Discordant Influence of Blastomyces dermatitidis Yeast-Phase-Specific Gene BYS1 on Morphogenesis and Virulence

Abstract

ABSTRACT Blastomyces dermatitidis is a thermally induced dimorphic fungus capable of causing lung and systemic infections in immunocompetent animal hosts. With the publication of genomic sequences from three different strains of B . dermatitidis and the development of RNA interference as a gene-silencing tool, it has become possible to easily ascertain the virulence and morphological effects of knocking down the expression of candidate genes of interest. BYS1 ( Blastomyces yeast-phase-specific 1), first identified by Burg and Smith, is expressed at high levels in yeast cells and is undetectable in mold. The deduced protein sequence of BYS1 has a putative signal sequence at its N terminus, opening the possibility that the BYS1 -encoded protein is associated with the yeast cell wall. Herein, strains of B . dermatitidis with silenced expression of BYS1 were engineered and tested for morphology and virulence. The silenced strains produced rough-surfaced cultures on agar medium and demonstrated a propensity to form pseudohyphal cells on prolonged culture in vitro and in vivo , as measured in the mouse lung. Tests using a mouse model of blastomycosis with either yeast or spore inocula showed that the bys1 -silenced strains were as virulent as control strains. Thus, although silencing of BYS1 alters morphology at 37°C, it does not appear to impair the pathogenicity of B . dermatitidis .