THE INCIDENCE OF KILLER ACTIVITY AND EXTRACELLULAR PROTEASES IN TROPICAL YEAST COMMUNITIES

The presence of killer and proteolytic yeasts was studied among 944 is olates representing 105 species from tropical yeast communities. We fo und 13 killer toxin producing species, with Pichia kluyveri being the most frequent. Other killer yeast isolates were Candida apis, Candida bombicola, Candida fructus, Candida krusei, Candida sorbosa, Hansenias pora uvarum, Issatchenkia occidentalis, Kloeckera apis, Kluyveromyces marxianus, Pichia membrannefaciens, Pichia ohmeri-like, and Sporobolom yces roseus. The communities from which killer yeasts were isolated ha d strains sensitive to them, and there were interspecific and intraspe cific differences in the spectra of their killer activities. Pichia kl uyveri had the broadest spectra of activity against sensitive isolates , and it apparently produced different toxins. The coexistence of sens itive and killer yeasts using the same substrate suggests that there i s spatial separation in microhabitats or temporal separation in differ ent stages of successions. Basidiomycetous yeasts were more frequently proteolytic than ascomycetous yeasts. Extracellular proteases could b e important for the yeasts to have access to more nitrogen nutrients a nd obtain a better balance with available carbon sources.