How do gut bacteria interact with pollutant chemicals? Atttend in person or Join on Zoom Dr Indra Roux (MRC Toxicology Unit) The human gut contains trillions of bacteria from hundreds of species that live as interacting communities. The gut microbiome plays key roles in health, from aiding digestion to modulating immunity. The composition of the microbiome changes throughout our lives and is strongly influenced by external factors, such as diet, medications and environmental exposures. Among these exposures are pollutant chemicals, such as pesticides, that can be found in food and water, yet there was limited information of their direct effects on gut bacteria. This motivated our team to systematically map interactions between pollutants and gut bacteria, uncovering hundreds of unexpected inhibitory interactions involving industrial and agricultural chemicals. But what are the genetic mechanisms that determine pollutant sensitivity or resistance? To address this question, we developed genome-wide genetic tools for common but understudied gut bacteria. Using large scale transposon sequencing screens, we investigated how bacteria modulate survival under pollutant stress. Our results reveal genetic pathways that determine chemical sensitivity, including mechanisms with implications to antibiotic cross-resistance. More broadly, this work highlights the gut microbiome as an emerging target of toxicology.