Abstract
This study examined the specific association between earthworms, Eisenia fetida, and the
host-specific bacteria in their nephridia, or excretory organs, in order to determine if
bacterial colonization of the nephridia resulted in morphological changes in the
eukaryotic nephridial cells in contact with the prokaryotic symbionts. It was
hypothesized that the bacteria, Acidovorax sp., may induce ultrastructural changes in the
nephridia of Eisenia fetida, as has been discovered in other host-microbial systems. The
nephridial tissue architecture of symbiont-containing worms was compared with that of
worms that developed from eggs treated with antibiotics (asymbionts) by transmission
electron microscopy. Presence or absence of bacteria was confirmed by fluorescence in
situ hybridization. Results suggest the presence of Acidovorax is necessary for normal
development of nephridial structures, in particular microvilli and/or stereocilia on the
luminal surface of nephridial epithelial cells.
