Student Research – Looking for the insect bacteria called Wolbachia

Imagine:…

physicians across the United States…documenting similar events. In each case, an unfertilized egg in a woman had spontaneously begun to develop, ultimately producing a healthy female baby.

One young researcher, who had analyzed the timing and locales of the virgin births, suggested a spreading infection might be causing the incidents. The Federal Centers for Disease Control and Prevention in Atlanta quickly dismissed the idea, calling it “ridiculous.”

Several months later came a well-publicized report in the Journal of the American Medical Association concluding that the number of infertile couples was rising rapidly worldwide. The international uproar intensified when physicians began to observe another reproductive curiosity: Some newborns that were genetically male appeared to be female. One week, the New England Journal of Medicine and the National Enquirer ran articles with the headline, “Is this the end of mankind, or just men?”

Science fiction? Definitely. For many insect species and other arthropods, however, the truth can be as strange as fiction when bacteria known as Wolbachia are around.

Wolbachia is a tiny bacterium that only lives within insects (it can’t be cultured or maintained outside of the insect). Wolbachia infected arthropods and nematodes  often exhibit remarkable reproductive behaviors. The bacteria are transmitted through the ovaries and into eggs. This bacteria is inherited because it lives in reproductive organs and is passed down through the generations inside of infected eggs. Some ways in which Wolbachia has been found to effect reproductive behavior (and many of these behaviors were considered to be fixed genetic behaviors before the effects of the Wolbachia were understood) include:
-Death of infected males,
-Feminization of males
-Reproduction of infected females without males.  Trichogramma wasps are very common examples of a parthenogenic species that’s evolved to procreate without males with the help of Wolbachia. When they’re given antibiotics they’re able to reproduce with males!  Some researchers think that parthenogenesis may always be attributable to the effects of Wolbachia.
-Cytoplasmic incompatibility: the inability of Wolbachia-infected males to successfully reproduce with uninfected females or females infected with another Wolbachia strain.

The week of December 14 Watershed School biology students are contributing to a national effort to learn more about Wolbachia. We’ll be doing DNA extractions from insects (collected earlier by students) in an effort to identify the presence of the DNA of this tiny bacterium. Because Wolbachia cannot be cultured outside of the host insects, the only generally feasible method to determine the presence of this bacterium is to test for the presence of its unique DNA within the insect’s DNA. This calls for the use of some highly sophisticated equipment and techniques – supplied to Watershed through the generosity of the Howard Hughes Medical Institute http://www.hhmi.org/ the Marine Biological Laboratory http://www.mbl.edu/ and the Cornell Institute for Biology Teachers http://cibt.bio.cornell.edu/

Why are people interested in this particular organism?
1- The distribution and activity of Wolbachia, throughout the arthropod world, provide very exciting new information helpful in our understanding of evolution.
2- Human Health: Wolbachia may help control the transmission of arthropod-borne diseases such as Malaria, Dengue fever, Filariasis, Trypanosomiasis, West Nile, Chagas disease. Below is a link to site associated with an organization close to using Wolbachia to defeat Dengue Fever: http://www.mosquitoage.org/en/HOME/tabid/3844/Default.aspx

MANY THANKS to Shlomit Auciello for taking the pictures for this gallery of DNA extraction photos – Photos by Shlomit Auciello/The Herald Gazette and VillageSoup.

(the frame of the image is restricted –click on them to get the full photo):