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Appl. Environ. Microbiol. doi:10.1128/AEM.01180-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Metabolic engineering of Lactobacillus plantarum for production of L-ribulose

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

^* To whom correspondence should be addressed. Email: miia.helanto{at}tkk.fi.

	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 heterofermenatative 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. 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 isomerisation of L-arabinose to L-ribulose was very unfavourable 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 L-arabinose concentration (c_A) 100 g l^-1, borate concentration (c_B) 500 mM and temperature (T) 48^oC, where the statistical software predicted initial L-ribulose production rate (r_i) 29.1 g l^-1 h^-1, best achievable process productivity (r_max) 14.8 g l^-1 h^-1 and conversion of L-arabinose to L-ribulose (x) 0.70 mol mol^-1.

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