Buildings as metacommunities

Background/Question/Methods

The indoor environment is an ecosystem teeming with diverse life forms invisible to the naked eye: microorganisms. During the time we spend indoors we are submerged in an ocean of air that holds hundreds of thousands of individual microbial cells per cubic meter. Even greater densities of microbes inhabit the surfaces surrounding you.  This indoor ecosystem is your primary habitat, where you will spend 90% of your life. Consequently, the way we design and operate the indoor environment has a profound impact on our health and well-being. To understand the relationship between building ecology, building design, and building performance, we initiated a sampling campaign in a LEED Silver certified facility at the University of Oregon - the Lillis Business Complex.  We address three main questions: 1) Does microbial community structure indoors vary predictably across space, time and environment? 2) Do sustainable building operations - specifically natural ventilation versus mechanical ventilation - influence microbial communities indoors? 3) Does microbial community composition vary as a function of human occupancy load indoors? To answer these questions, we collected architectural, environmental, and biological data in Lillis from August 4 – 10, 2011.  Biological data were collected by continuously sampling microbial communities from air for one week in 8 classrooms and by recording human occupancy load across time. Airborne bacterial community composition in each sample was quantified using high-throughput Illumina sequencing of the 16S rRNA gene. Architectural and environmental data included air temperature and relative humidity within classrooms and within HVAC systems, surface temperatures of floors and ceilings, airflow rates, and exterior climate information such as temperature, relative humidity and solar radiation.

Results/Conclusions

The dominant bacterial taxa in indoor air included Proteobacteria, Actinobacteria, and Bacteroidetes. The diversity and composition of airborne bacterial communities differed among outdoor air, mechanically ventilated classrooms and naturally-ventilated classrooms. The structure of airborne bacterial communities (taxonomic and phylogenetic beta diversity) varied predictably in space (room sampled), time (date and time of sampling), and environment (temperature and relative humidity). Natural ventilation via a "night flush" of outdoor air resulted in a distinctive airborne bacterial community in classrooms compared to the communities in mechanically ventilated classrooms. Microbial community composition indoors varied predictably as a function of human occupancy, with the abundance of certain bacterial taxa associated with higher densities of human occupancy in classrooms. Our results provide additional evidence that building design and operation influence the structure and dynamics of indoor ecosystems.