Abstract
Rocky outcrops covered with thick Fe and Mn oxide coatings, which are known as ferromanganese (Fe-Mn) crusts, are commonly found on slopes of aged seamounts in bathyal and abyssal zones. Although the presence of diverse microorganisms on these Fe-Mn crusts has been reported, little is known about their metabolism. Here, we report the metabolic potential of the microbial community in an abyssal crust collected in the Takuyo-Daigo Seamount, in the north-western Pacific. We performed shotgun metagenomic sequencing of the Fe-Mn crust, and detected putative genes involved in dissolution and precipitation of Fe and Mn, nitrification, sulfur oxidation, carbon fixation, and decomposition of organics in the metagenome. In addition, four metagenome-assembled genomes (MAGs) of abundant members in the microbial community were recovered from the metagenome. The MAGs were affiliated with Thaumarchaeota, Alphaproteobacteria, and Gammaproteobacteria, and were distantly related to previously reported genomes/MAGs of cultured and uncultured species. Putative genes involved in the above reactions were also found in the crust MAGs. Our results suggest that crust microbial communities play a role in biogeochemical cycling of C, N, S, Fe, and Mn, and imply that they contribute to the growth of Fe-Mn crusts.
Highlights
Ferromanganese (Fe-Mn) oxide coatings, such as Fe-Mn crusts and nodules, have been found in the pelagic deep ocean
To assess the relative abundance of each microorganism in the metagenome, read coverages for contigs containing a coding DNA sequences (CDSs) of the ribosomal protein S3 gene, a single-copy marker gene that was used for such analysis (e.g., [53]), were analyzed
Discrepancies in the order of members observed among the results (Fig 1) were probably due to differences in the copy number of each gene and/or the efficiency of the PCR amplification
Summary
Ferromanganese (Fe-Mn) oxide coatings, such as Fe-Mn crusts and nodules, have been found in the pelagic deep ocean. The thickness of the crust is over 10 cm, which corresponds to a passage time of over ten million years (Myr) based on their extremely slow growth rate (1–10 mm/Myr) [1,2,3,4]. Fe-Mn oxides adsorb dissolved metallic ions from seawater [5, 6], and they are referred to as the “chemical scavengers of the sea” [7].
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