Folate and Bifidobacteria
Folate is the generic term for a group of chemically related and biologically active forms of vitamin B9, needed by all organisms. Folic acid is the fully oxidized synthetic form of the vitamin. The chapter starts with nomenclature and chemical structure of folate forms followed by methodologies for extraction and chemical analysis of bacterial folate. Folates are unstable and susceptible to interconversion reactions so the special care needed to correctly determine folates in bacteria is discussed. Next follows folate biosynthesis, which happens commonly in plants and many microbes, including most bifidobacteria, but is absent in mammals, such as humans. Relevant genes, enzymes, and intermediate metabolites are described. Thereafter, the chapter continues to review folate metabolism, which describes cycling of different one-carbon units, using folate as vehicle, necessary for, for example, nucleic acid biosynthesis (purines and thymidine), amino acid homeostasis (glycine, serine, and methionine), and methylation of macromolecules, such as proteins and DNA, which includes epigenetic maintenance. Next follows a section on how biotechnology can be applied to produce high levels of microbial folate, to be used either as a food additive or as folate-producing probiotics. Finally, the main concerns and health implications from insufficient folate intake are described.