Here we concentrated in L. johnsonii, a potentially probiotic bacterial species that is of major interest to the pharmaceutical and food industries as it includes several known probiotic strains [25, 28, 29]. We successfully identified and isolated 39 L. johnsonii strains from fecal-bacterial populations of few host species. Strain typing of these isolates together with six additional strains of human origin revealed

LGK974 high levels of genetic variation among the L. johnsonii strains. Both SSR and MLST analyses were found to be effective for typing, providing high-resolution discrimination also among isolates originated in the same animal species. The genetic relationships among the strains inferred by the two analyses were similar, clearly dividing the L. johnsonii strains into three clusters. buy INK 128 Each cluster consisted of strains from different diverse hosts, i.e., chickens, humans or mice (Figure 2). These consistent results, obtained by different typing methods, suggest far phylogenetic separation among L. johnsonii isolates presenting host specificity. Such association of particular L. johnsonii strains with the host taxonomy could arise as a result of co-evolution of the host and its GIT microbiota [2, 41–43]. Interestingly, host driven evolution was observed in another

lactobacilli species, L. reuteri[44]. According to the recently suggested “”hologenome theory”" [45], the host and its symbiont microbiota (together defined as the “”holobiont”") are one unit of selection in evolution. Indeed, previous analysis of the L. johnsonii genome showed the absence of genes required for several metabolic pathways [29] emphasizing the high dependence of L. johnsonii on its host and further supports the concept that L. johnsonii and its host are one evolutionary unit of selection. Since chickens, humans and mice are distinct genetic species divided during evolution, L. johnsonii strains associated with them may be evolutionary separated as part of the distinct holobionts. In addition, analysis conducted

on the tRFLP results of 50 host individuals suggest an association of L. intestinalis and E. faecium cluster with host taxonomic Obatoclax Mesylate (GX15-070) groups (Figure 1), and further support co-evolution of the host and its intestinal bacteria. The E. faecium species cluster was relatively rare in hosts belonging to the Rodentia taxonomic order, and alternatively, L. intestinalis was found to be more frequent within that group. These observations may indicate possible competition or a similar function of these two bacteria in the same niche, each within its appropriate microenvironment. Environmental factors, such as diet, are highly important in shaping the host gut’s microbiota composition [4–6, 46]. However, in our study, no correlation was found between the presence of each of the four bacterial species tested and the hosts’ food consumption (herbivore, omnivore and carnivore) or geographical location. Conclusions L.