Method for producing L-theanine via fermentation by a genetically engineered bacterium and the application thereof

A method for producing L-theanine via a fermentation by a genetically engineered bacterium, wherein the method is as follows:

• inoculating a seed solution into a fermentation medium by 10-15% inoculum size, wherein a pH value is controlled within 6.7-7.2 during the fermentation, a temperature is maintained within 28-36° C., and a dissolved oxygen is within 10-30%;
• adding a glucose solution by a fed-batch way to maintain a glucose concentration in the fermentation medium less than 1 g/L after glucose in the fermentation medium is completely consumed;
• wherein, an optical density-linked (OD-linked) ethylamine supplementary strategy is taken in the fermentation;
• when OD60onm is above 8-12, addition of ethylamine is started, and an ethylamine fed-batch rate (g-L−1-h−1) is adjusted for once every 0.8-1.2h;
• the ethylamine fed-batch rate (g-L−1.h−1)=0.5×OD600m value/(fermentation volume (L) x fermentation time (h));
• and
• the genetically engineered bacterium is obtained by serving a strain using a strain as an original strain, wherein the original strain is obtained after integrating a single copy of a RNA polymerase gene T7RNAP, a dual copy of a γ-glutamylmethylamide synthetase gene gmas, and a knockout of a xylose operon transcription factor gene xyIR and a knockout of a succinyl-CoA synthetase gene sucCD on a genome of Escherichia coli W3110, and then by integrating an exogenous fructose 6-phosphate phosphoketolase gene xfp, an exogenous phosphoacetyl transferase gene pta, an exogenous acetyl-CoA synthetase gene acs, an exogenous citrate synthase gene gltA, and an exogenous phosphoenolpyruvate carboxylase gene ppc on the genome, and knocking out an acetokinase gene ackA.