Lysine production from the sugar alcohol mannitol: Design of the cell factory Corynebacterium glutamicum SEA-3 through integrated analysis and engineering of metabolic pathway fluxes
2018
Hoffmann, Sarah Lisa | Jungmann, Lukas | Schiefelbein, Sarah | Peyriga, Lindsay | Cahoreau, Edern | Portais, Jean-Charles | Becker, Judith | Wittmann, Christoph
The amino acid lysine is among the world’s most important biotechnological products, and enabling its manufacture from the most attractive new materials is an ever-present challenge. In this study, we describe a cell factory of Corynebacterium glutamicum, which produces lysine from mannitol. A preliminary mutant C. glutamicum SEA-1 obtained by the deletion of the mannitol repressor MtlR in the glucose-based, lysine-producing strain C. glutamicum LYS-12 produced only small amounts of lysine. This limitation was due to a significant accumulation of fructose and a limited NADPH supply, which caused a low flux of only 6% into the oxidative pentose phosphate (PP) pathway. Subsequent expression of fructokinase slightly increased production but failed to substantially redirect the flux from the Emden-Meyerhof-Parnas (EMP) pathway to the PP pathway. This suggested the design of C. glutamicum SEA-3, which overexpressed the NADP-dependent glyceraldehyde 3-phosphate dehydrogenase GapN from Streptococcus mutans and coupled the EMP pathway flux to NADPH formation. When grown on mannitol, the SEA-3 strain had a lysine yield of 0.24 mol mol⁻¹ and a specific productivity of 1.3 mmol g⁻¹ h⁻¹, approximately 60% and 75% higher, respectively, than those of the basic producer SEA-1. A computational pathway analysis revealed that this design would potentially enable a lysine yield of 0.9 mol mol⁻¹, providing room for further development. Our findings open new avenues for lysine production from marine macroalgae, which is farmed globally as an attractive third-generation renewable resource. Mannitol is a major constituent of these algae (up to 30% and higher) and can be easily extracted from their biomass with hot water.
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