STRESS TOLERANCE AND PATHOGENIC POTENTIAL OF A MANNITOL MUTANT OF CRYPTOCOCCUS-NEOFORMANS

Cryptococcus neoformans produces large amounts of the acyclic hexitol mannitol in culture and infected animals, but the functional and patho genic significance of mannitol production by this fungus is not known. We exposed C. neoformans H99 (Cn H99) to UV irradiation (1 x LD(50)) and screened survivors for mannitol production. A mutant, Cn MLP (Mann itol Low Producer), synthesized less mannitol from glucose (2.7 vs 8.2 nmol per 10(8) cells min(-1) at 37 degrees C) and contained less intr acellular mannitol (1 vs 11 mu mol per 10(6) cells at 37 degrees C) th an did Cn H99. Cn MLP and Cn H99 were similar with respect to carbon a ssimilation patterns, rates of glucose consumption, growth rates at 30 degrees C, urease and phenoloxidase activities, morphology, capsule f ormation, mating type, electrophoretic karyotype, rapid amplification of polymorphic DNA (RAPD) patterns and antifungal susceptibility. Howe ver, Cn MLP was more susceptible than was Cn H99 to growth inhibition and killing by heat and high NaCl concentrations. Also, the LD(50) val ues in mice injected intravenously were 3.7 x 10(6) c.f.u. for Cn MLP compared to 6.9 x 10(2) c.f.u. for Cn H99. Moreover, 500 c.f.u. Cn H99 intravenously killed 12 of 12 mice by 60 d, whereas all mice given th e same inoculum of Cn MLP survived. Classical genetic studies were und ertaken to determine if these differences were due to a single mutatio n, but the basidiospores were nonviable. These results suggest that th e abilities of C. neoformans to produce and accumulate mannitol may in fluence its tolerance to heat and osmotic stresses and its pathogenici ty in mice.