title: Dominant ectosymbiotic bacteria of cellulolytic protists in the termite gut also have the potential to digest lignocellulose.
abstract: Wood-feeding lower termites harbour symbiotic gut protists that support the termite nutritionally by degrading recalcitrant lignocellulose. These protists themselves host specific endo- and ectosymbiotic bacteria, functions of which remain largely unknown. Here, we present draft genomes of a dominant, uncultured ectosymbiont belonging to the order Bacteroidales, 'Candidatus Symbiothrix dinenymphae', which colonizes the cell surface of the cellulolytic gut protists Dinenympha spp. We analysed four single-cell genomes of Ca. S. dinenymphae, the highest genome completeness was estimated to be 81.6-82.3% with a predicted genome size of 4.28-4.31 Mb. The genome retains genes encoding large parts of the amino acid, cofactor and nucleotide biosynthetic pathways. In addition, the genome contains genes encoding various glycoside hydrolases such as endoglucanases and hemicellulases. The genome indicates that Ca. S. dinenymphae ferments lignocellulose-derived monosaccharides to acetate, a major carbon and energy source of the host termite. We suggest that the ectosymbiont digests lignocellulose and provides nutrients to the host termites, and hypothesize that the hydrolytic activity might also function as a pretreatment for the host protist to effectively decompose the crystalline cellulose components.
authors.affiliation: Biomass Research Platform Team, RIKEN Biomass Engineering Program Cooperation Division, RIKEN Center for Sustainable Resource Science, Tsukuba, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yuki
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kuwahara
authors.affiliation: Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, Hamamatsu, Japan.|Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Shintani
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Izawa
authors.affiliation: Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Sato
authors.affiliation: Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors.forename: David
authors.initials: D
authors.lastname: Starns
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.|Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Hongoh
authors.affiliation: Biomass Research Platform Team, RIKEN Biomass Engineering Program Cooperation Division, RIKEN Center for Sustainable Resource Science, Tsukuba, Japan.|Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors.forename: Moriya
authors.initials: M
authors.lastname: Ohkuma
mesh_terms: D000818:Animals; D041963:Bacteroidetes / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D004734:Energy Metabolism; D016678:Genome; D016680:Genome, Bacterial / Q000235:genetics; D006026:Glycoside Hydrolases / Q000235:genetics; D020049:Isoptera / Q000382:microbiology*; D008031:Lignin / Q000378:metabolism*; D056899:Oxymonadida / Q000235:genetics / Q000382:microbiology*; D013559:Symbiosis / Q000235:genetics
chemical_list: C036909:lignocellulose; D002482:Cellulose; D008031:Lignin; D006026:Glycoside Hydrolases