Author: Joel Brame
Brame, Joel, 2024 Breathing in Health: Assessing the potential of outdoor environments to transfer health-promoting butyrate-producing bacteria to people, Flinders University, College of Science and Engineering
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Background
Butyrate-producing bacteria ferment organic matter including fibres and amino acids into butyrate, a short-chain fatty acid that has important roles in human health and soils. Human gut bacterial assemblages include butyrate-producing bacteria that thrive in the anaerobic gut conditions. However, many physical and mental health conditions have been associated with a reduction in colonic butyrate-producing bacteria. Outdoor greenspaces may be rich reservoirs of butyrate-producing bacteria that could transfer to humans and supplement their abundances, especially for urban residents with less exposure to nature and biodiversity. Yet, outdoor butyrate producer abundances and the ecological characteristics that associate with them remain poorly resolved. In this thesis, I identify and describe the abundances of butyrate-producing bacteria in outdoor environments, particularly urban greenspaces, and the ecological conditions that associate with their abundances.
Methods and Results
I performed a literature search and found that the sources of gut colonisation of butyrate-producing bacteria after birth, particularly outdoor sources, remain largely unknown (= Chapter 1). I then used in-silico database interrogation and analyses of global shotgun metagenomic samples and Australian 16S rRNA soil samples to associate environmental characteristics with read abundances of human- accessible butyrate-producing bacteria. Butyrate-producing bacterial reads were widespread in environments such as soils and aquatic biomes throughout the world. In soils across continental Australia, butyrate producer read abundances were highest in temperate urban hinterlands and seasonally productive sandy croplands and associated strongly with iron (= Chapter 2). I then obtained soil shotgun metagenomic data and air 16S rRNA data from replicates (total n = 33) of two types of greenspaces (sports fields and nature parks) across metropolitan Adelaide, Australia, to describe the effects of ecological characteristics on aerobiome bacterial diversity and composition, soil butyrate-producing bacterial read abundances, butyrate production terminal genes, and soil butyrate concentrations. The aerobiomes of sports fields at a 0.5 m sampling height were more influenced by soil iron and pH and rainfall than by the surrounding woody plant species diversity (= Chapter 3). Sports fields had more genes for butyrate production and higher soil butyrate concentrations than nature parks. The aerobiomes of sports fields at a 0.5 m sampling height were more influenced by soil iron and pH and rainfall than by the surrounding woody plant species diversity (= Chapter 3; Figure 1). Soil conditions, especially iron, had strong positive effects on both butyrate-related genes and soil butyrate concentrations (= Chapter 4). Finally, in a Māori cohort human exposure trial, I obtained and analysed air and nasal 16S rRNA taxonomic read abundances to quantify the transfer of airborne bacteria onto people taking a walk in an amenity grassland park (= Chapter 5). I found that 30-minute exposure periods to urban greenspaces did not create consistent or notable changes in the nasal microbiome of visitors.
Overall, we describe the influence of several ecological conditions (i.e., greenspace type, woody plant species diversity, and soil physicochemical parameters) on the abundances and activity of butyrate-producing bacteria in soils and aerobiome diversity. Our findings contribute important new insights into the role of sports fields as key exposure reservoirs of butyrate and butyrate producing bacteria. These findings provide opportunities for landscape designers, urban planners, ecologists, and public health experts to work together on new ways to support human health via urban greenspaces.
Keywords: microbial ecology, microbiome, soil metagenomes, aerobiome, butyrate-producing bacteria, short-chain fatty acids, butyrate, ecosystem services, soil bacteria
Subject: Microbiology & Infectious Diseases thesis
Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Science and Engineering
Supervisor: Martin Breed