THE STRUCTURE AND IMMUNOLOGICAL PROPERTIES OF BACTEROIDES STERCORIS LIPOPOLYSACCHARIDE

The human body is a complex symbiotic system of diverse microorganisms comprising bacteria, yeasts, and viruses.[1] This massive and heterogenous assemblage of microbes, known as the microbiota, is key in physiological and pathological processes occurring in our body, which also include protection against pathogens and immune system development.[2] In this frame, a vast and dynamic community of microbes inhabits the human gut, i.e. the gut microbiota, and comprises commensals and beneficial species for human health. Nevertheless, most of these bacteria are Gram-negative and therefore they possess lipopolysaccharides (LPS) on their outer membranes.[3] LPS are glycoconjugates traditionally associated to potent immune inflammatory reactions in Mammals which occur in a manner that is strongly dependent on the LPS chemical structure. Nevertheless, many harmless Gram-negative colonize the gut without producing any dangerous immune response while promoting the well-being of the host by modulating the immune system itself. [1,3] Therefore, is LPS harmful or beneficial? Deciphering the chemistry responsible for the delicate balance between “beneficial” LPS and “harmful” LPS is pivotal to answer this question. In this communication I will show unreported data related to the characterization of the structure and immunological properties of the LPS from one of the predominant Gram-negative residing the human gut and considered a beneficial bacterium [3], i.e. Bacteroides stercoris. A novel chemical structure and uncommon immunological behaviour will be presented, providing insights into the chemistry that might be responsible for establishing harmless relationship between B. stercoris and the human host.