Rhizobia Isolated from the Relict Legume Vavilovia formosa Represent a Genetically Specific Group within Rhizobium leguminosarum biovar viciae

Twenty-two rhizobia strains isolated from three distinct populations (North Ossetia, Dagestan, and Armenia) of a relict legume Vavilovia formosa were analysed to determine their position within Rhizobium leguminosarum biovar viciae (Rlv). These bacteria are described as symbionts of four plant genera Pisum, Vicia, Lathyrus, and Lens from the Fabeae tribe, of which Vavilovia is considered to be closest to its last common ancestor (LCA). In contrast to biovar viciae, bacteria from Rhizobium leguminosarum biovar trifolii (Rlt) inoculate plants from the Trifolieae tribe. Comparison of house-keeping (hkg: 16S rRNA, glnII, gltA, and dnaK) and symbiotic (sym: nodA, nodC, nodD, and nifH) genes of the symbionts of V. formosa with those of other Rlv and Rlt strains reveals a significant group separation, which was most pronounced for sym genes. A remarkable feature of the strains isolated from V. formosa was the presence of the nodX gene, which was commonly found in Rlv strains isolated from Afghanistan pea genotypes. Tube testing of different strains on nine plant species, including all genera from the Fabeae tribe, demonstrated that the strains from V. formosa nodulated the same cross inoculation group as the other Rlv strains. Comparison of nucleotide similarity in sym genes suggested that their diversification within sym-biotypes of Rlv was elicited by host plants. Contrariwise, that of hkg genes could be caused by either local adaptation to soil niches or by genetic drift. Long-term ecological isolation, genetic separation, and the ancestral position of V. formosa suggested that symbionts of V. formosa could be responsible for preserving ancestral genotypes of the Rlv biovar.

Solubility Enhancement of Atrazine by Complexation with Cyclosophoraose Isolated from Rhizobium leguminosarum biovar trifolii TA-1

Rhizobium leguminosarum biovar trifolii TA-1, a kind of soil bacteria, produces cyclosophoraoses (Cys). Cyclosophoraoses contain various ring sizes with degrees of polymerization ranging from 17 to 23. Atrazine is a hardly-soluble herbicide that contaminates soil and drinking water, and remains in soil for a long time. To remove this insoluble contaminant from aqueous solutions, we have enhanced the solubility of atrazine by complexation with Cys. The complex formation of Cys and atrazine was confirmed using 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM), rotating frame nuclear overhauser spectroscopy (ROESY), and molecular modeling studies. The aqueous solubility of atrazine was enhanced 3.69-fold according to the added concentrations (20 mM) of Cys, compared to the 1.78-fold enhancements by β-cyclodextrin (β-CD). Cyclosophoraoses as an excellent solubility enhancer with long glucose chains that can effectively capture insoluble materials showed a potential application of microbial polysaccharides in the removal of hazardous hardly-soluble materials from aqueous solutions in the fields of biological and environmental industry.

Influência da inoculação de rizóbios sobre a germinação e o vigor de plântulas de alface

Os rizóbios, conhecidos por sua capacidade de fixar N2 em associação com leguminosas, também se mostram capazes de promover o crescimento de não-leguminosas, especialmente pela produção de ácido indol-acético (AIA). Neste trabalho, objetivou-se selecionar rizóbios produtores de AIA e avaliar o efeito de diferentes concentrações deste fitormônio sobre a germinação e o desenvolvimento inicial de plântulas de alface. Foram selecionados quatro isolados de Bradyrhizobium sp. e um isolado de Rhizobium leguminosarum biovar trifolii, os quais foram crescidos por quatro dias em meio levedura-manitol enriquecido com triptofano. Após esse período, avaliou-se a produção de AIA e procedeu-se à inoculação de sementes de alface com os isolados. O isolado TV-13, de R. leguminosarum biovar trifolii produziu 171,1µg mL-1 de AIA, causando prejuízos para o desenvolvimento das plântulas de alface. Por outro lado, os isolados de Bradyrhizobium sp. produziram entre 1,2 e 3,3µg mL-1 de AIA e aumentaram o vigor das plântulas em relação ao tratamento sem inoculação com rizóbios. Para verificar se essas diferenças foram decorrentes das concentrações de AIA, foram realizados mais dois experimentos, nos quais as sementes foram embebidas em culturas de TV-13 com ou sem a presença de triptofano ou em doses crescentes de AIA sintético. O isolado TV-13 crescido na presença de triptofano causou danos progressivos sobre o desenvolvimento das plântulas de alface, o que não ocorreu na ausência de triptofano. Também foi verificado um retardo na germinação das sementes quando submetidas a altas concentrações de AIA sintético. Os resultados indicam a influência do AIA sobre os parâmetros de germinação, de modo que a inoculação de sementes de alface com rizóbios que produzem baixas quantidades de AIA é uma prática recomendável.