Cellular integration and nuclear control of bacterial endosymbionts in parasites of the trypanosomatid subfamily Strigomonadinae

• Applicant: Professorin Dr. Eva C.M. Nowack
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558157353

The Strigomonadinae are a subfamily of trypanosomatids that live as parasites in the digestive tract of insects. All members of the Strigomonadinae contain a beta-proteobacterial endosymbiont that supplies its host with diverse metabolites. Intriguingly, similar to an organelle, endosymbiont and host cell cycles are tightly synchronized: There is a single endosymbiont per parasite that divides just before the parasite. Then, one of the freshly divided endosymbionts segregates to the new daughter host cell. To explore the molecular mechanisms underlying this striking level of cellular integration, previously, we established protocols for Angomonas deanei (Strigomonadinae) that allow for targeted gene deletions, knock-downs, and transgene expression. Furthermore, we identified by protein mass spectrometry so far seven endosymbiont-targeted host proteins (ETPs), three of which localize specifically at the endosymbiont division site. For one of these division site ETPs, the dynamin-like protein ETP9, we found an essential role in the division of the endosymbiont. The endosymbiont has lost many essential bacterial division genes, however still forms a division ring composed of the bacterial protein FtsZ. Hence, our work unveiled an endosymbiont division machinery of dual genetic origin, in which a neo-functionalized host protein apparently compensates for losses of bacterial division genes. However, the full complexity of this division machinery, the functions of other proteins involved, and their conservation throughout the Strigomonadinae are unknown, yet. The proposed work program is divided into two work packages (WPs). WP1 aims to determine the full set of nucleus-encoded proteins implicated in endosymbiont division in A. deanei, elucidate their biological functions, and test if endosymbionts can be exchanged between Strigomonadinae species and would remain division competent inside of an orthogonal host cell. WP2 aims to systematically characterize the recalibration of the nuclear gene set as a consequence of symbiosis establishment. It takes advantage of the growing availability of genomic data for the Strigomonadinae and their symbiont-free relatives that all share compact nuclear genomes of ~30 Mbp. By a combination of comparative genomics, proteomics, and cell biological approaches, in WP2 we aim to generate a Strigomonadinae-wide catalogue of host proteins involved in the symbiotic interaction and explore their origin, timepoint of acquisition, conservation throughout the Strigomonadinae, and the biological processes they are involved in. The results obtained will represent a milestone for our understanding of the cell biology of endosymbioses, by yielding insights into the molecular tools that allow a eukaryotic cell to control a bacterial endosymbiont, elucidating intermediate steps in the transition from endosymbiont to organelle, and providing a molecular blueprint for the engineering of synthetic endosymbioses in the future.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Cooperation Partners: Professor Dr. Julius Lukes; Professor Vyacheslav Yurchenko, Ph.D.