Agriculture and Agri-Food Canada, Ottawa, Ontario K1A OC6, Canada.
Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd, Quebec G1V 2J3, Canada.
Microbiology (Reading). 2010 Feb;156(Pt 2):505-520. doi: 10.1099/mic.0.034058-0. Epub 2009 Oct 29.
Phage-resistant and -susceptible bacteria from nodules of alfalfa and sweet clover, grown at a site without a known history of cultivation, were identified as diverse genotypes of Ensifer, Rhizobium and Phyllobacterium species based on sequence analysis of ribosomal (16S and 23S rRNA) and protein-encoding (atpD and recA) genes, Southern hybridization/RFLP and a range of phenotypic characteristics. Among phage-resistant bacteria, one genotype of Rhizobium sp. predominated on alfalfa (frequency approximately 68 %) but was recovered infrequently ( approximately 1 %) from sweet clover. A second genotype was isolated infrequently only from alfalfa. These genotypes fixed nitrogen poorly in association with sweet clover and Phaseolus vulgaris, but were moderately effective with alfalfa. They produced a near-neutral reaction on mineral salts agar containing mannitol, which is atypical of the genus Rhizobium. A single isolate of Ensifer sp. and two of Phyllobacterium sp. were recovered only from sweet clover. All were highly resistant to multiple antibiotics. Phylogenetic analysis indicated that Ensifer sp. strain T173 is closely related to, but separate from, the non-symbiotic species 'Sinorhizobium morelense'. Strain T173 is unique in that it possesses a 175 kb symbiotic plasmid and elicits ineffective nodules on alfalfa, sweet clover, Medicago lupulina and Macroptilium atropurpureum. The two Phyllobacterium spp. were non-symbiotic and probably represent bacterial opportunists. Three genotypes of E. meliloti that were symbiotically effective with alfalfa and sweet clover were encountered infrequently. Among phage-susceptible isolates, two genotypes of E. medicae were encountered infrequently and were highly effective with alfalfa, sweet clover and Medicago polymorpha. The ecological and practical implications of the findings are discussed.
从无已知种植史的地点的紫花苜蓿和三叶草根瘤中分离出的抗噬菌体和噬菌体敏感细菌，根据核糖体（16S 和 23S rRNA 和蛋白质编码（atpD 和 recA）基因、Southern 杂交/RFLP 和一系列表型特征的序列分析，鉴定为不同基因型的根瘤菌属、慢生根瘤菌属和叶杆菌属。在抗噬菌体细菌中，一种根瘤菌属的基因型在紫花苜蓿上占优势（频率约为 68%），但从三叶草中很少回收（约 1%）。第二种基因型仅从紫花苜蓿中很少分离出来。这些基因型与三叶草和菜豆结合固氮能力差，但与紫花苜蓿中度有效。它们在含有甘露醇的无机盐琼脂上产生近中性反应，这是非根瘤菌属的典型特征。仅从三叶草中分离出一种慢生根瘤菌属和两种叶杆菌属的菌株。所有这些菌株都对多种抗生素高度耐药。系统发育分析表明，慢生根瘤菌属菌株 T173 与非共生种“Sinorhizobium morelense”密切相关，但又相互分离。菌株 T173 是独特的，因为它具有一个 175 kb 的共生质粒，并在紫花苜蓿、三叶草、紫花苜蓿和大波斯菊上引发无效根瘤。这两种叶杆菌属是无共生的，可能代表细菌机会主义者。遇到三种与紫花苜蓿和三叶草共生有效的根瘤菌属 meliloti 基因型，但频率较低。在噬菌体敏感的分离株中，两种根瘤菌属 medicae 基因型很少遇到，并且与紫花苜蓿、三叶草和紫花苜蓿高度有效。讨论了这些发现的生态和实际意义。
