Bacterial cell envelope components of gut commensals: effects in host-microbe interaction

The bacterial cell envelope is a complex structure composed of proteins, lipids, and other molecules that form the physical boundary between bacteria and the environment. In the gut microbiome, commensal bacteria play a fundamental role in maintaining intestinal homeostasis and modulating host physiology. Due to their strategic location, bacterial cell envelope components interact directly with the host immune system, intestinal cells, mucus, and other gut structures, leading to diverse biological effects. Even though beneficial bacteria produce effector molecules, the functional diversity of these molecules, especially among gut bacteria, remains largely unknown. This review compiles current knowledge on the structure and function of bacterial cell envelope components, with a specific focus on gut microbiome commensals and their role in host interactions. It highlights key effector molecules, their immunological recognizers, and the downstream mechanisms involved in such microbial-host interactions, in addition to stating important knowledge gaps. Identifying and characterizing these molecular interactions is a crucial step toward developing novel biotherapeutic targets, particularly for inflammatory bowel diseases and other gut-related disorders. By reviewing current findings and outlining key research deficits, this review deepens our understanding of how bacterial cell envelope components shape host-microbe interactions.