Bifidobacterium and Lactobacillus are the main probiotic genera. Collectively, these two genera harbor over 200 species among which are many strains have been introduced as probiotics. These health-promoting microbes confer health benefits upon the host and so used in food productions and as supplements. Considering the economic importance of probiotics, the biochemistry, genomics, phylogeny and physiology of such genera have been exhaustively studied. According to the genomic data, the probiotic capabilities are strain specific which may be a result of the niche-specialization of the genomes of these bacteria to certain ecological niches like gastrointestinal tract of a diverse range of animals. These microbes have a wide distribution but the culture-based studies and either genomics data suggest selective affinity of some Lactobacillus and either Bifidobacterium species to certain ecological niches. An ongoing genome degradation, which is thought to be a result of passage through an evolutionary bottleneck, is the major trend in the evolution of lactobacilli. Further, evolutionary events resulted into two categories of lactobacilli: habitat generalists and habitat specialists. In place, the main trend in the evolution of bifidobacteria tend to be the gene acquisition. However, probiotic features are the results of a co-evolutionary relationship between these bacteria and their hosts and the aforementioned evolutionary tends have driven the evolution of these probiotic genera.
Keywords: Genomics; Microbe-host interaction; Microbial ecology; Probiotics; Reductive evolution; Strain-specific characters.
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