Saline area may tend to be a productive land; however, many of salt-affected soils have nitrogen limitation and depend on plant-associated diazotrophs as their source of ‘new’ nitrogen. Herein, a total of 316 salinity tolerant nitrogen-fixing endophytic bacteria were isolated from roots of the halophyte Suaeda sp. sampled from 22 different areas of Iran to prepare the collection of nitrogen-fixing bacterial endophytes and evaluate the plant growth–promoting effect of effective isolates on growth of the halophyte Suaeda maritima. All of the identified nitrogen-fixing endophytes were classified to Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes phylum while we did not detect common nitrogen-fixing endophyte of glycophytes like Azospirillum. The genera Pseudomonas and Microbacterium were both encountered in high abundance in all samples, indicating that they might play an advanced role in the micro-ecosystem of the halophyte Suaeda. In addition, the results also showed that not only soil salinity can affect halophyte endophytic composition but also other factors such as geographical location, plant species, and other soil properties may be involved. Interestingly, only Zhihengliuella halotolerans and Brachybacterium sp. belonging to Actinobacteria could grow in semi-solid N-free (NFb) medium supplemented with 6% NaCl and highly enhanced growth of S. maritima in vitro. Overall, this study offers useful new resources for nitrogen-fixing endophytic bacteria which may be utilized to improve approaches for providing bio-fertilizer useful in saline-based agriculture.

中文翻译：

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挖掘盐生植物Suaeda的各种物种的根，以获得具有耐盐能力的固氮内生细菌，具有促进植物生长的潜力。

盐碱地可能是一个生产性土地；然而，许多受盐影响的土壤都有氮的限制，并且依赖于植物相关的重氮营养菌作为“新”氮的来源。在此，从盐生植物Suaeda sp。的根中分离出总共316种耐盐性的固氮内生细菌。从伊朗22个不同地区取样，准备收集固氮细菌内生菌，并评估有效分离株对盐生植物Suaeda maritima生长的促进植物生长的作用。所有已确定的固氮内生菌都被分类为Proteobacteria，Actinobacteria，Fimicutes和Bacteroidetes。虽然我们没有检测到常见的糖类植物固氮菌内生菌，例如偶氮螺旋菌。假单胞菌属和微细菌属都在所有样品中都大量存在，表明它们可能在盐生植物Saeeda的微生态系统中发挥了先进的作用。此外，结果还表明，不仅土壤盐分会影响盐生植物内生成分，而且还可能涉及其他因素，例如地理位置，植物种类和其他土壤特性。有趣的是，只有致恒型盐菌和短杆菌属。属于放线菌属可以在补充有6％的NaCl半固体游离N-（NFB）培养基中生长和高度增强的生长S. maritima的体外。总体而言，这项研究为固氮内生细菌提供了有用的新资源，可以利用这些资源来改进提供可用于盐基农业的生物肥料的方法。