Sunday, April 29, 2007

Utilization of cellobiose by Saccharomyces cerevisiae strains harboring intracellular b-glucosidase and cellobiose phosphorylase

Christa Sadie, Rončl van Rooyen, and Willem H van Zyl. Microbiology, University of Stellenbosch, Stellenbosch, 7600, South Africa

Saccharomyces cerevisiae cannot utilize the abundant polymer, cellulose, as an energy source.  Several β-glucosidases have been introduced in S. cerevisiae enabling it to utilize cellobiose, the building disaccharide of cellulose for the production of ethanol.  We will report the expression of an intracellular cellobiose phosphorylase (CbP) and β-glucosidase (BGL) in S. cerevisiae for the first time.  Cellobiose phosphorylase cleaves and subsequently phosphorylates cellobiose, possibly having a metabolic advantage over the hydrolysis of cellobiose by β-glucosidase.  The secretion signal from a fungal β-glucosidase was removed and expressed constitutively from a multi-copy yeast expression vector S. cerevisiae SIGMA strain, designated (SIGMA[BGL]).  Similarly, the intracellular cellobiose phosphorylase was expressed in a S. cerevisiae CEN.PK 21-C strain (CEN.PK[CbP]).  Aerobic batch cultivation of the adapted SIGMA[BGL] and CEN.PK[CbP] strains showed an improved growth rate of 0.09 h-1 and 0.07 h-1 in 10 g/L cellobiose, respectively.  RNA Bio-Dot results revealed the induction of native transporters in the adapted SIGMA[BGL] strain, capable of transporting and utilizing cellobiose intracellularly.