Muriel Thomas is Director of Research at INRA and conducts her research at the Institut Micalis. She is co-author of 43 publications, 3 patents and 5 book chapters. For the past 10 years, his group has been interested in the "health" effects of bacteria in digestive and respiratory physiology. We studied the effects of the microbiota on homeostasis, renewal and secretory/absorptive functions of the intestinal epithelium in gnotobiotic animals carrying groups of bacteria representative of the newborn, the healthy adult, the adult with intestinal deficiency and food bacteria. From animals carrying simplified microbiotes, we have described the specific effects of different bacterial consortia on the colon epithelium. We have also recently expanded our scope of investigation to include the effects of the pulmonary microbiota on respiratory health. Our approach, at the border between physiology and microbiology, is supported by private or academic funding and contributes to the development of knowledge and applications related to intestinal and pulmonary microbiomes.