Fermentation Kinetics for Xylitol Production by a Pichia stipitis d-Xylulokinase Mutant Previously Grown in Spent Sulfite Liquor

Abstract

Spent sulfite pulping liquor (SSL) contains lignin, which is present as lignosulfonate, and hemicelluloses that are present as hydrolyzed carbohydrates. To reduce the biological oxygen demand of SSL associated with dissolved sugars, we studied the capacity of Pichia stipitis FPL-YS30 (xyl3Delta) to convert these sugars into useful products. FPL-YS30 produces a negligible amount of ethanol while converting xylose into xylitol. This work describes the xylose fermentation kinetics of yeast strain P.stipitis FPL-YS30. Yeast was grown in rich medium supplemented with different carbon sources: glucose, xylose, or ammonia-base SSL. The SSL and glucose-acclimatized cells showed similar maximum specific growth rates (0.146 h(-1)). The highest xylose consumption at the beginning of the fermentation process occurred using cells precultivated in xylose, which showed relatively high specific activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49). However, the maximum specific rates of xylose consumption (0.19 g(xylose)/g(cel) h) and xylitol production (0.059 g(xylitol)/g(cel) h) were obtained with cells acclimatized in glucose, in which the ratio between xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) was kept at higher level (0.82). In this case, xylitol production (31.6 g/l) was 19 and 8% higher than in SSL and xylose-acclimatized cells, respectively. Maximum glycerol (6.26 g/l) and arabitol (0.206 g/l) production were obtained using SSL and xylose-acclimatized cells, respectively. The medium composition used for the yeast precultivation directly reflected their xylose fermentation performance. The SSL could be used as a carbon source for cell production. However, the inoculum condition to obtain a high cell concentration in SSL needs to be optimized.

Conversion of rice straw to bio-based chemicals: an integrated process using Lactobacillus brevis

“…Various researchers have sought to identify or engineer strains capable of efficient utilization of the pentose derived from hemicellulose (Du Preez and Van Der Walt 1983; Zhang et al 1995; Ho et al 1998; Jeffries 2006; Rodrigues et al 2008). In most cases, however, glucose suppressed the consumption of pentoses showing a typical sequential utilization of mixed sugars (Laplace et al 1993; Lawford et al 1998, 2000; Mohagheghi et al 1998).…”

Biological and Pharmacological Potential of Xylitol: A Molecular Insight of Unique Metabolism

“…Thus, the microbes with active xylose reductase pathway are possible biocatalysts for xylitol production at a large scale. Although "pathway B" predominates in fungi, e.g., Aspergillus niger [15], yeast, e.g., Candida guilliermondii [16], Pichia spitis [17], Pichia caribbica [18] and Scheffersomyces amazonensis [19], and dairy yeast, e.g., Kluyveromyces marxianus [20], but few bacteria, e.g., Enterobacter sp. [21], Corynebacterium, Enterobacter [22], Bacillus and Pseudomonas [23], were also reported for xylitol production (Table 3).…”

Pichia stipitisgenomics, transcriptomics, and gene clusters

“…Pichia stipitis also has a number of other bioconversion-related traits: it modifies low-molecular-weight lignin moieties ( Targonski, 1992 ), reduces acyclic enones to the corresponding alcohols ( Conceicao et al , 2003 ), forms various esters and aroma components ( Fuganti et al , 1993 ) and can be engineered to produce lactic acid ( Ilmen et al , 2007 ) or xylitol ( Kim et al , 2001 ; Rodrigues et al , 2008 ;) in high yield. Strains of P. stipitis have also been selected for resistance to furfural and hydroxy-methyl furfural ( Liu et al , 2005 ).…”