• Wong, Brian (PI)

Project: Research project

Project Details


Cryptococcus neoformans is a leading cause of serious nervous system
infections in AIDS patients, but little is known at the biochemical or
molecular levels about microbial factors that contribute to its virulence
or to the pathogenesis of cryptococcosis. This project focuses on the role
of the acyclic polyol mannitol in virulence and pathogenesis. C.
neoformans produces large amounts of mannitol in culture and in infected
animals. Moreover, a mannitol-hypoproducing C. neoformans mutant that
resembles its wild-type parent with respect to several known virulence
factors is profoundly hypovirulent in mice. Therefore, the central
hypothesis to be examined in this project is that mannitol produced by C.
neoformans contributes to virulence and to the pathogenesis of
cryptococcosis. This hypothesis will be tested by pursuing two general
experimental approaches. In Specific Aim 1, classical genetics will be
used to determine if the C. neoformans mutations(s) responsible for
mannitol hypoproduction and abnormal growth kinetics at 37 degrees C are
linked. Next, extraneous mutations in the mannitol hypoproducing mutant
will be removed by repeated backcrossings to a wild-type strain. Lastly,
the virulence of the resulting isogenic strains will be compared in mice.
In Specific Aim 2, a mannitol-nonproducing C. neoformans mutant will be
constructed by disrupting a gene that encodes an enzyme required for
mannitol biosynthesis. The gene that encodes mannitol-1-PO4 dehydrogenase
(MPD) will be cloned, analyzed and disrupted using an integrative genetic
transformation system. Mice and rabbits will be challenged with the
resulting null mutant and its wild-type parent to determine if fungal
mannitol production contributes directly to virulence and to brain edema
formation. Specific Aim 3 is to determine if mannitol produced by C.
neoformans protects the fungus from the inhibitory and/or fungicidal
effects of human neutrophils, monocytes and macrophages in vitro and of
oxidants in cell-free systems. The proposed studies are important because
i) they may define a new virulence factor and pathogenetic mechanism in an
important infection of AIDS patients ii) they may also apply to diseases
caused by other polyol-producing fungal pathogens, iii) they may result in
identification and characterization of useful therapeutic targets, iv)
they should expand our understanding of C. neoformans at the molecular
level, and v) they may provide gene disruption methods that can be used to
study other aspects of C. neoformans biology.
Effective start/end date9/1/946/30/04


  • National Institutes of Health: $230,884.00
  • National Institutes of Health: $224,158.00
  • National Institutes of Health: $53,154.00
  • National Institutes of Health: $217,631.00


  • Medicine(all)
  • Immunology and Microbiology(all)


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