Paper ID: 33
1 Vrije Universiteit Brussel (Belgium)
2 Carlsberg Research Laboratory (Denmark)
3 Vrije Universiteit Brussel; Carlsberg Research Laboratory (Belgium)
Yeasts of the genus Saccharomycopsis can be isolated from diverse habitats around the globe. They exhibit a unique predacious behaviour, which allows them to feed on and kill suitable fungal prey cells. This is an act of nectrophic mycoparasitism, which is induced under starvation conditions. During predation prey cells are recognized and a penetration peg is formed, with which the prey cell is penetrated and killed. The host range is wide and includes yeasts, such as Saccharomyces cerevisiae and Candida albicans, but also filamentous fungi, e.g. Ashbya gossypii. Starvation of predator yeasts can be induced solely by the lack of methionine in the growth medium. We aim at understanding the biology of predation and characterize molecular pathways and genes required for successful killing of prey cells. To this end we have generated draft genomes of five predator yeasts: Saccharomycopsis fodiens, S. fermentans, S. crataegensis, S. schoenii and Saccharomycopsis spec. The genome sizes range from 12 Mb to 15 Mb. The genome data, which also include several contigs with telomeric repeats, suggest that loss of genes required for sulphate assimilation is causing methionine auxotrophy within Saccharomycopsis species. Interestingly, genomic signatures suggest that Saccharomycopsis species are part of the CTG clade, which reassigned the CTG codon from leucine to serine, e.g. also in C. albicans. This has guided our molecular approach towards tool development for studying predator yeasts. We have developed synthetic markers, e.g. SAK1 providing resistance against the antibiotic G418. Genome profiling indicated the presence of transposons and of gene families encoding proteins that may play a major role for predacious behaviour. This includes genes encoding proteins for cell-cell adhesion, so called flocculins; genes for cell wall degrading enzymes, e.g. chitinases; and proteases. These and other morphogenesis genes required for penetration peg formation offer excellent target genes to analyze predatory behavior in Saccharomycopsis. In order to quantify predation efficiency we have developed a quantitative predation assay. This is based on quantifying CFU of S. cerevisiae grown on a lawn of predator yeast cells.