Fourth International Bemisia Workshop International Whitefly Genomics Workshop
The Inside Story: Bacteriocyte-associated Endosymbionts of Whiteflies
1 Biology Department, University of St. Thomas, Houston, TX, USA. Correspondence: rrosell@stthom.edu
2 Entomology Department, University of California, Riverside, CA, USA
3 CSIRO, Brisbane, QLD, Australia
Whiteflies, members of the Sternorrhyncha that feed exclusively on phloem sap, harbor bacterial endosymbionts within specialized insect cells, bacteriocytes, which aggregate in the abdominal cavity to form the bacteriome. In whiteflies, the P-endosymbionts have been designated as “Candidatus Portiera aleyrodidarum”. It has been hypothesized that the pleomorphic bacteria present in whitefly bacteriocytes are the primary endosymbionts. The P-endosymbiont phylogeny has been reconstructed based on either 16S rDNA or 16S-23S rDNA and results support the separation of whiteflies into two subfamilies. In addition, Bemisia tabaci may house several secondary endosymbionts, including Wolbachia, aphid T-type endosymbionts and Arsenophonus (A-type endosymbionts) and Candidatus Fritschea bemisiae (chlamydiae). This study focuses on the endosymbionts from a broad range of whitefly species collected primarily in Australia and the U.S. The goals are threefold: 1) to further extend the phylogeny of whitefly P- and S-endosymbionts using 16SrDNA sequences from these whitefly species, 2) to examine phylogenetic congruence between the symbionts and the host, and 3) to morphologically characterize both P- and S-endosymbionts in these whitefly species. Phylogenetic analyses of P-endosymbiont 16S rDNA sequences from 50 whitefly species are partially consistent with previously published phylogenies. The data are unique in that we include the largest group of taxa and examine individual variability within each taxon instead of consensus data. The G+C content of our P-endosymbiont DNA samples ranged from 46.46 to 48.77 mol%, which is in the same scale as previous reports for Candidatus Portiera. In our morphology studies, yellow-orange bacteriomes were clearly visible through the 4th instar cuticle of some species, while in others there was no discernible coloration to indicate the presence of bacteriomes. This could simply mean that bacteriocytes are not as strongly pigmented in these species. In whitefly species that had a hard black cuticle in the immature stages, individuals were peeled off of the leaf and observed from beneath. Again, the visibility of bacteriomes varied among species. Thus far, we have examined the bacteriomes from 11 species using TEM. Visually the bacteria present are similar to those that previously described in B. tabaci. At least two morphological types of endosymbionts (P and S) were present in each species examined. Labeling studies are in progress to correlate morphology with species designation.
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