Asaia: A new chassis to fight mosquito-borne diseases

Asaia is a pink bacteria collected from tropical flowers in Thailand and Indonesia [ 1 ]. It has been proven to naturally live in the mosquito's intestinal tract and to have a hight rate of transmission between mosquitos, both horizontally (from one mosquito to another) and vertically (from parent to offspring)[ 2 ]. The vertical and horizontal transmission as well as the cross-colonizing capability of Asaia (as reported in litterature [ 3 ]) could assure the spread of the transformed agent through host populations. It also appears to be quite specific to mosquitos, and would therefore have little risk of spreading to others insects. However, there is experimental evidence that Asaia sp. is able to cross-colonize different species of mosquitoes and does not exert any pathogenic effect on the host[ 4 ]. Therefore, Asaia is considered to be useful to the mosquito, since its 100% prevalence as well as its preservation in laboratory conditions could not be interpreted [ 5 ].

These properties make it a very good candidate for our project, which consists in blocking the cycle of Malaria, impeding it from infect other people. To assess if asaia is actually a good organism to work on, our team at EPFL decided to study and characterize it: we worked on the strain SF2.1(Gfp) [ 2 ] and it appears it is relatively easy to manipulate. Our team hence provides iGEM with a new chassis, and amongst other things protocols for future teams that want to keep working on this very promising organism.

We believe it could be a really good instrument in the fight against malaria and other mosquito-borne diseases.

In this page we want to summarize the main properties coming out from our experiments.

Do you want to work with Asaia?

No problem! You can find in the following tech-sheets all the information, protocols and tricks you need to start your own project.

1. Growing Asaia [5]

2. Competent cells [5]

3. Transformation [5]

4. Cloning into Asaia [5]

Doubling Time

We measured the growth curve of Asaia at different pH (pH2-pH7) and at 30°C and 37°C to figure out the optimal growth conditions. We found that the optimal Temperature is 30°C, and the optimal pH is 5. At this conditions we measured a doubling time of 2h40min.

Antibiotic resistance

We characterized Asaia's properties against various antibiotics. We had noticed previously that Asaia is naturally resistant to Ampicillin (Amp) and Chloroamphenicol (Cm) to the standard concentrations for E. coli. We tested the behaviour of Asaia to 7 others antibiotic like Tetracyclin (Tet) and Kanamycin (Kan) at various concentrations.

Here you can see the doubling time in function of resistance concentration. When Asaia didn't grow, the doubling time is set at 10h

Here is our plate with different concentration of antibiotics. Green holes are filled with grown up Asaia.

Compatibility with E. coli

We noticed that the Origin of replication of Asaia is compatible with E. coli, but the opposite is not true. Therefore, we had to add Asaia's origin of replication to all our parts so they would function in both Asaia and E. coli

References

• 1. Kazushige Katsura, Asaia siamensis sp. nov., an acetic acid bacterium in the α-Proteobacteria,International Journal of Systematic and Evolutionary Microbiology (2001)
• 2. Guido Favia, Bacteria of the genus Asaia stably associate with Anopheles stephensi, an Asian malarial mosquito vector
• 3. Crotti et al, Acetic acid bacteria, new emerging symbionts of insects (2010)
• 4. Bessem et al, Typing of Asaia spp. bacterial symbionts in four mosquito species: molecular evidence for multiple infections (2010)
• 5. Guido et al,Bacteria of the genus Asaia stably associate with Anopheles stephensi, an Asian malarial mosquito vector (2007)