Cda1 and Cda2 coordinate deacetylation of chitin during infection to control fungal virulence.

Chitosan, a deacetylated form of chitin, is required for the virulence of . There are three chitin deacetylase genes (CDA) that are essential for chitosan production, and deletion of all three genes results in the absence of chitosan, loss of virulence, and induction of a protective host response when used as a vaccine. Cda1 plays a major role in deacetylating chitin during pulmonary infection of CBA/J mice. Inoculation with the 1Δ strain did not lead to a lethal infection. However, the infection was not cleared. The persistence of the fungus in the host suggests that chitin is still being deacetylated by Cda2 and/or Cda3. To test this hypothesis, we subjected strains deleted of two CDA genes to fungal virulence in CBA/J, C57BL/6 and BALB/c and found that 1Δ2Δ was avirulent in all mouse lines, as evidenced by its complete clearance. Consistent with the major role of Cda1 in CBA/J, we found that 2Δ3Δ was as virulent as its wild-type progenitor KN99. On the other hand, 1Δ3Δ displayed virulence comparable to that of 1Δ. The virulence of each mutant correlates with the amount of chitosan produced when grown under host-mimicking culture conditions. In addition, the avirulence of 1Δ2Δ was followed by the induction of a protective immune response in C57BL/6 and CBA/J mice, when a live or heat-killed form of the mutant was used as a vaccine respectively. Taken together, these data imply that, in , coordinated activity of both Cda1 and Cda2 is essential for mediating fungal virulence.