title: Transductional construction of a threonine-hyperproducing strain of Serratia marcescens: lack of feedback controls of three aspartokinases and two homoserine dehydrogenases.
abstract: To construct a threonine-hyperproducing strain of Serratia marcescens Sr41, the six regulatory mutations for three aspartokinases and two homoserine dehydrogenases were combined in a single strain by three transductional crosses. The constructed strain, T-1026, carried the lysC1 mutation leading to lack of feedback inhibition and repression of aspartokinase III, the thrA1(1) mutation desensitizing aspartokinase I to feedback inhibition, the thrA2(1) mutation releasing feedback inhibition of homoserine dehydrogenase I, the two hnr mutations derepressing aspartokinase I and homoserine dehydrogenase I, and the etr-1 mutation derepressing aspartokinase II and homoserine dehydrogenase II. The strain produced ca. 40 mg of threonine per ml of medium containing sucrose and urea. Furthermore, the productivity of strain T-1026 was compared with those of strains devoid of more than one of the six regulatory mutations.
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics*; D001222:Aspartate Kinase / Q000235:genetics*; D005246:Feedback; D005838:Genotype; D006715:Homoserine Dehydrogenase / Q000235:genetics*; D007527:Isoenzymes / Q000235:genetics*; D010770:Phosphotransferases / Q000235:genetics*; D012706:Serratia marcescens / Q000201:enzymology / Q000235:genetics*; D013045:Species Specificity; D013912:Threonine / Q000096:biosynthesis*; D014161:Transduction, Genetic
chemical_list: D007527:Isoenzymes; D013912:Threonine; D000429:Alcohol Oxidoreductases; D006715:Homoserine Dehydrogenase; D010770:Phosphotransferases; D001222:Aspartate Kinase