Abstract
Bacteriovorus eukaryotes such as nematodes are one of the major natural predators of bacteria. In their defense bacteria have evolved a number of strategies to avoid predation, including the production of deterrent or toxic metabolites, however little is known regarding the response of predators towards such bacterial defenses. Here we use the nematode C. elegans as a model to study a predators’ behavioral response towards two toxic bacterial metabolites, tambjamine YP1 and violacein. We found that C. elegans displays an innate avoidance behavior towards tambjamine YP1, however requires previous exposure to violacein before learning to avoid this metabolite. The learned avoidance of violacein is specific, reversible, is mediated via the nematode olfactory apparatus (aversive olfactory learning) and is reduced in the absence of the neurotransmitter serotonin. These multiple strategies to evade bacterial toxic metabolites represent a valuable behavioral adaptation allowing bacteriovorus predators to distinguish between good and bad food sources, thus contributing to the understanding of microbial predator-prey interactions.
Highlights
Aversive learning, which is reversible, based on the olfactory neurons and can detect toxins at a distance
Learning to associate sensory cues with threats is critical for minimizing aversive experience
Whilst the response of the animal model C. elegans towards pathogens has been extensively investigated, the behavioral response of this bacterial predator to defense metabolites originating from non-pathogenic, environmental bacteria has been largely overlooked
Summary
Aversive learning, which is reversible, based on the olfactory neurons and can detect toxins at a distance. At all time points nematodes trained using 20G8 (black bars) preferred the control bacteria over the test bacteria (CI always negative). Grown on 20G8vioA− (white bars) changed their preferences from the test bacteria at 1 hr (CI = 0.15) to the control bacteria at 6 hrs (CI =−0.4).
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