Page 171 - Read Online

Page 14 of 22 D’Aimmo et al. Microbiome Res Rep 2024;3:11 https://dx.doi.org/10.20517/mrr.2023.59

the pABA concentration did not affect the final folate content. In the same study, any relation between
carbon source and folate production was excluded, as well as the effect of pH. Furthermore, this vitamin’s
concentration was higher than the cell’s requirements in some cases. For this reason, it is possible to
[82]
hypothesize that biosynthesis is not regulated in some strains . Regarding Bifidobacterium folate
composition, the predominant form in most strains tested by D’Aimmo et al. is 5CH H folate, followed by
3
4
H -folate [58,74] . The HCO-H folate was not detected in Bifidobacterium spp.
4
4
Comparison of phenotypic and in silico data on folate production in bifidobacteria showed some
inconsistencies due to the quantification method used. Some studies [58,74,89] confirmed the data obtained in
silico, i.e., strains of human origin (in in silico study, all human bifidobacterial species contain folate genes)
can grow without folate supplementation [Table 1]. However, if a different quantification method was used,
as in the survey of Pompei et al. , different results were obtained, which did not completely support the in
[82]
silico data: indeed, these authors showed that 41 out of 57 tested bifidobacterial strains of human origin did
not produce folate in the folate-deficient medium (see for example results obtained for B. adolescentis
ATCC 15703 and B. longum subsp. longum ATCC 1570). By using HPLC folate detection assay, D’Aimmo
et al. and Sugahara et al. found that all tested bifidobacteria of human origin could grow and produce folate
in folate-deficient media, thus suggesting that differently than in animals, all human resident bifidobacteria
can produce folate [58,74,89] . Therefore, the importance of appropriate methods for evaluating folate production
by bifidobacterial strains has to be underlined.

Another outcome in the phenotypic study of folate production is the high variability in the amount of folate
produced between different strains [58,74,82,89] . Screening for folate production of the bifidobacteria isolates
from human adults and infants (1-6 months old) showed that strains derived from adults were the higher
producer of total folate (range from 580 to 935 μg/g dry matter) with the predominance of 5-methyl-H
4
folate and a low amount of H folate . In infants, the opposite results have been described with strains
[74]
4
typical of infant habitat producing low amounts of total folate (range from 35 to 200 μg/g dry matter) and
an inverted ratio of 5-methyl-H /H folate concerning adults. In agreement with the previously described
4
4
idea of coevolution of host-gut microbiome , it can be hypothesized that bifidobacteria present in the adult
[90]
gut were able to produce a high amount of folate, differently from strains derived from infants. These
findings could correlate with the diet and the folate requirement of the host: in infants, milk feeding is able
per se to fulfill the folate needs of the individuals, whereas, in adults, a more complex diet is sometimes
unable to cover all the folate needs. The relevance of the different ratios of 5-CH -H /H folate production in
4
3
4
adults and infants has been studied only in a few strains. Further studies are requested to have more
evidence and provide an ecological explanation.
In vivo studies for folate production
In vivo studies of folate production by bifidobacteria are very scarce. Pompei et al., for instance, evaluated in
vivo folate production in Wistar rats [82,91] . Folate-overproducing bifidobacteria B. adolescentis MB 227,
B. adolescentis MB 239, and B. pseudocatenulatum MB 116 were administered, with or without prebiotics, to
rats with induced folate deficiency. A higher increase of serum folate (16.4 ± 3.7 nmol/L) was found in the
group of animals receiving probiotic and prebiotic (fructo-oligosaccharide) compared to the group
receiving only probiotics (9.1 ± 0.3 nmol/L). Nevertheless, the rats fed probiotics showed a greater folate
increase than the control (4.8 ± 0.5 nmol/L) and than the prebiotic-only group (5.3 ± 1.4 nmol/L). This
suggests that ingesting folate-producing bifidobacteria may increase folate absorption into the bloodstream.
However, the impact on folate levels in humans may be somewhat less significant, as rats engage in
coprophagia, which results in an internal increase of folate for themselves.