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Our project:
Our team wants to help stopping the propagation of malaria, a disease which has a death toll of over a million per year.
Malaria is transmitted by the parasite Plasmodium whose life cycle is well-studied: The mosquitoes are the vectors which propagate the infection to humans. The infected human will then again infect mosquitoes consuming a blood meal which then completes the cycle.
Bacteria of the genus Asaia have been proven to be stably associated to a malaria propagating mosquitoe, Anopheles stephensi [1]. We plan to take advantage of this and use engineered Asaia to block the Plasmodium cycle.
Our progress:
We are now in our first week in the wet lab. Apart from training basic lab skills like making a PCR and running a gel we are growing Asaia and studying its properties. Furthermore we finished our first biobrick containing an origin of replication for Asaia.
Within the next week we also plan to test the propagation of Asaia within Drosophila.
Our plan:
The bacterium Asaia was chosen as a chassis mainly since it is naturally present in the mosquitoes gut. Furthermore it is transmitted vertically (to the offspring) and horizontally (during reproduction) which enables the engineered Asaia to propagate within a mosquito population.
We have discussed several ways of blocking the Plasmodium in the gut of the mosquito. We plan to test the following two approaches:
- Asaia produces an immunotoxin consisting of an antibody, which will bind to a specific site on the plasmodium and a toxin (a porin, which will perforate the cellular membrane of the parasite).
- p25 p28 are ookinete (a specific form of the plasmodium) surface proteins. It has been shown [2] that if these proteins are missing the formation of ookinetes and the transformation of plasmodium to the next stage are inhibited. We therefore want to engineer Asaia to inhibit these proteins.
The next step is to achieve a release of the toxin or the receptors into the gut of the mosquito. This could be done by lysis of the cells or ideally by secretion.
As a last and very challenging step we consider the option of a blood sensor, which triggers lysis or secretion. This would greatly increase the probability that there is a sufficient amount of immunotoxin to stop the plasmodium from being able to travel to the salivary gland and hence being transmitted to the next victim.
[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1885625/
[2] http://www.nature.com/emboj/journal/v20/n15/full/7593895a.html
Acknowledgements:
- We thank Prof. Guido Favia and Dr. Claudia Damiani from the University of Camerino for the Asaia strains and their helpful advice and protocols on how to grow and manipulate Asaia.
- We would like to thank Prof. Bruno Lemaître from EPFL for his advice and the possibility to conduct experiments with drosophila in his lab.
- We thank the Maerkl lab for bearing our presence in the lab. :)
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