mixed vent fluids.The high-flow example is represented by sulfiderich subsurface vent fluids discharging in "snow blower" bursts dominated by sulfur-oxidizing, microaerobic, and often moderately thermophilic Epsilonproteobacteria (Meyer et al., 2013a).Similar epsilonproteobacterial communities, dominated by the chemosynthetic, sulfur-oxidizing genera Sulfurimonas and Sulfurovum, were also found in cool, diffusive flow at the same location, Axial Seamount on the Juan de Fuca Ridge (Akerman et al., 2013).The authors proposed that both diffuse flow and episodic high-flow events tap into the same subsurface community of microaerobic sulfur oxidizers.Epsilonproteobacteria accounted again for most of the microbial taxa found in diffuse flow samples from the basalt-hosted vent sites of 9 • N East Pacific Rise, but not in similar habitats in the organic-rich hydrothermal sediments of Guaymas Basin in the Gulf of California, where other bacterial groups and hyperthermophilic archaea predominated (Campbell et al., 2013).Changing flow paths and reservoirs for subseafloor mixed fluids and their microbiota can also change the composition of venting microbial communities over time as reported by Kato and colleagues.At Suiyo Seamount in the Izu-Bonin Arc within the Western Pacific, a hot and reducing subsurface reservoir accessed by drilling underwent increasing seawater in-mixing over several years.Consequently, the crustal fluid community of sulfur-oxidizing chemolithotrophs changed to a mixed assemblage harboring abundant marine heterotrophic bacteria (Kato et al., 2013).While deep-sea hydrothermal vent sites are difficult to access and to sample, shallow water hydrothermal vents that can be reached by scuba divers provide an accessible alternative environment to study.Perhaps the best-investigated of these shallow-water vents are found on the coast of the Greek island Milos in the Aegean Sea, where hot, briny, reducing, CO 2 -rich vent fluids permeate the sandy seafloor sediments of Paleochori Bay.Giovannelli et al. (2013) show that in the surficial sediments the microbial community is dominated by Epsilonproteo-bacteria (genus Sulfurovum) similar to those seen in deep-sea vents; however proteobacterial lineages that are distinct from those of deep-sea vents were also detected.In contrast, in the deeper sediment layers of this sample vent field, Price et al. (2013) find Epsilonproteobacteria, but also Firmicutes, Planctomycetes, and Bacteroidetes coexisting with thermophilic archaea.In addition, arsenite-oxidizing bacteria were identified by

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