Specific hopanoid classes differentially affect free-living and symbiotic states of Bradyrhizobium diazoefficiens.
Specific hopanoid classes differentially affect free-living and symbiotic states of Bradyrhizobium diazoefficiens.
复制标题
DOI：
10.1128/mbio.01251-15
复制
发表时间：
2015-10-20
期刊：
影响因子：
6.4
通讯作者：
Newman DK
中科院分区：
文献类型：
--
作者：
Kulkarni G;Busset N;Molinaro A;Gargani D;Chaintreuil C;Silipo A;Giraud E;Newman DK
更好地了解细菌如何抵抗植物-微生物共生过程中遇到的压力，将提高我们刺激植物生长的能力。在这里，我们表明，共生系统包括固氮细菌固氮慢生根瘤菌和豆科植物Aeschynomene afraspera需要hopanoid生产最佳健身。虽然甲基化的（2 Me）hopanoids有助于植物细胞样微氧和酸性条件下的自由生活状态下的生长，他们在共生过程中被破坏。相比之下，在自由生活状态和共生过程中，在微需氧和各种应激条件（高温、低pH、高渗透压、胆汁盐、氧化应激和抗菌肽）下生长需要合成扩展（C35）类霍帕酸。这些缺陷可能是由于不存在游离或lipidA结合的C35 hopanoids或C30 hopanoids dipoptene的积累导致的刚性较低的膜。我们的研究结果还表明，C35 hopanoids是必需的共生只有与寄主Aeschynomene afraspera，而不是与大豆。这种差异很可能与存在的富含半胱氨酸的抗微生物肽在Aeschynomene结节，诱导细菌的形态和生理学的急剧修改。因此，植物共生体中的hopanoid突变体的研究提供了一个机会，以深入了解宿主-微生物的相互作用在共生进展的后期阶段，以及hopanoid提供健身优势的微环境条件。由于慢生根瘤菌为植物提供固定氮，这项工作具有潜在的农学意义。了解hopanoids如何促进细菌在土壤和植物宿主中的存活，可能有助于工程更强大的农艺菌株，特别是在由于气候变化而变得温暖和盐碱化的地区。此外，这项工作具有地球生物学意义：Hopanes，Hopanoids的分子化石，在地球历史的离散间隔中富集在古老的沉积岩中。这是第一个研究发现的作用2 Me-和C35 hopanoids的生态位的背景下，捕获许多压力的环境条件被认为是重要的（2 Me）-hopane沉积。虽然还有很多工作要做，以确定是否存在于植物宿主内的条件共享与岩石记录相关的壁龛，我们的研究结果代表了重要的一步，确定保守的机制，使hopanoids有助于健身。
A better understanding of how bacteria resist stresses encountered during the progression of plant-microbe symbioses will advance our ability to stimulate plant growth. Here, we show that the symbiotic system comprising the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens and the legume Aeschynomene afraspera requires hopanoid production for optimal fitness. While methylated (2Me) hopanoids contribute to growth under plant-cell-like microaerobic and acidic conditions in the free-living state, they are dispensable during symbiosis. In contrast, synthesis of extended (C35) hopanoids is required for growth microaerobically and under various stress conditions (high temperature, low pH, high osmolarity, bile salts, oxidative stress, and antimicrobial peptides) in the free-living state and also during symbiosis. These defects might be due to a less rigid membrane resulting from the absence of free or lipidA-bound C35 hopanoids or the accumulation of the C30 hopanoid diploptene. Our results also show that C35 hopanoids are necessary for symbiosis only with the host Aeschynomene afraspera but not with soybean. This difference is likely related to the presence of cysteine-rich antimicrobial peptides in Aeschynomene nodules that induce drastic modification in bacterial morphology and physiology. The study of hopanoid mutants in plant symbionts thus provides an opportunity to gain insight into host-microbe interactions during later stages of symbiotic progression, as well as the microenvironmental conditions for which hopanoids provide a fitness advantage. Because bradyrhizobia provide fixed nitrogen to plants, this work has potential agronomical implications. An understanding of how hopanoids facilitate bacterial survival in soils and plant hosts may aid the engineering of more robust agronomic strains, especially relevant in regions that are becoming warmer and saline due to climate change. Moreover, this work has geobiological relevance: hopanes, molecular fossils of hopanoids, are enriched in ancient sedimentary rocks at discrete intervals in Earth history. This is the first study to uncover roles for 2Me- and C35 hopanoids in the context of an ecological niche that captures many of the stressful environmental conditions thought to be important during (2Me)-hopane deposition. Though much remains to be done to determine whether the conditions present within the plant host are shared with niches of relevance to the rock record, our findings represent an important step toward identifying conserved mechanisms whereby hopanoids contribute to fitness.