Comparison of killer toxin-producing and non-producing strains of Filobasidium capsuligenum: proposal for two varieties.

The basidiomycetous yeast, Filobasidium capsuligenum, produces killer toxin against the opportunistic pathogen Cryptococcus neoformans. Not every strain isolated so far is able to produce the anti cryptococcal toxin. The aim of the present work was to study the relationship between the toxins and the toxin-producing and non-producing isolates. The toxin was coded on chromosomal DNA in each producing strain as molecular analysis revealed. In addition, both the killing spectra and biochemical properties of the toxins proved to be identical, thus intraspecific variation in the toxin was not found. For molecular typing of the isolates, the D1/D2 region of 26S rDNA, partial sequences of internal transcribed spacer (ITS) regions, PCR fingerprinting RAPD and mtDNA-RFLP patterns were examinated. Phylogenetic analyses based on the different approaches showed that strains with the ability of killer-toxin production and those without it differ significantly and cluster into two distinct groups. The differences between the two groups and the similarity within them suggest the authority to separate the species into varieties.