1. Field of the Invention
The present invention relates to a process for the preparation of D-pantothenic acid and salts thereof or mixtures comprising these compounds using microorganisms of the Enterobacteriaceae family in which at least the adk gene is enhanced.
2. Description of the Background
Pantothenic acid is produced worldwide in an order of magnitude of several thousand tons a year. It is used inter alia in human medicine, in the pharmaceuticals industry and in the foodstuffs industry. A large portion of the pantothenic acid produced is used for nutrition of stock animals such as poultry and pigs.
Pantothenic acid can be prepared by chemical synthesis, or biotechnologically by fermentation of suitable microorganisms in suitable nutrient solutions. In the chemical synthesis, DL-pantolactone is an important precursor. It is prepared in a multi-stage process from formaldehyde, isobutylaldehyde and cyanide, and in further process steps, the racemic mixture is separated, D-pantolactone is subjected to a condensation reaction with β-alanine, and D-pantothenic acid is obtained in this way.
The typical commercial form is the calcium salt of D-pantothenic acid. The calcium salt of the racemic mixture of D,L-pantothenic acid is also customary.
The advantage of the fermentative preparation by microorganisms lies in the direct formation of the desired stereoisomeric form, that is to say the D-form, which is free from L-pantothenic acid.
Various types of bacteria, such as e.g. Escherichia coli (E. coli), Arthrobacter ureafaciens, Corynebacterium erythrogenes, Brevibacterium ammoniagenes, and also yeasts, such as e.g. Debaromyces castellii, can produce D-pantothenic acid in a nutrient solution which comprises glucose, DL-pantoic acid and β-alanine, as shown in EP-A 0 493 060. EP-A 0 493 060 furthermore shows that in the case of E. coli, the formation of D-pantothenic acid is improved by amplification of pantothenic acid biosynthesis genes from E. coli which are contained on the plasmids pFV3 and pFV5 in a nutrient solution comprising glucose, DL-pantoic acid and β-alanine.
EP-A 0 590 857 and U.S. Pat. No. 5,518,906 describe mutants derived from E. coli strain IFO3547, such as FV5714, FV525, FV814, FV521, FV221, FV6051 and FV5069, which carry resistances to various antimetabolites, such as salicylic acid, α-ketobutyric acid, β-hydroxyaspartic acid, O-methylthreonine and α-ketoisovaleric acid. They produce pantoic acid in a nutrient solution comprising glucose, and D-pantothenic acid in a nutrient solution comprising glucose and β-alanine. It is furthermore stated in EP-A 0 590 857 and U.S. Pat. No. 5,518,906 that after amplification of the pantothenic acid biosynthesis genes panB, panC and panD, which are said to be contained on the plasmid pFV31, in the above-mentioned strains the production of D-pantoic acid in nutrient solutions comprising glucose and the production of D-pantothenic acid in a nutrient solution comprising glucose and β-alanine is improved.
WO 97/10340 furthermore reports on the favorable effect of the enhancement of the ilvGM operon on the production of D-pantothenic acid. Finally, EP-A-1001027 reports on the effect of the enhancement of the panE gene on the formation of D-pantothenic acid.
According to known procedures, the D-pantothenic acid or the corresponding salt is isolated from the fermentation broth and purified (EP-A-0590857 and WO 96/33283) and used accordingly in purified form, or the fermentation broth comprising D-pantothenic acid is dried in total (EP-A-1050219) and used in particular as a feedstuffs additive.