Experiments on Drosophilia

The final goal of our project is for our modified Asaia to survive and produce proteins in the mosquito's gut. Working with mosquitoes however requires special equipment that we do not have at EPFL, and we wondered if we could work on another insect which is less demanding. We therefore turned towards Drosophila, commonly known as the fruit fly, which is much easier to work with.

Considering the fact that bacteria that live in the guts of insects are not very common, we assumed that there was a fair chance that Asaia could persist in Drosophila and that we could use the it as an alternative to mosquitos for our basic experiments.

Using Drosophila melanogaster we aimed to address two questions: i) Is Asaia pathogenic for Drosophila? ii) Is Asaia able to colonize the Drosophila gut and persist?

Our main results

To find out if Asaia is toxic for Drosophila and if it can persist, we fed Asaia to flies. If we fed Asaia that expressed GFP to our flies, we could observe the fluorescent bacteria in the gut of the flies (Figure 1).

Then we moved on to find out more quantitatively if Asaia was toxic for our flies. We infected Drosophila with different bacterial strains, a pathogenic control starin (P. entomophila), a non-pathogenic control strain (Ecc 15) and our Asaia bacteria. For these experiments we used two different fly strains (Oregon and Relish). The strain Relish does not have an immune system. We found that Asaia does not cause significantly more deaths than the non-pathogenic bacteria or in the uninfected control (Figure 2).

Figure 2 Asaia is not toxic to Drosophila. Relish (A) and Oregon (B) flies were infected with different bacterial strains and monitored them over time. Deaths were counted and added up over the course of the experiment.

Drosophila

In parallel, we did experiments to assess if Asaia was persistant in Drosophila melanogaster . In fact, the fly is a much easier organism to grow and work on, in opposition to mosquitoes which need to feed on animals to reproduce. Our experiment was set in 3 steps:

• infection of the flies with GFP-Asaia*, and 3 other bacteria as controls
• retrieval of the flies after 3h (control of infection), 24h, 48h
• counting of the number of colonies for all time points and the 4 differents strains

The goal was to observe the persistance of Asaia in the Drosophila gut to see if it can be used as a model organism to study Asaia.

The results were negative for a the experience and we repeteated it 4 times.

graphe des drosophiles