Predacious yeasts.

Haustorium-mediated predation was observed in seven yeast species. Arthroascus javanensis, Botryoascus synnaedendrus, Guilliermondella selenospora, Saccharomycopsis fibuligera, and three hitherto unknown species penetrate and kill other yeasts. These yeasts share an unusual requirement for organic sulphur. One isolate recovered from Australian Hibiscus was studied in detail and found to attack a broad range of prey species, including ascomycetous and basidiomycetous yeasts as well as moulds. Predation was most effective when growth was on a solid surface and the medium was poor in complex nutrients. Organic sulphur (exemplified by methionine) was identified as a key factor. It serves as a nutritional benefit to the predator and, depending on the concentration, acts as either an inhibitor of predation or possibly a signal for detection of prey. Sampling of a yeast habitat with a medium selective for selenium-resistant yeasts indicated that auxotrophic and predacious yeasts might be more widespread than anticipated.