Collaborative Research: Unraveling Patterns of Infection and Co-Speciation among Earthworm-Bacterial Symbiont Associations

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Earthworms are among the most recognized soil-dwelling animals and occur on every continent except Antarctica. They are active in altering soil structure and nutrient availability in soils throughout the world, and known for their utility in composting. Earthworms harbor symbiotic bacteria of the Acidovorax genus in their internal kidney-like organs, the nephridia (ca. 200 per worm), that eliminate waste fluid ("urine"). Unlike the diverse microbiota of the gut, bacteria of the nephridia appear to form stable and specific associations such that particular species of earthworms harbor their own species of symbiotic Acidovorax. In addition, a second bacterial symbiont related to Actinobacteria was recently discovered in Eisenia fetida, suggesting even greater diversity among earthworm symbionts. The diversity of the bacteria associated with different earthworm taxa and their contribution to the success of earthworms are virtually unexplored. This collaborative research project integrates morphological identification and genetic sequence information to identify earthworms and their associated symbiotic bacteria from several continents. A suite of genes that have shown previous success in determining relationships among organisms has been selected to be sequenced. The data will be used to determine the genetic relationships among both the host earthworms and their bacterial partners to establish evolutionary patterns for this association. Discovery of novel species of both the host and symbiont is expected as well as a better understanding of the diversity of the earthworms and their associated bacteria. This research is crucial for understanding the processes occurring in the soil that influence soil chemistry and fertility through the activity of these widespread members of soil systems. Furthermore, one of the symbiotic bacterial lineages may be a source of novel anti-microbial compounds. The diversity and global distribution of earthworms offers an opportunity for the evolution of bacterial symbionts with potential for new bioactive compounds and enzymes.International collaborations are a necessary part of the research to accomplish collections from several continents and contribute to an international effort to accumulate sequences for rapid organism identification ("BarCode of Life"). The work will engage and provide training to young scientists in field collection, molecular methods for phylogenetic systematics and bacterial community analysis.