title: Obligate bacterial mutualists evolving from environmental bacteria in natural insect populations.
abstract: Diverse organisms are associated with obligate microbial mutualists. How such essential symbionts have originated from free-living ancestors is of evolutionary interest. Here we report that, in natural populations of the stinkbug Plautia stali, obligate bacterial mutualists are evolving from environmental bacteria. Of six distinct bacterial lineages associated with insect populations, two are uncultivable with reduced genomes, four are cultivable with non-reduced genomes, one uncultivable symbiont is fixed in temperate populations, and the other uncultivable symbiont coexists with four cultivable symbionts in subtropical populations. Symbiont elimination resulted in host mortality for all symbionts, while re-infection with any of the symbionts restored normal host growth, indicating that all the symbionts are indispensable and almost equivalent functionally. Some aseptic newborns incubated with environmental soils acquired the cultivable symbionts and normal growth was restored, identifying them as environmental Pantoea spp. Our finding uncovers an evolutionary transition from a free-living lifestyle to obligate mutualism that is currently ongoing in nature.
authors: Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan.|Tropical Biosphere Research Center, University of the Ryukyus, Okinawa 903-0213, Japan.
authors: Takahiro
authors: T
authors: Hosokawa
authors: Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan.
authors: Yoshiko
authors: Y
authors: Ishii
authors: Department of Liberal Arts, The Open University of Japan, Chiba 261-8586, Japan.
authors: Naruo
authors: N
authors: Nikoh
authors: DNA Sequencing Section, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.
authors: Manabu
authors: M
authors: Fujie
authors: Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.
authors: Nori
authors: N
authors: Satoh
authors: Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan.
authors: Takema
authors: T
authors: Fukatsu
mesh_terms: D000818:Animals; D001419:Bacteria / Q000145:classification* / Q000235:genetics* / Q000254:growth & development / Q000302:isolation & purification; D004783:Environmental Microbiology; D019143:Evolution, Molecular; D016680:Genome, Bacterial; D020062:Heteroptera / Q000382:microbiology* / Q000502:physiology; D017422:Sequence Analysis, DNA; D016019:Survival Analysis; D013559:Symbiosis