Multiplication of an ancestral gene encoding secreted fungalysin preceded species differentiation in the dermatophytes Trichophyton and Microsporum

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Abstract
Dermatophytes are human and animal pathogenic fungi which cause cutaneous infections and grow exclusively in the stratum corneum, nails and hair. In a culture medium containing soy proteins as sole nitrogen source a substantial proteolytic activity was secreted byTrichophyton rubrum,Trichophyton mentagrophytesandMicrosporum canis. This proteolytic activity was 55–75 % inhibited byo-phenanthroline, attesting that metalloproteases were secreted by all three species. Using a consensus probe constructed on previously characterized genes encoding metalloproteases (MEP) of the M36 fungalysin family inAspergillus fumigatus,Aspergillus oryzaeandM. canis, a five-memberMEPfamily was isolated from genomic libraries ofT. rubrum,T. mentagrophytesandM. canis. A phylogenetic analysis of genomic and protein sequences revealed a robust tree consisting of five main clades, each of them including aMEPsequence type from each dermatophyte species. EachMEPtype was remarkably conserved across species (72–97 % amino acid sequence identity). The tree topology clearly indicated that the multiplication ofMEPgenes in dermatophytes occurred prior to species divergence. In culture medium containing soy proteins as a sole nitrogen source secreted Meps accounted for 19–36 % of total secreted protein extracts; characterization of protein bands by proteolysis and mass spectrometry revealed that the three dermatophyte species secreted two Meps (Mep3 and Mep4) encoded by orthologous genes.