Wolbachia

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Wolbachia

Transmission electron micrograph of Wolbachia within an insect cell.
Credit:Public Library of Science / Scott O'Neill

Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Alpha Proteobacteria
Order:	Rickettsiales
Family:	Rickettsiaceae
Genus:	Wolbachia

Wolbachia is a genus of inherited bacterium which infects arthropod species, including a high proportion of insects. It is one of the world's most common parasitic microbes and is potentially the most common reproductive parasite in the biosphere, for example more than 16% of neotropical insect species carry this bacterium.^[1]

1 Association with disease
2 Role in sexual differentiation of hosts
3 Research history
4 See also
- 4.1 References
5 Footnotes
6 External links

Association with disease

Outside of Insecta, Wolbachia infects a variety of isopod species, spiders, mites, and many species of filarial nematodes (a type of parasitic worm), including those causing onchocerciasis ("River Blindness") and elephantiasis in humans as well as heartworms in dogs. Not only are these disease-causing filarial infected with Wolbachia, but Wolbachia seem to play an inordinate role in these diseases. A large part of the pathogenicity of filarial nematodes is due to host immune response toward their Wolbachia. Elimination of Wolbachia from filarial nematodes generally results in either death or sterility.^[2] Consequently, current strategies for control of filarial nematode diseases include elimination of Wolbachia via the simple doxycycline antibiotic rather than far more toxic anti-nematode medications.^[3]

Role in sexual differentiation of hosts

Within arthropods, Wolbachia is notable for significantly altering the reproductive capabilities of its hosts. These bacteria can infect many different types of organs, but are most notable for the infections of the testes and ovaries of their hosts.

Wolbachia are known to cause four different phenotypes:

Male killing: death of infected males. This allows related infected females to be more likely to survive and reproduce.
Feminization: infected males develop as females or infertile pseudo-females.
Parthenogenesis: reproduction of infected females without males.
Cytoplasmic incompatibility: the inability of Wolbachia-infected males to successfully reproduce with uninfected females or females infected with another Wolbachia strain. This has the advantage of making the Wolbachia strain more likely to become prevalent as opposed to other strains of Wolbachia. This can have the additional result of making Wolbachia more common as a whole.

Wolbachia are present in mature eggs, but not mature sperm. Only infected females pass the infection on to their offspring. It is thought that the phenotypes caused by Wolbachia, especially cytoplasmic incompatibility, may be important in promoting speciation.^[4]^[5] Wolbachia can also cause misleading results in molecular cladistical analyses.^[6]

Research history

The bacteria were first identified in 1924 by Hertig and Wolbach in Culex pipiens, a species of mosquito.^[7]

The genomes of Wolbachia from Drosophila melanogaster flies^[8] and Brugia malayi nematodes^[9] have been sequenced, and genome sequencing projects for several other Wolbachia strains are in progress. Wolbachia used to go from host to host but it evolved to stay in one host and it can now alter an infected females offspring so that they all became female and infected females can now reproduce without a male. As a result there are many species of wasps completely extinct of males because they are no longer necessary. A 2007 paper published in Science reports that a complete copy of the Wolbachia genome can be found within the genome of the fruit fly Drosophila ananassae and that Wolbachia appeared to have transmitted large segments of its genome into at least 7 other species.^[10]

Footnotes

^ Werren JH, Guo L, Windsor DW. 1995. Distribution of Wolbachia in neotropicalarthropods. Proc. R. Soc. London Ser. B 262:147–204
^ Hoerauf A, Mand S, Fischer K, et al (2003). "Doxycycline as a novel strategy against bancroftian filariasis-depletion of Wolbachia endosymbionts from Wuchereria bancrofti and stop of microfilaria production". Med. Microbiol. Immunol. 192 (4): 211–6. doi:10.1007/s00430-002-0174-6. PMID 12684759.
^ Taylor MJ, Makunde WH, McGarry HF, Turner JD, Mand S, Hoerauf A (2005). "Macrofilaricidal activity after doxycycline treatment of Wuchereria bancrofti: a double-blind, randomised placebo-controlled trial". Lancet 365 (9477): 2116–21. doi:10.1016/S0140-6736(05)66591-9. PMID 15964448.
^ Zimmer, Carl (2001). "Wolbachia: A Tale of Sex and Survival". Science 292 (5519): 1093-5. doi:10.1126/science.292.5519.1093. ISSN 0036-8075.
^ Telschow A, Flor M, Kobayashi Y, Hammerstein P, Werren JH. (2007). "Wolbachia-induced unidirectional cytoplasmic incompatibility and speciation: mainland-island model.". PLoS_ONE 2 (1): e701. doi:10.1371/journal.pone.0000701. ISSN (Electronic) 1932-6203 (Electronic).
^ Johnstone RA, Hurst GDD (1996). "Maternally inherited male-killing microorganisms may confound interpretation of mitochondrial DNA variability". Biological Journal of the Linnean Society 58 (4): 453–470. ISSN 0024-4066.
^ Hertig M & Wolbach SB (1924). "Studies on Rickettsia-like microorganisms in insects". Journal of Medical Research 44: 329–74.
^ Wu M, Sun LV, Vamathevan J, et al (2004). "Phylogenomics of the reproductive parasite Wolbachia pipientis wMel: a streamlined genome overrun by mobile genetic elements". PLoS Biol. 2 (3): E69. doi:10.1371/journal.pbio.0020069. PMID 15024419.
^ Foster J, Ganatra M, Kamal I, et al (2005). "The Wolbachia genome of Brugia malayi: endosymbiont evolution within a human pathogenic nematode". PLoS Biol. 3 (4): e121. doi:10.1371/journal.pbio.0030121. PMID 15780005.
^ Dunning Hotopp, JC et al.. "Widespread Lateral Gene Transfer from Intracellular Bacteria to Multicellular Eukaryotes", Science, August 30, 2007.