Seasonal variation of fermentation rate inSaccharomyces spp. (Ascomycota)?

Yeast species of the genus Saccharomyces show some reaction to visible light – although they lack photo pigments and the typical clock genes of fungi – that can be explained by damage of the cytochrome electron transport chain of the mitochondria. Evidence for a circadian clock, entrainable by cyclic environmental stimuli, exists for periodic changing temperature and light as zeitgeber. Whether seasonality follows from the existence of a circadian clock – which is a necessary requirement for annual rhythms – remains unknown. Due to an accidental observation, we were able to show that fermentation taking place in complete darkness and at constant temperature is influenced in some yeast strains by the history of the inoculum culture. Using yeast cultures growing on agar plates and exposed to diffuse daylight for three weeks either in March or in May as inoculum, leads to significantly different fermentation rates in the inoculated grape juice in both months: rates are higher in March when day length is shorter than in May. In must inoculated with cultures that grew in darkness or daylight, respectively, higher fermentation rates occur by the former. Other yeast strains react to artificial white light in the same way. We used strains of S. cerevisiae, S. eubayanus, S. kudriavzevii, S. uvarum and furthermore hybrid strains of two or even three of these species. The most pronounced reaction to daylight was shown by the S. eubayanus x S. uvarum x S. cerevisiae hybrid, followed by S. cerevisiae x S. kudriavzevii hybrids, S. eubayanus and S. cerevisiae. S. uvarum was sensitive to artificial white light. These observations can hardly be explained by some kind of photo damage because they base on an effect that persists through many cell division cycles after yeasts were exposed to light. If it really represents seasonality epigenetic memory is likely involved, since fermentation lasts for many days and yeast generations. If the existence of a circadian clock and seasonal behaviour in Saccharomyces is confirmed these yeasts could become an important tool in basic research concerning epigenetic memory.