ABSTRACT/PROJECT SUMMARYIt remains elusive how the human fungal pathogen Aspergillus fumigatus is able to adapt to and persevere withinthe hypoxic microenvironment of the host, a characteristic critical to pathogenesis and disease progression. Thegoal of this proposal is to expand our understanding of fungal pathogenesis, focusing on the novel role of fungalcollagen-like proteins and their influence on the fungal extracellular matrix and hypoxia fitness. The A. fumigatuscollagen-like protein, CgnA, was identified for its critical role in the hypoxia fitness of an in vitro hypoxia-evolvedstrain, where a null mutant of cgnA in this background suppresses the in vitro hypoxic growth and the alteredcolony morphology of the hypoxia-evolved strain. Furthermore, the hypoxia-evolved strain displays a completedetachment of the fungal extracellular matrix (ECM) component galactosaminogalactan (GAG), revealing barehyphae, a phenotype repeated in the parental strain with over expression of the CgnA upstream regulator. Giventhe well-characterized role of GAG in the virulence of A. fumigatus, expression of CgnA is likely to significantlyalter the host response to A. fumigatus in vivo. However, the role of GAG in hypoxia adaptation, and the influenceof secreted GAG versus attached GAG within the host microenvironment remain unexplored and are the focusof this proposal. To address these novel roles for CgnA and the extracellular matrix, electron microscopy andadherence assays with exogenous GAG will be performed. To determine the role of CgnA in hypoxia fitness andfungal pathogenesis, a nanoparticle oxygen reporter will be used to quantify hypoxic stress in the presence andabsence of GAG, and fungal host survival and in vivo immunological assays will be performed, respectively. Theresults of this proposal will define a novel link between unstudied collagen-like fungal proteins, the extracellularmatrix, hypoxia fitness, and fungal virulence, an area that has not been previously explored in human pathogenicfungi.