Adaptation yields a highly efficient xylose‐fermenting Zymomonas mobilis strain

Abstract

Zymomonas mobilis is a superb ethanol producer with productivity exceeding yeast strains by several fold. Although metabolic engineering was successfully applied to expand its substrate range to include xylose, xylose fermentation lagged far behind glucose. In addition, xylose fermentation was often incomplete when its initial concentration was higher than 5%. Improvement of xylose fermentation is therefore necessary. In this work, we applied adaptation to improve xylose fermentation in metabolically engineered strains. As a result of adaptation over 80 days and 30 serial transfers in a medium containing high concentration of xylose, a strain, referred as A3, with markedly improved xylose metabolism was obtained. The strain was able to grow on 10% (w/v) xylose and rapidly ferment xylose to ethanol within 2 days and retained high ethanol yield. Similarly, in mixed glucose-xylose fermentation, a total of 9% (w/v) ethanol was obtained from two doses of 5% glucose and 5% xylose (or a total of 10% glucose and 10% xylose). Further investigation reveals evidence for an altered xylitol metabolism in A3 with reduced xylitol formation. Additionally xylitol tolerance in A3 was increased. Furthermore, xylose isomerase activity was increased by several times in A3, allowing cells to channel more xylose to ethanol than to xylitol. Taken together, these results strongly suggest that altered xylitol metabolism is key to improved xylose metabolism in adapted A3 strain. This work further demonstrates that adaptation and metabolic engineering can be used synergistically for strain improvement.

METABOLIC ADAPTATION STRATEGY USING Zymomonas mobilis CP4 CELLS FOR THE PRODUCTION OF SECOND GENERATION ETHANOL

“…Agrawall et al [36] also reported that metabolic adaptation was essential for ethanol production by modified strains ofZ. mobilis ZM4 (pZB5).…”

“…Therefore, although improvements regarding fermentation with this genetically modified Z. mobilis are still needed, the fermentation time and the ability to ferment xylose were both improved. Figure 3 summarizes the metabolic adaptation process insynthetic medium, suggesting that the recombinant Z. mobilis colonies increased ethanol production in the earlier cycles (1-30)but maintained such levels in subsequent cycles (31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50). This strategy allowed the recombinant to produce ethanol from xylose more efficiently becausehigher participation in ethanol production is derived from this pentose in the latter cycles.…”

Optimization of key factors affecting hydrogen production from sugarcane bagasse by thermophilic anaerobic pure culture

“…Hence, the discovery of a strain with the capacity to co-utilize all of the sugars derived from biomass is one of the main tasks in cellulosic energy production [38]. Although several genetic and evolutionary engineering approaches achieved efficient pentose utilization in some industrial cell factories, such as those using Zymomonas mobilis [39] and Saccharomyces cerevisiae [40], CCR still remains a major bottleneck. However, it is encouraging that SCUT27/Δldh could consume hexose and pentose almost simultaneously in the SCB hydrolysate, as this could be advantageous in improving productivity and shortening fermentation time in lignocellulosic fuel production.…”

Rewiring carbon catabolite repression for microbial cell factory

“…(8,(53)(54)(55)(56). Several genetic and evolutionary engineering approaches helped achieve efficient pentose utilization in Z. mobilis and S. cerevisiae (57). Substrate ranges of the above mentioned recombinant strains were also expanded to utilize the disaccharide cellobiose (58)(59)(60).…”