The physics of adhesion of Giardia duodenalis and it’s structural basis: Understanding the key process for colonization of the small intestine by a globally prevalent human protozoan parasite and etiologic agent of Giardiasis

• Applicants: Dr. Anton Aebischer; Professorin Dr. Karin Jacobs; Dr. Jan Philipp Jung
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Biophysics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491920994

Giardia duodenalis (also G. intestinalis or G. lamblia) designates a species complex of protozoan parasites that are the etiologic agents of human giardiasis a globally prevalent gastrointestinal disease. Parasites life cycle involves two forms, replicating trophozoites that colonize the small intestine, and the excreted Dauerform, the cyst. Giardia trophozoites sport four pairs of flagella that warrant the necessary motility to reach and attach to the epithelial cell layer enabling infection. Parasite attachment involves an early phase of surface skimming and finally establishing contact to the epithelial cell layer. Attachment is facilitated by a unique organelle, the so-called ventral disc that is composed of a microtubule array, associated with disc-associated proteins (DAP). However, the detailed mechanical function of the ventral disc had not been fully understood, yet. An originally proposed hydrodynamic mode of attachment requires beating of the ventral flagella and a rigid disc structure to create and maintain a suction force. Work by the team of our Co-applicant Scott Dawson (UC Davis) challenged the hydrodynamic model since mutant parasites defective in ventral flagellar beating can still attach and adhere to solid supports like glass. Thus, the actual physics of attachment remains undefined. We postulate that Giardia exerts attachment/detachment cycles as an active process that relies on suction and/or clutching, which is hardwired into the ventral disc’s mechanical properties. Therefore, we aim to elucidate the detailed mechanical function of the ventral disc As important steps during the 1st funding period we succeeded in establishing a new methodology to assess direct adhesion force measurements using Atomic Force Microscopy-based FluidFM on individual trophozoites and initialized optical diffraction tomography and Brillouin microscopy to gain further insight into the disc’s physical properties in collaboration with the team of Jochen Guck (MPI, Erlangen). Further, we succeeded in establishing a CRISPR/Cas-based method to create DAP-deficient mutant strains, and in culturing organoid-derived enterocyte cell monolayers, and make those monolayers accessible to FluidFM-based force measurements. Based on that foundation we plan to i) investigate the attachment of trophozoites to synthetic and natural model surfaces by FluidFM-based force spectroscopy and Flow chamber models ii) assign adhesion force components to respective structural entities by analyses of DAP knockout strains iii) identifying mechanical signals recorded by host cells upon interaction with trophozoites. These finding will enable us to develop a comprehensive physical model of the mechanics of the ventral disc and Giardia trophozoites attachment.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2332: Physics of Parasitism
• International Connection: USA
• Co-Investigator: Dr. Christian Klotz
• Cooperation Partner: Professor Dr. Scott Dawson