Razie Robatjazi - Department of Biotechnology, Iranian Research Organization for Science and Technology, Tehran, Iran
Mehrdad Azin - Department of Biotechnology, Iranian Research Organization for Science and Technology, Tehran, Iran
Hadis Aryaee - Department of Biotechnology, Iranian Research Organization for Science and Technology, Tehran, Iran

BACKGROUND AND OBJECTIVESThe industrial microbiological production of the L-lysine amino acid through fermentation is of significant importance. This amino acid finds wide application in food supplements, additives, therapeutic agents, peptide synthesis precursors, agricultural chemicals, and various industries. Consequently, optimizing and economizing its production process is crucial. One of the primary sources of this amino acid is the genetically modified strain of Corynebacterium glutamicum. This study aimed to optimize the use of different carbon sources at varying concentrations to enhance the production of L-lysine.MATERIALS AND METHODSThe study utilized Corynebacterium glutamicum PTCC ۱۶۰۶, a double auxotrophic mutant (Met-, Thr-) procured from the Iranian Research Organization for Scientific and Technology. Optimization of L-lysine production was achieved through the use of varying carbon sources at different concentrations. The Chinard method was employed for the analytical estimation of L-lysine acid, while the sugar content of the production culture was measured using the DNS method. The process was subsequently scaled up to a ۱۰-liter fermenter in batch and fed-batch modes.RESULTS AND DISCUSSIONThe optimized culture medium contained ۱۳% (w/v) dextrose. It was observed that a two-stage fed-batch fermentation using ۵% dextrose and ۱% CSL resulted in L-lysine production ranging between ۷۲ to ۹۱ g/L. The lysine production by this condition was ۵۷g/l more than the batch culture. The findings suggest that dextrose, as a carbon source, positively impacts the production of lysine. Furthermore, C. glutamicum produces L-lysine, L-methionine, L-threonine, and L-isoleucine amino acids via the aspartate pathway. Using the double auxotroph strain for L-methionine and L-threonine enhances carbon flux in favor of lysine production.CONCLUSIONThe study data suggests a ۶۰% increase in lysine production. Increasing dextrose and the presence of L-methionine and L-threonine in the culture medium of the auxotrophic mutant C. glutamicum, in conjunction with sufficient aeration in the fermenter, augments the production of L-lysine. Obviously, A two-stage fed batch culture create a significant increase in the product concentration.

Corynebacterium glutamicum, L-lysine, fed-batch fermentation, auxotrophic mutant