title: Xylitol production from xylose mother liquor: a novel strategy that combines the use of recombinant Bacillus subtilis and Candida maltosa.
abstract: BACKGROUND
  Xylose mother liquor has high concentrations of xylose (35%-40%) as well as other sugars such as L-arabinose (10%-15%), galactose (8%-10%), glucose (8%-10%), and other minor sugars. Due to the complexity of this mother liquor, further isolation of xylose by simple method is not possible. In China, more than 50,000 metric tons of xylose mother liquor was produced in 2009, and the management of sugars like xylose that present in the low-cost liquor is a problem.
  
  
  RESULTS
  We designed a novel strategy in which Bacillus subtilis and Candida maltosa were combined and used to convert xylose in this mother liquor to xylitol, a product of higher value. First, the xylose mother liquor was detoxified with the yeast C. maltosa to remove furfural and 5-hydromethylfurfural (HMF), which are inhibitors of B. subtilis growth. The glucose present in the mother liquor was also depleted by this yeast, which was an added advantage because glucose causes carbon catabolite repression in B. subtilis. This detoxification treatment resulted in an inhibitor-free mother liquor, and the C. maltosa cells could be reused as biocatalysts at a later stage to reduce xylose to xylitol. In the second step, a recombinant B. subtilis strain with a disrupted xylose isomerase gene was constructed. The detoxified xylose mother liquor was used as the medium for recombinant B. subtilis cultivation, and this led to L-arabinose depletion and xylose enrichment of the medium. In the third step, the xylose was further reduced to xylitol by C. maltosa cells, and crystallized xylitol was obtained from this yeast transformation medium. C. maltosa transformation of the xylose-enriched medium resulted in xylitol with 4.25 g L-1·h-1 volumetric productivity and 0.85 g xylitol/g xylose specific productivity.
  
  
  CONCLUSIONS
  In this study, we developed a biological method for the purification of xylose from xylose mother liquor and subsequent preparation of xylitol by C. maltosa-mediated biohydrogenation of xylose.
authors.affiliation: Laboratory of Microbial Metabolism and School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, 800# Dongchuan Road, Shanghai, China.
authors.forename: Hairong
authors.initials: H
authors.lastname: Cheng
authors.forename: Ben
authors.initials: B
authors.lastname: Wang
authors.forename: Jiyang
authors.initials: J
authors.lastname: Lv
authors.forename: Mingguo
authors.initials: M
authors.lastname: Jiang
authors.forename: Shuangjun
authors.initials: S
authors.lastname: Lin
authors.forename: Zixin
authors.initials: Z
authors.lastname: Deng
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000235:genetics / Q000378:metabolism; D001412:Bacillus subtilis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D002175:Candida / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D014993:Xylitol / Q000096:biosynthesis*; D014994:Xylose / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D014994:Xylose; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase; D014993:Xylitol