Uzum Zerrin, Silipo Alba, Lackner Gerald, De Felice Antonia, Molinaro Antonio, Hertweck Christian
Leibniz Institute for Natural Product Research and Infection Biology (HKI), Department of Biomolecular Chemistry, Beutenbergstrasse 11a, 07745 Jena (Germany).
Chembiochem. 2015 Feb 9;16(3):387-92. doi: 10.1002/cbic.201402488. Epub 2014 Dec 21.
The rice seedling blight fungus Rhizopus microsporus has an unusual symbiosis with a bacterium, Burkholderia rhizoxinica, which lives within the fungal cytosol and produces a potent phytotoxin that causes severe losses in agriculture. To gain insight into symbiosis factors we investigated the endosymbiont's exopolysaccharide (EPS), a secreted matrix that plays pivotal roles in mediating cell-environment interactions. By a combination of homo- and heteronuclear 2D NMR experiments, we elucidated a previously unknown EPS structure: a repeating tetrasaccharide unit bearing a nonstoichiometric acetyl group on a mannose residue. We also analyzed the EPS biosynthesis gene cluster and generated a targeted mutant to compare the phenotypes. Scanning electron microscope images revealed a reduced ability of the mutant to form extracellular polymers around cell aggregates. Phylogenetic analyses suggest that the symbiont's EPS genes are retained through evolutionary processes.
水稻恶苗病菌微小根霉与一种细菌——根霉素伯克霍尔德菌存在着不同寻常的共生关系，这种细菌生活在真菌的胞质溶胶中，并产生一种强效植物毒素，给农业造成严重损失。为了深入了解共生因子，我们研究了内共生体的胞外多糖（EPS），这是一种分泌性基质，在介导细胞与环境的相互作用中起着关键作用。通过同核和异核二维核磁共振实验相结合的方法，我们阐明了一种此前未知的EPS结构：一个重复的四糖单元，在一个甘露糖残基上带有一个非化学计量的乙酰基。我们还分析了EPS生物合成基因簇，并构建了一个靶向突变体来比较其表型。扫描电子显微镜图像显示，突变体在细胞聚集体周围形成细胞外聚合物的能力有所下降。系统发育分析表明，共生体的EPS基因是通过进化过程保留下来的。
