Molecular basis for ethyl acetate production and sulfonate transport in the yeast Saccharomyces cerevisiae

Promovendus/a: Sylvester Holt

Promotor(en): Prof. dr. Johan Thevelein, Mevrouw Maria Remedios Foulquié Moreno

Ethyl acetate is a commonly used organic solvent which gives an undesirable solvent-like off-flavor in beer brewing. Here, we have identified genes responsible for the variation in ethyl acetate production by the yeast Saccharomyces cerevisiae after deletion of the previously known major effector enzyme, Atf1. This identified two superior genes, including a novel enzyme which is specific for ethyl acetate production. The specific mutations inside the identified genes were engineered in yeast and confirmed in alcoholic fermentations. They may be used to develop new brewing yeast strains with improved flavor production, having less solvent-like or fruitier “banana”-like flavor profiles.

Besides Saccharomyces cerevisiae, other yeast species, the so-called non-conventional yeast species can be used to improve the flavor profile during commercial beer production. Of all the strains that were tested, yeast strains from the species Pichia kluyverii showed great potential by producing a high level of isoamyl acetate.

In the second line of research, we have identified novel transporters for sulfur compounds. Together with carbon, nitrogen, and phosphate, sulfur is an essential nutrient for the growth of yeast. We showed that Soa1 is the last remaining transporter for inorganic sulfur (sulfate, sulfite and thiosulfate) in the S. cerevisiae genome. Soa1 is a member of an entirely new family of transporters present in all kinds of fungi. Interestingly, these transporters appear to be solely responsible for the uptake of sulfonates and sulfate esters, the most important source of sulfur in forest soils, where yeasts and other fungi are frequently isolated. This will enable improved investigation of the genetic basis for differences among fungi in ecologically relevant niches.