Zygosaccharomyces Medium

Mix and dissolve the following ingredients. Glucose Yeast extract Tryptone Distilled water Agar (if desired) 

Once dissolved, dilute to volume with distilled water (1000 mL) and autoclave at 121°C/250°F for 15 min. 

After sterilization, place the flask containing the medium in a 45°C/113°F to 50°C/122°F water bath and allow the temperatures to equilibrate. 

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Presumptive identification of a yeast suspected to be Zygosaccharomyces can be made by growing the isolate on the Zygosaccharomyces medium supplemented with 1% v/v acetic acid. Whereas Saccharomyces will not grow, most species of Zygosaccharomyces will (Z. bailii and Z. bisporus). Some species, however, will not (Z. rouxii). Other selective media for Zygosaccharomyces dtre available (Makdesi and Beuchat, 1996). 

Occurrence of this type of fermentation is caused by the alkalinity of the medium, since various salts or hydroxides can be used with practically the same result. It is interesting to note that a yeast, Zygosaccharomyces acidifaciens, has been observed to bring about this third form of fermentation as its normal glycolytic process. 

Zygosaccharomyces bailii [8] were isolated in our laboratory. The others strains come from culture collection. The basal culture medium was "G" medium to which carbon sources were added to a final concentration of 0.5 % (w/v). The cultures were incubated at 28°C in Erlenmeyer flasks filled to one tenth of their volume. Growth was monitored by measuring the absorbance at 420 nm. The cultures were incubated at 28 C and shaken (80 oscillations per min, 8 cm amplitude). 

Makdesi, A.K. and L.R. Beughat. 1996. Improved selective medium for enumeration of benzoate-resistant, heat-stressed Zygosaccharomyces bailii. Food Microbiol. 13 281-290. 

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