The yeasts constitute a large group of microorganisms characterized by the ability to grow and survive in different and stressful conditions and then to colonize a wide range of environmental and human ecosystems. The competitive traits against other microorganisms have attracted increasing attention from scientists, who proposed their successful application as bioprotective agents in the agricultural, food and medical sectors. These antagonistic activities rely on the competition for nutrients, production and tolerance of high concentrations of ethanol, as well as the synthesis of a large class of antimicrobial compounds, known as killer toxins, which showed clearly a large spectrum of activity against food spoilage microorganisms, but also against plant, animal and human pathogens. This review describes the antimicrobial mechanisms involved in the antagonistic activity, their applications in the processed and unprocessed food sectors, as well as the future perspectives in the development of new bio-drugs, which may overcome the limitations connected to conventional antimicrobial and drug resistance.

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Wickerhamomyces anomalus killer strains are important for fighting pathogenic yeasts and for controlling harmful yeasts and bacteria in the food industry. Targeted disruption of key genes in b-glucan synthesis of a sensitive Saccharomyces cerevisiae strain conferred resistance to the toxins of W. anomalus strains BS91, BCA15 and BCU24 isolated from olive brine. Competitive inhibition of the killing activities by laminarin and pustulan refer to b-1,3-and b-1,6-glucans as the main primary toxin targets. The extracellular exoglucanase-encoding genes WaEXG1 and WaEXG2 from the three strains were sequenced and were found to display noticeable similarities to those from known potent W. anomalus killer strains. Accession Nos for WaEXG1 genes for the strains in brackets are JQ734563 (BS91), JQ734564 (BCA15) and JQ734565 (BCU24); for WaEXG2 genes JQ734566 (BS91), JQ734567 (BCA15) and JQ734568 (BCU24), respectively.

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Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria (CREA),