Folate production by bifidobacteria as a potential probiotic property

Abstract

The ability of 76 Bifidobacterium strains to produce folate was investigated. In order to evaluate folic acid productivity, bifidobacteria were cultivated in the folate-free semisynthetic medium SM7. Most of the tested strains needed folate for growth. The production and the extent of vitamin accumulation were not a function of species but were distinctive features of individual strains. Six strains among the 17 that grew without folate produced significantly higher concentrations of vitamin (between 41 and 82 ng ml(-1)). The effects of exogenous folate and p-aminobenzoic acid (PABA) concentrations on folate production were evaluated. In contrast to most of the other strains, the folate yield of B. adolescentis MB 239 was not negatively affected by either PABA or exogenous folic acid. Folate production by B. adolescentis MB 239 was studied in the pH range of the colonic environment, and a comparison of folate production on raffinose, lactose, and fructo-oligosaccharides, which belong to three important groups of fermentable intestinal carbon sources, was established. Differences in folate biosynthesis by B. adolescentis MB 239 were not observed as a function either of the pH or of the carbon source. Fecal culture experiments demonstrated that the addition of B. adolescentis MB 239 may increase the folate concentration in the colonic environment.

FIG. 1.

Intracellular and extracellular folate concentrations in 48-h cultures of B. adolescentis MB 114, MB 115, MB 227, and MB 239 and B. pseudocatenulatum MB 116 and MB 237. Mean values from three separate experiments are reported; SDs were always less than 3.0 ng ml⁻¹.

FIG. 2.

Net extracellular folate production in 48-h cultures of B. adolescentis MB 114, MB 115, MB 227, and MB 239 and B. pseudocatenulatum MB 116 and MB 237 in SM7 supplemented with 0, 10, 25, or 50 ng ml⁻¹ folate. Mean values from three separate experiments are reported; SDs were always less than 4.0 ng ml⁻¹.

FIG. 3.

Extracellular folate concentrations in 48-h cultures of B. adolescentis MB 114, MB 115, MB 227, and MB 239 and B. pseudocatenulatum MB 116 and MB 237 in SM7 supplemented with 0, 0.3, 10, or 100 μM PABA. Mean values from three separate experiments are reported; SDs were always less than 3.0 ng ml⁻¹.

FIG. 4.

Batch fermentation of B. adolescentis MB 239 in SM7 with controlled pH (6.5). Symbols: ○, DW, (dry weight); •, extracellular folate concentration.