FUSARIUM MUSAE, A NEW POTENTIAL TRANSKINGDOM PATHOGEN.

In recent years, the number of reported fungal infections has increased significantly, prompting experts to recognize invasive fungal diseases as a major public health concern. The rising threat of fungal infections has roots across the full One Health spectrum, including climate change, population growth, globalization, deforestation, and intensive farming. These factors alter the interactions between humans, animals, and the environment, enabling pathogens to evolve new survival strategies. In particular, the excessive application of fungicides both in agricultural and clinical settings not only contributes to the increase of fungal resistance but also complicates the treatment landscape for immunocompromised patients, thus increasing the at-risk population. A consistent number of clinically relevant pathogens recently have been identifies as already known pathogens in agricultural field. This ability of certain pathogens to cause infection in hosts across different kingdoms is known as transkingdom pathogenicity. In this context, plant pathogens, once primarily an agriculture concern due to their role in food contamination (e.g., mycotoxins) and significant crop losses, have now emerged as direct threats to human health through their ability to cross kingdoms and infect humans. In response to fungal infection emergence, the fungal priority pathogens list (FPPL) was established in 2022, highlighting species of global concern that pose serious risks of morbidity and mortality due to limited therapeutic options and diagnostic challenges that often result in late detection. Fusarium spp. are included in the “high priority group” of FPPL due to their demonstrated inherent resistance to many antifungal agents and yet global incidence rates of fusariosis remain unclear due to insufficient studies. Many Fusarium species are recognized for their transkingdom pathogenicity. Among the most recently identified is F. musae, a causative agent of crown rot disease in bananas that has also been implicated in superficial infections in immunocompromised human patients. This thesis aims to investigate F. musae as a model organism for studying transkingdom pathogens, integrating methodologies from various fields to understand its behavior across different hosts. Using a global collection of F. musae strains isolated from both bananas and human patients, we characterized the species' genetic diversity and clarified its phylogenetic relationship to F. verticillioides through multilocus phylogenetic analyses. Chromosome-level genome sequencing provided an initial comprehensive view of F. musae genomics, while mitochondrial haplotype comparisons revealed potential cross-host transmission events. In vitro sensitivity tests revealed that F. musae is less susceptible to azole treatments than F. verticillioides, potentially offering it adaptive advantages. Finally, infection models with banana fruits and Galleria mellonella larvae confirmed F. musae’s transkingdom pathogenicity, providing the first experimental evidence of its transkingdom infectious capacity and the first bioluminescence readout to quantify F. musae fungal burden and to track disease progression in different hosts. The contemporary threat of this species was confirmed by isolating F. musae from symptomatic bananas in Milan (Italy) markets. Indeed, our research encompassed a comprehensive study on transkingdom pathogens, integrating diverse fields such as morphology, phenotypic analysis, genetics, taxonomy, molecular biology, infection biology, and evolutionary fitness. Our findings highlight the importance of interdisciplinary collaboration in tackling this priority threat. By enhancing our understanding of fungal transkingdom pathogens, this work aims to inform food safety strategies and address the emerging risks posed by F. musae to consumer health. Ultimately, this research aligns with the One Health initiative, emphasizing the need for interdisciplinary collaboration in tackling this complex and emerging category of fungi. We established a set of protocols for investigating fungal infections and outlined strategies to address emerging fungal species. This research contributes to the development of new food safety standards and raises awareness in medical and agricultural fields about the significance of fungal infections within the One Health framework, emphasizing the risks posed by transkingdom pathogens.