Metabolites of Bacterial-Feeding Nematodes Stimulate Bacterial Indole-3-Acetic Acid (IAA) Synthesis

Interorganismal metabolites play significant roles in regulating behaviors and communications between organisms. Nematodes are the most abundant animals on earth, and function well in soil ecosystem due to their interactions with microbes. Bacterial-feeding nematodes stimulate the activity of indole-3-acetic acid (IAA)-producing bacteria and increase the content of IAA in soil. However, we do not fully understand how bacterial-feeding nematodes interact with bacteria and affect IAA synthesis. In this study, the model nematode Caenorhabditis elegans and three species of soil-dwelling IAA-producing bacteria ( Bacillus amyloliquefaciens JX1, Arthrobacter pascens ZZ21 and A. chlorphenolicus L4) were employed to determine the effect of nematodes on the IAA biosynthesis of bacteria. Then the metabolites and extracts of C. elegans were tested the effect on three bacterial IAA synthesis (but only A. pascens ZZ21 for the extracts). Lastly, two soil-dwelling bacterial-feeding nematodes ( Mesorhabditis sp. and Acrobeloides sp.) and two IAA-producing bacteria ( B. amyloliquefaciens JX1 and A. pascens ZZ21) were subsequently used to explore the universality of this interaction. Our results showed that the metabolites or extracts of nematodes could promote the IAA biosynthesis of IAA-producing bacteria, and implied this stimulatory effect maybe widely spread in metabolites of bacterial-feeding nematodes and IAA-producing bacteria, but vary with nematodes and bacteria species. Our findings indicate that bacterial-feeding nematodes could mediate the interaction between nematodes and bacteria by their metabolites, except for their feeding behavior, and offer insights into the ecological function of the metabolites of nematodes.