Wolbachia pipientis is an intracellular bacteria that was first observed in the ovaries and testes of the mosquito, Culex pipiens, over 70 years ago. Recent studies have demonstrated that this bacterium is widespread among invertebrates and may naturally occur in over 20% of all insects, including many mosquitoes. Despite this broad host range Wolbachia is not infectious and it does not infect any vertebrates, including humans.
Insect cell containing Wolbachia (as shown by arrows)
Wolbachia’s intracellular lifestyle imposes significant limitations on its ability to spread as it can only be transmitted vertically (from parent to offspring) via cells in the female’s egg. As a result Wolbachia’s success is directly linked to the reproductive success of its insect host. Interestingly, Wolbachia maximises its own success by ensuring that infected females produce more offspring than uninfected females.
Wolbachia-infected females can mate successfully with both infected and uninfected males, however, when uninfected females mate with males infected with Wolbachia, some or all of her fertilised eggs die. This means that females infected with Wolbachia produce comparably more offspring, all of which are carrying Wolbachia. This unique reproductive advantage will effectively maintain and push Wolbachia into populations of dengue mosquitoes.
In this research project we are particularly interested in a Wolbachia strain that shortens adult lifespan of the insect host. One such strain was recently found in the fruit fly, Drosophila, where it causes up to 50% reduction in adult lifespan. The bacteria over-replicate in the host causing pathology, which leads to early death. Despite this detrimental effect on host survival, life-shortening Wolbachia persist in the population due to the reproductive advantage they give to the insect host. In addition to causing life-shortening in the infected insect we have also recently learnt that Wolbachia can directly interfere with the ability of dengue (and other human pathogens) from growing in the mosquito.
Our project’s original aim is to transfer life-shortening Wolbachia from Drosophila to the Aedes mosquitoes that transmit dengue.
The transmission of Wolbachia between insect species is thought to occur very rarely in nature due to the bacteria’s intracellular lifestyle.
In this project the transfer of Wolbachia to mosquitoes has been achieved using specialised microinjection techniques. Successful transfer of Wolbachia between insect species is very difficult to achieve and this has been a major advance for scientists involved in this project.
Wolbachia links:
www.wolbachia.sols.uq.edu.au