Laguerre Gisèle, Nour Sarah M, Macheret Valérie, Sanjuan Juan, Drouin Pascal, Amarger Noëlle
Laboratoire de Microbiologie des Sols, Centre de Microbiologie du Sol et de l'Environnement, INRA, 17 rue Sully, BP 86510,F-21065 Dijon Cedex, France1.
Departamento de Microbiologı́a del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidı́n, CSIC, Profesor Albareda 1, E-18008 Granada, Spain2.
Microbiology (Reading). 2001 Apr;147(Pt 4):981-993. doi: 10.1099/00221287-147-4-981.
The nodC and nifH genes were characterized in a collection of 83 rhizobial strains which represented 23 recognized species distributed in the genera Rhizobium, Sinorhizobium, Mesorhizobium and Bradyrhizobium, as well as unclassified rhizobia from various host legumes. Conserved primers were designed from available nucleotide sequences and were able to amplify nodC and nifH fragments of about 930 bp and 780 bp, respectively, from most of the strains investigated. RFLP analysis of the PCR products resulted in a classification of these rhizobia which was in general well-correlated with their known host range and independent of their taxonomic status. The nodC and nifH fragments were sequenced for representative strains belonging to different genera and species, most of which originated from Phaselous vulgaris nodules. Phylogenetic trees were constructed and revealed close relationships among symbiotic genes of the Phaseolus symbionts, irrespective of their 16S-rDNA-based classification. The nodC and nifH phylogenies were generally similar, but cases of incongruence were detected, suggesting that genetic rearrangements have occurred in the course of evolution. The results support the view that lateral genetic transfer across rhizobial species and, in some instances, across Rhizobium and Sinorhizobium genera plays a role in diversification and in structuring the natural populations of rhizobia.
对83株根瘤菌菌株的nodC和nifH基因进行了表征，这些菌株代表了根瘤菌属、中华根瘤菌属、中慢生根瘤菌属和慢生根瘤菌属中23个已确认的物种，以及来自各种宿主豆科植物的未分类根瘤菌。根据可用的核苷酸序列设计了保守引物，能够从大多数研究菌株中分别扩增出约930 bp和780 bp的nodC和nifH片段。对PCR产物的RFLP分析对这些根瘤菌进行了分类，该分类总体上与其已知的宿主范围密切相关，且与其分类地位无关。对属于不同属和种的代表性菌株的nodC和nifH片段进行了测序，其中大多数菌株来自菜豆根瘤。构建了系统发育树，揭示了菜豆共生菌共生基因之间的密切关系，而不论其基于16S - rDNA的分类如何。nodC和nifH系统发育通常相似，但检测到不一致的情况，这表明在进化过程中发生了基因重排。结果支持这样一种观点，即跨根瘤菌物种，在某些情况下跨根瘤菌属和中华根瘤菌属的横向基因转移在根瘤菌自然种群的多样化和结构形成中发挥作用。
