Background: The bond with our microbiota starts at birth and has co-evolved where fitness of
the two participants has become interdependent. Recent comprehensive analysis of the
infant microbiota indicates that the family Bifidobacteriaceae is dominant (~80%), compared
with approx. 10% for the phylum Firmicutes. Importantly, high levels of bifidobacteria in the
infant gut have been associated with the timely development and maturation of mucosal
immunity and reduced infection rates.
Members of this genus have been used in a wide variety of studies to promote health and as
probiotics, however the mechanisms behind these events are as yet not fully characterised.
Bifidobacteria are Gram-positive, anaerobic, non-spore forming, non-motile, non-filamentous
rods with high G+C content belonging to the phylum Actinobacteria. Indeed, Bifidobacterium
represents one of the largest genus within the Actinobacteria, and includes at present 51
species. In the context of early life, bifidobacteria are also found within breast milk, and these
strains have enzymes capable of metabolising milk oligosaccharides, enabling growth and
persistence, suggesting co-evolution of bacteria-host and diet. Bifidobacteria have also been
extensively detected in the gut of mammals, birds and social insects.
Due to their associated health benefits, there is significant need to explore the diversity of the
bifidobacterial population at a global level and within individuals. Although the genetic
diversity of Bifidobacterium has been determined based on several marker genes or a
relatively small number of genomes, the global diversity and evolution scenario for the entire
genus remain unresolved.
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