Phages of Yeast and Bacteria

Abstract

For many years, stuck and sluggish fermentations have been – and still remain – a major problem for winemakers. While stuck fermentations can usually be characterized by high residual sugar contents at the end of the alcoholic fermentation, sluggish fermentations are accompanied by a low rate of sugar utilization (Bisson 1999). In both scenarios, malfermentations can be caused by a variety of factors, most of which lead to a decrease in the metabolism of the fermenting yeast strain associated, by a decrease in biomass production, cell viability, and/or fermentation rate. One such factor potentially causing a variety of oenological problems during wine fermentation is the production of toxic proteins by certain yeasts: soon after the initial discovery of toxin-secreting killer strains in the wine yeast S. cerevisiae in the early 1960s of the last century (Bevan and Makower 1963), it became evident that killer yeasts and their secreted protein toxins (so-called killer toxins) can cause severe stuck fermentations, particularly under conditions when yeast starter cultures become suppressed by wild-type killer strains present on the grapes (Bussey 1981; Young 1987; Perez et al. 2001; Medina et al. 1997). Bacteriophage attack of food-fermenting bacteria has always been a major cause of economic losses, particularly in the dairy industry (Sanders et al. 1987; Everson 1991). Research on phages and phage–host interactions in lactic acid bacteria (LAB) has thus developed, with the ultimate goal of preventing phage-induced lysis of starter strains. In the wine industry, the LAB bacterium Oenococcus oeni (formerly Leuconostoc oenos) is the organism of choice to promote malolactic fermentation (MLF), a process of major importance for the oenological properties of most wines. The economical importance of MLF and of its favored promoting agent (O. oeni), combined with the experience coming from the dairy industry, has prompted the research of bacteriophages – in this case, oenophages – as a potential cause of MLF failure.