Abstract
Iron oxidizers are widespread in marine environments and play an important role in marine iron cycling. However, little is known about the overall distribution of iron oxidizers within hydrothermal systems, including settings with little hydrothermal activity. Moreover, the extent to which different phylogenetic groups of iron oxidizers exhibit niche specialization toward different environmental settings, remains largely unknown. Obtaining such knowledge is critical to unraveling the impact of the activity of iron oxidizers and how they are adapted. Here, we used 16S rRNA sequencing to characterize the distribution of iron oxidizers in different environmental settings within the Jan Mayen hydrothermal vent fields (JMVFs). Putative iron oxidizers affiliated to Zetaproteobacteria and Betaproteobacteria were detected within iron mounds, bottom seawater, basalt surfaces, and surface layers of sediments. The detected iron oxidizers were compared to sequence types previously observed in patchily distributed iron mats associated with diffuse venting at the JMVFs. Most OTUs of iron oxidizers reoccurred under different environmental settings, suggesting a limited degree of niche specialization. Consequently, most of the detected iron oxidizers seem to be generalists with a large habitat range. Our study highlights the importance of gathering information about the overall distribution of iron oxidizers in hydrothermal systems to fully understand the role of this metabolic group regarding cycling of iron. Furthermore, our results provide further evidence of the presence of iron-oxidizing members of Betaproteobacteria in marine environments.
Highlights
IntroductionZetaproteobacteria were first discovered in iron-rich hydrothermal vents at Loïhi seamount (Moyer et al, 1995; Emerson and Moyer, 2002) and have primarily been detected in hydrothermal systems (Emerson et al, 2007; McAllister et al, 2011; Field et al, 2015; Scott et al, 2015; Makita et al, 2017; Vander Roost et al, 2017)
In parallel we further investigated the potential connection between the relative abundance of ironoxidizing Betaproteobacteria and Zetaproteobacteria and how this may apply to other environmental settings at the Jan Mayen hydrothermal vent fields (JMVFs)
In an attempt to identify FeOζ in hydrothermally more active areas of the JMVFs than the samples considered in Figures 2–4, we investigated a previously published 16S rRNA gene amplicon dataset from a nearby, microbial mat dominated by sulfide-oxidizing Epsilonproteobacteria, growing at the base of an active venting chimney (Lanzén et al, 2012; Urich et al, 2014)
Summary
Zetaproteobacteria were first discovered in iron-rich hydrothermal vents at Loïhi seamount (Moyer et al, 1995; Emerson and Moyer, 2002) and have primarily been detected in hydrothermal systems (Emerson et al, 2007; McAllister et al, 2011; Field et al, 2015; Scott et al, 2015; Makita et al, 2017; Vander Roost et al, 2017). Current knowledge suggests that all Zetaproteobacteria are specialists in iron oxidation, either using oxygen as an electron acceptor under microaerophilic conditions, or nitrate under anaerobic conditions (Glazer and Rouxel, 2009; Fleming et al, 2013; Kilias et al, 2013; Field et al, 2015; Jesser et al, 2015). This class appears to play an important role in the marine iron cycle. Low concentrations may not necessarily reflect Fe(II) availability within the Zetaproteobacterial microniches (Chiu et al, 2017), this demonstrates that Zetaproteobacteria may be active in environments with low overall Fe(II) availability
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