Summary:
Insects are threatened by outbreaks of a fatal disease that leaves them as zombies by controlling their behavior. The physical mechanism by which the disease spreads, however, is unknown. In this project, you will design and test a synthetic fungal spore cannon and investigate it’s dynamics using high-speed videography.
Description:
Houseflies are threatened by outbreaks of a fatal disease that leaves them as zombies, spreading the disease throughout the population by controlling their behavior. The cause of the disease is a pathogenic fungus, Entomophthora muscae, whose vegetative part grows throughout the fly’s body. When it reaches the brain and central nervous system the fungus takes full control of the fly’s behavior. The fly crawls to a high position, anchors itself to the surface with his tubular mouth, moves up its wings to allow easy dispersal of the fungus – and then dies. The fungus forms small stalks (conidiophores) that protrude through the soft parts of the fly’s body, and on each of them grows a nearly-spherical spore (conidium; typically 20-30 micron in diameter). This can be observed as yellowish rings on the fly. The conidia are then forcibly discharged from the conidiophores, forming fungal artillery that is aimed at infecting other houseflies.
The main research goal of this project is to study the mechanism and dynamics of this spore artillery. Fungi have developed active methods to discharge spores often based on condensation, absorption or evaporation of water. Although humidity is clearly a mutual factor, a wide variety of mechanisms has been observed, reflecting the wide variety of spore-carrying structures of fungi. Two well-known examples are the “fluid pressure catapult” where one or more spores are forced out of a small bag containing fluid; or the “momentum catapult” where a single spore is released from a stalk after a small, condensed droplet spreads over the spore, releasing surface energy. For E. muscae the spore structure is different, and the discharge mechanism yet unknown. It happens at extremely fast time scales (below a millisecond) so we need a high-speed camera to study the mechanism. We will work with lab-cultivated E. muscae, as well as a related fungal species that can grow in-vitro. For these cultures we collaborate with Prof. Henrik de Fine Licht and his Evolutionary Insect Pathology group at the University of Copenhagen. They will study the biological and genetic factors that play a role in the spore discharge mechanism. Here at DTU you will study the physics of the spore artillery: the spore dynamics and unraveling the discharge mechanism.
Examples of research tasks using high-speed videography and modeling:
1. Visualize spore trajectories to deduce the ejection velocity from the deceleration of the spore due to drag.
2. Study the spore discharge mechanism. You will identify the role of humidity: is spore discharge rate and/or velocity enhanced for low or high humidity (i.e. an evaporation- or absorption-based scenario)? Another research angles is to study re-location of fluid and conidiophore material. Can we observe the location of rupture of the stalk? Are fluid and/or conidiophore fragments ejected with the spore? How does the spore spread out after landing?
3. Develop a model of the spore discharge mechanism based on the pressure build-up (positive or negative), and the geometry and material properties of the spore and stalk.
Supervisor: Kaare H. Jensen, DTU Physics, building 309, room 124.
Contact information:
email: khjensen@fysik.dtu.dk
phone: +45 22315241
www: http://www.jensen-research.com
