Microbial biogeography of a university campus

Humans interact with microorganisms on a daily basis in the built environment. Microorganisms inhabit the surfaces of homes, workplaces, and schools, with the potential to impact human health and disease. University campuses represent a unique opportunity to explore the distribution of microorganisms of the built environment because of high population densities, throughput, and variable building usages. For example, the main campus of the University of Waterloo spans four square kilometres, hosts over 40,000 individuals daily, and is comprised of a variety of buildings, including lecture halls, gyms, restaurants, residences, and a daycare.Representative left and right entrance door handles from each of the 65 buildings at the University of Waterloo were swabbed at three timepoints during an academic term in order to determine if microbial community assemblages correlate with building usage, and whether these communities are stable temporally. Across all door handles, the dominant phyla were Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes, which comprised 89.0% of all reads. A total of 713 genera were observed, 16 of which constituted a minimum of 1% of the 2,458,094 total rarefied reads. Archaea were found in low abundance (0.026%), but were present on 42.8% of door handles on 96% of buildings, indicating that they are ubiquitous at very low levels on door handle surfaces. Although inter-handle variability was high, several individual building entrances harboured distinct microbial communities that were largely consistent over time. The presence of visible environmental debris on a subset of handles was associated with distinct microbial communities (beta diversity), increased richness (alpha diversity), and higher biomass (ATP). This study demonstrates highly variable microbial communities associated with frequently contacted door handles on a university campus. Nonetheless, the data also revealed several building-specific and temporally stable bacterial and archaeal community patterns, with a potential impact of accumulated debris on detected microbial communities.