Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados, Irapuato, 36824, Mexico.
Unidad de Genómica Avanzada, Centro de Investigación y de Estudios Avanzados, Irapuato, 36824, Mexico.
ISME J. 2020 Jul;14(7):1743-1754. doi: 10.1038/s41396-020-0638-y. Epub 2020 Apr 9.
Rhizopus microsporus is an early-diverging fungal species with importance in ecology, agriculture, food production, and public health. Pathogenic strains of R. microsporus harbor an intracellular bacterial symbiont, Mycetohabitans (formerly named Burkholderia). This vertically transmitted bacterial symbiont is responsible for the production of toxins crucial to the pathogenicity of Rhizopus and remarkably also for fungal reproduction. Here we show that R. microsporus can live not only in symbiosis with bacteria but also with two viral members of the genus Narnavirus. Our experiments revealed that both viruses replicated similarly in the growth conditions we tested. Viral copies were affected by the developmental stage of the fungus, the substrate, and the presence or absence of Mycetohabitans. Absolute quantification of narnaviruses in isolated asexual sporangiospores and sexual zygospores indicates their vertical transmission. By curing R. microsporus of its viral and bacterial symbionts and reinfecting bacteria to reestablish symbiosis, we demonstrate that these viruses affect fungal biology. Narnaviruses decrease asexual reproduction, but together with Mycetohabitans, are required for sexual reproductive success. This fungal-bacterial-viral system represents an outstanding model to investigate three-way microbial symbioses and their evolution.
微小毛霉是一种早期分化的真菌物种，在生态学、农业、食品生产和公共卫生方面具有重要意义。致病菌株的微小毛霉携带着一种细胞内细菌共生体，即Mycetohabitans（以前称为伯克霍尔德菌）。这种垂直传播的细菌共生体负责产生对毛霉致病性至关重要的毒素，同时也对真菌的繁殖起着重要作用。在这里，我们表明微小毛霉不仅可以与细菌共生，还可以与 Narnavirus 属的两种病毒成员共生。我们的实验表明，这两种病毒在我们测试的生长条件下具有相似的复制能力。病毒拷贝数受真菌发育阶段、基质和 Mycetohabitans 的存在与否的影响。在分离的无性游动孢子和有性接合孢子中对 narnavirus 进行绝对定量表明它们是垂直传播的。通过消除微小毛霉的病毒和细菌共生体，并重新感染细菌以重新建立共生关系，我们证明这些病毒会影响真菌的生物学特性。Narnavirus 会降低无性繁殖，但与 Mycetohabitans 一起，是有性生殖成功所必需的。这种真菌-细菌-病毒系统代表了一个极好的模型，可以研究三方微生物共生及其进化。
