The conserved and divergent roles of carbonic anhydrases in the filamentous fungi Aspergillus fumigatus and Aspergillus nidulans

P>Carbon dioxide (CO2) and its hydration product bicarbonate (HCO3-) are essential molecules in various physiological processes of all living organisms. The reversible interconversion between CO2 and HCO3- is in equilibrium. This reaction is slow without catalyst, but can be rapidly facilitated by Zn2+-metalloenzymes named carbonic anhydrases (CAs). To gain an insight into the function of multiple clades of fungal CA, we chose to investigate the filamentous fungi Aspergillus fumigatus and A. nidulans. We identified four and two CAs in A. fumigatus and A. nidulans, respectively, named cafA-D and canA-B. The cafA and cafB genes are constitutively, strongly expressed whereas cafC and cafD genes are weakly expressed but CO2-inducible. Heterologous expression of the A. fumigatus cafB, and A. nidulans canA and canB genes completely rescued the high CO2-requiring phenotype of a Saccharomyces cerevisiae Delta nce103 mutant. Only the Delta cafA Delta cafB and Delta canB deletion mutants were unable to grow at 0.033% CO2, of which growth defects can be restored by high CO2. Defects in the CAs can affect Aspergilli conidiation. Furthermore, A. fumigatus Delta cafA, Delta cafB, Delta cafC, Delta cafD and Delta cafA Delta cafB mutant strains are fully virulent in a low-dose murine infection.