Abstract
Over the last decade it has become increasingly clear that Zetaproteobacteria are widespread in hydrothermal systems and that they contribute to the biogeochemical cycling of iron in these environments. However, how chemical factors control the distribution of Zetaproteobacteria and their co-occurring taxa remains elusive. Here we analysed iron mats from the Troll Wall Vent Field (TWVF) located at the Arctic Mid-Ocean Ridge (AMOR) in the Norwegian-Greenland Sea. The samples were taken at increasing distances from high-temperature venting chimneys towards areas with ultraslow low-temperature venting, encompassing a large variety in geochemical settings. Electron microscopy revealed the presence of biogenic iron stalks in all samples. Using 16S rRNA gene sequence profiling we found that relative abundances of Zetaproteobacteria in the iron mats varied from 0.2 to 37.9%. Biogeographic analyses of Zetaproteobacteria, using the ZetaHunter software, revealed the presence of ZetaOtus 1, 2 and 9, supporting the view that they are cosmopolitan. Relative abundances of co-occurring taxa, including Thaumarchaeota, Euryarchaeota and Proteobacteria, also varied substantially. From our results, combined with results from previous microbiological and geochemical analyses of the TWVF, we infer that the distribution of Zetaproteobacteria is connected to fluid-flow patterns and, ultimately, variations in chemical energy landscapes. Moreover, we provide evidence for iron-oxidizing members of Gallionellaceae being widespread in TWVF iron mats, albeit at low relative abundances.
Highlights
Biological communities in hydrothermal systems are driven by chemotrophic primary producers, utilizing the energy available in chemical disequilibria, forming when reduced hydrothermal fluids mix with oxic seawater
In an Non-metric multi-dimensional scaling (NMDS) ordination based on BrayCurtis distances, we found that parallel samples from the same iron mat formed distinct clusters (Fig 3)
Our results indicate that the opposite is true: we found no correlation between estimated cell numbers and relative abundances of Gallionellaceae as opposed to a highly significant correlation between relative abundances of Zetaproteobacteria and Gallionellaceae, providing strong evidence for Gallionellaceae being an intrinsic part of the microbial communities in the iron mats
Summary
Biological communities in hydrothermal systems are driven by chemotrophic primary producers, utilizing the energy available in chemical disequilibria, forming when reduced hydrothermal fluids mix with oxic seawater. The geological and geochemical setting varies between and within hydrothermal systems, giving rise to shifting chemical energy landscapes [1, 2]. Revealing how this variation shapes the distribution of functional groups of microorganisms is important for understanding the microbial ecology of hydrothermal systems, and for our general understanding of how geochemistry is linked to microbiology. Hydrothermal systems are considered to play a significant role in the marine iron cycle, with estimated releases. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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