Table_3_Habitat, Snow-Cover and Soil pH, Affect the Distribution and Diversity of Mortierellaceae Species and Their Associations to Bacteria.docx

Mortierellaceae species are among the most frequent and globally distributed soil fungi. However, the factors shaping their diversity and distribution remain obscure. Several species have been reported to be associated to bacteria, but the kind and frequency of such associations were not addressed up to now. We hypothesized that such associations could be important for Mortierellaceae ecology. Therefore, our aim was to understand the driving factors responsible for the Mortierellaceae diversity, community composition and bacterial associations in alpine and subalpine habitats. For answering our question, we collected both snow-free and snow-covered soil at sampling sites from different habitats: bare alpine soil in a glacier forefield, alpine dwarf-willow habitats, and high-altitude Pinus cembra forests. The isolations were carried out by direct cultivation without any antibiotics to the isolation media. Altogether, we obtained 389 Mortierellaceae isolates representing 29 operational taxonomic units (OTUs). Many OTUs could be placed to the genera Mortierella sensu stricto, Dissophora, Entomortierella, Gamsiella, Linnemannia, and Podila, but others could not unambiguously be assigned to a genus. Our results demonstrate that both, the distribution as well as the diversity of the Mortierellaceae species, were significantly influenced by habitat, soil pH, and snow-cover. We noticed that >30% of our isolates were associated to a non-contaminant bacterium. The bacteria associated to our Mortierellaceae isolates belonged to seven different genera. Pseudomonas was the most frequently detected genus associated to the isolated Mortierellaceae species and it was found to be species-specific. Mortierellaceae–bacteria pairs, including those with Pseudomonas, were influenced by location, habitat, and snow-cover. The majority of the fungus–bacterium associations were potentially epihyphal, but we also detected potential endohyphal bacterial species belonging to Mycoavidus, Burkholderiaceae, and Paraburkholderia. Taken together, the non-random associations we detected suggest that fungus–bacterium associations are ecologically meaningful – an interesting path that needs to be investigated further.

被孢霉科（Mortierellaceae）是全球分布最广泛、最常见的土壤真菌类群之一。然而，塑造其多样性与分布格局的驱动因子仍不明晰。已有研究报道该科部分物种可与细菌形成关联，但此类关联的具体类型与发生频率迄今尚未得到明确阐释。我们据此提出假说：此类真菌-细菌关联对被孢霉科的生态过程具有重要意义。本研究旨在明确高寒及亚高寒生境中，驱动被孢霉科物种多样性、群落组成及其细菌关联格局的核心因子。为解答上述科学问题，我们在三类不同生境的采样点采集了积雪覆盖与无积雪覆盖的土壤样本：冰川前缘裸露高寒土壤、高寒矮柳生境，以及高海拔瑞士五针松（Pinus cembra）林。本研究采用直接培养法进行菌株分离，分离培养基未添加任何抗生素。本研究共获得389株被孢霉科菌株，隶属于29个操作分类单元（operational taxonomic units, OTUs）。其中多数OTUs可归类至狭义被孢霉属（Mortierella sensu stricto）、Dissophora属、虫生被孢霉属（Entomortierella）、Gamsiella属、Linnemannia属以及Podila属，剩余部分则无法明确归属至任一已知属。研究结果表明，生境类型、土壤pH值以及积雪覆盖情况，均对被孢霉科物种的分布与多样性具有显著调控作用。我们发现，超过30%的分离菌株可与非污染性细菌形成关联。与被孢霉科菌株关联的细菌隶属于7个不同的属，其中假单胞菌属（Pseudomonas）是最常见的关联菌属，且其与宿主的关联具有物种特异性。被孢霉科-细菌共生组合（包括与假单胞菌形成的组合）的分布格局，同样受到采样地点、生境类型与积雪覆盖情况的影响。多数真菌-细菌关联为潜在的菌丝表生关联，但本研究也检测到了隶属于Mycoavidus属、伯克霍尔德菌科（Burkholderiaceae）以及副伯克霍尔德菌属（Paraburkholderia）的潜在菌丝内生细菌。综合来看，本研究检测到的非随机真菌-细菌关联表明，此类共生关系具有重要的生态学意义——这是一个值得进一步深入探究的有趣研究方向。