The role ofCaenorhabditis elegansinsulin‐like signaling in the behavioral avoidance of pathogenicBacillus thuringiensis

Abstract

Pathogens cause damage, and their elimination requires activation of the costly immune response. A highly economic defense strategy should thus be the behavioral avoidance of pathogens, as manifested in humans by all aspects of hygiene or revulsion at pathogen-rich material. Despite its potential importance, behavioral defenses have as yet received only little attention in biomedical research--in stark contrast to the physiological immune system. In the present study, the genetics of such behavioral defenses are elucidated in a simple model organism, the nematode Caenorhabditis elegans. We show for the first time that mutations in the insulin-like receptor (ILR) pathway lead to two distinct behavioral responses against pathogenic strains of the gram-positive bacterium Bacillus thuringiensis (BT), including the physical evasion of pathogens and their reduced oral uptake. Since this pathway also contributes to nematode stress resistance, the results surprisingly reveal a genetic link between physiological and behavioral defenses. Considering that many signaling pathways have conserved their functions across evolution, including the ILR pathway, this signaling cascade may represent an interesting candidate regulator for behavioral defenses in more complex organisms, including humans.

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.…”

Bacillus thuringiensis DB27 Produces Two Novel Protoxins, Cry21Fa1 and Cry21Ha1, Which Act Synergistically against Nematodes

“…Previous studies have shown that C. elegans exhibits avoidance behavior when challenged with different pathogens (39). B. thuringiensis was one of the pathogens that C. elegans strongly avoided (40). Other nematode-pathogenic Bacillus spp., such as B. nematocida, evolved strategies to attract nematodes (41).…”

Neuronal and molecular substrates for optimal foraging in Caenorhabditis elegans

“…We hypothesized that the food-leaving decision would be regulated by postingestive inputs (e.g., nutritional state or feeding history). Insulin signaling has previously been linked to perception of feeding state and food-related behavioral plasticity (30)(31)(32)(33). This finding prompted us to analyze adaptive food-leaving in mutants defective in the insulin pathway.…”