Caenorhabditis elegans NPR-1–mediated behaviors are suppressed in the presence of mucoid bacteria

Abstract

Caenorhabditis elegans exhibits a diverse range of behaviors in response to bacteria. The presence of bacterial food influences C. elegans aerotaxis, aggregation, locomotion, and pathogen avoidance behaviors through the activity of the NPR-1 neuropeptide receptor. Here, we show that mucoid strains of bacteria that produce an exopolysaccharide matrix do not induce NPR-1-dependent behaviors. In the presence of mucoid strains of bacteria, the C. elegans laboratory wild-type (WT) strain N2 exhibits behaviors characteristic of wild isolates and mutants with reduced NPR-1 activity. Specifically, N2 exhibits lawn bordering and roaming behavior on mucoid nonpathogenic bacteria and loss of pathogen avoidance on mucoid Pseudomonas aeruginosa. Alginate biosynthesis by laboratory and clinical isolates of mucoid P. aeruginosa is necessary and sufficient to attenuate NPR-1-mediated behavior and it suppresses C. elegans pathogen avoidance behavior. Our data suggest that the specific interaction with nonmucoid bacteria induces NPR-1-dependent behaviors of C. elegans. These observations provide an example of how exopolysaccharide matrix biosynthesis by a community of bacteria may inhibit specific host responses to microbes.

Biofilm Formation Protects Escherichia coli against Killing by Caenorhabditis elegans and Myxococcus xanthus

“…It is possible that E. coli biofilm matrix components could act as a chemo-repellant to nematodes. Indeed, P. aeruginosa polysaccharide production changes the feeding behavior of C. elegans (64). However, a similar number of worms were attracted to either WT or csgBA bcsA mutant colony biofilms in our colony occupancy experiment, demonstrating that the biofilm matrix likely acts as a mechanical barrier to nematode feeding.…”

Pseudomonas fluorescens NZI7 repels grazing by C. elegans, a natural predator

“…Some may be involved in the synthesis of precursor molecules needed for the synthesis of the EDB product, while others could be involved in the synthesis of a second nematode repellent factor. We also identified an additional class of mutants, exemplified by a mutation affecting the algU/mucA operon, where the mucoid phenotype of mutant bacteria may compromise the ability of nematodes to respond to bacterial signals and of bacteria to repel nematode predation (Reddy et al, 2011). It should be noted that mutations affecting the production of additional nematode repellent factors may not have been detected in the grid screen if these factors are highly diffusible or individually contribute only a small fraction of the total NZI7 repellent activity.…”

“…An edible mutant containing an insertion close to the 3 0 end of algU, and immediately upstream of the algU regulatory proteins mucA and mucB, was observed to have a mucoid phenotype, which has been reported to result in loss of pathogen avoidance in P. aeruginosa interactions with C. elegans (Reddy et al, 2011). Edible mutants with insertions in genes with predicted roles in aromatic amino acid metabolism (anthranilate and chorismate synthase genes) and thiamine biosynthesis could be chemically complemented by addition of 1 mM anthranilate or thiamine to the growth medium, respectively (Supplementary Figure S3).…”

Behavioral avoidance of pathogenic bacteria by Caenorhabditis elegans

“…In the context of avoidance of pathogenic bacteria, animals with intact hyperoxia-avoidance behavior, such as neuropeptide receptor 1 (npr-1) mutants or C. elegans wild isolates, fail to avoid lawns of P. aeruginosa relative to the laboratory strain N2 [12]. Interestingly, in the N2 strain the suppression of aerotaxis behavior by bacterial food is blocked on mucoid bacteria [28]. As a result, the N2 wild type strain fails to avoid a lawn of mucoid Pseudomonas as if it were an npr-1 mutant.…”