SummaryThe ability of a pathogen to adapt to the host environment is usually required for the initiation of disease. Here we have investigated the importance of the Aspergillus nidulans PacC-mediated pH response in the pathogenesis of pulmonary aspergillosis. Using mutational analysis, we demonstrate that, in neutropenic mice, elimination of the A. nidulans pH-responsive transcription factor PacC, blocking the ambient pH signal transduction pathway or prevention of PacC proteolytic processing acutely attenuates virulence. Infections caused by these alkali-sensitive mutants are characterized by limited growth in vivo and a reduction of inflammatory cell infiltration. In stark contrast, constitutive activation of PacC causes increased mortality marked by extensive fungal invasive growth. PacC action is therefore required for, and able to enhance virulence, demonstrating that the A. nidulans pH-responsive transcription factor PacC plays a pivotal role in pulmonary pathogenesis.

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Randomly amplified polymorphic DNA (RAPD) analysis of 33Paracoccidioides brasiliensis strains from Argentina, Brazil, Colombia, Peru, and Venezuela produced reproducible amplification products which were sufficiently polymorphic to allow differentiation of the strains. Types generated with five primers (OPG 03, OPG 05, OPG 14, OPG 16, and OPG 18) resulted in a high discriminatory index (0.956). The discriminatory index was slightly reduced (0.940) when only two primers (OPG 3 and OPG 14) were used. A dendrogram based on these results showed a high degree of similarity among the strains, and genetic differences were expressed in clusters related to geographical regions but not to pathological features of the disease. With a few exceptions, strains were sorted into five groups by geographical origin as follows: group I, Venezuelan strains; group II, Brazilian strains; group III, Peruvian strains; group IV, Colombian strains; and group V, Argentinian strains. The group containing the most disparate strains was group V (discriminatory index, 0.633); the discriminatory index for the other four groups was 0.824. The use of primer OPG 18 by itself was sufficient to discriminate species specificity, and the use of primer OPG 14 by itself was sufficient to discriminate among the geographical locations of the strains in the sample. This method may be helpful for epidemiological studies ofP. brasiliensis.

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The conserved family of fungal Ste11 mitogen activated protein kinase/kinases play important roles in several signalling cascades. We have cloned the STE11 homologue from the fungal pathogen Candida glabrata. The C. glabrata gene is present in a single copy in the genome, contains a well-conserved catalytic domain typical of the serine-threonine protein kinases and a sterile alpha motif widespread in signalling and nuclear proteins. Hypothetical translation of C. glabrata STE11 suggests that the protein has 64% identity and 77% similarity at the amino acid level to Saccharomyces cerevisiae Ste11. We have shown that C. glabrata STE11 can complement the mating defect and partially rescue the reduced nitrogen starvation induced filamentation of S. cerevisiae ste11 mutants. Functional analysis of a C. glabrata ste11 null mutant demonstrates that Ste11 is required for adaptation to hypertonic stress but is largely dispensable for maintenance of cell wall integrity. It also plays a role in C. glabrata nitrogen starvation induced filamentation. Survival analysis revealed that C. glabrata ste11 mutants, while still able to cause disease, are attenuated for virulence compared to reconstituted, STE11 cells. These data suggest that C. glabrata Ste11, in a similar fashion to the S. cerevisiae protein, functions in a number of different signalling modules.