Abstract
Abstract. Industrial-scale mining of deep-sea polymetallic nodules will remove nodules in large areas of the sea floor. The regrowth of the nodules by metal precipitation is estimated to take millions of years. Thus, for future mining impact studies, it is crucial to understand the role of nodules in shaping microbial diversity and function in deep-sea environments. Here we investigated microbial-community composition based on 16S rRNA gene sequences retrieved from sediments and nodules of the Peru Basin (4130–4198 m water depth). The nodule field of the Peru Basin showed a typical deep-sea microbiome, with dominance of the classes Gammaproteobacteria, Alphaproteobacteria, Deltaproteobacteria, and Acidimicrobiia. Nodules and sediments host distinct bacterial and archaeal communities, with nodules showing lower diversity and a higher proportion of sequences related to potential metal-cycling Bacteria (i.e. Magnetospiraceae, Hyphomicrobiaceae), bacterial and archaeal nitrifiers (i.e. AqS1, unclassified Nitrosomonadaceae, Nitrosopumilus, Nitrospina, Nitrospira), and bacterial sequences found in the oceanic crust, nodules, hydrothermal deposits, and sessile fauna. Sediment and nodule communities overall shared a low proportion of operational taxonomic units (OTUs; 21 % for Bacteria and 19 % for Archaea). Our results show that nodules represent a specific ecological niche (i.e. hard substrate, high metal concentrations, and sessile fauna), with a potentially relevant role in organic-carbon degradation. Differences in nodule community composition (e.g. Mn-cycling bacteria, nitrifiers) between the Clarion–Clipperton Fracture Zone (CCZ) and the Peru Basin suggest that changes in environmental setting (e.g. sedimentation rates) also play a significant role in structuring the nodule microbiome.
Highlights
Polymetallic nodules occur in abyssal plains (4000–6000 m water depth) and consist primarily of manganese and iron as well as many other metals and rare earth elements (Crerar and Barnes, 1974; Kuhn et al, 2017)
We propose that the decreased diversity of abundant operational taxonomic units (OTUs) in nodules, observed especially for Bacteria, suggests selection for colonists adapted to specific ecological niches associated with nodules
The sediments of nodule fields in the Peru Basin host a specific microbial community of bacterial taxa reported for organic-carbon-poor environments (i.e. Chloroflexi, Planctomycetes) and potentially involved in metal cycling (i.e. Magnetospiraceae, Hyphomicrobiaceae)
Summary
Polymetallic nodules (or manganese nodules) occur in abyssal plains (4000–6000 m water depth) and consist primarily of manganese and iron as well as many other metals and rare earth elements (Crerar and Barnes, 1974; Kuhn et al, 2017). The mechanisms of nodule formation are not completely elucidated. The formation of nodules is a slow process that is estimated to range between thousands and millions of years per millimetre of growth (Kerr, 1984; Boltenkov, 2012). Rising global demand for metals has renewed interests in commercial mining of deep-sea nodule deposits.
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