Nutrition and phylogeny of predacious yeasts

Abstract

Yeast predation was studied with respect to the range of its distribution among ascomycetous yeasts, the range of yeast species that can be affected, and nutritional aspects of the phenomenon. The yeasts identified as predators belong to the Saccharomycopsis clade as defined on the basis of rDNA sequence relatedness. The 11 recognized species in the clade, plus three undescribed but related Candida species, were shown to be incapable of utilizing sulfate as sole source of sulfur, and all but two (Saccharomycopsis capsularis and Saccharomycopsis vini) were observed to penetrate and kill other yeasts under some conditions. Other unrelated sulfate transport-deficient yeasts (strains in the genera Pichia and Candida and the two known species of Starmera) are not predacious. The predacious species vary considerably as to the optimal environmental conditions that favour predation. Some are inhibited by the presence of rich nitrogenous nutrients, organic sulfur compounds, or higher concentrations of ammonium nitrogen, whereas other species may be stimulated under the same conditions. An attempt was made to correlate prey susceptibility to the excretion of substances that stimulate the growth of predators, but no correlation was detected between the two phenomena. The range of susceptible prey covers both ascomycetes and basidiomycetes, and includes Schizosaccharomyces pombe, which was previously thought to be immune. The achlorophyllous alga Prototheca zopfii is not killed by predacious yeasts, but the initial steps of penetration have been observed in some cases. Predacious species attack other predacious species, and in some cases, young cultures may penetrate older cultures of the same strain.

Yeasts

“…Yeasts may also exhibit antagonism to other yeasts, either by the secretion of specific killer toxins (mycocins) that disrupt the ion permeability of the cytoplasmic membrane, or by the erection of infection pegs that penetrate indiscriminately the walls of neighbouring yeast cells. The latter activity is characteristic of the ascomycetous genus Saccharomycopsis (Lachance et al, 2000).…”

Draft Genome Sequence of Saccharomycopsis fermentans CBS 7830, a Predacious Yeast Belonging to the Saccharomycetales

“…S. fermentans (formerly classified as Arthroascus fermentans ) was isolated in 1994 from the soil of a Taiwanese orchard and was shown to ferment glucose (references 6 and 7 and references therein). Saccharomycopsis species are natural auxotrophs for organic sulfur ( 8 ). In S. fibuligera , the absence of genes involved in sulfate assimilation has been observed ( 4 ).…”

Draft Genome Sequence of Saccharomycopsis fodiens CBS 8332, a Necrotrophic Mycoparasite with Biocontrol Potential

“…A totally different aspect of Saccharomycopsis yeast biology is the ability to act as necrotrophic mycoparasites, killing other fungi via penetration pegs ( 9 ). The broad host range includes both ascomycetes and basidiomycetes, yeasts, and filamentous fungi ( 10 ). This broad host range apparently enables Saccharomycopsis predators to use their penetration pegs like Swiss army knives.…”