title: Systematic capsule gene disruption reveals the central role of galactose metabolism on Cryptococcus neoformans virulence.
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.
authors.affiliation: Unité de Mycologie Moléculaire, CNRS URA3012, Institut Pasteur, France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Moyrand
authors.forename: Thierry
authors.initials: T
authors.lastname: Fontaine
authors.forename: Guilhem
authors.initials: G
authors.lastname: Janbon
mesh_terms: D000818:Animals; D016667:Bacterial Capsules / Q000096:biosynthesis*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015139:Blotting, Southern; D001921:Brain / Q000382:microbiology; D050260:Carbohydrate Metabolism / Q000235:genetics; D003455:Cryptococcus neoformans / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity; D005690:Galactose / Q000378:metabolism*; D017353:Gene Deletion; D015151:Immunoblotting; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011134:Polysaccharides / Q000096:biosynthesis; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis; D014534:UDPglucose 4-Epimerase / Q000235:genetics / Q000378:metabolism; D014774:Virulence / Q000235:genetics; D000099237:UDP-Galactose Translocators
chemical_list: D001426:Bacterial Proteins; D005690:Galactose; D009004:Monosaccharide Transport Proteins; D011134:Polysaccharides; D011135:Polysaccharides, Bacterial; D014534:UDPglucose 4-Epimerase; D000099237:UDP-Galactose Translocators; C043689:galactoxylomannan; C027478:glucuronoxylomannan