High diversity within a simple worm

Research team from Kiel demonstrates the importance of a natural bacterial community in one of the classical model organisms

The worm Caenorhabditis elegans is one of the best studied model organisms in biology: For decades this tiny roundworm or nematode has been helping researchers to investigate diverse biological phenomena such as developmental processes and nervous system functions. For this work, scientists throughout the world are using a certain C. elegans strain which has been adapted to the laboratory environment and does not harbour any bacteria in its gut under these conditions. A research team from the Evolutionary Ecology and Genetics research group at Kiel University, led by Professor Hinrich Schulenburg, now demonstrated that a full appreciation of the nematode’s biology must take into account its interplay with the numerous microorganisms that live inside of the worm in nature. The Kiel researchers recently published their results on the effects of the so-called microbiome on nematode life history in the renowned journal BMC Biology.

This first systematic analysis of a natural nematode microbiome shows that the animals possess a species-rich bacterial community. Most common are Proteobacteria of the genera Pseudomonas, Stenotrophomonas or Ochrobactrum. According to the researchers, the microbial composition is key for a more realistic view of the biology of this little worm. Their work for example showed that the natural microbiome gives the animals an evolutionary advantage and protects them against pathogens.

Even more importantly: Previously, only sterile worms were used to study various biological principles in the several hundred C. elegans laboratories across the world. The new findings open a novel gateway into research with this worm. Scientists can now use the bacteria identified by the Schulenburg lab for their investigations in the future. “We are only at the beginning of research into the complex relationships between organisms and their associated microbes. We assume that bacteria have shaped multi-cellular life from the beginning. In future, our model will help us understand how exactly microbes influence evolution of their host organisms and in what way they determine key organismal functions such as development or immune defence against pathogens “, emphasised Schulenburg, a member of the “Kiel Life Science” research focus at Kiel University.

In order to determine the significance of the bacterial community for the worms, the researchers initially collected a total of 180 nematode samples at various sites in northern Germany, France and Portugal. The bacteria obtained from these animals were then transferred to sterile worms to study their effects on nematode life history traits. “By bringing the complex microbial community from nature into the laboratory under highly controlled conditions we can obtain a much more precise picture of the relationships between the worm as a host and its associated bacteria. This deep level of understanding would not be possible if we only studied the worms in the field”, said the lead author Dr. Philipp Dirksen.

Their study approach enabled the Kiel research team to determine a central influence of the microbiome on C. elegans. The microbiome increases the fitness of the animals under normal, but also highly stressful environmental conditions. For example, worms with their microbiome are better able to produce offspring at high temperatures than sterile worms. Various Pseudomonas bacteria also help the worms to protect themselves against fungal infections. The composition of the microbiome itself is determined by individual properties of the host, including for example their genetic characteristics. Overall worms with a natural microbiome seem to show higher fitness and reproduce at higher rates – a clear indication of an evolutionary advantage, which the bacteria provide for their host.

This new work now yields a novel and highly efficient model for the new scientific field of metaorganism research, which focusses on in-depth investigation of the interactions between organisms and their associated microorganisms. A few weeks ago the new Collaborative Research Centre (CRC) 1182 “Origin and Function of Metaorganisms” was established on this topic at Kiel University, in which Schulenburg’s research group is centrally involved.

The Kiel research team investigated for the first time the natural bacterial community of the roundworm Caenorhabditis elegans.
Image: Antje Thomas, Hinrich Schulenburg

The bacteria (coloured orange) mainly populate the digestive tract of the roundworm.
Image: Philipp Dirksen

Three-dimensional visualisation of the microbiome of Caenorhabditis elegans.
Animation: Dr. Philipp Dirksen

Original publication:
Philipp Dirksen, Sarah Arnaud Marsh, Ines Braker, Nele Heitland, Sophia Wagner, Rania Nakad, Sebastian Mader, Carola Petersen, Vienna Kowallik, Philip Rosenstiel, Marie-Anne Félix and Hinrich Schulenburg (2016): The native microbiome of the nematode Caenorhabditis elegans: Gateway to a new host-microbiome model. BMC Biology
Link: http://dx.doi.org/10.1186/s12915-016-0258-1

Prof. Hinrich Schulenburg
Arbeitsgruppe Evolutionsökologie und Genetik,
Zoologisches Institut, CAU Kiel
Tel.: +49 (0)431-880-4141
E-mail: hschulenburg@zoologie.uni-kiel.de