ORIGINAL PAPER Alginate immobilization of recombinant Escherichia coli whole cells harboring L-arabinose isomerase for L-ribulose production Ye-Wang Zhang • Ponnandy Prabhu • Jung-Kul Lee Received: 28 August 2009 / Accepted: 9 November 2009 Ó Springer-Verlag 2009 Abstract Recombinant Escherichia coli whole cells harboring Bacillus licheniformis L-arabinose isomerase (BLAI) were immobilized with alginate. The operational conditions for immobilization were optimized with response surface methodology. Optimal alginate concen- tration, Ca 2? concentration, and cell mass loading were 1.8% (w/v), 0.1 M, and 44.5 g L -1 , respectively. The interactions between Ca 2? concentration, alginate concen- tration, and initial cell mass were significant. After immobilization of BLAI, cross-linking with 0.1% glutar- aldehyde significantly reduced cell leakage. The half-life of immobilized whole cells was 150 days, which was 50-fold longer than that of free cells. In seven repeated batches for L-ribulose production, the productivity was as high as 56.7 g L -1 h -1 at 400 g L -1 substrate concentration. The immobilized cells retained 89% of the initial yield after 33 days of reaction. Immobilization of whole cells har- boring BLAI, therefore, makes a suitable biocatalyst for the production of L-ribulose, particularly because of its high stability and low cost. Keywords L-Arabinose isomerase  Immobilization  L-Ribulose  RSM Introduction Alginate is a naturally occurring binary linear heteropolymer that contains 1,4-linked b-D-mannuronic and a-L-guluronic acid residues. It is one of the best candidate matrixes for entrapment because of its good biocompatibility and pro- cessing capacity [1, 2]. Entrapment is one of the simplest methods available for enzyme or cell immobilization under mild conditions, and results in minimal denaturation of the immobilized biocatalyst compared with other immobiliza- tion methods [3]. Rare sugars are unique monosaccharides or derivatives that rarely occur in nature. They are expected to have a wide range of uses, from sweeteners to functional foods and drugs. L-Ribulose is an important rare sugar that can be used as a precursor for the synthesis of antiviral drugs. It can be manufactured through chemical procedures from L-arabinose [4], D-ribose [5], or D-mannono-1,4-lactone [6]. However, production of L-ribulose by biocatalysis using L-arabinose isomerase (L-AI, EC 5.3.1.4) can be a valuable industrial process. The starting material is L-arabinose, a common component of lignocellulosic materials, which has a cost estimate of around only $0.10 per kg [7]. Thus, the cost of the biocatalyst, L-AI, is the main obstacle to the industrialization of biological L-ribulose production. Although L-AIs from different microorganisms, such as Escherichia coli [8], Thermoanaerobacter mathranii [9], Thermotoga neapolitana [10], Thermotoga maritima [11], Geobacillus stearothermophilus, and Alicyclobacillus acidocaldarius [12], have been cloned and characterized, the specificity and productivity of conversion of L-arabinose to Y.-W. Zhang  J.-K. Lee (&) Department of Chemical Engineering, Konkuk University, 1 Hwayang-Dong, Gwangjin-Gu, Seoul 143-701, Korea e-mail: jkrhee@konkuk.ac.kr P. Prabhu Department of Bioscience and Biotechnology, Konkuk University, 1 Hwayang-Dong, Gwangjin-Gu, Seoul 143-701, Korea J.-K. Lee Institute of Biomedical Science and Technology, Konkuk University, 1 Hwayang-Dong, Gwangjin-Gu, Seoul 143-701, Korea 123 Bioprocess Biosyst Eng DOI 10.1007/s00449-009-0397-7