Molecular dialogue between the human gut microbiota and the host: a Lactobacillus and Bifidobacterium perspective

Abstract

The human gut represents a highly complex ecosystem, which is densely colonized by a myriad of microorganisms that influence the physiology, immune function and health status of the host. Among the many members of the human gut microbiota, there are microorganisms that have co-evolved with their host and that are believed to exert health-promoting or probiotic effects. Probiotic bacteria isolated from the gut and other environments are commercially exploited, and although there is a growing list of health benefits provided by the consumption of such probiotics, their precise mechanisms of action have essentially remained elusive. Genomics approaches have provided exciting new opportunities for the identification of probiotic effector molecules that elicit specific responses to influence the physiology and immune function of their human host. In this review, we describe the current understanding of the intriguing relationships that exist between the human gut and key members of the gut microbiota such as bifidobacteria and lactobacilli, discussed here as prototypical groups of probiotic microorganisms.

Fig. 1

Schematic representation of the human gastrointestinal tract showing its different compartments and the relative abundance of bacteria (a). b The relative abundance of the main microbial phyla detected in the adult fecal samples [12]. c The aggregate microbiota composition of the genus Lactobacillus as determined from adult fecal sample analysis [12]. d The aggregate microbiota composition of the genus Bifidobacterium as determined from adult fecal sample analysis [12]

Fig. 2

Schematic overview of the Gram-positive cell wall together with main macromolecular structures that have been implicated in host–microbe interaction. Specific components of the cell envelope are shown such as peptidoglycan layer, wall and lipoteichoic acids (WTA and LTA), exopolysaccharide (EPS), as well as secreted proteins (SP), membrane proteins (MP), cell wall-associated proteins (CWP), lipoproteins (LPP), membrane-associated proteins (MAP), surface layer proteins (SLP), fimbrial proteins (Fim), and tad proteins (TAD). Furthermore, the sortase-dependent assembly apparatus (SRT) is indicated