Open AccessProduction of Extracellular Polysaccharides by CAP Mutants of Cryptococcus neoformans
Author(s) -
Jan Grijpstra,
Gerrit J. Gerwig,
Han A. B. Wösten,
Johannis P. Kamerling,
Hans de Cock
Publication year - 2009
Publication title -
eukaryotic cell
Language(s) - English
Resource type - Journals
eISSN - 1535-9778
pISSN - 1535-9786
DOI - 10.1128/ec.00013-09
Subject(s) - polysaccharide , secretion , mutant , biology , biochemistry , glucuronic acid , cryptococcus neoformans , bacterial capsule , virulence , microbiology and biotechnology , gene
The human pathogenCryptococcus neoformans causes meningoencephalitis. The polysaccharide capsule is one of the main virulence factors and consists of two distinct polysaccharides, glucuronoxylomannan (GXM) and galactoxylomannan (GalXM). How capsular polysaccharides are synthesized, transported, and assembled is largely unknown. Previously, it was shown that mutations in theCAP10 ,CAP59 ,CAP60 , andCAP64 genes result in an acapsular phenotype. Here, it is shown that these acapsular mutants do secrete GalXM and GXM-like polymers. GXM and GalXM antibodies specifically reacted with whole cells and the growth medium of the wild type andCAP mutants, indicating that the capsule polysaccharides adhere to the cell wall and are shed into the environment. These polysaccharides were purified from the medium, either with or without anion-exchange chromatography. Monosaccharide analysis of polysaccharide fractions by gas-liquid chromatography/mass spectrometry showed that wild-type cells secrete both GalXM and GXM. TheCAP mutants, on the other hand, were shown to secrete GalXM and GXM-like polymers. Notably, the GalXM polymers were shown to contain glucuronic acid. One-dimensional1 H nuclear magnetic resonance confirmed that theCAP mutants secrete GalXM and also showed the presence of O-acetylated polymers. This is the first time it is shown thatCAP mutants secrete GXM-like polymers in addition to GalXM. The small amount of this GXM-like polymer, 1 to 5% of the total amount of secreted polysaccharides, may explain the acapsular phenotype.