Department of Plant Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA.
School of Life Sciences, Arizona State University, Tempe, AZ, USA.
ISME J. 2018 Jun;12(7):1743-1757. doi: 10.1038/s41396-018-0053-9. Epub 2018 Feb 23.
Bacterial interactions with animals and plants have been examined for over a century; by contrast, the study of bacterial-fungal interactions has received less attention. Bacteria interact with fungi in diverse ways, and endobacteria that reside inside fungal cells represent the most intimate interaction. The most significant bacterial endosymbionts that have been studied are associated with Mucoromycota and include two main groups: Burkholderia-related and Mycoplasma-related endobacteria (MRE). Examples of Burkholderia-related endobacteria have been reported in the three Mucoromycota subphyla. By contrast, MRE have only been identified in Glomeromycotina and Mucoromycotina. This study aims to understand whether MRE dwell in Mortierellomycotina and, if so, to determine their impact on the fungal host. We carried out a large-scale screening of 394 Mortierellomycotina strains and employed a combination of microscopy, molecular phylogeny, next-generation sequencing and qPCR. We detected MRE in 12 strains. These endosymbionts represent novel bacterial phylotypes and show evidence of recombination. Their presence in Mortierellomycotina demonstrates that MRE occur within fungi across Mucoromycota and they may have lived in their common ancestor. We cured the fungus of its endosymbionts with antibiotics and observed improved biomass production in isogenic lines lacking MRE, demonstrating that these endobacteria impose some fitness costs to their fungal host. Here we provided the first functional insights into the lifestyle of MRE. Our findings indicate that MRE may be antagonistic to their fungal hosts, and adapted to a non-lethal parasitic lifestyle in the mycelium of Mucoromycota. However, context-dependent adaptive benefits to their host at minimal cost cannot not be excluded. Finally, we conclude that Mortierellomycotina represent attractive model organisms for exploring interactions between MRE and fungi.
细菌与动植物的相互作用已经研究了一个多世纪；相比之下，细菌-真菌相互作用的研究受到的关注较少。细菌以多种方式与真菌相互作用，而生活在真菌细胞内的内细菌代表了最密切的相互作用。研究最多的重要细菌内共生体与 Mucoromycota 有关，包括两个主要群体：与 Burkholderia 相关的内细菌（MRE）和与 Mycoplasma 相关的内细菌。在三个 Mucoromycota 亚目中已经报道了与 Burkholderia 相关的内细菌的例子。相比之下，MRE 仅在 Glomeromycotina 和 Mucoromycotina 中被鉴定。本研究旨在了解 MRE 是否存在于 Mortierellomycotina 中，如果存在，确定它们对真菌宿主的影响。我们对 394 株 Mortierellomycotina 菌株进行了大规模筛选，并结合显微镜、分子系统发育、下一代测序和 qPCR 进行了研究。我们在 12 株菌株中检测到 MRE。这些内共生体代表了新的细菌类群，并显示出重组的证据。它们在 Mortierellomycotina 中的存在表明，MRE 存在于整个 Mucoromycota 中的真菌中，它们可能存在于它们的共同祖先中。我们用抗生素使真菌失去内共生体，并观察到缺乏 MRE 的同基因系的生物量产量增加，这表明这些内细菌对其真菌宿主施加了一些适应成本。在这里，我们首次提供了对 MRE 生活方式的功能见解。我们的研究结果表明，MRE 可能对其真菌宿主具有拮抗作用，并适应了 Mucoromycota 菌丝体中的非致死性寄生生活方式。然而，不能排除它们对宿主具有依赖于背景的适应性益处，同时成本最小。最后，我们得出结论，Mortierellomycotina 是探索 MRE 与真菌相互作用的有吸引力的模式生物。
