The Biology of the Thermally Dimorphic Fungal Pathogen Penicillium marneffei

Abstract

Fungal pathogens are a significant public health problem, being responsible for a large and growing percentage of deaths from hospital-acquired infections (Asmundsdottir et al., 2002; Chakrabarti & Shivaprakash, 2005; McNeil, et al., 2001). A group of these pathogens are dimorphic, alternating between two different growth forms (Gow, 1995). The yeast form is unicellular, generally spherical, ellipsoid, or cylindrical in shape, and uninucleate due to coupled mitosis and cytokinesis (Figure 9.1). The filamentous form consists of highly polarized fibrillar cells, which elongate by apical growth, placing crosswalls called septa at regular intervals, exhibit incomplete cell separation, have the capacity to generate new grow foci by branching and are generally multinucleate. The ability to alternate between the yeast and filamentous growth forms is a tightly regulated process known as dimorphic switching. The different growth forms represent cell types with different physiological properties, which are adapted to their respective environments. Interestingly, for most pathogenic dimorphic fungi only one growth form predominates during infection. Therefore, dimorphic switching is an intrinsic property of pathogenicity (Berman & Sudbery, 2002; Andrianopoulos, 2002; Lengeler et al., 2000).