Microbial interactions - pathogenicity

Bacterial interactions of Pristionchus pacificus and Caenorhabditis elegans

Free-living nematodes predominately feed on bacteria as a food source in the natural environment although some can be pathogenic. C. elegans and P. pacificus differ strikingly in the ability to cope with some of these virulent pathogens e.g. P. pacificus is resistant to Staphylococcus aureus and Pseudomonas aeruginosa, whilst C. elegans is susceptible (Rae et al. 2008). To gain an overview of what effect naturally isolated bacteria have on these nematodes we have screened through a library of 1400 Bacillus strains specifically to isolate strains that are pathogenic to both nematodes. From this collection we have identified 3 strains (all Bacillus cereus) that show a remarkable ability to kill C. elegans within 12 hours, yet P. pacificus remains resistant (Rae et al. 2010). Using forward genetics we have isolated C. elegans resistance mutants that are able to grow and reproduce on these toxic bacteria and the genes responsible are currently being mapped. As well as using forward and reverse genetics as a tool to identify genes involved in immunity in both nematodes we are using whole genome microarrays to investigate the transcriptional response when both nematodes are fed an array of bacterial pathogens.
We are also interested in how bacteria have evolved to kill nematodes, currently we have screened through thousands of mutants (Serratia marcescens and B. cereus) and have identified an array of virulence genes responsible for pathogenicity. Ultimately by understanding how bacteria kill nematodes we can see if these pathogenicity genes are also important for virulence against mammals.
 

Scientists involved:

Dr. Robbie Rae, Postdoc
Igor Iatsenko, Ph.D. Student
Amit Sinha, Ph.D. Student
Hanh Witte, Technician

Selected References:

Rae, R., Iatsenko, I., Witte, H. & Sommer, R. J. (2010): A subset of naturally isolated Bacillus strains show extreme virulence to the free-living nematodes Caenorhabditis elegans and Pristionchus pacificus. Environmental Microbiology, 11, 3007-3021.
Rae, R., Riebesell, M., Dinkelacker, I., Wang, Q., Herrmann, M., Weller, A. M., Dieterich, C. & Sommer, R. J. (2008): Isolation of naturally associated bacteria of necromenic Pristionchus nematodes and fitness consequences. J. Exp. Biology, 211, 1927-1936.