초록
<P><B>Abstract</B></P> <P>β-Glucosidase was selected to be a reporter to study metabolic burden imposed by its expression in yeast. Cell growth, fermentation yield and enzymatic activity were used as indicators of the metabolic burden borne by 14 recombinant yeast strains. Various factors were found to affect metabolic burden, including <I>BGL</I>I gene source, gene dose, trafficking of the enzyme (either cell-surface display or secretion), and oxygen supply. While <I>BGL</I>I gene from <I>Aspergillus aculeatus</I> provided better performance for the host cells than that from <I>Saccharomycopsis fibuligera</I>, displaying β-glucosidase on the cell surface generally led to lower μ<SUB>m</SUB>, total activity and ethanol titer, and longer lag period, lower (aerobic condition) or higher (anaerobic condition) biomass yield than that of secreting β-glucosidase. The negative effect on growth increased with gene dose level until a final failure to grow. This growth difference implies that displaying β-glucosidase on the cell surface imposes an extra metabolic burden. The molecular basis and mechanisms for this phenomenon need to further be investigated in order to develop better strategies for utilizing displayed and secreted enzymes in biotechnology and yeast breeding.</P> <P><B>Highlights</B></P> <P> <UL> <LI> β-Glucosidase is an important enzyme in medicine and industry (cellulosic ethanol). </LI> <LI> Fourteen recombinant yeast strains were constructed and evaluated in cellobiose media. </LI> <LI> Difference shown on activity; growth lag period, μ<SUB>m</SUB>, biomass; ethanol titer, rate, yield. </LI> <LI> Extra metabolic burden from displaying over secreting, Aa <I>BGL</I>I superior to Sf <I>BGL</I>I. </LI> <LI> The study helps to optimize expressing strategy in biotechnology and yeast breeding. </LI> </UL> </P>