Biotechnological production of L-ribose from L-arabinose.

L-Ribose is a rare and expensive sugar that can be used as a precursor for the production of L-nucleoside analogues, which are used as antiviral drugs. In this work, we describe a novel way of producing L-ribose from the readily available raw material L-arabinose. This was achieved by introducing L-ribose isomerase activity into L-ribulokinase-deficient Escherichia coli UP1110 and Lactobacillus plantarum BPT197 strains. The process for L-ribose production by resting cells was investigated. The initial L-ribose production rates at 39 degrees C and pH 8 were 0.46 +/- 0.01 g g(-1) h(-1) (1.84 +/- 0.03 g l(-1) h(-1)) and 0.27 +/- 0.01 g g(-1) h(-1) (1.91 +/- 0.1 g l(-1) h(-1)) for E. coli and for L. plantarum, respectively. Conversions were around 20% at their highest in the experiments. Also partially purified protein precipitates having both L-arabinose isomerase and L-ribose isomerase activity were successfully used for converting L-arabinose to L-ribose.

Metabolic engineering of Lactobacillus plantarum for production of L-ribulose.

L-Ribulose is a rare and expensive sugar that can be used as a precursor for the production of other rare sugars of high market value such as L-ribose. In this work we describe a production process for L-ribulose using L-arabinose, a common component of polymers of lignocellulosic materials, as the starting material. A ribulokinase-deficient mutant of the heterofermentative lactic acid bacterium Lactobacillus plantarum NCIMB8826 was constructed. Expression of araA, which encodes the critical enzyme L-arabinose isomerase, was repressed by high glucose concentrations in batch cultivations. A fed-batch cultivation strategy was therefore used to maximize L-arabinose isomerase production during growth. Resting cells of the ribulokinase-deficient mutant were used for the production of L-ribulose. The isomerization of L-arabinose to L-ribulose was very unfavorable for L-ribulose formation. However, high L-ribulose yields were obtained by complexing the produced L-ribulose with borate. The process for L-ribulose production in borate buffer by resting cells was optimized using central composite designs. The experiment design suggested that the process has an optimal operation point around an L-arabinose concentration of 100 g liter(-1), a borate concentration of 500 mM, and a temperature of 48 degrees C, where the statistical software predicted an initial L-ribulose production rate of 29.1 g liter(-1) h(-1), a best-achievable process productivity of 14.8 g liter(-1) h(-1), and a conversion of L-arabinose to L-ribulose of 0.70 mol mol(-1).