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°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