Abstract
Deep-sea oceanic crust constitutes the largest region of the earth’s surface. Accumulating evidence suggests that unique microbial communities are supported by iron cycling processes, particularly in the young (<10 million-year old), cool (<25°C) subsurface oceanic crust. To test this hypothesis, we investigated the microbial abundance, diversity, and metabolic potentials in the sediment-buried crust from “North Pond” on western flank of the Mid-Atlantic Ridge. Three lithologic units along basement Hole U1383C were found, which typically hosted ∼104 cells cm-3 of basaltic rock, with higher cell densities occurring between 115 and 145 m below seafloor. Similar bacterial community structures, which are dominated by Gammaproteobacterial and Sphingobacterial species closely related to iron oxidizers, were detected regardless of variations in sampling depth. The metabolic potentials of the crust microbiota were assayed by metagenomic analysis of two basalt enrichments which showed similar bacterial structure with the original sample. Genes coding for energy metabolism involved in hydrocarbon degradation, dissimilatory nitrate reduction to ammonium, denitrification and hydrogen oxidation were identified. Compared with other marine environments, the metagenomes from the basalt-hosted environments were enriched in pathways for Fe3+ uptake, siderophore synthesis and uptake, and Fe transport, suggesting that iron metabolism is an important energy production and conservation mechanism in this system. Overall, we provide evidence that the North Pond crustal biosphere is dominated by unique bacterial groups with the potential for iron-related biogeochemical cycles.
Highlights
Oceanic crust microbiology has long been ignored and is not well studied due to technical constraints; the crust has been assumed to harbor active microorganisms that may significantly contribute to global biogeochemical cycles and weathering of the seafloor landscape (Schrenk et al, 2010; Wang et al, 2013)
The number of high quality bacterial 16S rRNA gene sequences obtained by high-throughput sequencing were between 7,952 and 16,146, resulting in more than 548 operational taxonomic units (OTUs) at 97% SSU rRNA gene sequence similarity
Our results demonstrate that the microbial abundances in the basalts are less than 6.1 × 104 cells cm−3, with the microbial communities dominated by Gammaproteobacteria and Sphingobacteria (Figures 1 and 2)
Summary
Oceanic crust microbiology has long been ignored and is not well studied due to technical constraints; the crust has been assumed to harbor active microorganisms that may significantly contribute to global biogeochemical cycles and weathering of the seafloor landscape (Schrenk et al, 2010; Wang et al, 2013). Extracellular enzyme activity tests, functional gene analysis, carbon and sulfur isotopic signatures and laboratory incubations demonstrated the presence of active microorganisms involved in methane- and sulfur-cycling and organic matter transformations (Mason et al, 2010; Lever et al, 2013; Jacobson Meyers et al, 2014; Robador et al, 2015; Supplementary Table S1) These studies were restricted to seafloor-exposed basaltic habitats (Templeton et al, 2005; Einen et al, 2008; Santelli et al, 2008), subsurface crustal environments with high temperature basalts (Nigro et al, 2012; Jungbluth et al, 2013), and mantle-type rock (Brazelton et al, 2010; Mason et al, 2010). The microbial life of the young, cool subsurface basalts in ridge flank systems, which represent a more common hydrologically active type of ocean crust (Edwards et al, 2012), has not been characterized yet
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
