Submitted to: Molecular Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/13/2013
Publication Date: 4/8/2014
Citation: Xiangfeng, J., Wong, A., Chaston, J.M., Colvin, J., McKenzie, C.L., Douglas, A.E. 2014. The bacterial communities in a plant phloem sap feeding insect. Molecular Ecology. 23:1433-1444. Doi:10.1111/mec.12637. Interpretive Summary: The purpose of this study is to quantify the bacterial diversity in Bemisia tabaci whiteflies, by pyrosequencing 16S rRNA gene fragments amplified with general bacterial primers. B. tabaci is a morphological pest species of cosmopolitan distribution that comprises a complex of >30 partially or completely reproductively isolated candidate species. This study has two specific aims. The first was to quantify the bacterial diversity in 7 B. tabaci species, including two highly invasive species, B. tabaci MEAM1 and B. tabaci MED (also known as biotypes B and Q, respectively). The second aim was to compare the bacterial diversity in long-term B. tabaci MEAM1 cultures reared on different plants or with/without plant begomoviruses vectored by this species. Secondary symbionts have been implicated in the capacity of B. tabaci insects to vector begomoviruses of plants, and the prevalence and abundance of some secondary symbionts are reported to vary with rearing plant for B. tabaci and other phloem feeders. This first comprehensive analysis of the bacterial diversity in any phloem feeding insect demonstrates a remarkably low diversity, raising fundamental questions about the processes that shape the variation in diversity of host-associated microbiota in different animals.
Technical Abstract: The resident microbiota of animals represents an important contribution to the global microbial diversity, but it is poorly known in most animals other than humans. This study investigated the bacterial communities in 7 species of the whitefly Bemisia tabaci complex by pyrosequencing bacterial 16S rRNA gene amplicons. Representatives of just 9 bacterial genera were identified, with 7 previously described vertically-transmitted taxa accounting for >99.9-100% of the reads in each sample. The number of OTUs tended to saturation in every biological sample and, after correction for sequencing error, each sample was concluded to bear 3-5 bacterial taxa, with low diversity (Shannon’s index: 0.36-1.46, Simpson’s index: 0.17-0.74). The abundance of the bacterial symbionts in B. tabaci MEAM1 was elevated in insect cultures bearing begomoviruses (tomato mottle virus and tomato yellow leaf curl virus) relative to a non-viruliferous culture, and varied significantly with rearing plant. Generally, the abundance of the different symbionts varied in concert, suggesting that they were regulated by common or linked insect mechanism(s). These host controls over bacterial abundance, together with the frequencies of vertical and horizontal transmission and the fitness of insects with different bacterial complements, were identified as candidate factors contributing to the variation in composition and diversity of the bacterial communities in B. tabaci. The demonstration of a very low bacterial diversity in this insect contributes to an emerging pattern of lower bacterial diversity in many invertebrates than in vertebrate animals, although the factors shaping this pattern remain to be established.