title: Defensive bacteriome symbiont with a drastically reduced genome.
abstract: Diverse insect species harbor symbiotic bacteria, which play important roles such as provisioning nutrients and providing defense against natural enemies [1-6]. Whereas nutritional symbioses are often indispensable for both partners, defensive symbioses tend to be of a facultative nature [1-12]. The Asian citrus psyllid Diaphorina citri is a notorious agricultural pest that transmits Liberibacter spp. (Alphaproteobacteria), causing the devastating citrus greening disease or Huanglongbing [13, 14]. In a symbiotic organ called the bacteriome, D. citri harbors two distinct intracellular symbionts: a putative nutrition provider, Carsonella_DC (Gammaproteobacteria), and an unnamed betaproteobacterium with unknown function [15], for which we propose the name "Candidatus Profftella armatura." Here we report that Profftella is a defensive symbiont presumably of an obligate nature with an extremely streamlined genome. The genomes of Profftella and Carsonella_DC were drastically reduced to 464,857 bp and 174,014 bp, respectively, suggesting their ancient and mutually indispensible association with the host. Strikingly, 15% of the small Profftella genome encoded horizontally acquired genes for synthesizing a novel polyketide toxin. The toxin was extracted, pharmacologically and structurally characterized, and designated diaphorin. The presence of Profftella and its diaphorin-biosynthetic genes was perfectly conserved in the world's D. citri populations.
authors.affiliation: Electronics-Inspired Interdisciplinary Research Institute (EIIRIS), Toyohashi University of Technology, Toyohashi 441-8580, Japan. nakabachi@eiiris.tut.ac.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nakabachi
authors.forename: Reiko
authors.initials: R
authors.lastname: Ueoka
authors.forename: Kenshiro
authors.initials: K
authors.lastname: Oshima
authors.forename: Roberta
authors.initials: R
authors.lastname: Teta
authors.forename: Alfonso
authors.initials: A
authors.lastname: Mangoni
authors.forename: Mihaela
authors.initials: M
authors.lastname: Gurgui
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Oldham
authors.forename: Gerhild
authors.initials: G
authors.lastname: van Echten-Deckert
authors.forename: Keiko
authors.initials: K
authors.lastname: Okamura
authors.forename: Kohei
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Inoue
authors.forename: Moriya
authors.initials: M
authors.lastname: Ohkuma
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Hongoh
authors.forename: Shin-ya
authors.initials: SY
authors.lastname: Miyagishima
authors.forename: Masahira
authors.initials: M
authors.lastname: Hattori
authors.forename: Jörn
authors.initials: J
authors.lastname: Piel
authors.forename: Takema
authors.initials: T
authors.lastname: Fukatsu
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000633:toxicity; D020562:Betaproteobacteria / Q000235:genetics*; D005075:Biological Evolution; D002460:Cell Line / Q000187:drug effects; D002957:Citrus; D020563:Gammaproteobacteria / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D006430:Hemiptera / Q000382:microbiology*; D008969:Molecular Sequence Data; D061065:Polyketides / Q000378:metabolism; D012336:RNA, Ribosomal, 16S; D051381:Rats; D013559:Symbiosis / Q000235:genetics*; D018675:Toxicity Tests
chemical_list: D001427:Bacterial Toxins; D061065:Polyketides; D012336:RNA, Ribosomal, 16S