Examining successional trajectories of microbial communities colonizing restroom surfaces and the stability of late successional community structure.. San Diego State University Restroom Study

The indoor environment is the dominant ecosystem for the majority of industrialized humanity and is unlike any biome previously experienced by our species1. Bacteria commonly associated with our bodies dominate the Built Environment (BE). Using a unique ecosystem model - a public restroom - we show that surface-associated microbial communities follow a predictable ecological succession, from a community dominated by fecal microbiota to one dominated by skin and ‘outdoor’ microbiota. We analyzed microbial communities following intensive decontamination of floors, toilet seats, and soap dispensers in 4 public restrooms hourly, daily, and weekly. Only toilet seat communities showed differentiation based on gender, with Lactobacillus dominating female restrooms and Roseburia and Blautia dominating male restrooms. On restroom floors, a late successional community developed within 5-8 hours, and showed remarkably stability over weeks to months. Despite late-successional dominance by skin- and outdoor-associated microbiota, the core microbiome (OTUs shared across all samples) was composed almost exclusively of human gut bacteria, suggesting that a relatively homogenous pool of abundant fecal microbes is constantly dispersed to all restroom surfaces. Viral and bacterial abundances were strongly correlated, and showed a remarkably low ratio, suggesting that hosts are mostly dormant in this system. OTU abundances were not significantly correlated with measured physical parameters (e.g. temperature and humidity). Together, these data indicate that human-associated microbes dominate restroom surfaces and follow neutral (stochastic) community assembly. We suggest that BE surface environments are microbial ‘deserts’, where resources are scarce and persistence depends upon dormancy or continuous dispersal, and we show that overzealous cleaning regimes in public restrooms lead to a transient dominance of human fecal microbiota, while normal soap and water cleaning results in a stable community dominated by skin-associated microbes.