The enteric microbiota is widely known to influence gut homeostasis both in mammals and insects, but the mechanisms behind these interactions are largely unknown. Previous studies have shown that the commensal bacteria Lactobacillus plantarum induces generation of reactive oxygen species (ROS) and activates CncC/Nrf2 signalling in Drosophila intestinal epithelia. Now, Rheinallt Jones and colleagues describe how L. plantarum-induced redox signalling activates proliferation of stem cells in the Drosophila larval midgut, which is composed of differentiated enterocytes and undifferentiated adult midgut progenitors (AMPs). By treating larvae with L. plantarum, the researchers discover that ROS are confined to enterocytes, creating a ‘ROS sheltered zone’ around AMPs. In response to ROS, enterocytes activate CncC/Nrf2 signalling, which induces proliferation in the AMP population. Furthermore, L. plantarum induces expression of the cytokine-encoding gene upd2 in the gut, which acts downstream of CncC/Nrf2 signalling to induce AMP proliferation through the JAK/STAT pathway. This work builds upon previous findings to reveal a mechanistic link between L. plantarum-induced ROS generation and AMP proliferation.