Engineered bacteria titrate hydrogen sulfide and induce concentration-dependent effects on host in a gut microphysiological system.

Hydrogen sulfide (H 2 S) is a gaseous microbial metabolite whose role in gut diseases is debated, largely due to the difficulty in controlling its concentration and the use of non-representative model systems in previous work. Here, we engineered E. coli to titrate H 2 S controllably across the physiological range in a gut microphysiological system (chip) supportive of the co-culture of microbes and host cells. The chip was designed to maintain H 2 S gas tension and enable visualization of co-culture in real-time with confocal microscopy. Engineered strains colonized the chip and were metabolically active for two days, during which they produced H 2 S across a sixteen-fold range and induced changes in host gene expression and metabolism in an H 2 S concentration-dependent manner. These results validate a novel platform for studying the mechanisms underlying microbe-host interactions, by enabling experiments that are infeasible with current animal and in vitro models.