Metabolic engineering of cobalamin (vitamin B12) production in Bacillus megaterium |
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Authors: | Rebekka Biedendieck Marco Malten Heiko Barg Boyke Bunk Jan‐Henning Martens Evelyne Deery Helen Leech Martin J. Warren Dieter Jahn |
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Affiliation: | 1.Protein Science Group, Department of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, UK.;2.Novozymes A/S, Krogshøjvej 36, 2880 Bagsvaerd, Denmark.;3.BASF SE, Carl‐Bosch‐Strasse 38, 67056 Ludwigshafen, Germany.;4.Institute of Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany.;5.ALEXIS Corporation, Industriestrasse 17, 4415 Lausen, Switzerland. |
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Abstract: | Cobalamin (vitamin B12) production in Bacillus megaterium has served as a model system for the systematic evaluation of single and multiple directed molecular and genetic optimization strategies. Plasmid and genome-based overexpression of genes involved in vitamin B12 biosynthesis, including cbiX, sirA, modified hemA, the operons hemAXCDBL and cbiXJCDETLFGAcysGAcbiYbtuR, and the regulatory gene fnr, significantly increased cobalamin production. To reduce flux along the heme branch of the tetrapyrrole pathway, an antisense RNA strategy involving silencing of the hemZ gene encoding coproporphyrinogen III oxidase was successfully employed. Feedback inhibition of the initial enzyme of the tetrapyrrole biosynthesis, HemA, by heme was overcome by stabilized enzyme overproduction. Similarly, the removal of the B12 riboswitch upstream of the cbiXJCDETLFGAcysGAcbiYbtuR operon and the recombinant production of three different vitamin B12 binding proteins (glutamate mutase GlmS, ribonucleotide triphosphate reductase RtpR and methionine synthase MetH) partly abolished B12-dependent feedback inhibition. All these strategies increased cobalamin production in B. megaterium. Finally, combinations of these strategies enhanced the overall intracellular vitamin B12 concentrations but also reduced the volumetric cellular amounts by placing the organism under metabolic stress. |
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