초록
<P><B>Background</B></P><P>Alkali used for pH control during fermentation and acidification for downstream recovery of succinic acid (SA) are the two largest cost contributors for bio-based SA production. To promote the commercialization process of fermentative SA, the development of industrially important microorganisms that can tolerate low pH has emerged as a crucial issue.</P><P><B>Results</B></P><P>In this study, an in situ fibrous bed bioreactor (isFBB) was employed for the metabolic evolution for selection of <I>Y. lipolytica</I> strain that can produce SA at low pH using glucose-based medium. An evolved strain named <I>Y. lipolytica</I> PSA3.0 that could produce SA with a titer of 19.3 g/L, productivity of 0.52 g/L/h, and yield of 0.29 g/g at pH 3.0 from YPD was achieved. The enzyme activity analysis demonstrated that the pathway from pyruvate to acetate was partially blocked in <I>Y. lipolytica</I> PSA3.0 after the evolution, which is beneficial to cell growth and SA production at low pH. When free-cell batch fermentations were performed using the parent and evolved strains separately, the evolved strain PSA3.0 produced 18.4 g/L SA with a yield of 0.23 g/g at pH 3.0. Although these values were lower than that obtained by the parent strain PSA02004 at its optimal pH 6.0, which were 25.2 g/L and 0.31 g/g, respectively, they were 4.8 and 4.6 times higher than that achieved by PSA02004 at pH 3.0. By fed-batch fermentation, the resultant SA titer of 76.8 g/L was obtained, which is the highest value that ever achieved from glucose-based medium at low pH, to date. When using mixed food waste (MFW) hydrolysate as substrate, 18.9 g/L SA was produced with an SA yield of 0.38 g/g, which demonstrates the feasibility of using low-cost glucose-based hydrolysate for SA production by <I>Y.</I> <I>lipolytica</I> in a low-pH environment.</P><P><B>Conclusions</B></P><P>This study presents an effective and efficient strategy for the evolution of <I>Y. lipolytica</I> for SA production under low-pH condition for the first time. The isFBB was demonstrated to improve the metabolic evolution efficiency of <I>Y. lipolytica</I> to the acidic condition. Moreover, the acetate accumulation was found to be the major reason for the inhibition of SA production at low pH by <I>Y. lipolytica</I>, which suggested the direction for further metabolic modification of the strain for improved SA production. Furthermore, the evolved strain <I>Y. lipolytica</I> PSA3.0 was demonstrated to utilize glucose-rich hydrolysate from MFW for fermentative SA production at low pH. Similarly, <I>Y.</I> <I>lipolytica</I> PSA3.0 is expected to utilize the glucose-rich hydrolysate generated from other carbohydrate-rich waste streams for SA production. This study paves the way for the commercialization of bio-based SA and contributes to the sustainable development of a green economy.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s13068-018-1233-6) contains supplementary material, which is available to authorized users.</P>