This highly-anticipated study on the effect of natural daylight treatments on whole bacterial communities in household dust from the University of Oregon’s Biology and the Built Environment Center is now available!

Daylight exposure modulates bacterial communities associated with household dust

Ashkaan K. Fahimipour , Erica M. Hartmann, Andrew Siemens, Jeff Kline, David A. Levin, Hannah Wilson, Clarisse M. Betancourt-Román, GZ Brown, Mark Fretz, Dale Northcutt,
Kyla N. Siemens, Curtis Huttenhower, Jessica L. Green and Kevin Van Den Wymelenberg.  Microbiome (2018) 6:175: https://doi.org/10.1186/s40168-018-0559-4

Abstract
Background: Microbial communities associated with indoor dust abound in the built environment. The
transmission of sunlight through windows is a key building design consideration, but the effects of light exposure on
dust communities remain unclear. We report results of an experiment and computational models designed to assess
the effects of light exposure and wavelengths on the structure of the dust microbiome. Specifically, we placed
household dust in replicate model “rooms” with windows that transmitted visible, ultraviolet, or no light and
measured taxonomic compositions, absolute abundances, and viabilities of the resulting bacterial communities.

Results: Light exposure per se led to lower abundances of viable bacteria and communities that were
compositionally distinct from dark rooms, suggesting preferential inactivation of some microbes over others under
daylighting conditions. Differences between communities experiencing visible and ultraviolet light wavelengths were
relatively minor, manifesting primarily in abundances of dead human-derived taxa. Daylighting was associated with
the loss of a few numerically dominant groups of related microorganisms and apparent increases in the abundances
of some rare groups, suggesting that a small number of microorganisms may have exhibited modest population
growth under lighting conditions. Although biological processes like population growth on dust could have
generated these patterns, we also present an alternate statistical explanation using sampling models from ecology;
simulations indicate that artefactual, apparent increases in the abundances of very rare taxa may be a null expectation
following the selective inactivation of dominant microorganisms in a community.

Conclusions: Our experimental and simulation-based results indicate that dust contains living bacterial taxa that can
be inactivated following changes in local abiotic conditions and suggest that the bactericidal potential of ordinary
window-filtered sunlight may be similar to ultraviolet wavelengths across dosages that are relevant to real buildings.

Keywords: Dust, Daylight, Microbiome, Built environment