Journal Article

Reductive Evolution of Bacterial Genome in Insect Gut Environment

Naruo Nikoh, Takahiro Hosokawa, Kenshiro Oshima, Masahira Hattori and Takema Fukatsu

in Genome Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 3, issue , pages 702-714
Published in print January 2011 |
Published online July 2011 | e-ISSN: 1759-6653 | DOI: http://dx.doi.org/10.1093/gbe/evr064

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Obligate endocellular symbiotic bacteria of insects and other organisms generally exhibit drastic genome reduction. Recently, it was shown that symbiotic gut bacteria of some stinkbugs also have remarkably reduced genomes. Here, we report the complete genome sequence of such a gut bacterium Ishikawaella capsulata of the plataspid stinkbug Megacopta punctatissima. Gene repertoire and evolutionary patterns, including AT richness and elevated evolutionary rate, of the 745,590 bp genome were strikingly similar to those of obligate γ-proteobacterial endocellular insect symbionts like Buchnera in aphids and Wigglesworthia in tsetse flies. Ishikawaella was suggested to supply essential amino acids for the plant-sucking stinkbug as Buchnera does for the host aphid. Although Buchnera is phylogenetically closer to Wigglesworthia than to Ishikawaella, in terms of gene repertoire Buchnera was similar to Ishikawaella rather than to Wigglesworthia, providing a possible case of genome-level convergence of gene content. Meanwhile, several notable differences were identified between the genomes of Ishikawaella and Buchnera, including retention of TCA cycle genes and lack of flagellum-related genes in Ishikawaella, which may reflect their adaptation to distinct symbiotic habitats. Unexpectedly, Ishikawaella retained fewer genes related to cell wall synthesis and lipid metabolism than many endocellular insect symbionts. The plasmid of Ishikawaella encoded genes for arginine metabolism and oxalate detoxification, suggesting the possibility of additional Ishikawaella roles similar to those of human gut bacteria. Our data highlight strikingly similar evolutionary patterns that are shared between the extracellular and endocellular insect symbiont genomes.

Keywords: Ishikawaella capsulata; Megacopta punctatissima; extracellular gut symbiosis; genome reduction; genome sequencing

Journal Article.  6301 words.  Illustrated.

Subjects: Bioinformatics and Computational Biology ; Evolutionary Biology ; Genetics and Genomics

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