Metabolic Engineering of Lactobacillus plantarum for Production of l -Ribulose

Abstract

ABSTRACT 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 .