Structure and metabolic potential of the prokaryotic communities from the hydrothermal system of Paleochori Bay, Milos, Greece

Abstract

IntroductionShallow hydrothermal systems share many characteristics with their deep-sea counterparts, but their accessibility facilitates their study. One of the most studied shallow hydrothermal vent fields lies at Paleochori Bay off the coast of Milos in the Aegean Sea (Greece). It has been studied through extensive mapping and its physical and chemical processes have been characterized over the past decades. However, a thorough description of the microbial communities inhabiting the bay is still missing.MethodsWe present the first in-depth characterization of the prokaryotic communities of Paleochori Bay by sampling eight different seafloor types that are distributed along the entire gradient of hydrothermal influence. We used deep sequencing of the 16S rRNA marker gene and complemented the analysis with qPCR quantification of the 16S rRNA gene and several functional genes to gain insights into the metabolic potential of the communities.ResultsWe found that the microbiome of the bay is strongly influenced by the hydrothermal venting, with a succession of various groups dominating the sediments from the coldest to the warmest zones. Prokaryotic diversity and abundance decrease with increasing temperature, and thermophilic archaea overtake the community.DiscussionRelevant geochemical cycles of the Bay are discussed. This study expands our limited understanding of subsurface microbial communities in acidic shallow-sea hydrothermal systems and the contribution of their microbial activity to biogeochemical cycling.

Novel Insights on the Bacterial and Archaeal Diversity of the Panarea Shallow-Water Hydrothermal Vent Field

“…The particularly high ASV richness values detected at the Bottaro Crater Vent sediments are consistent with previous findings for this specific site [13,19,23]. Conversely, the lower prokaryotic diversity found in the sediment of the Hot Vent (Table S1) confirms that hightemperature vent fluids can locally decrease the prokaryotic ASV richness, as previously observed in other vent sites also [19,43,61]. As anticipated, microbial diversity at the ASV level was distinct (~100% dissimilarity) between planktonic and benthic prokaryotic assemblages (Figure S3).…”

“…These bacterial and archaeal taxa are usually more abundant in sediments not interested in hydrothermal activity and typically decrease when approaching the hot vent fluids [14,19,43,54]. This agrees well with the results reported here for the Bottaro Crater spot investigated, which experienced a major gas explosion in November 2002 and now displays a much weaker, milder temperature of venting, with temperatures much lower than other hot vent sites of the Panarea hydrothermal vent field [16].…”

“…Anaerolineaceae and Calditrichaceae have been reported as key bacterial taxa of shallow-water hydrothermal vents, involved not only in organic carbon remineralization but also in nitrogen cycling [15,42,43], and include moderate thermophilic chemoheterotrophs, which grow by fermentation of peptides or carbohydrates compounds and have been described as anaerobic digesters in several organic-rich habitats [44][45][46]. Analogously, bacteria within the orders Ardenticantales and Woesearchaeales (ammonium-oxidizing archaea) are known as key components of the microbial assemblages at hydrothermal vents, also participating in C, N, and especially Fe cycling [47][48][49].…”