Systematic Capsule Gene Disruption Reveals the Central Role of Galactose Metabolism on Cryptococcus Neoformans Virulence

Mol Microbiol. 2007 May;64(3):771-81. doi: 10.1111/j.1365-2958.2007.05695.x.

Abstract

The polysaccharidic capsule is the main virulence factor of Cryptococcus neoformans. It primarily comprised of two polysaccharides: glucuronoxylomannan (GXM, 88% of the capsule mass) and galactoxylomannan (GalXM, 7% of the capsule mass). We constructed a large collection of mutant strains in which genes potentially involved in capsule biosynthesis were deleted. We used a new post-genomic approach to study the virulence of the strains. Primers specific for unique tags associated with the disruption cassette were used in a real-time PCR virulence assay to measure the fungal burden of each strain in different organs of mice in multi-infection experiments. With this very sensitive assay, we identified a putative UDP-glucose epimerase (Uge1p) and a putative UDP-galactose transporter (Ugt1p) essential for C. neoformans virulence. The uge1Delta and ugt1Delta strains are temperature sensitive and do not produce GalXM but synthesize a larger capsule. These mutant strains (GalXM negative, GXM positive) are not able to colonize the brain even at the first day of infection whereas GXM-negative strains (GalXM positive) can still colonize the brain, although less efficiently than the wild-type strain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Capsules / biosynthesis*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Blotting, Southern
  • Brain / microbiology
  • Carbohydrate Metabolism / genetics
  • Cryptococcus neoformans / genetics*
  • Cryptococcus neoformans / metabolism*
  • Cryptococcus neoformans / pathogenicity
  • Galactose / metabolism*
  • Gene Deletion
  • Immunoblotting
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Monosaccharide Transport Proteins / genetics
  • Monosaccharide Transport Proteins / metabolism
  • Mutation*
  • Phenotype
  • Polymerase Chain Reaction
  • Polysaccharides / biosynthesis
  • Polysaccharides, Bacterial / biosynthesis
  • UDPglucose 4-Epimerase / genetics
  • UDPglucose 4-Epimerase / metabolism
  • Virulence / genetics

Substances

  • Bacterial Proteins
  • Monosaccharide Transport Proteins
  • Polysaccharides
  • Polysaccharides, Bacterial
  • UDP-galactose translocator
  • galactoxylomannan
  • glucuronoxylomannan
  • UDPglucose 4-Epimerase
  • Galactose