Caenorhabditis elegans populations shape their microbial environment.

Nematodes represent one of the most abundant and ecologically significant taxonomic groups on earth, playing diverse roles in the cycling of organic matter. However, little is known about their effects on their microbial environment. To explore such effects, we took advantage of the bacteriovore free-living nematode Caenorhabditis elegans, which has been shown to assemble a characteristic gut microbiome from different microbial environments. Worm populations (initially germ-free) were raised in several microbially-distinct natural-like environments emulating the environment from which C. elegans are often isolated, allowing worms to go through four generations encompassing the typical boom-to-bust population growth cycle. Samples from worms, their environments, and from control environments without worms were analyzed using next-generation 16S rRNA gene sequencing. Data analysis showed that microbial diversity increased in the environment, either when worms were present or not, but that trajectories of change were different depending on the presence of worms. Importantly, the presence of worms led with time to convergence in the composition of their microbial environments, particularly affecting the abundance of members of bacterial families that are part of the C. elegans gut microbiome. Our findings reveal that C. elegans not only responds to environmental microbial changes but also shapes them, suggesting new roles for nematodes in modulating environmental microbial diversity and ecosystems.