Controlling mosquito-borne illnesses, such as Dengue fever or West Nile virus, has historically been difficult due to a lack of effective vaccines and concerns about the environmental impact of insecticides. Thus scientists have turned to manipulating a parasitic bacterium within mosquitoes as a way to control the reproductive fitness of mosquito populations that transmit human disease.
In a new study in Nature Communications, an international team including scientists from the Marine Biological Laboratory and the University of Chicago identified a new mobile DNA element in this bacterium, called Wolbachia, which may contribute to improved control strategies for the disease.
The researchers reconstructed near-complete genomes of Wolbachia isolated from individual ovaries of four Culex pipiens mosquitoes. In the process, they identified a circular piece of DNA (or plasmid) that can replicate independently of the chromosomes. Because it is a mobile DNA element, it can transfer from one cell to another and can have great implications for the fitness and evolution of a microbial species. Mobile genetic elements that can spread through different Wolbachia cells hold promise for controlling mosquito populations that may carry disease.
“Our data show that this novel plasmid is widespread across natural Wolbachia populations that infect C. pipiens mosquitoes throughout the world, which implies it has an essential role. The idea that it may enable transformation of the Wolbachia populations is simply very exciting,” said the study’s senior author, A. Murat Eren (Meren), an assistant professor of medicine at the University of Chicago and an MBL Fellow.
Wolbachia is transmitted from mother to offspring and can influence the reproductive behavior of its mosquito host. Wolbachia can modify sperm so if an infected male mates with an uninfected female, or with one that carries a different strain of Wolbachia, embryos cannot develop. The mechanism behind this embryonic killing lies within another mobile genetic element in the Wolbachia genome.
“Wolbachia populations do not lend themselves to direct genetic modification. While a natural plasmid sounds very promising to bypass those limitations, we do not yet have any evidence to suggest the possibility or efficacy of any transformation through this plasmid,” Meren said. ”We just discovered its existence, and the time will tell how useful it is.”