Wolbachia are a type of bacteria that live inside the cells of many animals, but mostly insects. They are passed on from mother to child through the mother’s eggs.
They can often be bad for the insect host: they might kill all male offspring, destroy the host’s gonads, or make it harder for the host female to make eggs with sub-par blood. This is why Wolbachia has been pursued as a potential tool for reducing mosquito populations that carry dangerous human pathogens like Dengue virus and malaria.
On the other hand, Wolbachia can be a good thing for the host. In some species, Wolbachia infection can protect the host from viral infections. And, as a new paper in the journal Science demonstrates, they can ramp up the host female’s egg production by increasing the activity of the germline stem cells. (This article does a very nice job of explaining the paper and its implications).
For this study, the authors used a relative of the common laboratory workhorse Drosophila melanogaster, known as D. mauritiana. D. mauritiana is a fruit fly that is only found on two little islands off the coast of Africa, Mauritius and Rodriguez. The flies are naturally infected with their own specific strain of Wolbachia.
The authors of the paper noticed that infected females produced about 4 times the eggs of uninfected females, apparently due to the presence of Wolbachia inside the cells that give rise to eggs. They found that the activity of these cells was increased in infected females–about 2-fold–but not enough to explain all the extra eggs being produced.
So, where do the extra eggs come from? Wolbachia is helping the flies out in two ways. The bacteria ramp up egg production and shut off the normal programmed cell death inside the ovary.
It appears that male D. mauritiana are out of luck, though. Even though Wolbachia were found in the germline stem cells of testes, they weren’t ramping up sperm production. Males can’t transmit the bacteria to their offspring, so Wolbachia really have no incentive to help the boys out (see: male-killing).
These tiny bacteria appear to have lots of different strategies for manipulating their host’s reproduction (and gene expression), but exactly how they do it is still a mystery. I’ll keep you posted if anyone figures it out!
Fast, E., Toomey, M., Panaram, K., Desjardins, D., Kolaczyk, E., & Frydman, H. (2011). Wolbachia Enhance Drosophila Stem Cell Proliferation and Target the Germline Stem Cell Niche Science, 334 (6058), 990-992 DOI: 10.1126/science.1209609