This grant supports two additional years of research by a team at the Berkeley Indoor Microbial Research Consortium, which aims to expand our understanding of the microbial ecology of the built environment as mediated by interactions among organisms, particulate matter, and volatile and nonvolatile chemicals. Under the direction of principal investigator (PI) Thomas Bruns, professor of plant and microbial ecology at the University of California, Berkeley, the proposed work plan is organized around four objectives: Build an integrated understanding of the role of occupancy and occupant behaviors on bioaerosols and microbially derived chemical emissions in residential environments. The biological measurements will be made in collaboration with the Berkeley Chemistry of Indoor Environments (CIE) team (see Berkeley CIE proposal) as part of the intensive field campaign taking place in one-to-two residences. Characterize the chemistry of biological interactions among microorganisms on residential indoor surfaces, incorporating both mVOC measurements and the study of nonvolatile chemical compounds, as measured through nanospray desorption electrospray ionization mass spectrometry (NanoDESI MS). Determine the metabolic state and activity of indoor microbes. Develop improved methods for sampling and assaying microbial communities in built environments. Research findings will be shared through peer-reviewed publications, presentations at conferences and meetings, and through blogs on microBE.net. At least three postdoctoral fellows will be trained in the course of the project.