However, at present little is known about the dispersal capability of dominant deep-sea vent mesophiles, and if their large population sizes would lead to increased dispersal ranges as has been seen in other studies ( Finlay and Fenchel, 2004). For example, the dispersal range of bacteria belonging to the widespread hydrogen/sulphur-oxidizing thermophilic genus Persephonella (order Aquificales) was found to be <2500 km ( Mino et al., 2013), possibly reflecting their small population size. However, recent studies using the multilocus sequence analysis (MLSA) ( Maiden, 2006) have successfully captured the endemism of such cosmopolitan deep-sea vent thermophiles ( Flores et al., 2012 Mino et al., 2013 Price et al., 2015). In contrast, similar microbial community members, including Epsilonproteobacteria, Aquificales, Thermococcales, Methanococcales, Archaeoglobales and ‘deep-sea hydrothermal vent euryarchaeota 2', have been identified in geographically separated hydrothermal regions ( Takai et al., 2006 Callac et al., 2013), suggesting that their populations are globally mixed. Although deep-sea hydrothermal vents are connected through the ocean via the currents, deep-sea vent macrofauna exhibit a clear geographical isolation ( Rogers et al., 2012). However, only a few biogeographic studies have been reported on marine extremophiles.ĭeep-sea hydrothermal vents are one of the most extreme environments where macrofauna thrive, enabled by symbiotic relationships with microorganisms. Extremophiles from terrestrial environments requiring specific growth conditions (e.g., high temperature, low pH, high salinity) have served as good models for detailed investigations on the microbial dispersal capability ( Papke et al., 2003 Whitaker et al., 2003). For instance, allopatric speciation was detected in a single species of a hyperthermophilic archaeon inhabiting terrestrial hot springs ( Whitaker et al., 2003). Additionally, by using higher resolution techniques, microbial geographical separation has been assessed for some microbes at the subspecies level. Although unlimited dispersal due to large cell numbers and small cell size has long been generalized ( Baas-Becking, 1934), microbial communities with an unexpectedly high degree of spatial complexity have been reported from some ecosystems ( Martiny et al., 2006 Hanson et al., 2012). This is the first report on MLSA of deep-sea hydrothermal vent Epsilonproteobacteria, which is indicative of allopatric speciation.īiogeography is a fundamental principle in ecology, but whether it applies to microorganisms is controversial. Nevertheless, Sulfurimonas may possess a higher dispersal capability compared with deep-sea hydrothermal vent thermophiles. Genetic differentiation among Sulfurimonas populations was primarily influenced by geographical distance rather than gas composition of vent fluid or habitat, although in situ environmental conditions of each microhabitat could not be examined. Phylogenetic analysis of the 11 concatenated genes showed a clear geographical isolation corresponding to the hydrothermal regions they originated from, suggesting limited dispersal. This genetic variation was predominantly due to mutation rather than recombination. Sequence typing based on 11 protein-coding genes revealed high genetic variation, including some allele types that are widespread within regions, resulting in 102 nucleotide sequence types (STs). Here, we apply the multilocus sequence analysis (MLSA) to assess the genetic variation of 109 Sulfurimonas strains with ⩾98% 16S rRNA gene sequence similarity, which were isolated from four different geographical regions (Okinawa Trough (OT), Mariana Volcanic Arc and Trough (MVAT), Central Indian Ridge (CIR) and Mid-Atlantic Ridge (MAR)). Although the biogeography of vent macrofauna is well understood, the corresponding knowledge about vent microbial biogeography is lacking. Rich animal and microbial communities have been found at deep-sea hydrothermal vents.
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