Wolbachia – a Heritable Endosymbiont Patricia Sidelsky Symbiosis / /

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

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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 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

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

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

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

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?????? /

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. Hurst, Gregory et al. Male-Killing Wolbachia in Two Species of Insect. National Center for Biotechnology Information – ncbi. Johanowicz,Denise et Marjorie Foy.Wolbachia Endosymbionts. Florida Entomologist.1998: Protein Data Bank Rigaud, T., Juchault, P., and Mocquard, J. P Experimental study of the sex ratio of broods in terrestrial Crustacea Armadillium vulgare. Possible implications in natural populations. J. Evol. Biol. 1991: Sun,Ling. Et al. Gene Organization in the dnaA Region of Wolbachia. Jornal of Bacterioology ):

References( con) Wernegreen,Jennifer Endosymbiosis: Lessons in Conflict Resolution. Plos Biology. March 2004, 2: Werren,John H. Biology of Wolbachia. Annual Review of Entomology : Werren, John H. and Leo Beukboom. Sex Determination, Sex Ratios, and Genetic Conflict.Annual Review of Ecological Systematics. 1998,29: Werren, John H. and David Windsor. Wolbachia Infection Frequencies in Insects: Evidence of a Global Equilibrium. Proceedings of the Royal Society : Werren, John H. Wolbachia Run Amok. Proceedings of the National Academy of Science : Wu,Martin et al. Phylogenomics of the Reproductive Parasite Wolbachia pipientis wMeI: A Streamlined Genome Overrun by Mobile Genetic Elements. Plos Biology. 2004,2: