Histoplasma capsulatum: Chemical variability of the yeast cell wall

Abstract

Four strains of HistopIasma capsulatum were analyzed to observe any variations in their cell wall composition. Strair~ G-184B produced the same amount of sugars reported by Domer (2) although qualitative analyses agreed with Kanetsuna's report (4) as far as the presence of glucose, galaetose, and mannose was concerned. Our results agree with previous reports in classifying H. capsutatum into chemotypes I and II, the latter having more ~-glucan in its cell wall. A decrease in the amount of fraction 2 (e-glucan) of strain G-184B was observed when the strain was subcultured in vitro for many years, an effect similar to that reported for Paracoccidioides brasiliensis (12,13).Histoplasma capsulatum, the causative agent of histoplasmosis, is a dimorphic fungus which grows in a filamentous fashion (M form) in soil, or in vitro at 23°C, and as a budding yeast (Y form) in the infected host or in vitro at 37°C.To elucidate some aspects related to dimorphism on H. capsulatum, Domer, Hamilton, and Harkin (3) studied both the Y and M cell wall compositions of strain SwB, concluding that the yeast cell wall contained more chitin and less mannose and amino acids than the mycelial cell wall. Later, Berliner (1) described two morphological types in H. capsulatum, types A (albino) and B (brown), which differed in their M phase morphologies, their Y phases being indistinguishable. Type A mycelia grew as white colonies without diffusible pigment, with broad, white, aereal hyphae, few macroconidia and many microconidia, whereas type B mycelia grew as pigment-producing brown colonies with narrow, brown, fiat hyphae, many macroconidia and few microconidia.Almost simultaneously with Berliner's report, Pine and Boone (7) on the basis of combined serological and chemical data, showed that two major serotypes could be distinguished chemically; strains were later separated by Domer into chemotypes I and II (2). These studies, and another one by Kanetsuna et al. (4) indicated that each of Berliner's types A and B could be subdivided into Domer's chemotypes, the main difference being the presence of c~-glucan in the yeast cell wall of chemotype II and its absence from chemotype I.A closely related fungus, Paracoccidioides brasiliensis, has also been reported to have e-glucan in its yeast cell wall (5) although its amount varies as a function of the culture medium, being virtually lost when cultured in vitro for long periods of time (12). A hypothesis has been proposed (12, I3) by which this polysaccharide keeps a close relationship to virulence in this microorganism It would therefore be of interest to relate the presence or absence of this carbohydrate polymer to the virulence of strains of H. capsulatum. As a first step to explore such a relationship, the yeast phase cell walls of four strains belonging to the types and chemotypes described, were analyzed chemically in regard to their glycan composition. 279Med Mycol Downloaded from informahealthcare.com by Flinders University of South Australia on 02/07/15For personal use only.

Histoplasma variation and adaptive strategies for parasitism: new perspectives on histoplasmosis.

“…The distinct chemotypes were later confirmed by Reiss (95) The spontaneous disappearance of a virulence-associated phenotype during culture has many precedents among pathogenic organisms, and phase variation is a common theme linked with adaptation of different environments (both outside and inside of hosts). Culture-associated loss of ot-(1,3)-glucan had been seen previously during extended in vitro passage of H. capsulatum (99), and this loss probably was due to the progressive accumulation of smooth variants in cultures being transferred without single-colony cloning.…”

An α‐(1,4)‐amylase is essential for α‐(1,3)‐glucan production and virulence in Histoplasma capsulatum

“…We further sought to verify the decrease of α‐(1,3)‐glucan in the amy1 ‐null strain with a biochemical analysis of cell wall polysaccharide composition. Chemical and ultrastructural studies on the cell wall of H. capsulatum yeast have shown that the alkali‐soluble, precipitable fraction is composed of > 99% glucose with α‐(1,3)‐linkages (Kanetsuna et al ., 1974; San‐Blas et al ., 1978). Yeast cell wall polysaccharides were fractionated based on their distinct alkali solubilities and the fraction containing α‐(1,3)‐glucan was examined for its glucose content using standard colorimetric sugar detection techniques.…”

The cell wall of fungal human pathogens: Its possible role in host-parasite relationshipsA review

“…In strain G-184A, Domer (47) and San-Bias et al (147) reported the presence of 47-48% hexoses, whereas Kanetsuna et at. (76) reported as much as 82% for the same strain.…”