Kre6-dependent β-1,6-glucan biosynthesis only occurs in the conidium of Aspergillus fumigatus.

The structural role of β-1,6-glucan has remained under-investigated in filamentous fungi compared to other fungal cell wall polymers, and previous studies have shown that the cell wall of the mycelium of A. fumigatus did not contain β-1,6-glucans. In contrast, the current solid-state NMR investigations showed that the conidial cell wall contained a low amount of β-1,6-glucan. ssNMR comparisons of the A. fumigatus and C. albicans β-1,6-glucans showed they are structurally similar. The deletion of the KRE6 gene which is the only KRE gene in the A. fumigatus genome resulted in a mutant depleted of β-1,6-glucan which has a growth phenotype similar to the parental strain. Even though it is not an essential polymer in A. fumigatus, β-1,6-glucan plays a role in cell wall organization since the kre6Δ mutant showed a higher sensitivity to Congo-red and Calcofluor white which are known to be general cell wall inhibitors. It is also another example of the significant structural differences seen between conidium and mycelium of filamentous fungi.IMPORTANCEThis study shows for the first time that β-1,6-glucans are found in Aspergillus fumigatus. Interestingly, this polysaccharide was specifically identified in conidia.