Worm and Its Microbiome Show Remarkable Resilience to Toxins Using Near-Natural Compost Mesocosm Experiment

The ability to adapt to changing environments is crucial for the survival and evolution of living organisms.

However, adaptation is not only a matter of individual organisms but also of their interactions with other living beings, especially the microorganisms that live in and on them.

These microorganisms, collectively known as the microbiome, can influence various aspects of the host organism's physiology, behavior, and fitness.

Therefore, understanding how hosts and microbes co-evolve in response to environmental changes is an important question in biology.

A recent study investigated how a simple animal host, the nematode Caenorhabditis elegans, and its associated microbiome adapted to a novel and complex environment over time.

The study used a novel experimental approach that allowed the researchers to track changes in both host and microbiome at multiple levels.

The results showed that the host and microbiome can jointly contribute to the environmental adaptation of the metaorganism, but also that different evolutionary trajectories can emerge depending on the initial conditions.

The study also has implications for human health, as it suggests that changes in the microbiome can affect host fitness and vice versa.

The Role of the Microbiome in meta Meta-organism Adaptation

(Photo : FRANK PERRY/AFP via Getty Images)

All multicellular organisms, from the simplest animal and plant organisms to humans, live in close association with a variety of microorganisms, known as the microbiome, which colonizes on and in their tissues and forms symbiotic relationships with the host.

The microbiome can provide essential functions such as nutrient uptake, regulation of the immune system, or even neurological processes, that result from the interactions between host organism and microbial symbionts.

The functional cooperation between host and microorganisms, which scientists refer to as a meta organism, is being studied in detail at Kiel University in the Collaborative Research Center (CRC) 1182 "Origin and Function of Metaorganisms".

Scientists assumed that the microbiome can contribute significantly to the environmental adaptation of an entire organism.

This may be due to the rapid adaptability of microorganisms, which can react many times faster to changing environmental conditions than their host organism.

Numerous studies have already shown that the microbiome responds to changing environmental factors such as higher temperatures, for example, by changing its species composition and thus contributing to the environmental adaptation of the host organism.

However, many of these studies have so far focused only on the microbiome, but not the host.

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A novel experiment to study host-microbiome co-evolution

Researchers from the Evolutionary Ecology and Genetics group led by Professor Hinrich Schulenburg at the Institute of Zoology at Kiel University have now focused on the joint influences of host organisms and the microbiome in a new study.

To this end, they developed an innovative cultivation method to investigate the adaptations of a metaorganism to novel environmental conditions: the nematode Caenorhabditis elegans evolved in a long-term experiment over 100 days together with an originally specified selection of microorganisms under complex and near-natural environmental conditions in a compost habitat.

The researchers then analyzed changes both on the part of the hosts and in the microbiome and found that under certain conditions both contribute jointly to the optimal adaptation of the whole organism to a new environment.

The Kiel researchers, who cooperated in this study with Professor Brendan Bohannan and his team from the University of Oregon in the U.S., recently published their results in The ISME Journal.

The researchers observed that adaptation took different trajectories in different mesocosm lines, with some increasing in fitness and others decreasing, and that interactions between host and microbiome played an important role in these contrasting evolutionary paths.

They chose two exemplary mesocosms (one with a fitness increase and one with a decrease) for detailed study.

For each example, they identified specific changes in both microbiome composition (for both bacteria and fungi) and nematode gene expression associated with each change in fitness.

Their study provided experimental evidence that adaptation to a novel environment can be jointly influenced by the host and microbiome.

The researchers hoped that their novel experimental approach can be applied to other model systems and environments and that it can help to reveal general principles of metaorganism evolution.

They also suggested that their findings have implications for human health, as they show that changes in the microbiome can affect host fitness and vice versa.

Therefore, understanding how hosts and microbes co-evolve may be crucial for developing effective therapies for diseases involving microbial dysbiosis.

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