Face to face with microbes at National Street Tree Symposium

By Celeste Cook, Extension Officer, Tasmania & South Australia

Treenet’s 23rd National Street Tree Symposium delivered some great speakers this year, with my personal highlight being Jacob Mills, a microbiologist who has been looking into the effect of urban environments on the human microbiome. Jacob’s work confirms what a lot of us in the greenlife industry already know, a healthier urban environment for humans requires a biodiverse plant community.

Treenet’s 23rd National Street Tree Symposium was held from 1-2 September 2022 at the National Wine Centre & Adelaide Botanic Garden in Adelaide, South Australia. The symposium’s theme was ‘Face to face with trees’, and the program included an array of speakers on diverse and interesting topics from mechanisms for evaluating tree value to climate change. Many of these presentations were pertinent to the entire greenlife industry.

I travelled to the symposium to further my knowledge on influencing factors for the tree production community. Whilst there, I heard Jacob Mills from the University of Adelaide speak about his work in studying the composition of the urban microbiome and its effect on human health. Jacob’s two most recent studies provided an insight into his interest in ecosystem microbiomes and their relationship with the human microbiome, described by Jacob on his website as follows:

“We need to understand that we are nature. That we’re a walking ecosystem of bacteria, worms, and all sorts of little creatures in and on a human ‘mountain’. We’re in a co-dependent relationship with them, so much so that our health hinges on how well they’re doing. The ecosystem that we are gets its integrity from the health of the greater ecosystems that we walk through”¹.

I think most people that have worked in the greenlife industry feel that there is a direct correlation between their health and exposure to greenlife. Jacob, however, is looking at quantifying this phenomenon in his studies. The two studies presented during the symposium will make this clear through the comparison microbiomes associated with urban ecosystems.

The first study involved a group of school children. This study examined the effect of the urban habitat on increasing human microbiome diversity and reducing associated disease, i.e., will the good microorganisms outnumber the bad on the skin surface when exposed to more biodiverse environments? In simple terms, this involved swabbing participants’ arms before and after treatment with a sanitiser and then exposing them to one of three environments: a school classroom, a sports field, and a biodiverse forest. The microbiota species from the first and second swabs were then compared.

Results indicated that exposure to the forest not only replenished the lost species but also created a more biodiverse population of skin microbiota². The sports field treatment had a similar slightly less diverse effect, with the classroom exposure samples significantly less diverse in species. Children exposed to sports fields and forests also acquired new core bacteria after exposure to green spaces, potentially buffering against disturbances to the skin microbiota’s diversity, while individuals who remained in the classroom lost microbes throughout the experiment.

Although the exact health impacts are not yet known, this data and that of similar studies point towards implications for the way schools and other social areas are developed and planned, highlighting the benefits to creating urban environments that value plant biodiversity as a component of human health. This may be potentially important as urbanisation and a lack of microbial biodiversity has been linked to public health issues and rising non-communicable disease rates.

The second of Jacob’s studies presented at the symposium also involved a study of a microbiome. However, this time the researchers measured the diversity of the soil microbiome and its association with vegetative biodiversity in three different urban ecosystems. Although the findings from this study were not conclusive, they did support a relationship between the diversity of the vegetative community and the microbial diversity in the soil³. There is also a link between vegetative biodiversity and higher organic carbon content and cation exchange capacities of soils.

We all know that biodiversity in our urban environments is lacking at the macro scale and that improvements made to these areas has a positive impact on the immediate environment, the climate and human mental health. Although these studies are not definitive, they do indicate that improving diversity in our urban environments may improve human health as well as human wellbeing at the micro scale. I look forward to following Jacob Mills’ studies to see what develops in this space.

References

1. Mills, Jacob 2022, ‘Microbes and the universe’, viewed 9 September 2022, www.jacobmills.org
2. Mills, JG, Selway, CA, Thomas, T, Weyrich, LS & Lowe AJ 2022, ‘Schoolyard Biodiversity Determines Short-Term Recovery of Disturbed Skin Microbiota in Children’, Microbial Ecology,  viewed 9 September 2022, https://link.springer.com/article/10.1007/s00248-022-02052-2
3. Mills, JG, Selway, CA, Weyrich, LS, Skelly, C, Weinstein, P, Thomas, T, Young, JM, Marczylo, E, Yadav, S, Yadav, V, Lowe, AJ & Breed, MF 2022, ‘Rare genera differentiate urban green space soil bacterial communities in three cities across the world’, Access Microbiology, 4(1), viewed 9 September 2022, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8895604/