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Effect of hypertonic solutes upon the polysaccharide capsule in Cryptococcus neoformans
Mycoses
|January 1, 1989
Summary
High salt conditions reduce the capsule size of Cryptococcus neoformans by suppressing polysaccharide production and causing physical contraction. A mutant was identified with increased polysaccharide production in high salt.
Area of Science:
- Medical Mycology
- Molecular Biology
- Biochemistry
Background:
- The polysaccharide capsule of Cryptococcus neoformans is a key virulence factor.
- Hypertonic environments lead to visibly smaller yeast cell capsules.
Purpose of the Study:
- To quantitatively investigate the suppression of capsule production in Cryptococcus neoformans under hypertonic conditions.
- To determine if salt induces physical contraction of the capsule or suppresses its production.
Main Methods:
- Chemical assays were used to measure cell-bound and dissolved capsular polysaccharide.
- Dialysis experiments were performed to assess salt-induced physical contraction of the capsule.
- Mutants with altered colony morphology on hypertonic agar were isolated and characterized.
Main Results:
- Molar NaCl suppressed cell-bound polysaccharide production 2.5- to 5-fold.
- Dialysis against 1 M NaCl caused physical contraction of the capsular gel.
- A hypercapsular mutant was identified, producing twice the polysaccharide in 1 M NaCl compared to wild type, with the trait segregating as a chromosomal gene.
Conclusions:
- Hypertonic conditions suppress Cryptococcus neoformans capsule production and induce physical contraction.
- A novel gene regulating capsular polysaccharide production in response to salt stress may have been identified through mutant analysis.