Phenotypic Switching in Cryptococcus neoformans Results in Changes in Cellular Morphology and Glucuronoxylomannan Structure

Abstract

Cryptococcus neoformans strains exhibit variability in their capsular polysaccharide, cell morphology, karyotype, and virulence, but the relationship between these variables is poorly understood. A hypovirulent C. neoformans 24067A isolate, which usually produces smooth (SM) colony types, was found to undergo phenotypic switching and to produce wrinkled (WR) and pseudohyphal (PH) colony types at frequencies of approximately 10−4 to 10−5 when plated on Sabouraud agar. Cells from these colony types had large polysaccharide capsules and PH morphology, respectively. Scanning electron microscopy showed that different colony types were the result of altered cellular packing in the colony. Phenotypic switching was associated with quantitative and qualitative changes in capsular polysaccharide. Specifically, the glucuronoxylomannan (GXM) of the WR polysaccharide differed in the proportion of structural reporter groups and in increased xylose residue content linked at the 4 to 0 position. The relative virulence of the colony types was WR > PH > SM, as measured by CFU in rat lungs after intratracheal infection. Karyotype instability was observed in strain 24067A and involved primarily two chromosomes. Colonies with an alternative colony type exhibited more karyotype changes, which did not revert to the original karyotype in reverted colonies. In summary, this study revealed that phenotypic switching inC. neoformans (i) can produce WR colonies consisting of cells with either large capsule or PH morphology, (ii) is associated with production of structurally different GXM, (iii) is commonly associated with karyotype changes, (iv) can produce cells of PH morphology, and (v) can increase the virulence of a strain. Hence, phenotypic switching is an adaptive mechanism linked to virulence that can generate cell types with very different biological characteristics.

Life within a community: benefit to yeast long-term survival

“…J Bacteriol 123: 1139-1143, in Fig. 1c from Fries et al (1999). Phenotypic switching in Cryptococcus neoformans results in changes in cellular morphology and glucuronoxylomannan structure.…”

“…neoformans strains also form a variety of colony morphotypes (smooth, wrinkled and pseudohyphal) that differ in the content and composition of their extracellular capsule ( Fig. 1c) (Fries et al, 1999).…”

“…The composition of the capsule differs in different colony morphotypes, and appears to be important for Cr. neoformans pathogenicity (Fries et al, 1999).…”

Phenotypic switching and its implications for the pathogenesis ofCryptococcus neoformans

“…For fungi, phenotypic switching was first described 20 years ago in Candida albicans (Slutsky et al, 1985(Slutsky et al, , 1987 and the underlying molecular mechanisms have since been extensively studied (Perez- Martin & Uria, 1999;Miller & Johnson, 2002). In more recent years, phenotypic switching has also been demonstrated in other fungi including Cryptococcus neoformans (Goldman et al, 1998;Fries et al, 1999Fries et al, , 2001Kugler et al, 2000;Lachke et al, 2000;Sinha et al, 2000). Phenotypic switching in fungi is defined as the spontaneous emergence of colonies with altered colony morphology at rates higher than the somatic mutation rates (Soll, 1992).…”

MPLEx: a method for simultaneous pathogen inactivation and extraction of samples for multi-omics profiling

“…Pathogens with exposed lipid membranes are more susceptible to disinfectants including detergents and other solvents [23][24][25] . Organic solvents render many pathogens non-infectious by solubilizing and disrupting their lipid membranes or envelopes [26][27][28] , and inactivation of pathogens by organic solvents has been leveraged for vaccine development [29][30][31][32] , transfusion fluids [33][34][35][36] , and sanitation [37][38][39] . In systems biology studies of pathogenic bacteria and viruses, it would be highly efficient to both inactivate pathogens and extract the molecular components needed for proteomic, metabolomic, and lipidomic analyses in a single step.…”