Distinguishing Polymer Turnover from De Novo Biosynthesis Reveals Dynamic Cell Wall Remodeling During Aspergillus fumigatus Conidial Germination

Dynamic remodeling of extracellular matrices underlies development, environmental adaptation, and host-pathogen interactions, yet distinguishing polymer turnover from de novo biosynthesis in intact cells remains a major challenge. Here, we combined high-resolution solid-state NMR with selective 13C-labeling strategies to distinguish pre-existing cell-wall polymers from newly synthesized polysaccharides during Aspergillus fumigatus conidial germination. Germination was accompanied by substantial remodeling of the rigid cell wall, characterized by decreased {beta}-1,3-glucan and increased chitin and -1,3-glucan, whereas the mobile wall fraction remained comparatively stable except for the emergence of galactosaminogalactan. Surprisingly, {beta}-1,3-glucan turnover proceeded independently of the major {beta}-1,3-glucanases encoded by the A. fumigatus genome and was dispensable for germination. Instead, isotope-labeling experiments revealed that newly assimilated carbon is preferentially directed toward -1,3-glucan biosynthesis, whereas deletion of the -1,3-glucan synthase genes triggered compensatory accumulation of chitin and {beta}-1,3-glucan. These results reveal a compartmentalized cell-wall remodeling program that coordinates selective turnover with de novo polysaccharide synthesis during fungal germination and establish isotope-edited solid-state NMR as a general approach for distinguishing inherited from newly synthesized polymers in complex carbohydrate matrices.