Deep sea cold seeps are a sink for mercury and source for methylmercury

Li, Jiwei; Dong, Xiyang; Tang, Yongjie; Zhang, Chuwen; Yang, Yali; Zhang, Wei; Liu, Shanshan; Yuan, Wei; Feng, Xinbin; Heimbürger-Boavida, Lars-Eric; Wang, Feiyue; Shang, Lihai; Peng, Xiaotong

doi:10.1038/s43247-024-01484-7

Cited by 3 publications

References 61 publications

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Oviparous Catsharks Accumulate Mercury in Deep-Sea Brine Pool Nurseries

Sisma-Ventura,

Herut,

Segal

et al. 2024

Environ. Sci. Technol. Lett.

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Since the Eocene, oviparous deep-sea sharks and rays have used deepsea hydrocarbon seeps and hydrothermal vents as nurseries, where they lay eggs en masse. Benthic fluxes in these extreme habitats may enrich seawater with toxic metals such as mercury (Hg). We asked whether this phenomenon may lead to Hg accumulation in elasmobranchs. We thus analyzed total Hg (THg) in muscle, liver, and kidney tissues of oviparous Galeus melastomus catsharks and their embryos, which aggregate in vast numbers near deep-sea brine pools in the southeastern Mediterranean Sea. These Hg-rich brines (≤238 ng L −1 ) are a likely liable geogenic Hg source in this nursery. Shark tissues carried substantial THg [2.7 μg (g of wet weight) −1 , median], and extreme values were found in kidneys [≤26.7 μg (g of wet weight) −1 ], likely due to environmental uptake. Increased THg in embryos [0.64 ± 0.31 μg (g of wet weight) −1 ] implies substantial maternal offloading (∼20%). Our results hint at the potential adaptation of elasmobranchs to Hg-enriched environments via accumulation and elimination of Hg in kidneys.

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Oviparous Catsharks Accumulate Mercury in Deep-Sea Brine Pool Nurseries

Sisma-Ventura,

Herut,

Segal

et al. 2024

Environ. Sci. Technol. Lett.

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Reductive dehalogenation by diverse microbes is central to biogeochemical cycles in deep-sea cold seeps

Han,

Deng,

Peng

et al. 2024

Preprint

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Reductive dehalogenation is crucial for halogen cycling and environmental remediation, yet its ecological role is incompletely understood, especially in deep-sea environments. To address this gap, we investigated the diversity of reductive dehalogenases (RDases) and ecophysiology of organohalide reducers in deep-sea cold seeps, which are environments rich in halogenated compounds. Through genome-resolved metagenomic analysis 165 global cold seep sediment samples, we identified four types of RDases, namely prototypical respiratory, transmembrane respiratory, and cytosolic RDases, and one novel clade. These RDases are encoded by physiologically diverse microbes across four archaeal and 36 bacterial phyla, significantly broadening the known diversity of organohalide reducers. Halogen geochemistry, metatranscriptomic data, and metabolomic profiling confirm that organohalides occur at as high as 18 mg/g in these sediments and are actively reduced by microorganisms. This process is tightly linked to other biogeochemical cycles, including carbon, hydrogen, nitrogen, sulfur, and trace elements. RDases from cold seeps have diverse N-terminal structures across different gene groups, and rdhA genes in these environments are mostly functionally constrained and conserved. Altogether, these findings suggest that reductive dehalogenation is a central rather than supplemental process in deep-sea environments, mediated by numerous diverse microbes and novel enzymes.

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Cold seeps are hotspots of deep-sea nitrogen-loss driven by microorganisms across 21 phyla

Jiang,

Cao,

Han

et al. 2024

Preprint

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Nitrogen bioavailability, governed by the balance of fixation and loss processes, is a key factor regulating oceanic productivity, ecosystem functions, and global biogeochemical cycles. The key nitrogen-loss organisms—denitrifiers and anaerobic ammonium-oxidizing (anammox) bacteria—are not well understood in marine seafloor environments, especially in deep-sea cold seeps. In this study, we combined geochemical measurements,15N stable isotope tracer analysis, metagenomics, metatranscriptomics, and three-dimensional protein structural simulations to investigate the diversity of denitrifying and anammox microbial communities and their biogeochemical roles in these habitats. Geochemical evidence from 301 sediment samples shows significantly higher nitrogen-loss rates in cold seeps compared to typical deep-sea sediments, with an estimated annual nitrogen loss of 6.16 Tg from seafloor surface sediments. Examination of a total of 147 million non-redundant genes reveals a high prevalence and active expression of nitrogen-loss genes, including nitrous-oxide reductase (NosZ; 6.88 genes per million or GPM on average), nitric oxide dismutase (Nod; 1.29 GPM), and hydrazine synthase (HzsA; 3.35 GPM) in surface sediments. Analysis of 3,164 metagenome-assembled genomes from this habitat has expanded the known diversity of nitrous-oxide reducers to six phyla and nitric oxide-dismutating organisms to one phylum and two new orders, while ten phyla host anammox bacteria going beyondPlanctomycetota. These microbes show diverse structural adaptations and complex gene cluster arrangements that potentially enable survival in the harsh conditions of cold seeps. These findings suggest that cold seeps, despite their low temperatures, are significant, previously underestimated hotspots of nitrogen loss, potentially contribute substantially to the global nitrogen cycle.

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Deep sea cold seeps are a sink for mercury and source for methylmercury

Cited by 3 publications

References 61 publications

Oviparous Catsharks Accumulate Mercury in Deep-Sea Brine Pool Nurseries

Oviparous Catsharks Accumulate Mercury in Deep-Sea Brine Pool Nurseries

Reductive dehalogenation by diverse microbes is central to biogeochemical cycles in deep-sea cold seeps

Cold seeps are hotspots of deep-sea nitrogen-loss driven by microorganisms across 21 phyla

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