Obtaining of osmoresistant mutants in L-histidine-producing coryneform bacterium to improve efficiency of target amino acid biosynthesis

Background: L-histidine, an essential amino acid, plays an important role in the regulation of vital metabolic processes in living organisms. Global L-histidine production was valued at $0.24 billion in 2024 and is expected to double by 2033. This amino acid is utilized extensively in the pharmaceutical, food, and livestock industries. 75% of the world's L-histidine is produced by microbial means, with coryneform bacteria being the predominant organism. Coryneform bacteria are a valuable model for studying the response of bacteria to osmotic stress. Increased osmotic pressure in the fermentation process is observed due to the changing composition of the nutrient medium during the synthesis of the target amino acid, which has a negative effect on bacterial cells. To increase survival under such conditions without altering metabolic functions, microorganisms synthesize substances called osmolytes, one of which is the amino acid L-histidine. Objective: The aim of this study is to obtain osmotolerant coryneform L-histidine producer mutants and evaluate their synthesizing activity in increased osmotic pressure. Methods: Osmotolerant mutants were obtained from the L-histidine producer Brevibacterium flavum LGS2 by chemical mutagenesis using 1-methyl-3-nitro-1-nitrosoguanidine. The impact of elevated osmotic pressure on the synthesis of the target amino acid was determined in submerged fermentation within a shaker incubator at 220 rpm, 30°C for 72 hours. The amount of histidine was determined by thin-layer chromatography. Results: Chemical mutagenesis, excluding gene-modifying technologies, was employed to obtain 16 osmoresistant mutants of B. flavum LGS2 capable of growing in mediums containing concentrations greater than or equal to 0.5 M NaCl. The findings indicated that three mutants demonstrated the highest yield, with an average production of 21.6 g/L L-histidine, in comparison to the 16.5 g/L produced by the control strain. Conclusion: In the study, the obtained osmoresistant mutants exhibited an increased level of L-histidine synthesis, exceeding the productivity of the initial strain by an average of 13.2%. The scientific innovation of this research lies in its practical application of mutations that increase osmotic pressure resistance, addressing real-world issues. This shows the potential for improving the productivity of industrial strains that produce L-histidine. Keywords: biologically active compound, L-histidine, strain-producer, chemical mutagenesis, osmoresistant mutant