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Applied and Environmental Microbiology, February 2007, p. 750-755, Vol. 73, No. 3
0099-2240/07/$08.00+0     doi:10.1128/AEM.02208-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Reduced Folate Supply as a Key to Enhanced L-Serine Production by Corynebacterium glutamicum{triangledown}

Michael Stolz,1 Petra Peters-Wendisch,1 Helga Etterich,1 Tanja Gerharz,2 Robert Faurie,2 Hermann Sahm,1 Holger Fersterra,3 and Lothar Eggeling1*

Institute for Biotechnology, Research Centre Juelich, 52425 Juelich, Germany,1 Amino GmbH, An der Zuckerraffinerie 10, 38373 Frellstedt, Germany,2 InnoSweet GmbH, Langer Kamp 5, 38106 Braunschweig, Germany3

Received 20 September 2006/ Accepted 18 November 2006

The amino acid L-serine is required for pharmaceutical purposes, and the availability of a sugar-based microbial process for its production is desirable. However, a number of intracellular utilization routes prevent overproduction of L-serine, with the essential serine hydroxymethyltransferase (SHMT) (glyA) probably occupying a key position. We found that constructs of Corynebacterium glutamicum strains where chromosomal glyA expression is dependent on Ptac and lacIQ are unstable, acquiring mutations in lacIQ, for instance. To overcome the inconvenient glyA expression control, we instead considered controlling SHMT activity by the availability of 5,6,7,8-tetrahydrofolate (THF). The pabAB and pabC genes of THF synthesis were identified and deleted in C. glutamicum, and the resulting strains were shown to require folate or 4-aminobenzoate for growth. Whereas the C. glutamicum {Delta}sdaA strain (pserACB) accumulates only traces of L-serine, with the C. glutamicum {Delta}pabABC{Delta}sdaA strain (pserACB), L-serine accumulation and growth responded in a dose-dependent manner to an external folate supply. At 0.1 mM folate, 81 mM L-serine accumulated. In a 20-liter controlled fed-batch culture, a 345 mM L-serine accumulation was achieved. Thus, an efficient and highly competitive process for microbial L-serine production is available.

* Corresponding author. Mailing address: Institute of Biotechnology, Research Centre Juelich, D-52425 Juelich, Germany. Phone: 0049 2461 615132. Fax: 0049 2461 612710. E-mail: l.eggeling{at}fz-juelich.de.

{triangledown} Published ahead of print on 1 December 2006.

Applied and Environmental Microbiology, February 2007, p. 750-755, Vol. 73, No. 3
0099-2240/07/$08.00+0     doi:10.1128/AEM.02208-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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