Comparison with the xylose utilization capacity of xylose isomerases and xylulose kinases from different sources
Xylose isomerase (xylA ) and xylulose kinase (xylB ) exist in the form of gene clusters. The xylose isomerase metabolic pathway from different sources established in C. glutamicum have different xylose utilization capacities, this might be the result of the genetic codon preference between the xylAB source strain andC. glutamicum (Meiswinkel et al., 2013). The xylAB genes derived from E. coli MG1655 and X. campestris were expressed under IPTG induced vector pXMJ19, in which the Ptac is the promoter for gene expression. The resulting expression plasmids were labeled p19Plac-EcoAB and p19Ptac-XcaAB. The two plasmids were transformed into C. glutamicum SO26, resulted the C. glutamicum EAB and XAB. Fig.2a showed the growth curve and xylose consumption of strain EAB and XAB during 72h fermentation. The results indicated that xylAB from X. campestris achieved higher xylose consumption (45.1 g/L) compared with xylAB fromE. coli MG1655 (25.0 g/L). The growth OD600increased from 12.05 (EAB) to 12.95 (XAB). The L-ornithine concentration in the supernatant of fermentation was determined (Fig.2b). The L-ornithine production titer of the strain XAB (21.6 ± 0.19 g/L) is 18.7% higher than strain EAB (18.2 ± 0.35 g/L), and the corresponding xylose yield of XAB is 0.48 g/g. The C. glutamicum XAB demonstrated the better capacity of xylose utilization and L-ornithine synthesis than strain EAB.