Decreased susceptibility of Malassezia furfur to UV light by synthesis of tryptophane derivatives

Recently, tryptophane (Trp)-dependent synthesis of pigments and fluorochrom es in Malassezia furfur was de scribed. The possible significance of this m etabolic pathway for the microorganism remains to be explored. Since the up per parts of the human epidermis are a natural habitat of M. furfur, increa sed exposure to UV light may be hazardous. Five reference strains and one w ild type strain of M. furfur were grown on m-Dixon agar, in which the nitro gen source peptone had been substituted either by pigment-inducing tryptoph ane or arginine. The yeast cells thus obtained were harvested after 6 days, washed with physiological saline and inoculated on to the modified Dixon m edium. Immediately after inoculation, the yeast cells were irradiated with UVA (100, 150 and 200 Jcm(-2) single dose) or UVB (100, 500, 1000, 1500, 20 00 mJcm(-2), single dose; 500, 1500, 2500 mJcm(-2) cumulative dose). Irresp ective of the primary nitrogen source (Trp or Arg), unexposed controls show ed nearly identical cell yield after 5 days. In the case of irradiation, ho wever, growth reduction of cells cultured on Trp was lesser than that of ce lls fed with arginine. High significance (p<0.0001) was found especially wi th the upper UVA and WE doses. Differences were also found among the indivi dual test strains, the wild strain being most sensitive. One strain (CBS 60 94) failed to produce pigment on Trp medium, and there were no differences in the growth behavior of subcultures of this strain fed with either argini ne or tryptophane under irradiation. In conclusion, synthesis of pigments a nd fluorochromes by M. furfur implies the generation of potent UV filters i n the UVA and UVB spectrum.