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Type: Thesis
Title: Biodiversity, Environmental Microbiomes and Human Health
Author: Liddicoat, Craig Anthony
Issue Date: 2019
School/Discipline: School of Biological Sciences
Abstract: Emerging evidence suggests that exposure to microbial diversity and key species (Old Friends) from biodiverse, natural environments may provide critical immune training and regulation. Conversely, reduced contact with the right kind of environmental microbial communities (microbiota) and their genetic material (microbiomes) may contribute to the modern growth in immunoregulatory disorders with potential to impact both infectious and non-communicable diseases. However, possible connections between biodiversity, environmental microbiomes and human health remain understudied due to their multidisciplinary nature. There is limited knowledge of the composition, modes of action, and environmental distribution of Old Friends. We do not know if it is microbial diversity per se, key species, or a combination of both, that may have protective effects. Yet, importantly, the environment-host microbiota pathway offers promise for cost-effective population health interventions (e.g. through restoring biodiverse green space in cities) at a time when health care systems around the world are seeing unsustainable growth in utilisation and budget demands. Therefore, a primary goal of this thesis was to build knowledge of potential connections, with a view to informing policy. Specifically, the aims were to: 1. Test whether the notion of beneficial biodiversity-health relationships are supported in existing Australia-wide datasets 2. Examine what types or attributes of environments might be most associated with health benefits, to focus more detailed study 3. Identify microbial taxa that associate with natural vs. degraded environments and potential links to human health 4. Gather controlled experimental evidence of microbiota transfer from biodiverse environments to hosts, to explore potential mechanistic links. I employed multidisciplinary methods reflecting the nature of the research topic. From continent-wide environmental mapping and hospital admission datasets, I found that landscape-scale measures of biodiversity correlated with reduced rates of respiratory disease and ranked highly among known predictors. Also, I found that populations living near soils with high cation exchange capacity—a proxy for soil microbial diversity—experienced lower rates of infectious and parasitic disease. I developed a new merged-sample bootstrap resampling technique enabling deep analysis of soil bacterial 16S rRNA microbiome data from a grassy woodland restoration chronosequence, from which key indicator groups were identified. Human-associated opportunistic and pathogen-containing taxa were found to be favoured in disturbed environments, yet reduced in mature, biodiverse environments. Finally, in a randomised controlled experiment with mice exposed to airborne dust from soil spanning a biodiversity gradient, I found changes to gut microbiota and reduced anxiety-like behaviour in females corresponding to the high biodiversity treatment. Among bacterial taxa that increased in the gut of high treatment mice, I identified a putative sporeforming, anaerobic environmental microbe capable of producing a key metabolite, butyrate, linked to mammalian gut health and mental health. These findings suggest naturally-diverse soil microbial communities may provide a health protecting role due to: ecological controls on potential opportunistic pathogens, increased immunomodulatory microbial diversity, and enhanced capacity to support beneficial key species and metabolite production pathways, for example via the gut-brain-microbiome axis. Implications of this work include opportunities to improve public health through increased exposure to biodiverse green space and soils.
Advisor: Weinstein, Philip
Waycott, Michelle
Bi, Peng
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2019
Keywords: Biodiversity hypothesis
microbial old friends
hygiene hypothesis
green space
Provenance: This thesis is currently under Embargo and not available.
Appears in Collections:Research Theses

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