Metabolism of glucose and xylose as single and mixed feed in Debaryomyces nepalensis NCYC 3413: production of industrially important metabolites

Abstract

Efficient conversion of hexose and pentose (glucose and xylose) by a single strain is a very important factor for the production of industrially important metabolites using lignocellulose as the substrate. The kinetics of growth and polyol production by Debaryomyces nepalensis NCYC 3413 was studied under single and mixed substrate conditions. In the presence of glucose, the strain produced ethanol (35.8 ± 2.3g/l), glycerol (9.0 ± 0.2g/l), and arabitol (6.3 ± 0.2g/l). In the presence of xylose, the strain produced xylitol (38 ± 1.8g/l) and glycerol (18 ± 1.0g/l) as major metabolites. Diauxic growth was observed when the strain was grown with different combinations of glucose/xylose, and glucose was the preferred substrate. The presence of glucose enhanced the conversion of xylose to xylitol. By feeding a mixture of glucose at 100g/l and xylose at 100g/l, it was found that the strain produced a maximum of 72 ± 3g/l of xylitol. A study of important enzymes involved in the synthesis of xylitol (xylose reductase (XR) and xylitol dehydrogenase (XDH)), glycerol (glycerol-3-phosphate dehydrogenase (G3PDH)) and ethanol (alcohol dehydrogenase (ADH)) in cells grown in the presence of glucose and xylose revealed high specific activity of G3PDH and ADH in cells grown in the presence of glucose, whereas high specific activity of XR, XDH, and G3PDH was observed in cells grown in the presence of xylose. To our knowledge, this is the first study to elaborate the glucose and xylose metabolic pathway in this yeast strain.