title: Intranuclear verrucomicrobial symbionts and evidence of lateral gene transfer to the host protist in the termite gut.
abstract: In 1944, Harold Kirby described microorganisms living within nuclei of the protists Trichonympha in guts of termites; however, their taxonomic assignment remains to be accomplished. Here, we identified intranuclear symbionts of Trichonympha agilis in the gut of the termite Reticulitermes speratus. We isolated single nuclei of T. agilis, performed whole-genome amplification, and obtained bacterial 16S rRNA genes by PCR. Unexpectedly, however, all of the analyzed clones were from pseudogenes of 16S rRNA with large deletions and numerous sequence variations even within a single-nucleus sample. Authentic 16S rRNA gene sequences were finally recovered by digesting the nuclear DNA; these pseudogenes were present on the host Trichonympha genome. The authentic sequences represented two distinct bacterial species belonging to the phylum Verrucomicrobia, and the pseudogenes have originated from each of the two species. Fluorescence in situ hybridization confirmed that both species are specifically localized, and occasionally co-localized, within nuclei of T. agilis. Transmission electron microscopy revealed that they are distorted cocci with characteristic electron-dense and lucent regions, which resemble the intranuclear symbionts illustrated by Kirby. For these symbionts, we propose a novel genus and species, 'Candidatus Nucleococcus trichonymphae' and 'Candidatus Nucleococcus kirbyi'. These formed a termite-specific cluster with database sequences, other members of which were also detected within nuclei of various gut protists, including both parabasalids and oxymonads. We suggest that this group is widely distributed as intranuclear symbionts of diverse protists in termite guts and that they might have affected the evolution of the host genome through lateral gene transfer.
authors: Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors: Tomoyuki
authors: T
authors: Sato
authors: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors: Hirokazu
authors: H
authors: Kuwahara
authors: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors: Kazuma
authors: K
authors: Fujita
authors: 1] Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan [2] Department of Biotechnology, University of Yamanashi, Kofu, Japan.
authors: Satoko
authors: S
authors: Noda
authors: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors: Kumiko
authors: K
authors: Kihara
authors: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors: Akinori
authors: A
authors: Yamada
authors: Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan.
authors: Moriya
authors: M
authors: Ohkuma
authors: 1] Japan Collection of Microorganisms, RIKEN BioResource Center, Tsukuba, Japan [2] Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Tokyo, Japan.
authors: Yuichi
authors: Y
authors: Hongoh
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004269:DNA, Bacterial / Q000235:genetics; D041981:Gastrointestinal Tract / Q000382:microbiology; D022761:Gene Transfer, Horizontal; D017404:In Situ Hybridization, Fluorescence; D020049:Isoptera / Q000382:microbiology*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013559:Symbiosis; D061327:Verrucomicrobia / Q000502:physiology*
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S