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要旨

We investigated the bacterial interactions of Pristionchus nematodes that are associated with scarab beetles e.g. P. pacificus is found on the oriental beetle, P. maupasi on cockchafers and P. entomophagus on dung beetles. To gain an overview of the bacteria Pristionchus associates with in nature we conducted large-scale metagenomic sequencing of bacteria present on the nematodes cuticle and in the intestine. We also isolated bacterial species from P. pacificus, P. entomophagus and P. maupasi emerging from their associated beetles and used olfaction, fecundity and mortality assays to determine the relationship Pristionchus has with each bacterium. Using large-scale 16S sequence analysis of individual Pristionchus we found that these nematodes harbor a large diversity of living bacteria in their gut including animal and plant pathogenic species. In bacterial discrimination assays Pristionchus showed distinct olfactory and fitness profiles to each bacteria and displayed a continuum of interactions from bacterial dissemination by the worm to nematode mortality. Pristionchus can recognize, respond to and are averted from bacterial species that have low nutrition and cause poor health. Interestingly Pristionchus strongly avoids Bacillus species without previous contact unlike C. elegans, which has to be trained to avoid pathogenic bacteria. We are also examining the interactions between Pristionchus and Bacillus species. Bacillus spores were isolated from the Schönbuch forest (Tübingen, Germany) and were exposed to Pristionchus to test for pathogenicity and aversion behavior. Surprisingly, Pristionchus exhibits different behavioral responses to the Bacillus species isolated. We have begun screening for mutants that are resistant to pathogenic Bacillus species as well as mutants that show loss of repulsion when faced with unattractive Bacillus.