Honors College

Document Type

Honors Thesis




Eleanor Groden

Committee Members

Andrei Alyokhin, David Lambert, Stellos Tavantzis, François G. Amar

Graduation Year

May 2011

Publication Date

Spring 5-2011


Pristionchus entomophagus is a necromenic nematode commonly associated with dung beetles (Geotrupes spp.) in Europe. Recently, it has been found in Maine emerging from cadavers of M. rubra, an ant native to Europe that is currently established and pestiferous in Maine (Groden and Stack 2011). Laboratory assays inoculating M. rubra with these nematodes caused significant mortality. This study aimed to characterize the bacterial associates of P. entomophagus in order to further understand its pathogenic relationship with M. rubra. Bacterial samples were collected from the cuticle and gut of the nematodes, and the hemolymph of infected hosts. Single spore isolates were established, cultured, and identified using bacterial 16s rRNA gene sequencing. Following BLAST search comparisons of 24 isolate sequences that I obtained, I identified 14 species of bacteria associated with P. entomophagus and its infected hosts. All of these species have been reported as associated with nematodes, insects, the rhizosphere of plants, fungi, or soil. Three species in particular, Serratia marcescens, S. nematodiphila, and S. proteamaculans have all been directly linked to insect mortality in previous studies (Zhang et al. 2009, Nishiwaki et al. 2007, Al Own et al. 2011). Furthermore, S. proteamaculans was found in association with P. entomophagus in the United Kingdom. In comparing the bacterial isolates found in association with the hemolymph of infected hosts to isolates gathered from P. entomophagus, two species, Pseudomonas fluorescens and Delftia sp. were found in both the hemolymph and in association with the external surface of the nematode. The potential mechanism of pathogenicity employed by P. entomophagus is discussed based on the similarities and differences between the species isolated from the nematode and infected hosts.