Reductive evolution of bacterial genome in insect gut environment
Naruo Nikoh1, Takahiro Hosokawa, Kenshiro Oshima
1Department of Liberal Arts, The Open University of Japan, Chiba, Japan.
Genome Biology and Evolution
|July 9, 2011
Summary
Genome reduction in symbiotic bacteria is common. This study sequenced Ishikawaella capsulata, a stinkbug gut symbiont, revealing genome similarities to other insect symbionts, suggesting convergent evolution in gene content.
Area of Science:
- Microbial genomics
- Insect symbiosis
- Evolutionary biology
Background:
- Obligate endocellular symbiotic bacteria in insects typically undergo significant genome reduction.
- Gut symbionts of stinkbugs also exhibit reduced genomes, indicating a common evolutionary trajectory.
- Ishikawaella capsulata is a gut symbiont of the plataspid stinkbug Megacopta punctatissima.
Purpose of the Study:
- To determine the complete genome sequence of Ishikawaella capsulata.
- To compare its genome with other known insect symbionts.
- To understand the evolutionary patterns and functional adaptations of Ishikawaella capsulata.
Main Methods:
- Whole-genome sequencing of Ishikawaella capsulata.
- Comparative genomic analysis with endocellular symbionts like Buchnera and Wigglesworthia.
- Phylogenetic analysis and gene repertoire comparison.
Main Results:
- The 745,590 bp genome of Ishikawaella capsulata shows striking similarities in gene repertoire and evolutionary patterns (AT richness, elevated evolutionary rate) to obligate γ-proteobacterial endocellular insect symbionts.
- Despite phylogenetic distance, Ishikawaella shares gene content similarities with Buchnera, suggesting genome-level convergence.
- Ishikawaella retains TCA cycle genes, lacks flagellum genes, and has fewer cell wall/lipid metabolism genes than many endocellular symbionts, indicating adaptation to its specific symbiotic niche.
- Ishikawaella's plasmid encodes genes for arginine metabolism and oxalate detoxification, hinting at potential roles beyond essential nutrient provision.
Conclusions:
- Ishikawaella capsulata's genome evolution mirrors that of obligate endocellular insect symbionts, showcasing convergent genome-level adaptations.
- Distinct symbiotic habitats may drive differences in gene retention between Ishikawaella and Buchnera.
- The plasmid-encoded functions suggest potential multifaceted roles for Ishikawaella in its host, akin to human gut bacteria.
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