The Study Of Niacin And Arginine To Promote The Biosynthesis Of γ-Aminobutyric Acid In Lactobacillus Brevis

γ-aminobutyric acid is a naturally occurring non-protein amino acid that is widely found in plants,animals and microorganisms.GABA has been shown to improve brain function,improve memory,improve vision,benefit the liver and kidney,and lower blood pressure.In this study,Lactobacillus brevis TCCC 13007 obtained from laboratory filtering was used as the strain.Analysis of the mechanism of niacin to enhance GABA production in fermentation by L.brevis by using high performance liquid chromatography-mass spectrometry,the optimal chemically defined medium was determined by one-factor absence experiments and response surface experiments,optimization of fermentation media for whole-cell transformation,analysis of the mechanism by which arginine increases the efficiency of whole-cell transformation by gas chromatography-mass spectrometry were carried out.1.Analysis of the mechanism of niacin to enhance GABA production in fermentation by L.brevis by using LC-MS yielded 33 differential metabolites.The unsaturated fatty acid content was significantly higher in the experimental group with the addition of niacin than in the control group,while the saturated fatty acid content was significantly lower,inferring an increase in cell membrane permeability in the experimental group.The ability of niacin to increase the permeability of the cell membrane of L.brevis was demonstrated by the propidium iodide staining experiment.2.Nine of the twenty-eight compounds were identified by a one-factor absence experiment as being essential for the growth of the bacterium and six of the twenty-eight compounds were identified as having a promotion effect on the growth of the bacterium.The Plackett-Burman experiment was used to screen the three factors that had the greatest effect on the growth of the bacterium:arginine,serine and D-biotin.The optimum additions obtained using the steepest climb experiment were 1.6 g/L arginine,0.6 g/L serine and 0.05 g/L D-biotin.The Box-Behnken design demonstrated the interaction of the three factors to obtain the best concentration of arginine 1.68 g/L,serine 0.52 g/L and D-biotin 0.04 g/L.The optimized CDM was obtained by response surface experiments.The optimized CDM was demonstrated with an OD₆₀₀of 1.153after 13 h culture,a 13.4-fold increase over the original CDM.3.Single-factor and orthogonal tests for arginine,glucose,yeast extract,monosodium glutamate and D-biotin were carried out to obtain the best fermentation medium for whole-cell transformation:glucose 15 g/L,yeast extract 15 g/L,arginine0.5 g/L,D-biotin 0.06 g/L.The bacteria were fermented in the optimal fermentation medium for 24 h with an OD₆₀₀of 9.87,and then whole-cell transformed to produce GABA with a transformation yield of 103.67 g/L,a molar transformation rate of 95.6%for GABA.4.Analysis of the metabolic mechanism of arginine to improve the transformation efficiency of L.brevis using GC-MS resulted in fourteen differential metabolites.Pseudouridine,lysine,ornithine and glucose 6-phosphate were significantly higher in the experimental group with arginine than in the control group,demonstrating that arginine rapidly produces large amounts of ATP by way of the arginine deiminase pathway and that ATP is used to promote growth and expression of glutamic acid decarboxylase.