strict host-symbiont cospeciation and reductive genome evolution in insect gut bacteria严格host-symbiont cospeciation和还原基因组进化昆虫肠道细菌.pdf

PLoS BIOLOGY Strict Host-Symbiont Cospeciation and Reductive Genome Evolution in Insect Gut Bacteria 1,2 1,3 4 2 1* Takahiro Hosokawa , Yoshitomo Kikuchi , Naruo Nikoh , Masakazu Shimada , Takema Fukatsu 1 Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan, 2 Department of Systems Sciences, University of Tokyo, Meguro, Tokyo, Japan, 3 Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, United States of America, 4 Division of Natural Sciences, University of the Air, Chiba, Japan Host-symbiont cospeciation and reductive genome evolution have been identified in obligate endocellular insect symbionts, but no such example has been identified from extracellular ones. Here we first report such a case in stinkbugs of the family Plataspidae, wherein a specific gut bacterium is vertically transmitted via ‘‘symbiont capsule.’’ In all of the plataspid species, females produced symbiont capsules upon oviposition and their gut exhibited specialized traits for capsule production. Phylogenetic analysis showed that the plataspid symbionts constituted a distinct group in the c-Proteobacteria, whose sister group was the aphid obligate endocellular symbionts Buchnera. Removal of the symbionts resulted in retarded growth, mortality, and sterility of the insects. The host phylogeny perfectly agreed with the symbiont phylogeny, indicating strict host-symbiont cospeciation despite the extracellular association. The symbionts exhibited AT-biased nucleotide com