J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August-University Göttingen, Berliner Str. 28, 37073 Göttingen, Germany.
Microb Ecol. 2011 May;61(4):853-9. doi: 10.1007/s00248-011-9821-z. Epub 2011 Mar 1.
Non-trophic interactions are increasingly recognised as a key parameter of predator-prey interactions. In soil, predation by bacterivorous nematodes is a major selective pressure shaping soil bacterial communities, and many bacteria have evolved defence mechanisms such as toxicity. In this study, we show that extracellular secondary metabolites produced by the model soil bacterium Pseudomonas fluorescens CHA0 function as a complex defence strategy against bacterivorous nematodes. Using a collection of functional mutants lacking genes for the biosynthesis of one or several extracellular metabolites, we evaluated the impact of bacterial secondary metabolites on the survival and chemotactic behaviour of the nematode Caenorhabditis elegans. Additionally, we followed up the stress status of the nematodes by measuring the activation of the abnormal DAuer Formation (DAF) stress cascade. All studied secondary metabolites contributed to the toxicity of the bacteria, with hydrogen cyanide efficiently repelling the nematodes, and both hydrogen cyanide and 2,4-DAPG functioning as nematicides. Moreover, these metabolites elicited the DAF stress response cascade of C. elegans, showing that they affect nematode physiology already at sublethal concentrations. The results suggest that bacterial secondary metabolites responsible for the suppression of plant pathogens strongly inhibit bacterivorous nematodes and thus likely contribute to the resistance of bacteria against predators in soil.
非营养相互作用正日益被认为是捕食者-猎物相互作用的一个关键参数。在土壤中，食细菌线虫的捕食是塑造土壤细菌群落的主要选择压力，许多细菌已经进化出防御机制，如毒性。在这项研究中，我们表明，模式土壤细菌荧光假单胞菌 CHA0 产生的细胞外次生代谢物是一种针对食细菌线虫的复杂防御策略。我们使用了一组缺乏一种或几种细胞外代谢物生物合成基因的功能突变体，评估了细菌次生代谢物对线虫秀丽隐杆线虫存活和趋化行为的影响。此外，我们通过测量异常 DAuer 形成 (DAF) 应激级联的激活，跟踪线虫的应激状态。所有研究的次生代谢物都有助于细菌的毒性，其中氢氰酸有效地排斥线虫，氢氰酸和 2,4-DAPG 都具有杀线虫作用。此外，这些代谢物还引发了秀丽隐杆线虫的 DAF 应激反应级联，表明它们在亚致死浓度下就会影响线虫的生理机能。研究结果表明，抑制植物病原体的细菌次生代谢物强烈抑制食细菌线虫，因此可能有助于细菌在土壤中抵御捕食者。
