AEM Accepts, published online ahead of print on 30 October 2009

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Toju, H. Articles by Fukatsu, T. PubMed PubMed Citation Articles by Toju, H. Articles by Fukatsu, T. Agricola Articles by Toju, H. Articles by Fukatsu, T.

 Previous Article  |  Next Article 

Appl. Environ. Microbiol. doi:10.1128/AEM.02154-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

"Candidatus Curculioniphilus buchneri", a novel clade of bacterial endocellular symbionts from weevils of the genus Curculio

Hirokazu Toju, Takahiro Hosokawa, Ryuichi Koga, Naruo Nikoh, Xian Ying Meng, Nobutada Kimura, and Takema Fukatsu^*

National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan; and Department of Liberal Arts, The Open University of Japan, Chiba 261-8586, Japan

^* To whom correspondence should be addressed. Email: t-fukatsu{at}aist.go.jp.

Here we investigated the bacterial endosymbionts of weevils of the genus Curculio. From all four species of Curculio weevils examined, a novel group of bacterial gene sequences were consistently identified. Molecular phylogenetic analyses demonstrated that the sequences formed a distinct clade in the -Proteobacteria, which was not related to previously known groups of weevil endosymbionts such as Nardonella spp. and Sodalis-allied symbionts. In situ hybridization revealed that the bacterium was intracellularly harbored in a bacteriome associated with larval midgut. In adult females, the bacterium was localized in the germalia at the tip of each overiole, suggesting vertical transmission via ovarial passage. Diagnostic PCR surveys detected high prevalence of the bacterial infection in natural host populations. Electron microscopy identified reduced cell wall of the bacterial cells, and the bacterial genes exhibited AT-biased nucleotide composition and accelerated molecular evolution, which are suggestive of a long-lasting endosymbiotic association. On the basis of these results, we conclude that the novel endocellular bacteria represent the primary symbiont of Curculio weevils, and proposed the designation "Candidatus Curculioniphilus buchneri". In addition to Curculioniphilus, we identified Sodalis-allied -proteobacterial endosymbionts from the chestnut weevil C. sikkimensis, which exhibited partial infection frequencies in host insect populations and neither AT-biased nucleotide composition nor accelerated molecular evolution. We suggest that such Sodalis-allied secondary symbionts in weevils might provide a potential source for symbiont replacements as has occurred in an ancestor of Sitophilus grain weevils.