Institute of Environmental Biotechnology, Graz University of Technology Graz, Austria ; Institute of Plant Sciences, University of Graz Graz, Austria.
Institute of Environmental Biotechnology, Graz University of Technology Graz, Austria.
Front Microbiol. 2015 Feb 10;6:53. doi: 10.3389/fmicb.2015.00053. eCollection 2015.
Rhizobiales (Alphaproteobacteria) are well-known beneficial partners in plant-microbe interactions. Less is known about the occurrence and function of Rhizobiales in the lichen symbiosis, although it has previously been shown that Alphaproteobacteria are the dominating group in growing lichen thalli. We have analyzed the taxonomic structure and assigned functions to Rhizobiales within a metagenomic dataset of the lung lichen Lobaria pulmonaria L. One third (32.2%) of the overall bacteria belong to the Rhizobiales, in particular to the families Methylobacteriaceae, Bradyrhizobiaceae, and Rhizobiaceae. About 20% of our metagenomic assignments could not be placed in any of the Rhizobiales lineages, which indicates a yet undescribed bacterial diversity. SEED-based functional analysis focused on Rhizobiales and revealed functions supporting the symbiosis, including auxin and vitamin production, nitrogen fixation and stress protection. We also have used a specifically developed probe to localize Rhizobiales by confocal laser scanning microscopy after fluorescence in situ hybridization (FISH-CLSM). Bacteria preferentially colonized fungal surfaces, but there is clear evidence that members of the Rhizobiales are able to intrude at varying depths into the interhyphal gelatinous matrix of the upper lichen cortical layer and that at least occasionally some bacteria also are capable to colonize the interior of the fungal hyphae. Interestingly, the gradual development of an endosymbiotic bacterial life was found for lichen- as well as for fungal- and plant-associated bacteria. The new tools to study Rhizobiales, FISH microscopy and comparative metagenomics, suggest a similar beneficial role for lichens than for plants and will help to better understand the Rhizobiales-host interaction and their biotechnological potential.
根瘤菌目（α-变形菌）是植物-微生物相互作用中著名的有益伙伴。虽然先前已经表明 α-变形菌是生长中的地衣藻中的优势群体，但关于根瘤菌目在地衣共生体中的发生和功能知之甚少。我们分析了肺地衣 lobaria pulmonaria L 的宏基因组数据集的分类结构，并对地衣共生体中的根瘤菌目进行了功能分配。在总体细菌中，有三分之一（32.2%）属于根瘤菌目，特别是甲基杆菌科、慢生根瘤菌科和根瘤菌科。大约 20%的我们的宏基因组分配不能归入任何根瘤菌目谱系，这表明存在尚未描述的细菌多样性。基于 SEED 的功能分析集中在根瘤菌目上，揭示了支持共生的功能，包括生长素和维生素的产生、固氮和应激保护。我们还使用专门开发的探针通过荧光原位杂交（FISH-CLSM）后，用共聚焦激光扫描显微镜定位根瘤菌。细菌优先定殖于真菌表面，但有明确的证据表明，根瘤菌目的成员能够以不同的深度侵入地衣上部皮质层菌丝间的凝胶状基质中，并且至少偶尔一些细菌也能够定殖于真菌菌丝的内部。有趣的是，在地衣、真菌和植物相关细菌中，逐渐发展出一种共生细菌生活方式。研究根瘤菌的新工具，如 FISH 显微镜和比较宏基因组学，对地衣和植物一样具有类似的有益作用，并将有助于更好地理解根瘤菌-宿主相互作用及其生物技术潜力。
