Materials and Methods

The Flies

Working with flies:

We put the drosophila to sleep with CO ₂ and then manipulated them with fine paintbrushes and tweezers on a box were we could add CO ₂ at will.

Females / Males:

For each experiment we worked exclusively on female flies to reduce the variability. We chose to work on females rather than males because the females eat less randomly, as they have to lay eggs, are bigger and have a higher metabolism. We hence assumed that by working with females, we could achieve an higher uptake of bacteria.

Oregon / Relish:

We worked on the Drosophila wild type Oregon strain. We also conducted some experiments with the immunodeficient Drosophila mutant Relish, to determine if the innate immune system of Drosophila is harmful to asaia.

The Infection

The bacterial cultures were concentrated by centrifugation to obtain a sample which optical density measured at 600 nm was 100 (OD600=100). We then put 150 ul of the solution on filters that we placed over the medium which the flies feed on. Therefore the flies take up the bacteria whenever they eat [1].

Before infection the flies we starved for two hours to ensure and synchronize their food uptake..

The Bacterial Controls

We infected a set of flies with different types of bacteria whose reaction in the drosophila’s gut is are well known, and therefore use these as controls.

Positive control (Bacteria that should persist in the gut of the drosophila).
Pseudomonas entomophila (Pe) </br>
Erwinia carotovora carotovora 15 (ECC-15) </br>

Negative control (Bacteria that do not persist in the gut of drosophila).
Gac: non persistent Pe mutant </br>

Time of measurements

3h: Three hours after the infection we verified that the flies were actually properly infected. We expected to observe the presence of all types of bacteria (asaia, positive and negative control) as the flies would not have had time to produce an immune response against these bacteria.

24h: We should start observing a decline in the negative control whilst the positive control persists. We can also start observing the tendency of asaia.

48h: The positive control should still persist and the negative control should have almost disappeared. We can then compare asaia to the controls and conclude on the persistency of asaia. bove.