Effect of hypertonic solutes upon the polysaccharide capsule in Cryptococcus neoformans

Mycoses. 1989 Jan;32(1):14-23. doi: 10.1111/j.1439-0507.1989.tb02163.x.


The polysaccharide capsule is a characteristic virulence factor in the yeast-pathogen, Cryptococcus neoformans. Growth in hypertonic growth media results in yeast cells with visibly smaller capsules. We investigated this suppression quantitatively, using a chemical assay for cell-bound and dissolved capsular polysaccharide. Molar NaCl suppressed production of cell-bound polysaccharide by a factor of 2.5- to 5-fold. The possibility of salt-induced physico-chemical contraction of capsular gel was tested by dialysis of fixed cells from hypotonic medium against medium containing 1 M NaCl and against the original medium again, while capsular thickness, packed cell volume and cell-bound polysaccharide were followed. We detected a physical contraction of gel following dialysis against medium containing 1 M NaCl. Mutants which gave mucoid colonies on hypertonic agar were isolated. One of these gave twice as much polysaccharide as the wild type when cultivated in medium containing 1 M NaCl. The hypercapsular trait was passed through serial outcrosses to the wild type and segregated as a chromosomal gene. This mutant may represent a gene which regulates production of capsular polysaccharide.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cryptococcus / growth & development*
  • Cryptococcus neoformans / genetics
  • Cryptococcus neoformans / growth & development*
  • Culture Media
  • Mutation
  • Phenotype
  • Polysaccharides / metabolism*
  • Saline Solution, Hypertonic


  • Culture Media
  • Polysaccharides
  • Saline Solution, Hypertonic