Gut microbiome and secretion systems

The bacterial community within the gut are diverse and heterogenous. They regulate and modulate host metabolism in multiple ways. The residents of the bacterial community within the gut which mostly comprises of commensals, symbionts, pathobionts deploy a variety of strategies to regulate host metabolism. One such key strategy is secretory proteins. Bacteria in the gut have well developed secretory systems which resembles structurally like that of injection syringe and is used to inject a wide range of metabolites into the host cells. These metabolites upon entering the host cell or tissue disrupt vital biological processes. This may in turn prove to be beneficial for the host (incase of commensals and symbionts) or might also prove detrimental for the host (incase of pathogens). The secretion systems are of various type, for instance there are Type I-VI secretion systems in bacteria. The core machinery of the secretion system is conserved across all the bacteria while some of the accessory proteins get changed. Recently, it has been shown by a number of studies that gut commensals exactly like the pathogen encodes type III secretion systems which might help them to inject effector proteins into the host cells. The recent study also focused on the protein-protein interaction network between these effector molecules and host proteins. They also observed that the effector proteins get involved in host metabolic processes and can regulate the same in various manner. Till now there were no evidences that there exist a Type III secretion system in commensals but this study however, was an exception and proved others wrong showing that Type II secretion system could be equally important and pertinent even for the commensals.

From these studies it is evident that there are multiple ways by which gut bacterial community might regulate our overall health and well-being. Further studies are needed to unravel the different strategies used by gut commensals to regulate host metabolic processes. Type III secretion systems in gut commensals could be an important breakthrough in research related to gut microbiota as it necessarily shed light into the evolution of pathogenicity within bacteria. It also highlights the switch of bacteria from a commensal to pathogen or vice versa by acquiring or losing these secretory systems through horizontal gene transfer.