Abstract: The invention relates to a method for producing L-cysteine and its derivatives L-cystine and thiazolidine by fermenting a cysteine-producing microorganism strain in a fermentation medium. The invention is characterized in that L-methionine, L-isoleucine, or L-threonine in respective concentrations ranging from 0.1 to 10 g/L are added to the fermentation medium in the main culture.

Abstract: The invention relates to a method for producing L-cysteine and its derivatives L-cystine and thiazolidine by fermenting a cysteine-producing microorganism strain in a fermentation medium. The invention is characterized in that L-methionine, L-isoleucine, or L-threonine in respective concentrations ranging from 0.1 to 10 g/L are added to the fermentation medium in the main culture.

Abstract: A process is for preparing O-acetylserine, L-cysteine and sulphurous compounds derived therefrom using feedback-resistant serine acetyl transferases. In comparison with the wild-type enzyme, these serine acetyl transferases have reduced sensitivity to the inhibitor L-cysteine and a protein sequence which, in comparison with the wild-type enzyme, displays at least one mutation or deletion. The process has a mutation which lies in the sequence region of the amino acid in position 97 up to and including the amino acid in position 273 or the deletion lies in the carboxy terminal sequence region as from the amino acid in position 227, position 1 being the starter methionine of FIG. 5 (SEQ ID NO:1) and the mutation from Met to Ile in position 256 being excluded.

Abstract: A tryptophan producing strain of microorganism is selected from E. coli and Corynebacteria and is tryptophan feedback resistant and serine feedback resistant. The serine feedback resistance is by a mutation in a serA allele, where the mutated serA allele codes for a protein which has a Ki value for serine between 0.1 mM and 50 mM. The tryptophan feedback resistance is by a trpE allele which codes for a protein which has a Ki value for tryptophan between 0.1 mM and 20 mM. A process for preparing this microorganism and a process for using this microorganism are disclosed.

Abstract: Microorganisms and processes for the fermentative preparation of L-cysteine, L-cystine, N-acetylserine or thiazolidine derivatives. The microorganism strain which is suitable for the fermentative preparation of L-cysteine, L-cystine, N-acetylserine and/or thiazolidine derivatives, overexpresses at least one gene which encodes a protein which is directly suitable for secreting antibiotics, or other substances which are toxic for the microorganism, out of the cell.