Research Of L-Phenylalanine Fermentation Performance By PPC Knockout Strains Of Escherichia Coli

L-Phenylalanine (L-Phe) is a kind of essential amino acid that valuable for human being and animals. People could not supply L-Phe by themselves so they have to obtain it by food intake. L-Phe is widely used in Industrial fields such as food, medicine, dietary supplements and cosmetics. Microbial fermatation is mainly production method for L-Phe. It has advantage on cheaper raw materials and easier manipulation than other produce methods. Glucose considered the most frequently used carbon source because of fast utilized by organism. However, the low conversation makes it not efficient for whole fermentation process. The L-Phe yield of glucose is only0.275g·g-1that much less than many other amino acids. We wish to produce high concentration of L-Phe by efficiently using glucose with few cell mass. We selected a strain ppc knockout that blocked activity of phosphoenolpyruvate carboxylase which plays an anaplerotic role in replenishing intermediates in TCA cycle. The strains could stimulate more PEP consumed in biosynthetic of L-Phe and improved conversation from glucose in theory. The main studies are following:1ppc knocked out strains (ppc-) were not grown without addition in medium. L-Glutamate, L-Aspartate and citric acid supply intermediates of TCA cycle and they could satisfy condition of organism growth, ppc-strain reached1.15times as much L-Phe as control strain in condition of adding L-Gln by concentration of1g·L-1after12h.2ppc-deficient mutation strains enhanced acetic acid production because carbon fluxes would enter pyruvate synthesis route instead of supplying aromatic amino acid biosynthesis. In our experiments double deficient strains both ppc and pykA pykF had a positive effect on producing L-Phe.3In this study we used fed-batch process and DO-stat strategy for L-Phe fermatation by2.5liter fermenter. The results showed the maximal L-Phe concentration reached22.4g·L-1at37h while DCW is12.7g·L-1. The L-Phe yield of glucose achieved0.33g-g-1equal72%in theoretical conversation and reached1.74fold to ppc+strains. Compared with control strains, the fermatation of ppc-strains demonstrated more effective on production by less biomass, which can save energy power and oxygen system in fermentation process.