黑翅土白蚁共生放线菌多样性及其抗病原真菌活性

Diversity and antifungal potential of symbiotic actinobacteria from Odontotermes formosanus

摘要:

黑翅土白蚁(Odontotermes formosanus)作为地下土壤动物，易受到多种土壤病原真菌的侵害，其共生放线菌通过产生多种活性物质抵御病原真菌，协助白蚁与鸡枞菌(Termitomyces spp.)维持共生系统的稳定。目的 筛选并鉴定黑翅土白蚁共生放线菌的抗真菌活性及其次级代谢产物，揭示其在白蚁-真菌共生系统中所发挥的防御作用机制。方法 采用多种培养基从黑翅土白蚁相关样品中分离放线菌，结合平板对峙法筛选具有抗真菌活性的菌株，对活性菌株OFGS46进行全基因组测序，利用antiSMASH等工具预测其生物合成基因簇(biosynthetic gene clusters, BGCs)，并通过高效液相色谱-质谱联用(HPLC-MS)技术分析其次级代谢产物。结果 共获得23株放线菌，其中菌株OFGS46对炭角菌属(Xylaria sp.)和蓝状菌属(Talaromyces sp.)真菌表现出显著的拮抗活性，抑制率分别为(62.05±0.98)%和(79.99±0.58)%。本研究基于Illumina NovaSeq测序平台对菌株OFGS46进行全基因组测序，经质控共获得约1 Gb的高质量序列数据。经从头组装，得到总长度为8 470 479 bp的基因组草图。进一步通过CheckM等工具评估显示，该基因组组装完整度达99.91%，污染率为4.63%。HPLC-MS分析表明菌株OFGS46能够产生多种活性次级代谢产物，包括enduracidin A、WS9326A、kitacinnamycin A、WAP-8294A2、skyllamycin A、cahuitamycin A、pentamycin、scabichelin、coprisamide C及frankobactin A1等。结论 本研究系统揭示了黑翅土白蚁共生放线菌OFGS46通过合成多种抗菌化合物协同抑制蚁巢病原微生物，不仅从化学生态学层面阐释了共生菌在宿主免疫防御中能够抑制多种病原真菌，也为开发基于白蚁共生系统的新型抗菌资源提供了科学依据。

Abstract:

As a subterranean, soil-dwelling insect, Odontotermes formosanus is susceptible to infection by diverse soil-borne pathogenic fungi. Its symbiotic actinobacteria produce bioactive compounds to combat these pathogens, thereby maintaining a stable symbiotic system of O. formosanus with Termitomyces spp.Objective To screen and characterize antifungal metabolites from symbiotic actinobacteria of O. formosanus and to elucidate their defensive role in the termite-fungus symbiotic system.Methods Actinobacteria were isolated from O. formosanus-associated samples via diverse culture media. Antifungal strains were screened via dual-culture confrontation assays. The active strain OFGS46 was selected for whole-genome sequencing. Biosynthetic gene clusters (BGCs) were predicted by antiSMASH, and secondary metabolites were analyzed by HPLC-MS.Results Twenty-three actinobacteria strains were isolated. Strain OFGS46 exhibited inhibition rates of (62.05±0.98)% against Xylaria sp. and (79.99±0.58)% against Talaromyces sp. Whole-genome sequencing on the Illumina NovaSeq platform yielded approximately 1 Gb of high-quality data. De novo assembly generated a draft genome of 8 470 479 bp. CheckM evaluation demonstrated high assembly quality with 99.91% completeness and 4.63% contamination. HPLC-MS results revealed that strain OFGS46 was capable of producing multiple bioactive secondary metabolites, including enduracidin A, WS9326A, kitacinnamycin A, WAP-8294A2, skyllamycin A, cahuitamycin A, pentamycin, scabichelin, coprisamide C, and frankobactin A1.Conclusion This study systematically reveals that the symbiotic actinobacterium OFGS46 from O. formosanus suppresses nest pathogens through the production of diverse antimicrobial compounds. These findings not only elucidate, from a perspective of chemical ecology, the role of symbiotic bacteria in host immune defenses through suppressing multiple pathogenic fungi, but also provide a scientific basis for developing novel antimicrobial resources derived from the termite symbiotic system.