Abstract
Anaerobic fermentation using lignocellulosic hydrolysates as co-substrates is an economically attractive method to enhance 1,3-propanediol (1,3-PD) production by increasing the conversion yield from glycerol. Lignocellulosic hydrolysates contain the mixed sugars that are primarily glucose, xylose, and arabinose. Therefore, these three individual sugars were used, separately, as co-substrates with glycerol, in 1,3-PD production by a Clostridium diolis strain DSM 15410, resulting in an 18%–28% increase in the 1,3-PD yield. Co-fermentation of the mixed sugars and glycerol obtained a higher intracellular NADH/NAD+ ratio and increased the 1,3-PD yield by 22% relative to fermentation of glycerol alone. Thereafter, two kinds of lignocellulosic hydrolysates, corn stover hydrolysate and corncob molasses, were individually co-fermented with glycerol. The maximum 1,3-PD yield from glycerol reached 0.85 mol/mol. Fed-batch co-fermentation was also performed, improving the 1,3-PD yield (from 0.62 mol/mol to 0.82 mol/mol). These results demonstrate that the co-fermentation strategy is an efficient and economical way to produce 1,3-PD from glycerol.
Highlights
Driven by energy insecurity and environmental concerns, the sustainable production of chemicals, fuels, and materials has drawn increasing attention recently[1]
The effects of sugar addition on the intracellular NADH/NAD+ ratio and mRNA levels of the key genes involved in glycerol metabolism were investigated
Glycerol-glucose, glycerol-xylose, and glycerol-arabinose co-utilization by C. diolis DSM 15410 was first carried out to investigate the effects of sugar addition on glycerol utilization and 1,3-PD production
Summary
Co-fermentation of glycerol and glucose, xylose, or arabinose. Lignocellulosic hydrolysates, such as corn stover hydrolysate and corncob molasses, mainly contain glucose, xylose, and arabinose. Batch fermentation was performed using 20.0 g/L of glycerol and 10.0 g/L of mixed sugars including glucose, xylose, and arabinose (mass ratio = 1:1:1) as carbon sources. During the co-fermentation process, no apparent inhibition of glycerol utilization and 1,3-PD production was observed, suggesting that the addition of glucose, xylose, and arabinose mixtures did not repress the glycerol metabolism pathway significantly. Variations in the 1,3-PD production rate basically followed the NADH/NAD+ ratio, which suggested that NADH/NAD+ levels played a crucial role in NADH-dependent pathways such as 1,3-PD synthesis This result demonstrates that co-fermentation of glycerol and sugar mixtures contained in lignocellulosic hydrolysates can efficiently increase the level of intracellular reducing equivalents, which can further increase the 1,3-PD conversion yield. To investigate the effect of total sugar concentration on 1,3-PD production and save the cost of substrates, the ratios of glycerol to total sugars of corn stover hydolysate
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