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Applied and Environmental Microbiology, November 2007, p. 7083-7091, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.01180-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Metabolic Engineering of Lactobacillus plantarum for Production of L-Ribulose

M. Helanto,^* K. Kiviharju, M. Leisola, and A. Nyyssölä

Laboratory of Bioprocess Engineering, Department of Chemical Technology, Helsinki University of Technology, P.O. Box 6100, FIN-02015 Espoo, Finland

Received 25 May 2007/ Accepted 2 September 2007

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.

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* Corresponding author. Mailing address: Laboratory of Bioprocess Engineering, Department of Chemical Technology, Helsinki University of Technology, P.O. Box 6100, FIN-02015 Espoo, Finland. Phone: 358 9 4512577. Fax: 358 9 462 373. E-mail: miia.helanto{at}tkk.fi

Published ahead of print on 14 September 2007.

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Applied and Environmental Microbiology, November 2007, p. 7083-7091, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.01180-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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