Abstract: A novel microorganism of the genus Escherichia containing a hybrid plasmid prepared by integrating a plasmid with a deoxyribonucleic acid carrying the gene for aspartase which is obtained from a microorganism of the genus Escherichia. An industrially advantageous method for producing L-aspartic acid comprising contacting a culture of the novel microorganism, microbial cells collected from the culture or a processed material of the microbial cells with fumaric acid and ammonia to produce L-aspartic acid and then collecting L-aspartic acid thus produced is also disclosed.

Abstract: A novel microorganism of the genus Serratia containing a hybrid plasmid prepared by integrating a plasmid with a deoxyribonucleic acid carrying the gene for aspartase which is obtained from a microorganism of the genus Serratia. An industrially advantageous method for producing L-aspartic acid comprising contacting a culture of the novel microorganism, microbial cells collected from the culture or a processed material of the microbial cells with fumaric acid and ammonia to produce L-aspartic acid and then collecting L-aspartic acid thus produced is also disclosed.

Abstract: An improved method for the fermentative production of L-threonine in a high yield, which comprises cultivating a methionine metabolism-antagonist resistant mutant of Serratia marcescens having L-threonine productivity in a broth to form and accumulate L-threonine therein and recovering accumulated L-threonine from the broth.

Abstract: A method for the fermentative production of L-proline which comprises cultivating a L-proline-producing mutant of a microorganism belonging to the genus Serratia in a broth to produce and accumulate L-proline therein and collecting accumulated L-proline. The mutant is preferably that of Serratia marcescens which is deficient in L-proline oxidase and is resistant to proline analong under a high osmotic pressure.