ALT Beyond direct microbial colonization: multisensory experiences in nature and their potential to indirectly influence the gut microbiome via multiple biological systems and axes. For example, stress can impair gut immunity in part by downregulating NLRP6 activity, a key regulator of the inflammasome and microbial balance (42); elevated cortisol increases gut permeability (43), and nature walks (and listening to nature sounds) reduce cortisol (44) and increase parasympathetic tone (45, 46). Exposure to natural biodiverse materials can reduce pro-inflammatory cytokines (27, 28). All of these processes can influence the gut environment, composition, and dynamics.