Data_Sheet_1_Endosymbiotic bacteria within the nematode-trapping fungus Arthrobotrys musiformis and their potential roles in nitrogen cycling.DOCX

Endosymbiotic bacteria (ESB) have important effects on their hosts, contributing to its growth, reproduction and biological functions. Although the effects of exogenous bacteria on the trap formation of nematode-trapping fungi (NTF) have been revealed, the effects of ESB on NTF remain unknown. In this study, we investigated the species diversity of ESB in the NTF Arthrobotrys musiformis using high-throughput sequencing and culture-dependent approaches, and compared bacterial profiles to assess the effects of strain source and culture media on A. musiformis. PICRUSt2 and FAPROTAX were used to predict bacterial function. Our study revealed that bacterial communities in A. musiformis displayed high diversity and heterogeneity, with Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria as the dominant phyla. The ESB between A. musiformis groups isolated from different habitats and cultured in the same medium were more similar to each other than the other groups isolated from the same habitat but cultured in different media. Function analysis predicted a broad and diverse functional repertoire of ESB in A. musiformis, and unveiled that ESB have the potential to function in five modules of the nitrogen metabolism. We isolated nitrogen-fixing and denitrifying bacteria from the ESB and demonstrated their effects on trap formation of A. musiformis. Among seven bacteria that we tested, three bacterial species Bacillus licheniformis, Achromobacter xylosoxidans and Stenotrophomonas maltophilia were found to be efficient in inducing trap formation. In conclusion, this study revealed extensive ESB diversity within NTF and demonstrated that these bacteria likely play important roles in nitrogen cycling, including nematode trap formation.

内共生细菌（endosymbiotic bacteria，ESB）对其宿主具有重要作用，可影响宿主的生长、繁殖与生物学功能。尽管外源细菌对捕食线虫真菌（nematode-trapping fungi，NTF）捕器形成的影响已被阐明，但内共生细菌对捕食线虫真菌的作用仍未明确。本研究以捕食线虫真菌肌形节丛孢（Arthrobotrys musiformis）为研究对象，采用高通量测序与依赖培养的方法，探究其体内内共生细菌的物种多样性，并通过对比细菌群落特征，评估菌株来源与培养基对该真菌的影响。本研究采用PICRUSt2与FAPROTAX工具对细菌的功能进行预测。研究结果显示，肌形节丛孢体内的细菌群落具有较高的多样性与异质性，优势菌门为变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）、拟杆菌门（Bacteroidetes）与放线菌门（Actinobacteria）。相较于从同一栖息地分离、经不同培养基培养的菌株组，从不同栖息地分离、经相同培养基培养的肌形节丛孢菌株组，其体内的内共生细菌群落更为相似。功能预测分析表明，肌形节丛孢体内的内共生细菌具备广泛且多样的功能谱，且其在氮代谢的5个功能模块中均具有潜在功能。本研究从肌形节丛孢的内共生细菌中分离得到固氮菌与反硝化菌，并验证了其对该真菌捕器形成的作用。在本次测试的7株细菌中，地衣芽孢杆菌（Bacillus licheniformis）、木糖氧化无色杆菌（Achromobacter xylosoxidans）与嗜麦芽窄食单胞菌（Stenotrophomonas maltophilia）这3株细菌可有效诱导捕器形成。综上，本研究揭示了捕食线虫真菌体内丰富的内共生细菌多样性，并证实这些细菌可能在氮循环（包括线虫捕器形成）中发挥重要作用。