From Scientific American, March 2009:
Even in the teeming and varied world of bacteria, Wolbachia is something of a standout. Within its insect host, the bacterium acts as a gender-bending, egg-killing, DNA-hijacking parasite that is passed down from one generation to the next via the female to her eggs. Hosted by at least one fifth of all insect species, it is possibly the most prolific parasite on earth. But now Wolbachia itself is being hijacked, to help humans gain the upper hand in the long-running war against mosquito-borne diseases. Read more.