Wolbachia

Taxobox
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image_caption = Transmission electron micrograph of Wolbachia within an insect cell.
Credit:Public Library of Science / Scott O'Neill
name = "Wolbachia"
regnum = Bacteria
phylum = Proteobacteria
classis = Alpha Proteobacteria
ordo = Rickettsiales
familia = Rickettsiaceae
genus = "Wolbachia"

"Wolbachia" is a genus of inherited bacteria 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. One study concludes that more than 16% of neotropical insect species carry this bacterium [cite journal|last=Werren|first=J.H.|coauthors=Guo L, Windsor D. W.|year=1995|title=Distribution of "Wolbachia" in neotropical arthropods|journal=Proc. R. Soc. London Ser. B|volume=262|pages=147–204] and as many as 25-70% of all insect species are estimated to be potential hosts. [cite journal|title=The Discovery of Wolbachia in Arthropods and Nematodes – A Historical Perspective|first=Wieslaw J.|last=Kozeka|coauthors=Ramakrishna U. Rao|year=2007|volume=5|pages=1–14|doi=10.1159/000104228|unused_data=|Issues Infect Dis.]

History

The bacterium was first identified in 1924 by M. Hertig and S. B. Wolbach in "Culex pipiens", a species of mosquito. Hertig formally described the genus 1936 as "Wolbachia pipientis". [Cite journal |author=Hertig M & Wolbach SB |year=1924 |title=Studies on "Rickettsia"-like microorganisms in insects |journal=Journal of Medical Research |volume=44 |pages=329–74] There was little interest after the discovery until 1971 when it was discovered that "Culex" mosquito eggs were killed when the sperm of "Wolbachia" infected males fertilized infection-free eggs (Cytoplasmic incompatibility). [Cite journal|last=Yen|first=J. H.|coauthors=Barr, A. R.|year=1971|title=New hypothesis of the cause of cytoplasmic incompatibility in "Culex pipiens"|journal=Nature|volume=232|pages=657–658|doi=10.1038/232657a0] It is today of considerable interest due to the nature of interactions and evolutionary consequences.It was discovered that Wolbachia makes males dispensable in 1990 by Richard Stouthamer of the University of Califonia, Riverside. [Cite journal |author=Jonathan Knight |year=2001 |title=Meet the Herod Bug |journal= Nature |volume=421 |page=12-14]

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.
* Feminization: infected males develop as females or infertile pseudo-females.
* Parthenogenesis: reproduction of infected females without males. Some scientists have suggested that parthenogenesis may always be attributable to the effects of "Wolbachia". [cite book |author=Gerard J. Tortora, Berdell R. Funke, Cristine L. Case |title=Microbiology: an introduction |publisher=Pearson Benjamin Cummings |year=2007 |isbn=0805347909] An example of a Pathogenic species would be the Trichogramma wasp. [ [5] ]
* Cytoplasmic incompatibility: the inability of "Wolbachia"-infected males to successfully reproduce with uninfected females or females infected with another "Wolbachia" strain.Several species are so dependent on Wolbachia that they are unable to reproduce effectively without the bacteria in their bodies. [Cite Article |author=John H Warren |Title=Invasion of the Gender Benders |Volume=112 |Page=58]

"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. [Cite journal |last=Zimmer |first=Carl |authorlink=Carl Zimmer |year=2001 |title=Wolbachia: A Tale of Sex and Survival |journal=Science |issn=0036-8075 |volume=292 |issue=5519 |pages=1093–5 |doi=10.1126/science.292.5519.1093 |url=http://carlzimmer.com/articles/2001.php?subaction=showfull&id=1177558753&archive=&start_from=&ucat=4& |pmid=11352061] [Cite journal |author=Telschow A, Flor M, Kobayashi Y, Hammerstein P, Werren JH. |year=2007 |title=Wolbachia-induced unidirectional cytoplasmic incompatibility and speciation: mainland-island model |journal=PLoS_ONE |issn=1932-6203 (Electronic) |volume=2 |issue=1 |pages=e701 |doi=10.1371/journal.pone.0000701] Wolbachia can also cause misleading results in molecular cladistical analyses. [cite journal|author=Johnstone RA, Hurst GDD|year=1996|title=Maternally inherited male-killing microorganisms may confound interpretation of mitochondrial DNA variability |url=http://www.ingentaconnect.com/content/ap/bj/1996/00000058/00000004/art00047|journal=Biological Journal of the Linnean Society|issn=0024-4066|volume=58|issue=4|pages=453–470|doi=]

Horizontal gene transfer and genomics

The first "Wolbachia" genome to be determined was that of one that infects "Drosophila melanogaster" fliescite journal |author=Wu M, Sun LV, Vamathevan J, "et al" |title=Phylogenomics of the reproductive parasite Wolbachia pipientis wMel: a streamlined genome overrun by mobile genetic elements |journal=PLoS Biol. |volume=2 |issue=3 |pages=E69 |year=2004 |pmid=15024419 |doi=10.1371/journal.pbio.0020069 |url=http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020069&ct=1] . This genome was sequenced at The Institute for Genomic Research in a collaboration between Jonathan Eisen and Scott O'Neill. The second "Wolbachia" genome to be determined was one that infects "Brugia malayi" nematodescite journal |author=Foster J, Ganatra M, Kamal I, "et al" |title=The Wolbachia genome of Brugia malayi: endosymbiont evolution within a human pathogenic nematode |journal=PLoS Biol. |volume=3 |issue=4 |pages=e121 |year=2005 |pmid=15780005 |doi=10.1371/journal.pbio.0030121 |url=http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0030121] . Genome sequencing projects for several other "Wolbachia" strains are in progress. A complete copy of the "Wolbachia" genome sequence was found within the genome sequence of the fruit fly "Drosophila ananassae" and large segments were found in 7 other "Drosophila" species. [cite journal|title=Widespread Lateral Gene Transfer from Intracellular Bacteria to Multicellular Eukaryotes |author=Dunning Hotopp, J.C, Clark ME, Oliveira DC, Foster JM, Fischer P, Torres MC, Giebel JD, Kumar N, Ishmael N, Wang S, Ingram J, Nene RV, Shepard J, Tomkins J, Richards S, Spiro DJ, Ghedin E, Slatko BE, Tettelin H, Werren J.H.|publisher=Science |year=2007|issue=5845:pages=1753-1756|unused_data=|volume317]

In an application of DNA barcoding to the identification of species of "Protocalliphora" flies, it was found that several distinct morphospecies had identical cytochrome c oxidase I gene sequences, most likely through horizontal gene transfer by "Wolbachia" species as they jump across host species.T.L. Whitworth, R.D. Dawson, H. Magalon, E. Baudry (2007) DNA barcoding cannot reliably identify species of the blowfly genus "Protocalliphora" (Diptera: Calliphoridae). Proceedings of the Royal Society B: 274: 1731-1739]

Applications to human health

Outside of insects, "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.cite journal |author=Hoerauf A, Mand S, Fischer K, "et al" |title=Doxycycline as a novel strategy against bancroftian filariasis-depletion of Wolbachia endosymbionts from Wuchereria bancrofti and stop of microfilaria production |journal=Med. Microbiol. Immunol. |volume=192 |issue=4 |pages=211–6 |year=2003 |pmid=12684759 |doi=10.1007/s00430-002-0174-6] 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.cite journal |author=Taylor MJ, Makunde WH, McGarry HF, Turner JD, Mand S, Hoerauf A |title=Macrofilaricidal activity after doxycycline treatment of Wuchereria bancrofti: a double-blind, randomised placebo-controlled trial |journal=Lancet |volume=365 |issue=9477 |pages=2116–21 |year=2005 |pmid=15964448 |doi=10.1016/S0140-6736(05)66591-9]

The use of modified strains of "Wolbachia" to control mosquito populations has also been a topic of research. [cite journal|title=Generation of a novel "Wolbachia" infection in "Aedes albopictus" (Asian tiger mosquito) via embryonic microinjection|journal=Insect Biochemistry and Molecular Biology|volume=35|year=2005|pages=903–910|first=Zhiyong|last=Xi|coauthors=Jeffry L. Dean, Cynthia Khoo, Stephen. L. Dobson|doi=10.1016/j.ibmb.2005.03.015]

ee also

*Intragenomic conflict

References

*

Footnotes

External links

* [http://www.bacteriamuseum.org/species/Wolbachia.shtml Virtual Museum of Bacteria]
* [http://www.wolbachia.sols.uq.edu.au/index.html Wolbachia research portal] National Science Foundation
*
*eol|17123196
* [http://discover.mbl.edu Howard Hughes Medical Institute High School Lab Series]