Our Microscopic Neighbors: How External Factors Affect Viability and Microbial Dynamics of Bacteria in the Built Environment

Abstract

The built environment (BE) consists of human-made structures, and the bacteria of the BE can potentially affect human health because of their constant proximity to humans. This has led to increasing public concern of whether the bacteria in the BE are harmful. Therefore, previous studies have analyzed the composition of the BE microbiome and the external factors that affect its formation and dynamics to assess if bacteria in the BE can affect human health. However, there is a gap in literature in determining the viability of bacteria in the BE with culture-independent molecular methods and assessing the relative importance of external factors in affecting the dynamics of bacteria in the BE. Therefore, the objectives of this study are to systematically profile a BE and quantify bacterial viability and to determine which external factors affect the BE bacterial population the most by isolating these factors as independent variables and measuring the resulting bacterial viability. By profiling a typical home BE, we found that the home BE microbiome has low viability by using the PMA-ddPCR approach to evaluate bacterial viability and that a large fraction of the bacteria comes from the human microbiome. We also found that water content level was the primary driver of variations in viability on BE surfaces, while location was the primary driver of differences in bacterial richness. We then isolated four external factors, surface material, human interaction, relative humidity, and temperature, to exclude confounding factors and to determine the relative impact that each factor had on bacterial viability in the BE. We discovered that relative humidity and human interaction had the largest impact, temperature had moderate impact, and surface material had the least impact. This research will better inform the scientific community of the bacterial viability in the BE, and which external factors are most important in changing microbial viability. Consequently, this understanding will update our conception of the BE microbiome to better assess whether bacteria in the BE can affect human health and to take steps in maintaining a healthy microbiome indoors.