Wolbachia Classified in a monophyletic clade in Domain Bacteria A member of Alphaproteobacteria – Related to Rickettsia Sequencing of 16sRNA connects Wolbachia to Ehrlichia and Rickettsia 16srRNA sequences used to determine relationships between Rickettsia Estimated to infect 15-20% of arthropods. New estimates include as many as 50% of insect species Broad host range – Insects, isopods, mites, and arachnids. They have been isolated from crustaceans. More recently found in Nematodes Manipulate the reproduction in their hosts in a number of unusual ways
Host - Endosymbiont Wolbachia are found in the reproductive tissues of their hosts The bacterial obligatory endosymbionts are passed vertically in the cytoplasm of the eggs of their hosts The Wolbachia affects sex determining factors in insects – affects the sex of the insect progeny The host exerts population control of bacteria A force in speciation in arthropods Viewed as a possibility for the evolution of insects Wolbachia infected ovaries of insect host Amy Hise, Science
Wolbachia and Reproduction Vertical transmission – cytoplasmic inheritance Causes male killing and sterility in males Induces parthenogenesis Cytoplasmic incompatability( conflict between cytoplasmic and nuclear components) Insect egg containing Wolbachia http://www.rochester.edu/.../ images/Wolb_egg.jpg
Symbiont related Sexual Anomalies Thelytoky occurs in Trichogramma wasps In wasps there is a haplofiploid situation with males haploid and females diploid. Virgin Females produce diploid females without fertilization. The n( haploid) is converted to 2n( diploid) This occurs early in the first mitotic division Feminization of males Occurs in Isopods Suppresses the androgenic gland and causes males to become functional females http://www.biconet.com/flies/FC3.html http://www.biodiversity.org.uk/.../images/isopods.jpg
Cytoplasmic Incompatability and vertical transmission If both male and female insects are infected with Wolbachia – the progeny will be infected If the female is infected and the male is not infected, the progeny will all be infected. If the female is not infected and the male is infected there will not be any progeny http://www.cdc.gov/ncidod/eid/vol4no4/beard6t.gif
Examples of symbiont – host interactions Male killing mechanism has been studied in two species of insect In Adalia bipunctata and Acraea encedon the presence of Wolbachia halves the hatch size and changes the female/male ratio Microbial nature of infection has been verified by treatment with rifampin and sulphamethoxazole After treatment with antibiotics the hatch size returns to normal and the with a normal sex ratio Condition can be artificially induced by injection of macerated infected insect into pupae of uninfected ( Hurst et al) Adalia bipunctata – http :bugguide.net/ node/view/13976bugguide.net/ node/view/13976 Acraea encedon- www2.nrm.se/.../e/ acraea_encedonfumosa.htmlwww2.nrm.se/.../e/ acraea_encedonfumosa.html
Why Male Killing ? Reduces competition for food ( H) Reduces cannibalism in siblings (H) Improves female fitness for breeding- selective advantage (H) Insures propagation of Wolbachia endosymbionts to future generations ( S + H) H= Host selective advantage S= Symbiont selective advantage
Mechanism of Action Bacterial modification of sperm by bacterial interactions Bacteria present in testes interact with DNA binding proteins – These may be similar to H1, histones may be similar to H1, histones The same bacterial strain must be present in the female in order to rescue the egg Mitotic defects appear in the early divisions of the fertilized egg( during cleavage) HI – Protein database
Wolbachia – Evidence for specificity of infection PCR for 16sRNA from infected lines Product purified and ligated into pGEM vector Plasmids were transformed into DH5a Colonies with insert were detected 39 /42 positive for Wolbachia insert and not other bacteria 16sRNA Transformants are recognized by blue color on agar plate
Wolbachia and genetics Genome recently sequenced Loss of genes due to obligatory nature of relationship between bacteria and host Loss of genes over time due to dependency on host Many repetitive elements and insertion sequences in the genome Imply high level of intergenomic and intragenomic recombination Genomic map of Wolbachia NCBI http://www.ncbi.nlm.nih.gov http://www.ncbi.nlm.nih.govhttp://www.ncbi.nlm.nih.gov
Genetics of Wolbachia Wolbachian genome consists of one circular chromosome 1.26Mbp – 1195 proteins – GC content 35% Contains genes with Ankyrin repeats – Ankyrins connect endosymbionts to the cell cytoskleton which is an adaptation for intracellular existence Ankyrin repeats – Ankyrins connect endosymbionts to the cell cytoskleton which is an adaptation for intracellular existence Type Four Secretion System – required for persistence of endosymbiont in host – conserved in Rickettsia Female Drosophila melanogaster – laying egg P. Sidelsky – Motic Camera
Lateral Transfer of Genes Evidence of lateral( horizontal) transfer of genes in Wolbachia species in Drosophila melanogaster and Nasonia vitripennis. Drosophila and Nasonia can maintain infection by two strains of Wolbachia Exchange between bacteria that coinfect in the same cells ( density dependent) ( density dependent) Exchange between endosymbiont and host( gene loss) IS sequences in Wolbachia suggest Bacteriophage transfer between Wolbachia strains. Recent research has detected 3 prophage sequences in the Wolbachia genome. ( Wu et al)
Importance of study Wolbachia does not infect humans – studying Wolbachia can lead to a better understanding of Rickettsial – host interactions for medical applciations Understanding Wolbachia can lead to vector control in infections such as Rocky Mountain Spotted Fever ( Rickettsia and tic) ( Rickettsia and tic) Since Wolbachia infects diverse species of insects including beetles, fruit flies, and mosquitoes, it could be evaluated for a form of biological control Used as a model to study speciation Mediterranean Fruit Fly http://creatures.ifas.ufl.edu/fruit/mediterranean_fruit_fly.htm
Wolbachia and River Blindness Wolbachia has also been identified in filarial worms ( Nematoda) ( Nematoda) One of these worms causes Riverblindness(Onchoceriasis) Wolbachia provides metabolic support through many pathways for the worm. for the worm. Contributes to inflammatory responses Instead of antihelminth drug protocols – will antibiotics be a cure?????? http://tools.neb.com/wolbachia /
References Anderson,Cort and Timothy Karr. Wolbachia:Evolutionary Novelty in a Rickettsial Bacteria. BMC Evolutionary Biology, 2001:1-10. Huigens,M.E. On the Evolution of Wolbachia Induced Parthenogenesis in Trichogramma Wasps. http://www.gcw.nl/dissertations/3389/dis3389.pdf http://www.gcw.nl/dissertations/3389/dis3389.pdfhttp://www.gcw.nl/dissertations/3389/dis3389.pdf Hurst, Gregory et al. Male-Killing Wolbachia in Two Species of Insect. National Center for Biotechnology Information – ncbi. http://www.ncbi.nlm.nih.gov/ http://www.ncbi.nlm.nih.gov/ Johanowicz,Denise et Marjorie Foy.Wolbachia Endosymbionts. Florida Entomologist.1998: 310-316. Protein Data Bank - http://www.rcsb.org/pdb/ http://www.rcsb.org/pdb/ Rigaud, T., Juchault, P., and Mocquard, J. P. 1991. Experimental study of the sex ratio of broods in terrestrial Crustacea Armadillium vulgare. Possible implications in natural populations. J. Evol. Biol. 1991: 603 - 607. Sun,Ling. Et al. Gene Organization in the dnaA Region of Wolbachia. Jornal of Bacterioology. 199.18115):4708-4710.
References( con) Wernegreen,Jennifer Endosymbiosis: Lessons in Conflict Resolution. Plos Biology. March 2004, 2:307-311. Werren,John H. Biology of Wolbachia. Annual Review of Entomology. 1997.42:587-609. Werren, John H. and Leo Beukboom. Sex Determination, Sex Ratios, and Genetic Conflict.Annual Review of Ecological Systematics. 1998,29:233- 261. Werren, John H. and David Windsor. Wolbachia Infection Frequencies in Insects: Evidence of a Global Equilibrium. Proceedings of the Royal Society. 200 267: 1277-1285 Werren, John H. Wolbachia Run Amok. Proceedings of the National Academy of Science. 1997. 92: 11154-11155 Wu,Martin et al. Phylogenomics of the Reproductive Parasite Wolbachia pipientis wMeI: A Streamlined Genome Overrun by Mobile Genetic Elements. Plos Biology. 2004,2:327-333.