Killer yeast in winemaking: A comprehensive review

The killer phenomenon refers to the ability of certain yeasts to produce toxins that are lethal to sensitive yeast strains and filamentous fungi. Killer toxins exert antimicrobial activity among other things, wine spoilage microorganisms. For this reason, the role of yeast killer toxins in winemaking has gained considerable attention due to their potential to control spoilage organisms and enhance the quality of wine. Killer toxins are proteinaceous compounds produced by certain yeast strains, notably Saccharomyces cerevisiae and various non-Saccharomyces yeasts, which exhibit antimicrobial properties against competing yeast species. However, the production of killer toxins is species and strain dependent. Moreover, this production is modulated by environmental factors, which makes it difficult to exploit this property in an oenological context. Furthermore, studies on killer toxins are often carried out based on agar test results or using purified toxin, which makes it difficult to extrapolate these activities to wine conditions. There are also relatively few studies on killer activity in real ecological contexts and some studies are contradictory. This review will not present the mechanisms of action of killer proteins which have been widely described in the literature [1–9]. We propose a focus on killer toxins in oenological conditions to synthesize knowledge on the role of the killer phenomenon in microbial and fermentation dynamics in wine. But also, to understand their role in the optimization of fermentations, in bioprotection, and in yeast interaction phenomena. The purpose of this review is also to highlight the contradictions and their origins and the scientific gaps relating to the study of this phenomenon in oenological conditions.