Ecophysiological responses of the biocontrol yeast Candida sake to water, temperature and pH stress

N. T EIXIDO ´, I. VINAS, J. USALL, V. SANCHIS AND N. MAGAN. 1998.The growth responses of the biocontrol agent Candida sake to changes in water activity (aw), temperature and pH and their interactions, and accumulation of sugars (glucose, trehalose) and sugar alcohols (glycerol, erythritol, arabitol and mannitol) were determined in vitro in nutrient yeast dextrose based media. The aw temperature profile for growth was between 0·995 and 0·90 and 4‐37 °C with the non-ionic solute glycerol, and between 0·995 and 0·92 and 10‐30 °C with the ionic solute NaCl. Regardless of solute, there was a longer lag time prior to growth as aw was reduced, and at marginal temperatures for growth. Relative growth rates were compared at different aw levels and temperatures and it was found that aw, temperature, solute and two and three‐way interactions were statistically significant. By contrast, C. sake was tolerant of a wide range of pH levels (3‐7) regardless of aw, although growth rates were reduced at marginal temperatures and aw. In non-stressed basal NYDB, glucose and arabitol were the predominant endogenous reserves accumulated in the cells of C. sake. However, when nutrient status was diluted (75%) and stressed by the addition of glycerol or NaCl (0·98 and 0·96 aw), significant changes in the accumulation of sugars and sugar alcohols occurred. In glycerol-stressed media, glucose and glycerol were the major compounds accumulated, with markedly lower arabitol and little trehalose or mannitol present. With NaCl-stressed media, glycerol was the only sugar alcohol accumulated, with very low levels of the sugars and other sugar alcohols. This study has defined the ecological niche within which C. sake would be active as a biocontrol agent for the first time and suggests that endogenous reserves can be significantly modified by nutrient and aw stress; these changes may be useful for improving environmental competence of such micro-organisms in the environment.