Es. Jacobson et Gm. Compton, DISCORDANT REGULATION OF PHENOLOXIDASE AND CAPSULAR POLYSACCHARIDE INCRYPTOCOCCUS-NEOFORMANS, Journal of medical and veterinary mycology, 34(4), 1996, pp. 289-291
We examined the regulation of two fungal virulence factors, phenoloxid
ase and capsular polysaccharide, in an ex-type strain of the fungal pa
thogen, Cryptococcus neoformans. Both were made during the stationary
phase of cultural growth. Exogenous iron increased phenoloxidase activ
ity three-fold (from 8.7 to 27.7 units mg(-1), P < 0.05) but decreased
capsular polysaccharide three-fold (from 9.0 to 3.4% packed cell volu
me, P < 0.01). A temperature shift from 25 to 37 degrees C decreased p
henoloxidase activity three-fold (from 60.6 to 23.7 units mg(-1), P <
0.01) but not capsular polysaccharide (8.5 to 6.7% packed cell volume,
P not significant). Thus, cryptococcal virulence factors are not regu
lated coordinately. Moreover, although the phenoloxidase synthesizes a
n antioxidant, melanin, the enzyme is not induced by the oxidant, hydr
ogen peroxide, or by a combination of hydrogen peroxide and solubilize
d ferric ion. As cryptococcal melanin is cheaply made from exogenous c
atechols, perhaps C. neoformans does not need to regulate the phenolox
idase strongly but, rather, can afford to synthesize the phenoloxidase
at a moderate rate whenever it finds its growth limited.