Phaseolus lunatus (Lima bean) is an important legume for the poor population of the Brazilian northeast region. The legume is able to take advantage of the nitrogen fixation process, but the diversity of indigenous microsymbionts is poorly known. In this study, 29 bacteria isolated from root nodules of P. lunatus inoculated under greenhouse conditions with soils from Piauí State, in the northeast semi-arid region of Brazil, were obtained and characterized. Classical morphological and biochemical essays revealed high phenotypic diversity, splitting the bacteria into four clusters. Genetic fingerprinting by BOX-PCR indicated outstanding diversity, with the 29 strains positioned in 19 different clusters with 30% of final similarity. Nine genera were confirmed in the analysis of the 16S rRNA gene, with two typical nodulating N₂-fixing clades, Bradyrhizobium and Agrobacterium/Rhizobium, accounting for 38% and 21% of the isolates, respectively; the results were confirmed with the housekeeping gyrB gene, that also indicated putative new species. Bradyrhizobium was confirmed as the main symbiont, being present in nodules of all plants. All rhizobia except for those with higher resemblance to agrobacteria carry nifH genes. Six other genera were isolated as nodules endophytes, Bacillus, Burkholderia, Enterobacter, Franconibacter, Pseudomonas and Williamsia. Several of these endophytes exhibited one or more important biochemical properties, such as the synthesis of catalase, gelatinase and the ability to solubilize phosphate, that might confer ecological advantages to the rhizobia associated with them in the harsh environment of the Brazilian semi-arid, explaining the high rate of co-infection detected in the nodules.

中文翻译：

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巴西东北皮奥伊州土壤接种的菜豆结节中固氮和共存细菌的多相表征

菜豆（豆豆）是巴西东北地区贫困人口的重要豆类。豆科植物能够利用固氮过程的优势，但对本地微共生菌的多样性知之甚少。在这项研究中，从月球假单胞菌根瘤中分离出29种细菌在温室条件下，用巴西东北半干旱地区的皮奥伊州的土壤进行了接种。古典的形态学和生化论文揭示了高表型多样性，将细菌分为四个簇。通过BOX-PCR进行的基因指纹分析显示了出色的多样性，其中29个菌株位于19个不同的簇中，具有30％的最终相似性。在分析16S rRNA基因中确认了9个属，其中两个典型的结节N ₂固定进化枝，缓生根瘤菌和农杆菌/根瘤菌，分别占分离物的38％和21％。结果通过管家gyrB基因得到证实，该基因还表明可能存在新物种。缓生根瘤菌被确认是主要的共生体，存在于所有植物的根瘤中。除与农杆菌具有较高相似性的根瘤菌外，所有根瘤菌均携带nifH基因。分离出六个其他属，分别为内生结节杆菌，芽孢杆菌，伯克霍尔德氏菌，肠杆菌，Franconibacter，假单胞菌和Williamsia。这些内生菌中的几种表现出一种或多种重要的生化特性，例如过氧化氢酶，明胶酶的合成和溶解磷酸盐的能力，这可能在巴西半干旱的恶劣环境中赋予与它们相关的根瘤菌生态优势。在结节中检出的合并感染率很高。