Selecting aerotolerance in next generation probiotics: molecular lessons from a Bifidobacterium bifidum strain able to form colonies on the surface of agar plates.

One of the main challenges for exploiting the therapeutic potential of next generation probiotics is their inclusion into functional foods, which is hampered by extreme oxygen sensitivity. This is indeed an unmet technological problem for classical probiotics, such as human gut bifidobacteria, in which Bifidobacterium animalis subsp. lactis is the preferred species in fermented milks due to their aerotolerance. Aerobic conditions are present during the processes of producing, handling, manufacturing and storing probiotics. Bifidobacterium bifidum species contains several probiotic strains from invaluable therapeutic potential, but also with the lower resistance to oxygen among human bifidobacteria. In this paper we present strain Bifidobacterium bifidum 3BIT4A, which is the first human bifidobacteria with enough resistance to oxygen to form colonies on the surface of agar plates under an aerobic atmosphere. This ability is absent even in the probiotic bifidobacteria strains from the species B. animalis subsp. lactis. The strain 3BIT4A, generated after random UV mutagenesis from an intestinal isolate, incorporates 26 single nucleotide polymorphisms that activate the expression of native oxidative-defense mechanisms such as the alkyl hydroxyperoxide reductase, the glycolytic pathway and several genes coding for enzymes involved in redox reactions. In the present work, we discuss the molecular mechanisms underlying the aerotolerance phenotype of B. bifidum 3BIT4A, which will open new strategies for the selection and inclusion of probiotic gut strains and next generation probiotics into functional foods.