Trophic interactions are crucial for carbon cycling in food webs. Traditionally, eukaryotic micropredators are considered the major micropredators of bacteria in soils, although bacteria like myxobacteria and Bdellovibrio are also known bacterivores. Until recently, it was impossible to assess the abundance of prokaryotes and eukaryotes in soil food webs simultaneously. Using metatranscriptomic three-domain community profiling we identified pro- and eukaryotic micropredators in 11 European mineral and organic soils from different climes. Myxobacteria comprised 1.5–9.7% of all obtained SSU rRNA transcripts and more than 60% of all identified potential bacterivores in most soils. The name-giving and well-characterized predatory bacteria affiliated with the Myxococcaceae were barely present, while Haliangiaceae and Polyangiaceae dominated. In predation assays, representatives of the latter showed prey spectra as broad as the Myxococcaceae. 18S rRNA transcripts from eukaryotic micropredators, like amoeba and nematodes, were generally less abundant than myxobacterial 16S rRNA transcripts, especially in mineral soils. Although SSU rRNA does not directly reflect organismic abundance, our findings indicate that myxobacteria could be keystone taxa in the soil microbial food web, with potential impact on prokaryotic community composition. Further, they suggest an overlooked, yet ecologically relevant food web module, independent of eukaryotic micropredators and subject to separate environmental and evolutionary pressures.

营养相互作用对于食物网中的碳循环至关重要。传统上，真核微捕食者被认为是土壤中细菌的主要微捕食者，尽管粘细菌和蛭弧菌等细菌也是已知的食菌动物。直到最近，还不可能同时评估土壤食物网中原核生物和真核生物的丰度。使用元转录组三域群落分析，我们在来自不同气候的 11 种欧洲矿物和有机土壤中鉴定了亲和真核微捕食者。粘细菌占所有获得的 SSU rRNA 转录物的 1.5-9.7%，占大多数土壤中所有已识别的潜在细菌的 60% 以上。属于粘球菌科的命名和特征良好的捕食性细菌几乎不存在，而Haliangiaceae和Polyangiaceae占主导地位。在捕食试验中，后者的代表显示出与粘球菌科一样广泛的猎物光谱。来自真核微捕食者（如变形虫和线虫）的 18S rRNA 转录本通常不如粘细菌 16S rRNA 转录本丰富，尤其是在矿质土壤中。尽管 SSU rRNA 不直接反映有机体丰度，但我们的研究结果表明粘细菌可能是土壤微生物食物网中的关键类群，对原核生物群落组成具有潜在影响。此外，他们提出了一个被忽视但与生态相关的食物网模块，该模块独立于真核微捕食者并受到不同的环境和进化压力。