Diet-dependent surplus killing in nematodes

Environmental fluctuations may force organisms to adapt their diet. Such metabolic interferences may result in developmental alterations and can ultimately contribute to disease. However, evidence for strong associations between diet and complex behavioural phenotypes are scarce. Here, we describe an example, where different bacterial diets increase the ability of predatory nematodes to kill their prey. We found that this effect is dependent on undergoing complete development in presence of specific bacteria. Based on a mutational screen in bacteria of the genus Novosphingobium, we found several metabolic pathways that when mutated, abolished the ability to boost predatory killing behaviour. Among these, we identified vitamin B12 as one component that was able to increase killing behaviour in supplemented worms. In addition, knockouts of nematode genes involved in vitamin B12 dependent pathways showed reduced capacity to kill their prey. Our study shows how different metabolic composition of bacteria can induce developmental changes in their hosts that ultimately result in complex behavioural phenotypes and provides a starting point to elucidate the mechanistic basis of these processes in further detail.