Restoring Urban and Human Microbiotas

Abstract

Humans harbour communities of coevolved microbiota known as ‘old friends’ and together we form ‘holobionts’ – multi-cellular organisms teeming with microbes that perform many critical functions for their host. These microbiota are important for our healthy physiological and immunological development, and disturbances to them can result in disease states such as chronic inflammatory conditions. The absence of certain microbes from the human body has been linked to chronic conditions, such as asthma or anxiety, and more broadly to the state of inflammation in our brain, lungs, gut, and skin. Modern processes, such as the state of our industrial food system, loss of biodiversity, and increasing urbanisation, are causing a loss of exposure to these coevolved microbiota that have been linked to the proliferation of many diseases worldwide. Urbanisation is one of the most widespread impacts, due to human demographic changes and limited exposure to biodiversity, but urban ecological restoration is a way to provide exposure to these ‘old friends’ in urban settings. A key focus of this thesis is to explore the potential of ecological restoration in urban green spaces to restore beneficial microbial diversity. The proceeding chapters empirically explore the interplay between environmental microbial diversity, the diversity of vegetation communities used in urban ecological restoration, and microbial interactions with humans in green spaces. In Chapter 1, we reviewed the literature relating to the nexus of microbially-mediated health (in humans, other animals, and plants), urbanisation, and restoration ecology. In Chapter 2, we investigated the effect of native revegetation on restoring urban soil microbiota to a remnant state in an Australian city. We found that revegetation of complex biodiverse vegetation states supported soil microbial communities that were more similar to remnant vegetation blocks, compared to those of low biodiversity urban spaces such as lawns, vacant lots, and parklands. However, urban vegetation communities can vary widely across the Earth. Therefore, in Chapter 3, we investigated the broader relationship between urban vegetation complexity and soil microbiota in multiple cities. Here, we found that high vegetation complexity (typically defined by higher structural, functional, and species diversity) was generally associated with unique microbial communities when compared to low vegetation complexity. Lastly, in Chapter 4, we investigated the effect of native revegetation on restoring disturbed microbial communities of human skin. We found that natively revegetated green space had a stronger effect on restoring human skin microbial communities than sports field (turf) green space and that staying indoors had no effect on restoring skin microbiota. These findings have implications for the application of biodiversity management in public, private, and educational spaces. However, future work needs to focus beyond the microbial ecology and cover the physiological and immunological responses of children using ecologically restored green space and on the potential risks (e.g., zoonotic spill-over) of increasing urban biodiversity interaction with high population densities.