dInsects are the most abundant animals on Earth, and the microbiota within their guts play important roles by engaging in beneficial and pathological interactions with these hosts. In this study, we comprehensively characterized insect-associated gut bacteria of 305 individuals belonging to 218 species in 21 taxonomic orders, using 454 pyrosequencing of 16S rRNA genes. In total, 174,374 sequence reads were obtained, identifying 9,301 bacterial operational taxonomic units (OTUs) at the 3% distance level from all samples, with an average of 84.3 (؎97.7) OTUs per sample. The insect gut microbiota were dominated by Proteobacteria (62.1% of the total reads, including 14.1% Wolbachia sequences) and Firmicutes (20.7%). Significant differences were found in the relative abundances of anaerobes in insects and were classified according to the criteria of host environmental habitat, diet, developmental stage, and phylogeny. Gut bacterial diversity was significantly higher in omnivorous insects than in stenophagous (carnivorous and herbivorous) insects. This insect-order-spanning investigation of the gut microbiota provides insights into the relationships between insects and their gut bacterial communities.

BackgroundDNA barcoding, the analysis of sequence variation in the 5′ region of the mitochondrial cytochrome c oxidase I (COI) gene, has been shown to provide an efficient method for the identification of species in a wide range of animal taxa. In order to assess the effectiveness of barcodes in the discrimination of Heteroptera, we examined 344 species belonging to 178 genera, drawn from specimens in the Canadian National Collection of Insects.Methodology/Principal FindingsAnalysis of the COI gene revealed less than 2% intra-specific divergence in 90% of the taxa examined, while minimum interspecific distances exceeded 3% in 77% of congeneric species pairs. Instances where barcodes fail to distinguish species represented clusters of morphologically similar species, except one case of barcode identity between species in different genera. Several instances of deep intraspecific divergence were detected suggesting possible cryptic species.Conclusions/SignificanceAlthough this analysis encompasses 0.8% of the described global fauna, our results indicate that DNA barcodes will aid the identification of Heteroptera. This advance will be useful in pest management, regulatory and environmental applications and will also reveal species that require further taxonomic research.

Plant peroxidases (POD) reduce hydrogen peroxide (H 2 O 2 ) in the presence of an electron donor. Extracellular POD can also induce H 2 O 2 production and may perform a signiWcant function in responses to environmental stresses via the regulation of H 2 O 2 in plants. We previously described the isolation of 10 POD cDNA clones from cell cultures of sweetpotato (Ipomoea batatas). Among them, the expression of the swpa4 gene was profoundly induced by a variety of abiotic stresses and pathogenic infections (Park et al. in Mol Gen Genome 269:542-552 2003; Jang et al. in Plant Physiol Biochem 42:451-455 2004). In the present study, transgenic tobacco (Nicotiana tabacum) plants overexpressing the swpa4 gene under the control of the CaMV 35S promoter were generated in order to assess the function of swpa4 in planta. The transgenic plants exhibited an approximately 50-fold higher POD speciWc activity than was observed in control plants. Both transient expression analysis with the swpa4-GFP fusion protein and POD activity assays in the apoplastic washing Xuid revealed that the swpa4 protein is secreted into the apoplastic space. In addition, a signiWcantly enhanced tolerance to a variety of abiotic and biotic stresses occurred in the transgenic plants. These plants harbored increased lignin and phenolic content, and H 2 O 2 was also generated under normal conditions. Furthermore, they showed an increased expression level of a variety of apoplastic acidic pathogenesis-related (PR) genes following enhanced H 2 O 2 production. These results suggest that the expression of swpa4 in the apoplastic space may function as a positive defense signal in the H 2 O 2 -regulated stress response signaling pathway.

No abstract