DNA synthesis in relation to a varying vitamin B12 content in Propionibacterium shermanii cells

The content of DNA in Propionibacterium cells is nearly twice as low at vitamin B12 deficiency comparing with normal cells. The rate of labeled adenine incorporation into the DNA depends on vitamin B12 content in the cells. The addition of adenosylcobalamin and thymine to the medium makes DNA content rise in the cells of the B12-deficient culture. The addition of thymine to a suspension of B12-deficient cells accelerates the incorporation of labelled adenine into DNA. The authors discuss the phenomenon of bacterial "unbalanced division" and the control of replication by changing the level of DNA precursors.     

Inherited disorders of vitamin B12 utilization

Inborn errors of vitamin B12 (cobalamin) metabolism are associated with homocystinuria and methylmalonic aciduria, either alone or in combination. A number of these disorders have provided the first evidence for the existence of important steps in the transport or metabolism of cobalamin in eukaryotic cells. Eight complementation classes have been defined on the basis of somatic cell hybridization studies. Although the majority of patients present in infancy or early childhood, some are not diagnosed until adolescence or later. For some of these disorders, prenatal diagnosis and therapy with cobalamin during pregnancy has been attempted. Although only males have been described with cblE disease, all of these disorders are presumed to be autosomal recessive in inheritance. The clinical and laboratory aspects of the different complementation classes (cblA-cblG) are reviewed here.     

Production of Propionibacterium shermanii biomass and vitamin B12 on spent media

AIMS: The propionibacteria are commercially important due to their use in the cheese industry, and there is a growing interest for their probiotic effects. Stimulatory effects of lactic acid bacteria (LAB) on propionic acid bacteria have been observed. This study was designed to examine the possibility of using spent media previously used to grow LAB for the production of biomass and metabolites of Propionibacterium freudenreichii subsp. shermanii. METHODS AND RESULTS: Seventeen MRS and vegetable juice media were prefermented by various LAB and evaluated for their ability to subsequently support the growth of Propionibacterium, using automated spectrophotometry (AS). Growth of Propionibacterium in spent media was strongly affected by the LAB strain used to produce the spent medium. The native MRS medium (not prefermented) yielded the highest optical density values followed by prefermented media by Lactobacillus acidophilus, Bifidobacterium longum and Lactococcus lactis. Prefermented cabbage juice enabled good growth of Propionibacterium. For the production of organic acids and vitamin B12, cells of Propionibacterium were concentrated and immobilized in alginate beads in the aim of accelerating the bioconversions. More propionic acid was obtained in spent media than in native MRS. The concentration of vitamin B12 was higher in media fermented with free cells than those with immobilized cultures; with the free cells, its concentration varied from 900 to 1800 ng ml(-1) of media. CONCLUSIONS: It was demonstrated that spent media could be recycled for the production of Propionibacterium and metabolites, depending on the LAB strain that was previously grown. Media remediation is needed to improve the production of vitamin B12, especially with immobilized cells. SIGNIFICANCE AND IMPACT OF THE STUDY: This study presents an option for recycling of spent media generated by producers of LAB or producers of fermented vegetables. The propionic fermentation may result in three commercial products: biomass, vitamin B12 or organic acids, which may be used as starters, supplements or food preservatives. It is an attractive process from economical and environmental standpoints.     

Effect of nucleotide containing corrinoids on vitamin B 12 synthesis in Propionibacterium shermanii]

The influence of B12-CN, B12-OH, coenzyme B12, factor III and factor B on the synthesis of vitamin B12 and porphyrins by different strains of P. shermanii was investigated. Neither compound inhibited the development of propionic bacteria or suppressed porphyrin formation. All nucleotide containing analogues of vitamin B12 produced a strong repressive effect on the synthesis of corrinoid compounds regardless of the modifications in the upper and lower cobalt ligands. Factor B containing no nucleotide moiety did not show this effect. It is suggested that the nucleotide moiety of the vitamin B12 molecule is responsible for the binding of vitamin to protein aporepressor.     

Biosynthesis of vitamin B12. Some properties of the 5,6-dimethylbenzimidazole-forming system of Propionibacterium freudenreichii and Propionibacterium shermanii

1. Homogenates of Propionibacterium freudenreichii transform riboflavin into 5,6-dimethylbenzimidazole. This process is stimulated by nicotinamide. Homogenates of Propionibacterium shermanii form only small amounts of 5,6-dimethylbenzimidazole from riboflavin in the absence of nicotinamide, but also form appreciable amounts in the presence of nicotinamide. 2. The stimulation of the 5,6-dimethylbenzimidazole-forming system by nicotinamide shows a lag phase which is abolished by preincubation of the homogenate with nicotinamide. Since no lag phase is observed when nicotinamide is replaced by nicotinate, nicotinate seems to be the true stimulating agent. These observations are in agreement with the fact that nicotinamide is rapidly split to nicotinate in homogenates of P. freudenreichii. 3. The 5,6-dimethylbenzimidazole-forming homogenate system is only active at a high buffer concentration (0.3--0.5 M) and in the presence of oxygen. The system has a pronounced oxygen optimum. 4. Flavin mononucleotide and flavin-adenine dinucleotide are better substrates for the 5,6-dimethylbenzimidazole-forming homogenate system than riboflavin. But with [1'-14C]riboflavin as substrate the specific radioactivity of 5,6-dimethylbenzimidazole is higher than the specific radioactivity of flavin--adenine dinucleotide and lower than the specific radioactivie substrate for the formation of 5,6-dimethylbenzimidazole. 5. A tentative reaction sequence for the transformation of flavin mononucleotide into 5,6-dimethylbenzimidazole is discussed.     

Influence of 5,6-dimethylbenzimidazole (DMB) on vitamin B12 biosynthesis by strains of Propionibacterium

Work on vitamin B₁₂ biosynthesis in whey permeate using 5,6-dimethylbenzimidazole (DMB) as a precursor has often been carried out, but with no reference to the stage of fermentation at which it is to be added to the fermentation medium. In the present paper we report 168 h incubation as the optimum time for vitamin B₁₂ biosynthesis and the effect of DMB addition at four phases of fermentation, on vitamin B₁₂ productivity, growth and substrate utilization by three strains of Propionibacterium. The infusion of DMB at the end of 144 h of incubation (24 h before the end of fermentation) has been found optimum for maximum metabolic efficiency of the cultures.