| 摘要 |
#CMT# #/CMT# Producing L-cystine, comprises fermenting a microorganism strain in a fermentation medium, in which L-cystine is present in an amount of at least 70%, based on the total cysteine precipitated. The oxygen saturation of the fermentation medium during the L-cystine formation is maintained at 1-40+- 3%. #CMT#USE : #/CMT# The L-cystine is useful as food additive, preferably in baking industry, as an ingredient in cosmetics and as starting material for producing active pharmaceutical ingredients, preferably N-acetyl-cysteine and S-carboxymethyl-cysteine. #CMT#ADVANTAGE : #/CMT# The method: produces L-cystine with high yield; and exhibits easy purification of the product, preferably by precipitating or decanting. #CMT#BIOLOGY : #/CMT# Preferred Method: The oxygen saturation during the formation of L-cystine is maintained at 30+- 3%, preferably 10+- 3%. The oxygen is introduced into the fermentation medium by agitating the culture vessel using an agitating device or by blowing air or pure oxygen or a mixture of these gases into the fermentation medium. A carbon source is added into the fermentation medium such that the content of the carbon source in the fermenter during the cysteine production phase is not > 10 g/l. The incubation temperature is 15-45[deg] C, preferably 30-37[deg] C and the pH of the fermentation medium during the fermentation is 5-8.5, preferably 7. A sulfur source, preferably a sulfate or a thiosulfate is added during the fermentation. Preferred Components: The microorganism strain comprises a strain of the family Enterobacteriaceae, preferably a strain of the genus Escherichiaand Pantoea, preferably a strain of the species Escherichia coliand Pantoea ananatis. The microorganism strain exhibits either a serine-O-acetyl-transferase activity, with a feedback inhibition by L-cysteine, which is reduced by at least a factor of 2 in comparison to the corresponding wild type enzyme, or the microorganism strain by over expression of an efflux gene exhibits a cysteine export, which is increased by at least a factor of 2 in comparison to a wild type strain. The microorganism strain additionally exhibits a 3-phosphoglycerate dehydrogenase with a feedback inhibition by L-cysteine, which is reduced by at least a factor of 2, compared to the corresponding wild-type enzyme. #CMT#EXAMPLE : #/CMT# No suitable example given. |
