Mutagenesis and selective breeding of high ε-poly-L-lysine producing strain

e-poly-L-lysine(e-PL)is an L-lysine linear homopolymer,which was produced by bacteria belonging to the family Streptomycetaceae and ergot fungi.However,the production of wild strain is very low,limiting further study and utilization.For most bacteria including Streptomyces genus,L-lysine,a precursor of e-PL,is biosynthesized by the L-aspartate pathway.Aspartokinase(Ask),which is the first key enzyme in this pathway,is subject to complex regulation such as through feedback inhibition by the end-product amino acids.In addition,phosphoenolpyruvate carboxykinase is feedback-regulated by the L-aspartate.In order to remove these feedback inhibitions and to improve e-PL productivity,the resistant mutants were obtained,using sulfaguanidine(SG)+glycine+L-lysine+DL-3-hydroxynorvaline(AHV)as selective markers.Finally,a e-PL-producing strain,Streptomyces diastatochromogenes L9 were obtained.The productivity of this strain during flask fermentation was improved to 0.69g/L,which was 13% higher than that of the original strain.Moreover,its fermentation performance and genetic characteristics were very stable.