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More than half of the human population live in urban areas, making cities the most common interface where humans interact with their surroundings and other organisms, including microbes. Even though micro-organisms like bacteria and fungi are invisible to the naked eye, they perform versatile functions essential for proper ecosystem functioning (carried out by free-living microbes) as well as for a healthy animal life (carried out by host-associated microbes).

In this thesis, Tiffany Scholier studied how the urban environment influences the communities of bacteria and fungi, both in forest soil and in the gut of wild bank voles (Clethrionomys glareolus), to understand the differences in microbial communities between urban and more natural environments.

Bacterial and fungal microbial communities found in urban and non-urban forests were found to be distinct, both in terms of soil microbes and microbes living in the gut of bank voles.

— I found that the changes in the soil microbes in cities were generally associated with higher alkaline soil, which is possibly caused by rain run-off over alkaline concrete material such as streets and gutters, says Scholier.

At the same time, changes in the bank vole gut communities are likely linked to changes in the diet between urban and non-urban bank voles. For example, the diet of urban bank voles contained higher levels of protein. Additionally, a reciprocal transplant experiment where bank voles were transferred between urban and non-urban forests revealed that the gut microbes of bank voles partly retain the signal of the prior environment after translocation and partly adjust their microbes to the new environment.

This means that the microbes of migrated or transferred bank voles cannot fully shift towards the typical community associated with their present environment, which could potentially impair adaptation of these animals.

— Overall, these results contribute to the general knowledge about human-induced changes to microbes in the wild and highlight that the microbial communities in cities are inherently different that those you can encounter in more natural forests, Scholier sums.

M.Sc. Tiffany Scholier defends her doctoral dissertation ”Cities and their effects on free-living and host-associated microbe” on 18.8.2023 at 12:00 in lecture hall S212 in Seminaarinmäki. Opponent is Academy Research Fellow Thomas Lilley (University of Helsinki) and custos is Professor Tapio Mappes (Ģ��ֱ��). The language of the dissertation is English.

Publication details

The thesis “Cities and their effects on free-living and host-associated microbe” is available in the JYX repository: