Calcineurin-dependent galactomannan release in Aspergillus fumigatus

The galactomannan assay to diagnose invasive aspergillosis is recommended and clinically utilized, yet the mechanism of galactomannan release from Aspergillus fumigatus is unknown. We used an A. fumigatus strain lacking calcineurin A (cnaA), already shown to be critically important for pathogenicity, to evaluate galactomannan kinetics. During the logarithmic growth phase when glucose was consumed, β-D-galactofuranoside (galf)-antigens were released in the culture. However, after glucose became limited, GM release further increased in the supernatants of the wild type strain while there was no further increase of GM release in the ΔcnaA strain. β-Galactofuranosidase activity was also decreased in the ΔcnaA mutant, and the amount of galf-antigen in the cell wall fraction of the ΔcnaA mutant was approximately ten-fold higher. This suggests the possibility that the antigen is unable to be released due to a cell wall abnormality. This and previous work suggest a dynamic calcineurin-dependent cell wall during periods of growth, with galactomannan release from the cell wall possibly calcineurin-dependent and reflected in the decreased GM release and greatly increased cell wall fraction of galf in the ΔcnaA mutant.