D Thibaut

Biochemical and Genetic Studies on Vitamin B12 Synthesis in Pseudomonas dentrificans

Vitamin B12 is produced industrially by Pseudomonas denitrificans or by bacteria belonging to Propionibacterium species (i. e. Propionibacterium shermanii or Propionibacterium freudenreichii). Industrial strains were obtained after long lasting and intense programs aimed at improving the fermentation caracteristics and the productivity of natural isolates (Florent, 1986). These programs consist of numerous mutagenesis steps, each of them introducing a property resulting in improved characteristics of the strain for industrial purpose (i. e. higher productivity, higher growth rate in a defined medium, growth to a higher biomass, etc). At each mutagenesis step the clone of interest is selected randomly either (i) for its property to produce higher level of vitamin B12 or (ii) for its resistance to an antibiotic for instance or (iii) for a phenotype related to an improved production of vitamin B12 (Florent, 1986). These selection programs have allowed various companies to improve the production of the starting bacteria. For instance the Pseudomonas denitrificans wild type isolate, strain MB580, from which the industrial strain used by Rhone-Poulenc Sante derives produces 2.5 mg/1 of cobalamin. In the same conditions, the industrial strain presently used produces much more (Florent, 1986).