L-Ribose production from L-arabinose by immobilized recombinant Escherichia coli co-expressing the L-arabinose isomerase and mannose-6-phosphate isomerase genes from Geobacillus thermodenitrificans.

L-Ribose is an important precursor for antiviral agents, and thus its high-level production is urgently demanded. For this aim, immobilized recombinant Escherichia coli cells expressing the L-arabinose isomerase and variant mannose-6-phosphate isomerase genes from Geobacillus thermodenitrificans were developed. The immobilized cells produced 99 g/l L-ribose from 300 g/l L-arabinose in 3 h at pH 7.5 and 60 °C in the presence of 1 mM Co(2+), with a conversion yield of 33 % (w/w) and a productivity of 33 g/l/h. The immobilized cells in the packed-bed bioreactor at a dilution rate of 0.2 h(-1) produced an average of 100 g/l L-ribose with a conversion yield of 33 % and a productivity of 5.0 g/l/h for the first 12 days, and the operational half-life in the bioreactor was 28 days. Our study is first verification for L-ribose production by long-term operation and feasible for cost-effective commercialization. The immobilized cells in the present study also showed the highest conversion yield among processes from L-arabinose as the substrate.