Effect of the gut symbiont Enterococcus faecalis on seed comsumption by Harpalus pensylvanicus

Harpalus pensylvanicus is a beneficial beetle contributing to insect control and seed predation in many agricultural fields of the Midwestern United States.  Present in the guts of H. pensylvanicus are symbiotic microbes that contribute to the digestion of their seed diet.  Enterococcus faecalis is one symbiont that has been isolated from the gut of H. pensylvanicus.  We assessed the ability of E. faecalis to increase the amount of seed consumption by the insect.  This was tested through a feeding assay consisting of four treatments, in which seed consumption of each treatment was recorded.  The four treatments were antibiotic +, E. faecalis +; antibiotic +, E. faecalis -; antibiotic -, E. faecalis +; and antibiotic -, E. faecalis -.  Thirty beetles from each treatment were randomly selected for gut dissection, and macerated gut solutions were smeared onto Enterococcus selective media. Microbial colonies obtained from gut smear were streaked for isolation.  16S rRNA clone libraries were made of the isolated colonies, and identification of the isolates was made by comparison to known microbes in the Genbank database.  The results of the feeding assay showed that E. faecalis administered beetles of the antibiotic treatment consumed a greater weight of seeds.  The identified isolates of the clone libraries showed that an Enterococcus species, E. faecalis, Lactobacillus species, and Lactoccus garvieae were present in H. pensylvanicus gastrointestinal tract.