Daylight exposure modulates bacterial communities associated with household dust

Abstract

BackgroundMicrobial 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.ResultsLight 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.ConclusionsOur 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.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0559-4) contains supplementary material, which is available to authorized users.

Building upon current knowledge and techniques of indoor microbiology to construct the next era of theory into microorganisms, health, and the built environment

“…Architecture influences building biogeography and patterns of microbial dispersal indoors [44,46]; the building materials, surfaces, and products we use [43,83,84]; the indoor environmental conditions (e.g., temperature, humidity, light, and airflow) [55,85,86]; and the connectivity of the indoors to the outdoors and its associated microorganisms [34,87], all of which can affect the location of microorganisms in the built environment and survival once there. Despite the seeming inhospitality of the built environment [88], many microorganisms can survive indoors for months [89][90][91][92], and environmental conditions indoors can facilitate intermittent bacterial and fungal growth [86].…”

“…Moreover, there are plenty of nutrient substrates. Human skin squamous cells shed indoors serve as a ready food source for bacteria living in HVAC systems [93], and sufficient nutrients exist in house dust to host a living bacterial community even after 90 days of isolation [85].…”

“…While effective [155], it is logical to predict that resistance to UVC might develop over time with increased exposure. Only a few studies evaluate the effect of light on whole microbial communities related to the built environment, including those in house dust or on human skin [85,162,163]. A recent study demonstrated that different light wavelengths affect the survival of bacteria in complex dust communities differently: visible or UV light reduces the number of living bacteria in dust and results in a less humanassociated bacterial community than darkness does [85,143].…”

“…Only a few studies evaluate the effect of light on whole microbial communities related to the built environment, including those in house dust or on human skin [85,162,163]. A recent study demonstrated that different light wavelengths affect the survival of bacteria in complex dust communities differently: visible or UV light reduces the number of living bacteria in dust and results in a less humanassociated bacterial community than darkness does [85,143]. Similarly, indoor surface bacterial communities contained fewer human-associated taxa as the amount of illumination in hospital rooms increased [164].…”

From one species to another: A review on the interaction between chemistry and microbiology in relation to cleaning in the built environment

“…During their early stages of formation, biofilms can be removed using abrasive methods such as pressurized air or water, but once established, simple abrasion often fails to remove all or any of the microorganisms. Visible spectra of light, as well as ultraviolet light, triggers damage to cellular components by changing their biochemistry, reduces microbial biomass in dust, 135 and inactivates some pathogens. 133,134 Physical destruction of cells may involve radiation, desiccation, heat, and/or pressurization (eg, autoclaving).…”