ABSTRACT
Cryptococcus gattii is a primary pathogenic yeast, increasingly important in
public health, but factors responsible for its host predilection and
geographical distribution remain largely unknown. We have characterized
C. gattii STE12α to probe its role in biology
and pathogenesis because this transcription factor has been linked to
virulence in many human and plant pathogenic fungi. A full-length
STE12α gene was cloned by colony hybridization and
sequenced using primer walk and 3′ rapid amplification of cDNA
ends strategies, and a ste12αΔ gene knockout
mutant was created by URA5 insertion at the homologous site. A
semiquantitative analysis revealed delayed and poor mating in
ste12αΔ mutant; this defect was not reversed
by exogenous cyclic AMP. C. gattii parent and mutant
strains showed robust haploid fruiting. Among putative virulence
factors tested, the laccase transcript and enzymatic activity were down
regulated in the ste12αΔ mutant, with
diminished production of melanin. However, capsule, superoxide
dismutase, phospholipase, and urease were unaffected. Similarly, Ste12
deficiency did not cause any auxotrophy, assimilation defects, or
sensitivity to a large panel of chemicals and antifungals. The
ste12αΔ mutant was markedly attenuated in
virulence in both BALB/c and A/Jcr mice models of meningoencephalitis,
and it also exhibited significant in vivo growth reduction and was
highly susceptible to in vitro killing by human neutrophils
(polymorphonuclear leukocytes). In tests designed to simulate the
C. gattii natural habitat, the
ste12αΔ mutant was poorly pigmented on wood
agar prepared from two tree species and showed poor survival and
multiplication in wood blocks. Thus, STE12α plays
distinct roles in C. gattii morphogenesis, virulence,
and ecological
fitness.
Monoclonal antibody AHN-1 inhibits phagocytosis by human neutrophils
