Department of Botany and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria.
Bioresources Unit, Austrian Institute of Technology GmbH, Tulln, Austria.
Microbiol Spectr. 2022 Aug 31;10(4):e0017222. doi: 10.1128/spectrum.00172-22. Epub 2022 Jul 18.
Seeds offer an internal microbial niche, termed the endosphere, colonized by communities of endophytic bacteria. To elucidate the functions of seed endophytes during germination and early plant growth, studies with culturable isolates are essential. Conventional growth media favor few fast-growing taxa, while micro organisms with restricted nutrient requirements are usually outcompeted prior to isolation. Consequently, current knowledge of the interaction between seeds and their endophytes remains limited to only few bacterial taxa, despite a "black box" of unculturable isolates colonizing the endosphere. Here, we designed various solid media to mimic the endosphere of germinating soybean (Glycine max L.) seeds and assessed their effect on the diversity of culturable endophytic bacteria. The embryonic axis (i.e., the future plant) possessed higher richness and harbored more unique genera (i.e., , , , , and ) than cotyledons (i.e., seed storage organs). Overall, media containing germinating and ground seeds enabled culturing and isolation of the broadest diversity of endophytic bacteria, viewed through the molecular identification of 246 isolates. The use of multiple tailored media helped uncover trophic adaptation of the core taxa. Furthermore, comparison of seeds from four lots of distinct cultivars and origin revealed few overlapping taxa, indicating that the parental environment, including soil and fertilization regime, influenced seed endophytic diversity. Extended diversity of native seed endophytic bacteria revealed the functional relevance of unique , , and strains to seed germination under salt stress, exemplifying the importance of enhanced culturing approaches to elucidate the role of microbiota in seed germination. Plant growth-promoting endophytic isolates that appear to advance seed germination are often obtained from plant niches other than the seed endosphere. Isolating pure cultures of native endophytes from seeds during germination is crucial to investigate their function during early plant growth. Here, the diversity of endophytic bacteria isolated from seeds during soybean germination was enhanced by combining media tailored to the nutritional composition of the seed endosphere, including pregerminated seeds themselves. Our results show that isolation from distinct soybean seed compartments affected such diversity, with the embryonic axis harboring more unique taxa while displaying higher endophytic richness. Furthermore, using pools of seeds from separate lots, each corresponding to a certain cultivar and field site, supported isolation of further unique strains that often unveiled substantial effects on germination performance. Such findings are relevant to assist studies on the interactions between seeds and their native endophytic bacteria.
种子提供了一个内部微生物生境，称为内生生境，其内定植着内生细菌群落。为了阐明种子内生菌在萌发和早期植物生长过程中的功能，使用可培养分离株的研究是必不可少的。传统的生长培养基有利于少数快速生长的分类群，而营养需求受限的微生物通常在分离之前就被淘汰。因此，尽管内生生境中存在一个“黑箱”，其中定植着不可培养的分离株，但种子与其内生菌之间的相互作用的当前知识仍然仅限于少数几种细菌分类群。在这里，我们设计了各种固体培养基来模拟萌发大豆（Glycine max L.）种子的内生生境，并评估了它们对可培养内生细菌多样性的影响。胚胎轴（即未来的植物）比子叶（即种子贮藏器官）具有更高的丰富度和更多独特的属（即， ， ， ， 和 ）。总体而言，含有萌发和粉碎种子的培养基能够培养和分离最广泛的内生细菌多样性，通过对 246 个分离株的分子鉴定来观察。使用多种定制培养基有助于揭示核心分类群的营养适应。此外，对来自四个不同品种和来源的种子进行比较发现，重叠的分类群很少，这表明亲本环境，包括土壤和施肥制度，影响了种子内生菌的多样性。对本地种子内生细菌的广泛多样性的揭示表明，在盐胁迫下，独特的 ， ，和 菌株对种子萌发具有功能相关性，这体现了增强培养方法以阐明微生物群在种子萌发中的作用的重要性。在种子萌发过程中，似乎能促进种子萌发的植物促生内生菌通常是从种子内生生境外的植物生境中获得的。在种子萌发过程中从种子中分离出纯培养的本地内生菌对于研究其在早期植物生长过程中的功能至关重要。在这里，通过组合针对种子内生生境营养组成的培养基，包括预萌发的种子本身，增强了从大豆种子萌发过程中分离的内生细菌的多样性。我们的结果表明，从不同大豆种子隔室进行分离会影响这种多样性，其中胚胎轴定植着更多独特的分类群，同时表现出更高的内生菌丰富度。此外，使用来自不同批次种子的种子池，每个批次对应于特定的品种和田间地点，支持了进一步独特菌株的分离，这些菌株通常会对萌发性能产生重大影响。这些发现有助于辅助种子与其本地内生菌之间相互作用的研究。
