ALTHOUGH WE HAVE A WIDE RANGE OF PROCEDURES FOR CATALOGING TAXA, GENES AND FUNCTIONS OF THE HUMAN MICROBIOME IN HEALTH AND DISEASE CONDITIONS, WE STILL CANNOT RESPOND TO THE FACT THAT IT IS A STABLE MICROBIOTA. THE INTESTINAL MICROBIOTA, FOR EXAMPLE, UNFOLDS THROUGHOUT THE INDIVIDUAL’S DEVELOPMENT AND ITS COMPOSITION AND FUNCTION IS DIFFERENT DEPENDING ON AGE. THE CONCEPT OF STABILITY IMPLIES THE IDEA THAT IN THE FACE OF A DISTURBANCE THE MICROBIAL COMMUNITY RETURNS TO ITS INITIAL SITUATION IN TERMS OF COMPOSITION (RESILIENCE) OR FUNCTION (FUNCTIONAL REDUNDANCY) WHEN THE DISTURBING FACTOR DISAPPEARS. SHOULD WE THEN CONCLUDE THAT THE INTESTINAL MICROBIOTA OF A HEALTHY CHILD IS NOT STABLE COMPARED TO THAT OF A HEALTHY ADULT? WHY? WHY? THE QUESTION OF STABILITY CAN ALSO BE ADDRESSED FROM THE PERSPECTIVE OF AN IMPORTANT DISRUPTING AGENT OF THE INTESTINAL MICROBIOTA: ANTIBIOTICS. ITS ACTION MODIFIES THE COMPOSITION AND FUNCTION OF THE MICROBIOTA, WHICH USUALLY ENDS IN A PARTIAL RESILIENCE AND FUNCTIONAL REDUNDANCY AFTER THE DISAPPEARANCE OF TREATMENT. HOWEVER, THE STABILITY CAN BE BROKEN BY HAVING THE PRESENCE OF CLOSTRIDIUM DIFFICILE ON SOME OCCASIONS. IN THIS PROJECT WE AIM TO ADDRESS THE QUESTION OF THE TEMPORAL STABILITY OF THE INTESTINAL MICROBIOTA THROUGHOUT DEVELOPMENT AS WELL AS UNDER ANTIBIOTIC TREATMENT OR WHEN C. DIFFICILE APPEARS. WE WILL ELUCIDATE BY THE APPLICATION OF A NOVEL METHOD OF EVALUATION OF THE STABILITY OF THE MICROBIOTA DEVELOPED IN THE GROUP, AS WELL AS BY THE DETERMINATION OF THE COMPOSITION (METAGENOMA) AND FUNCTION (METATRANSCRIPTOMA AND METABOLOMA) OF THE INTESTINAL MICROBIOTA AND ITS INTERACTION WITH THE VIROMA, THE MECHANISMS THAT PROMOTE RESILIENCE AND FUNCTIONAL REDUNDANCY, SPECIFICALLY IDENTIFYING IN THE BAYESIAN AND CO-OCCURRENCE NETWORKS THOSE TAXA, FUNCTIONS OR ROUTES THAT CHANGE THROUGHOUT THE DEVELOPMENT OR THAT PROTECT US FROM THE ACCUMULATION OF RESISTANCE GENES IN BACTERIA CARRIERS.