“Defining Microbiota and Host Resilience to Physical Perturbations: A Multi-Scale Approach”

Seminar | February 14 | 12-1 p.m. | 106 Stanley Hall

 Carolina Tropini, Stanford University

 Bioengineering (BioE)

Physical perturbations are prevalent in the bacterial world. Changes in the environmental mechanical properties, temperature, pH, or osmotic pressure apply broad spectrum stresses to bacterial communities and drive evolution. Specifically, in the human gut, osmotic stress is a common disturbance caused by food intolerance, malabsorption, and widespread laxative use. In my postdoctoral studies, I assessed the resilience of the gut ecosystem to osmotic perturbation at multiple length and time scales. Osmotic stress caused consistent, lasting changes to human and mouse microbiotas in a mouse model, leading to the extinction of highly abundant taxa and expansion of less prevalent members. Using quantitative imaging, I showed that the mucosal interface separating bacteria from the epithelium was decimated during osmotic perturbation, but rapidly recovered when osmotic stress was removed. The immune system was also impacted, with temporary changes in cytokine levels and a lasting IgG response against commensal bacteria. Increased osmolality prevented bacterial growth in vitro, suggesting a host-independent mechanism for observed extinction events. Environmental availability of microbiota members that would otherwise go extinct restored composition to the pre-treatment state. These findings demonstrate that even mild osmotic perturbance can cause lasting changes to the microbiota and host, and lay the foundation for developing interventions that can increase system-wide resilience.