Vertical Stratification in Urban Green Space Aerobiomes

Abstract

BACKGROUND: Exposure to a diverse environmental microbiome is thought to play an important role in "educating" the immune system and facilitating competitive exclusion of pathogens to maintain human health. Vegetation and soil are key sources of airborne microbiota-the aerobiome. A limited number of studies have attempted to characterize the dynamics of near surface green space aerobiomes, and no studies to date have investigated these dynamics from a vertical perspective. Vertical stratification in the aerobiome could have important implications for public health and for the design, engineering, and management of urban green spaces. OBJECTIVES: The primary objectives of this study were to: a) assess whether significant vertical stratification in bacterial species richness and evenness (alpha diversity) of the aerobiome occurred in a parkland habitat in Adelaide, South Australia; b) assess whether significant compositional differences (beta diversity) between sampling heights occurred; and c) to preliminarily assess whether there were significant altitudinal differences in potentially pathogenic and beneficial bacterial taxa. METHODS: We combined an innovative columnar sampling method at soil level, 0.0, 0.5, 1.0, and 2:0 m, using passive petri dish sampling to collect airborne bacteria. We used a geographic information system (GIS) to select study sites, and we used high-throughput sequencing of the bacterial 16S rRNA gene to assess whether significant vertical stratification of the aerobiome occurred. RESULTS: Our results provide evidence of vertical stratification in both alpha and beta (compositional) diversity of airborne bacterial communities, with diversity decreasing roughly with height. We also found significant vertical stratification in potentially pathogenic and beneficial bacterial taxa. DISCUSSION: Although additional research is needed, our preliminary findings point to potentially different exposure attributes that may be contingent on human height and activity type. Our results lay the foundations for further research into the vertical characteristics of urban green space aerobiomes and their implications for public health and urban planning.

Exposure to Airborne Bacteria Depends upon Vertical Stratification and Vegetation Complexity

“…As mentioned, urban green space exposure can result in transfer of environmental bacteria to the skin and respiratory tract ( 21 ), and our study shows that the composition and diversity of aerobiome bacteria may differ between heights (from ground level to 2 m). Consequently, there could be different bacterial exposure levels and transfer loads depending on a person’s height and activity ( 27 ), however, further confirmatory research is needed. Our results suggest that this may not be the case in amenity grassland where bacterial alpha and beta diversity exhibited high levels of homogeneity among heights.…”

“…Mhuireach et al (2019) identified localised influences on aerobiomes, including weather and land management ( 22, 26 ). Our recent work has also demonstrated aerobiome vertical stratification between ground level and 2 m heights in an urban green space ( 27 ). Together, these studies suggest that individuals may be exposed to different aerobiomes depending on the type of habitat visited and human-scale height-based variation in environmental aerobiomes.…”

“…Sampling stations ( Fig. 10, b to e ) were constructed using timber (42 mm × 28 mm × m), steel brackets, hooks and guy-lines ( 27 ). We secured lab-grade clear plastic petri dishes (bases and lids) to the sampling stations, which were used to sample the aerobiome via passive sampling ( 22 ).…”

From the Ground up: Assessing Bacterial Diversity in the Air Space of an Urban Park

“…A recent proof-of-concept study in Environmental Health Perspectives described how the diversity of airborne bacterial communities decreased from ground level to in height in an urban park, noting that the makeup of the communities also varied, depending on height. 3 …”

“…A recent proof-of-concept study in Environmental Health Perspectives described how the diversity of airborne bacterial communities decreased from ground level to 2 m in height in an urban park, noting that the makeup of the communities also varied, depending on height. 3 "Exposure to a diverse set of microbes from our environment trains our immune systems to respond appropriately to pathogens," says Graham Rook, a professor of medical microbiology at University College London who was not involved in the study. Lack of exposure to bacterial diversity has been associated with autoimmune diseases, 4 allergies, 5 Alzheimer's disease, 6 and inflammatory bowel disease.…”