Dissecting the role of Plasmodium sporozoite curvature in gliding motility

Plasmodium parasites are unicellular, mosquito-borne pathogens that cause malaria in vertebrates such as mammals, birds and reptiles. These Plasmodium parasites undergo a complex lifecycle, necessitating their adaptation to different environmental niches. Transmission of Plasmodium begins, when an infectious bite from a female Anopheles mosquito delivers sporozoites in the skin. While in the skin, sporozoites rely on a substrate dependent mode of locomotion known as gliding to actively penetrate host tissue, find and enter blood vessels. Next, sporozoites are passively transported within the bloodstream to the liver where they differentiate into liver stage parasites. Liver stage parasites release merozoites into the bloodstream and start the blood stage phase of infection. Subsequently, mixed bloodstage parasites are ingested by mosquitos and differentiate into various forms before becoming infectious sporozoites again. Infectious sporozoites are polarized crescent shaped cells that typically move in circles on two-dimensional substrates in vitro and in helices in three-dimensional substrates or in vivo. In this thesis, the hypothesis that the curvature/crescent shape of the sporozoites is important for energy efficient corkscrew gliding motility and aids in recognition of blood vessels is investigated. To test the hypothesis two approaches were adopted. The first approach was to use micropillar arrays made of PDMS a plastic polymer, as blood vessel shape mimics. The aim of using pillar arrays was to understand how sporozoite shape guides their physical interactions. Here the results show that sporozoites associate with pillars that have diameters approximately similar to blood vessels. This suggests sporozoite curvature evolved in part to permit their association to blood vessels. The second approach was to generate a genetically manipulated parasite with altered curvature. In studies done in Toxoplasma gondii, PhIL1 a protein of the parasite pellicle was found to be important in maintaining parasite morphology. Here, PhIL1 was found to be essential in the blood stages of the parasite. Also, overexpressing PhIL1, IMC1h and IMC1l showed the sporozoite pellicle was very stable and yielded no curvature change. Although a change in curvature was elusive, the proteins considered here could be used in discovery of other curvature related proteins