Eugenia Marquina María, Enrique González Néstor, Castro Yulimar
Laboratorio de Fijación Biológica de Nitrógeno y Cultivos de Tejidos Vegetales in vitro, Departamento de Biología, Facultad de Ciencias, Universidad de Los Andes. Núcleo Pedro Rincón Gutiérrez, Edificio A, 2o piso, La Hechicera, Mérida, Venezuela.
Rev Biol Trop. 2011 Sep;59(3):1017-36.
Rhizobial taxonomy and systematics have progressed substantially, nevertheless, few studies have been developed on venezuelan species. This study evaluated the phenotypic and genetic variation between 12 venezuelan indigenous rhizobial isolates and 10 international referential strains, by phenotypical traits and DNA molecular markers. In this regard, a PCR-RFLP of the 16S rDNA gene, the presence of large plasmids, metabolic assays in solid media, salinity resistance, pH and temperature growth conditions, and intrinsic antibiotic resistance were assayed. In reference to the phenotypic attributes, we recognized three main groups: A group I, which comprised all the strains metabolizing between 67.5%-90% of the C and N sources. They were also acid-tolerant, as well as acid producers, capable of growing at 40 degrees C and in high salinity conditions (2-2.5% NaCl). With regard to the antibiotic sensitivity, this group was susceptible to a 30% of the antibiotic assayed. Strains belonging to Group II exhibited a lower salt tolerance (0.1-1.5%NaCl), as well as a lower acid tolerance, since they grew well at pH values equal or higher than 5.0. This group appeared to be resistant to all of the antibiotics assayed and only metabolized between 52.5%-82.5% of the C and N sources. Group III was represented by a single bacterial strain: it has a extremely low salt tolerance (0.1% NaCl). This strain grew at a pH equal or higher than 5.6, was susceptible to 50% of the antibiotics assayed and metabolized 72% of the C and N sources. On the basis of a PCR- RFLP of the 16S rDNA, three groups were also obtained. Members of the group A showed a close resemblance to Rhizobium tropici CIAT 899 and Sinorhizobium americanum CFN-EI 156, while Group B was closely related to Bradyrhizobium spp. Group C, was also represented by only one isolate. The Trebol isolate, was the only one strain able to form nodules and does not appear to be related to any of the referential rhizobial strains, suggesting a possible symbiotic horizontal gene transfer. Finally, in this work, there are evidences of a genetic diversity in the venezuelan rhizobial strains. A different geographical origin is perhaps an important factor affecting the diversity of the indigenous rhizobia in this study.
根瘤菌分类学和系统学已经取得了显著进展，然而，针对委内瑞拉根瘤菌种的研究却很少。本研究通过表型特征和DNA分子标记，评估了12株委内瑞拉本土根瘤菌分离株与10株国际参照菌株之间的表型和遗传变异。在这方面，对16S rDNA基因进行了PCR-RFLP分析、检测了大质粒的存在情况、在固体培养基中进行了代谢分析、测定了耐盐性、pH值和温度生长条件以及固有抗生素抗性。关于表型属性，我们识别出三个主要组：第一组，包含所有能代谢67.5%-90%的碳源和氮源的菌株。它们还耐酸，也是产酸菌，能够在40摄氏度和高盐条件（2%-2.5%氯化钠）下生长。关于抗生素敏感性，该组对30%的检测抗生素敏感。属于第二组的菌株表现出较低的耐盐性（0.1%-1.5%氯化钠）以及较低的耐酸性，因为它们在pH值等于或高于5.0时生长良好。该组似乎对所有检测的抗生素都有抗性，并且仅能代谢52.5%-82.5%的碳源和氮源。第三组仅由一个细菌菌株代表：它具有极低的耐盐性（0.1%氯化钠）。该菌株在pH值等于或高于5.6时生长，对50%的检测抗生素敏感，能代谢72%的碳源和氮源。基于16S rDNA的PCR-RFLP分析，也得到了三个组。A组的成员与热带根瘤菌CIAT 899和美洲中华根瘤菌CFN-EI 156非常相似，而B组与慢生根瘤菌属密切相关。C组也仅由一个分离株代表。Trebol分离株是唯一能够形成根瘤的菌株，并且似乎与任何参照根瘤菌菌株都没有关系，这表明可能存在共生水平基因转移。最后,在这项研究中，有证据表明委内瑞拉根瘤菌菌株存在遗传多样性。不同的地理起源可能是影响本研究中本土根瘤菌多样性的一个重要因素。
