The effect ofPhotorhabdus luminescens(Enterobacteriaceae) on the survival, development, reproduction and behaviour ofCaenorhabditis elegans(Nematoda: Rhabditidae)

Abstract

The free-living soil nematode Caenorhabditis elegans interacts with diverse microorganisms in its natural habitat. These microorganisms may serve as a food source or represent a harmful threat. As such, they constitute one of the most important ecological factors of the worm's natural environment. In this study, we examined the interaction between two natural isolates of C. elegans and three natural isolates of the entomopathogenic bacterium Photorhabdus luminescens. Two of the tested P. luminescens strains were clearly pathogenic. They consistently reduced the worm's developmental, survival and reproductive rate, most likely through the production of nematicidal compounds. The third natural isolate tested did not decrease worm fitness. These differences could be associated with a deletion of one gene (tcdA4) ( approximately 7kb) of the toxin complex D pathogenicity island, which was found in only the non-pathogenic strain. Our study additionally highlights the importance of behaviour in defence. Caenorhabditis elegans showed two distinct avoidance behaviours towards the pathogenic but not the non-pathogenic P. luminescens strains. In particular, nematodes physically escaped and also reduced the ingestion of pathogenic bacteria. Our results strongly suggest that C. elegans possesses the capacity to distinguish between and subsequently respond to harmful and non-harmful strains of the same bacterial species. The underlying mechanisms of such interactions are currently unknown. Their dissection will represent a major challenge for future research and should enhance our knowledge of the ecology of this important model organism in biological research.

Isolation of naturally associated bacteria of necromenicPristionchusnematodes and fitness consequences

“…C. elegans protects itself from potential pathogenic bacteria by avoidance behaviour and innate immunity pathways (Pujol et al, 2001;Nicholas and Hodgkin, 2004;Kurz and Ewbank, 2003). Avoidance behaviour of C. elegans has been recorded for B. thuringiensis, S. marcescens, P. aeruginosa, P. luminescens and M. nematophila using different molecular mechanisms (Pujol et al, 2001;Pradel et al, 2007;Yook and Hodgkin, 2007;Zhang et al, 2005;Beale et al, 2006;Schulenburg and Müller, 2004;Sicard et al, 2007;Hasshoff et al, 2007). In our experiments, bacteria that cause mortality to P. pacificus tend to score low in the chemotaxis index, ranging from -0.09±0.04 for Serratia sp.…”

Introduction. Ecological immunology

“…For example, the availability of food organisms biases anti-parasite defence in the nematode host Caenorhabditis elegans (Schulenburg & Mü ller 2004;Sicard et al 2007). Similarly, nutrient availability altered parasite resistance of mosquitoes ( Ferguson & Read 2002;Bedhomme et al 2004;Lambrechts et al 2006).…”

Increased responsiveness in feeding behaviour ofCaenorhabditis elegansafter experimental coevolution with its microparasiteBacillus thuringiensis

“…Therefore, it would be beneficial to evolve behavioural responses towards both food and pathogens [10, 13,14,[17][18][19]. One of these behaviours concerns feeding.…”

“…All nematodes were taken from the replicate populations of the final host generation of the evolution experiment. For each behavioural test, 30 hermaphroditic L4 nematodes were placed on 'worm balls' (5 cm diameter [13]), which were either inoculated with a mixture of pathogenic BT strains identical to the initial mixture of the evolution experiment or with the non-pathogenic strain. We chose non-evolved pathogenic strains which were identical in all treatments to exclude pathogen adaptations to the host and thus enhance comparability across treatment groups.…”

“…Under laboratory conditions, C. elegans can be specifically attracted by non-pathogenic bacteria [7-9] while it avoids various pathogenic strains [9][10][11][12][13][14]. Similarly, food uptake is reduced on pathogenic when compared with non-pathogenic bacteria [9][10][11]13].…”