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.