Breeding Of L-Serine Producer And Its Optimizing Conditions In Fermentation

Though L-serine is unnecessary in human bodies, it takes part in many physiologicalactivities and compound synthesis as intermediate. It also has been extensively used in chemistry,pharmaceutical industry, cosmetic and food. Screening and breeding of L-serine producer,methods of quantificational analysis and suitable fermentation conditions of shaking flask werestudies in this paper. The main research contents and results are as follows:The concentrations of L-serine and glycine in broth were qualitatively and quantitativelydetermined with paper chromatography and spectrophotometer. The determination conditions ofL-serine and glycine were established. The relationship between the content of L-serine in brothand the absorbency could be described by a expression. It was showed that the method has a highaccuracy and precision in the determination of L-serine and glycine. The method was also easyto operate and suitable for the screening of strains producing L-serineA bacterium, strain A3, which was isolated as an L-serine producer, was identified asMicrococcaceae on the basis of Bergey's Manual of Determinative bacteriology. The strainexcreted 1.4g/L L-serine when glycine was 20g/L in a medium.L-serine producer was derived from the parental strain A3 by chemical and physicalmutation methods, the plate screening with amino acid analogues: sulfaguanidine(SG),ethionine(Eth) and used glycine as sole carbon source. L-serine production by new mutant strainS63-31 with multiple resistant to amino acid analogues is increased to 6.5g/L underun-optimization condition.The effects of medium composition and fermentation conditions on L-serine production inflask were considered. The optimal seed medium compositions were determined as: glucose20g/L,corn steep liquor 25g/L, (NH4)2SO4 10 g/L, KH2PO4 1 g/L, MgSO4·7 H2O 0.2 g/L, CaCO320, pH7.0~7.2. The optimal fermentation medium compositions were determined as: glycine20g/L,corn steep liquor 15g/L, (NH4)2SO4 15 g/L, KH2PO4 2 g/L, MgSO4·7 H2O 0.4 g/L, CaCO320, pH8.0. It shows that L-serine increased in broth when suitable malonate, thrine and lowconcentration SDS was added to the broth. The yield of L-serine maintained at 7.36g/L with a26.27% molar conversion of glycine.