Earthworms (Annelida; Lumbricidae) harbour species-specific symbiotic bacteria in their nephridia (excretory organs) where the symbionts densely colonize a specific part of the nephridia called the ampulla . The symbiosis is universal among earthworms, the symbionts form a monophyletic cluster within the genus Acidovorax , and they are transmitted vertically . For these reasons, we suggest that the earthworm-Acidovorax association has evolved by co-speciation. This hypothesis was tested by a comparative study of earthworm and symbiont phylogeny. Different earthworm species were collected in Denmark and DNA was extracted from their nephridia. Earthworm phylogeny was resolved on the basis of mitochondrial cytochrome c oxidase subunit I (COI) by direct PCR amplification and sequencing from the nephridial DNA extract. Symbiont 16S rRNA gene sequences were retrieved by cloning and sequencing the extracted DNA. The presence of the symbionts in the ampulla was verified by performing fluorescence in situ hybridization (FISH) on all worm species using an Acidovorax-specific probe. Earthworm and symbiont phylogeny was largely congruent, indicating that host and symbiont have indeed co-evolved since the initial bacterial colonization of an ancestral lumbricid worm. However, the association is complicated by the recent discovery of additional, putative symbiotic bacteria which have been detected in the ampulla of several earthworms by FISH. Identity, distribution among earthworms, and function of these non-Acidovorax symbionts are still to be investigated.  Knop, J. 1926. Z Morph Ökol Tiere, 6(3):588-624.  Schramm, A. et al. 2003. Environ Microbiol 5(9):804-809.  Davidson, S.K. & Stahl, D.A. 2006. Appl Environ Microbiol 72(1):769-775.
Hidden Powers - Microbial Communities in Action.proceedings of the 11th International Symposium on Microbial Ecology (isme-11). Vienna, Austria, 2006
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11th International Symposium on Microbial Ecology (ISME-11), 2006