title: Predominant archaea in marine sediments degrade detrital proteins.
abstract: Half of the microbial cells in the Earth's oceans are found in sediments. Many of these cells are members of the Archaea, single-celled prokaryotes in a domain of life separate from Bacteria and Eukaryota. However, most of these archaea lack cultured representatives, leaving their physiologies and placement on the tree of life uncertain. Here we show that the uncultured miscellaneous crenarchaeotal group (MCG) and marine benthic group-D (MBG-D) are among the most numerous archaea in the marine sub-sea floor. Single-cell genomic sequencing of one cell of MCG and three cells of MBG-D indicated that they form new branches basal to the archaeal phyla Thaumarchaeota and Aigarchaeota, for MCG, and the order Thermoplasmatales, for MBG-D. All four cells encoded extracellular protein-degrading enzymes such as gingipain and clostripain that are known to be effective in environments chemically similar to marine sediments. Furthermore, we found these two types of peptidase to be abundant and active in marine sediments, indicating that uncultured archaea may have a previously undiscovered role in protein remineralization in anoxic marine sediments.
authors.affiliation: Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus 8000, Denmark. klloyd@utk.edu
authors.forename: Karen G
authors.initials: KG
authors.lastname: Lloyd
authors.forename: Lars
authors.initials: L
authors.lastname: Schreiber
authors.forename: Dorthe G
authors.initials: DG
authors.lastname: Petersen
authors.forename: Kasper U
authors.initials: KU
authors.lastname: Kjeldsen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Lever
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Steen
authors.forename: Ramunas
authors.initials: R
authors.lastname: Stepanauskas
authors.forename: Michael
authors.initials: M
authors.lastname: Richter
authors.forename: Sara
authors.initials: S
authors.lastname: Kleindienst
authors.forename: Sabine
authors.initials: S
authors.lastname: Lenk
authors.forename: Andreas
authors.initials: A
authors.lastname: Schramm
authors.forename: Bo Barker
authors.initials: BB
authors.lastname: Jørgensen
mesh_terms: D018829:Adhesins, Bacterial / Q000378:metabolism; D001105:Archaea / Q000145:classification / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology*; D000080867:Gingipain Cysteine Endopeptidases; D008386:Marine Biology; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000378:metabolism*; D010802:Phylogeny; D059748:Proteolysis; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D059010:Single-Cell Analysis
chemical_list: D018829:Adhesins, Bacterial; D000080867:Gingipain Cysteine Endopeptidases; D012336:RNA, Ribosomal, 16S; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; C019913:clostripain
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