초록
<P><B>Abstract</B></P> <P>As the initiation of fermentation using the yeast <I>Saccharomyces cerevisiae</I> is always associated with a rapid drop in stress resistance, it is critical to develop yeast cells with elevated stress tolerances as well as normal growth and metabolite rates. In our study, the <I>CYR1</I> promoter was serially truncated from the 3′end by 30bp steps to finely modulating the activity of Adenylate cyclase, encoded by <I>CYR1</I> and synthesizing cAMP from ATP. The constructed mutants AY15a-90 and AY15a-120, whose promoters carry 90- and 120-bp truncations, showed a 2- and 3-fold drop in adenylate cyclase activity, and improved heat and ethanol tolerances than AY15a. Interestingly, AY15a-90 and AY15a-120 also exhibited the same growth and fermentation rate as the strain AY15a. In very high gravity (VHG) fermentation at 40°C, the yield of ethanol for AY15a-90 and AY15a-120 were 14% and 15% higher than that of AY15a, respectively. These results showed high stress tolerance and high fermentation activity could be compatible by finely modulating the expression of <I>CYR1</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In the yeast <I>Saccharomyces cerevisiae</I>, the Ras-cAMP pathway plays an important role in regulating the stress response and growth. </LI> <LI> Adenylate cyclase is encoded by the <I>CYR1</I> gene and plays the central role in the Ras-cAMP signalling pathway. </LI> <LI> Even if some methods about modifying <I>CYR1</I> to obtain stress-tolerant mutants had been reported, mutants with too low adenylate cyclase activity could not be commercially used because of the low growth and metabolite rates. </LI> <LI> To determine an appropriate activity of adenylate cyclase, the <I>CYR1</I> promoter was serially truncated from the 3′end by 30bp steps in our study. </LI> <LI> This new strategy had been used for increased yeast stress tolerance and improved ethanol fermentation performance by finely modulating the expression of <I>CYR1</I> in the yeast AY15 and also the yeast <I>Saccharomyces cerevisiae</I> background. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P> <P>The <I>CYR1</I> promoter was serially truncated from the 3′end by 30bp steps to finely modulating the activity of Adenylate cyclase, encoded by <I>CYR1</I> and synthesizing cAMP from ATP. The constructed mutants AY15a-90 and AY15a-120, whose promoters carry 90- and 120-bp truncations, showed a 2- and 3-fold drop in adenylate cyclase activity, and improved heat and ethanol tolerances than AY15a.</P>