A demonstration of bacterial conjugation within the alimentary canal of Rhabditis nematodes

Rhabditis nematodes fed a diet of Escherichia coli defecate viable undigested bacteria. These bacteria retain phenotypic characteristics, including those encoded on plasmids. Nematodes can survive a 2-min surface sterilization with 2% chlorine bleach; internalized bacteria also survive this treatment and are released in the nematode wastes. Bacteria alone or on the surface of dead nematodes are unable to survive incubation with this solution. There were 3.2 × 10⁵ viable bacteria per nematode, indicating that sufficient bacteria were present for gene transfer. Transconjugants (lac⁻nal^Rstr^Rcm^R) were recovered in the nematode fecal material following a protocol where nematodes were initially fed a plasmidless lac⁻nal^Rstr^Scm^SE. coli and then, after surface sterilization, a lac⁺nal^SE. coli plasmid donor containing the conjugative R100JA (str^Rcm^R) plasmid. The presence of plasmids in the transconjugants was confirmed by gel electrophoresis. The occurrence of conjugation in the gut was confirmed by dissection of individual surface-sterilized nematodes and isolation of transconjugants.