Does metal exposure affect the development of the microbial environment of nestlings?

Many environmental chemicals have harmful effects on microbes that are essential for the wellbeing of organisms. The effects of metals on the microbiota in soil and plants have been studied most extensively. In contrast, we still know very little about the impacts of metals on the microbiota of birds. Our research aims to find answers to these questions.

Published: 4.11.2021
Writer: Miia Rainio

Microbes are evolutionarily very old and they play a major role in terrestrial and aquatic ecosystems. Many microbes are essential for the wellbeing of organisms, having important role in several processes in the body. For example, gut microbes are essential for the metabolic and energy production of the organisms: the microbes transform nutrients into a usable form for organisms and they contribute to the detoxification of harmful substances and their excretion from the body.

Microbes are also utilized in many ways in food and pharmaceutical industries. However, some of the microbes are harmful. They can contaminate food and cause infections, diseases, impaired immune defence and many other physiological changes in the body.

Of the several environmental chemicals with harmful effects on microbes, heavy metals were selected as the subject of our study. Metals are known to affect, for example, the diversity and abundance of microbial populations and to change the composition of microbial communities. Metals can also inhibit the ability of microbes to metabolize or remove harmful compounds from the host system . So far, the impacts of metals on microbiota have mostly been studied in soil and plants. The effects on humans and other mammals have also been explored, but very little is known about the impacts of metals on the microbiota of birds.

Within my new research project, we will study the impacts of metal pollution on the early-life microbial environment of three common bird species: great tit, blue tit and pied flycatcher. These species were selected for our study because they breed in nest boxes and are common in our study area. They represent both resident and migratory birds, thus enabling us to gain information about possible differences in microbial communities between the species as well as the susceptibility of the microbiome of the different species to metal exposure.


Hundreds of nest boxes and European collaboration

Small chicks are highly sensitive to environmental changes, and many chemicals may have detrimental effects on the early-life development of birds. In our project, we will study the diversity of gut and nest microbes as well as the differences in microbial communities between the metal polluted areas and clean control areas. Our study area is located in the surroundings of  metal smelters in the Harjavalta Industrial Park in south-western Finland. In this area, bird breeding has been studied for more than 30 years. The long-term studies have produced plenty of information about the impacts of metal pollution on the breeding behaviour and physiology of birds, as well as the changes in metal concentrations over the past three decades.

Across our study area, there are altogether 350 nest boxes for research purposes, placed both in the immediate vicinity of the emission source and farther away in the control areas. Moreover, faecal samples will be collected from polluted environments in different parts of Europe in order to gain a broader picture of the potential harmful effects of metal pollution on the microbiota of birds. In this work, we are assisted by an extensive collaborative network. Responses of microbiota to pollution, habitat, microclimate, taxonomy and dietary differences will be measured and connected to physiological and ecological measures of individual performance. Of the various physiological responses, we study, for example, the enzymes related to the antioxidant and immune defence systems. Correspondingly, of the ecological responses, the life-cycle characteristics and breeding success are of particular interest.


Nest manipulation experiments can be used to trace the source of exposure

During summer 2021, we collected faecal samples from the nestlings and nest material for the gut and nest microbiota analyses, which are currently in progress. From the samples, we will also determine the metal contents in order to study the associations between possible changes in microbial communities and the metal contents. Molecular biology methods will be applied to study the microbiota. First, bacterial DNA is isolated from the faecal and nest materials, after which the PCR (polymerase chain reaction) amplification technique is used to produce sufficient copies of the target gene region. The samples are then compiled into a sequencing library, with an individual code attached to each sample for identification. For the bacterial identification we use the NGS (next generation sequencing) technique to sequence the target gene region  to reveal the base sequence of the bacteria. Finally, bacterial species are identified from the open-source genomic databases.

By comparing the bacterial species between the polluted and control areas as well as between the study species, we get more information about the possible changes in microbial communities caused by metal exposure. The microbial results can also be linked with the breeding and physiological data in order to examine possible interactions. Nestlings can be exposed to metals either via nest material or the food  provided by their parents. In case we observe differences in microbial communities between the treatment groups, we will carry out nest manipulation experiments during the following field periods for the purpose of identifying the main source of exposure.

Our study design also enables us to  study changes in the metabolites of microbes by using the metabolomics techniques. Metabolomics studies the structure, function and interactions of small-molecular  metabolites in the body, providing information about the possible functional changes of microbial communities in the host system. Our research findings will provide new information about the impacts of metal exposure on the development of microbiota during the nestling period. In addition, they will offer a new perspective on generally inferior growth and nestling production, which have been repeatedly observed in the bird populations of urban and industrial environments, even if no direct toxic impacts of metals have been observed. 

Bilden av Miia Rainio.

PhD, Docent Miia Rainio is working as a post-doc researcher in the Department of Biology at the University of Turku. For her doctoral dissertation in 2013, she examined the impacts of metal pollution on the oxidative stress and antioxidant defence in birds. In recent years, she has studied the impacts of a herbicide, glyphosate, on the life-cycle characteristics, physiology and microbiome of plants, insects and birds.




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