Xylose and yeasts: A story beyond xylitol production

Six different yeasts were used to study their metabolism of glucose and xylose, and mainly their capacity to produce ethanol and xylitol. The strains used were Candida guilliermondii , Debaryomyces hansenii , Saccharomyces cerevisiae , Kluyveromyces marxianus , Meyerozyma guilliermondii and Clavispora lusitaniae, four isolated from a rural mezcal fermentation facility. All of them produced ethanol when the substrate was glucose. When incubated in a medium containing xylose instead of glucose, only K. marxianus and M. guilliermondii were able to produce ethanol from xylose. On the other hand, all of them could produce some xylitol from xylose, but the most active in this regard were K. marxianus , M. guilliermondii , Candida lusitaniae , and C. guilliermondii with the highest amount of xylitol produced. The capacity of all strains to take up glucose and xylose was also studied. Xylose, in different degrees, produced a redox imbalance in all yeasts. Respiration capacity was also studied with glucose or xylose, where C. guilliermondii , D. hansenii , K. marxianus and M. guilliermondii showed higher cyanide resistant respiration when grown in xylose. Neither xylose transport nor xylitol production were enhanced by an acidic environment (pH 4), which can be interpreted as the absence of a proton/sugar symporter mechanism for xylose transport, except for C. lusitaniae . The effects produced by xylose and their magnitude depend on the background of the studied yeast and the conditions in which these are studied. • Mezcal yeast strains were analyzed to use glucose or xylosefor ethanol/xylitol production. • Only K. marxianus and M. guilliermondii were able to produce ethanol from xylose. • All of them produced xylitol from xylose, but Candida guilliermondii produced the most. • Glucose and xylose as substrates showed different metabolic behavior among the strains. • Experiments at low pH suggest the absence of a proton/xylose symporter with exception of Candida lusitaniae . • No influence from mezcal environment was found in Saccharomyces cerevisiae with xylose.