Taxonomic classification of rhizobial strains recommended for soybean and common bean crops in Brazil based on the sequencing of the 16s rRNA gene

As culturas da soja [Glycine max (L.) Merrill] e do feijoeiro (Phaseolus vulgaris L.) são de grande importância econômica e social para o Brasil e ambas podem ter seu requerimento de nitrogênio suprido pela simbiose com bactérias da ordem Rhizobiales. Para garantir a maximização do processo biológico, deve-se proceder à inoculação de estirpes de rizóbio eficientes e competitivas, recomendadas pela pesquisa. No Brasil, foram comercializados, na safra 2001/2002, 14 milhões de doses de inoculantes, dos quais 99 % para as culturas da soja e do feijoeiro. Neste trabalho, determinou-se a posição taxonômica das estirpes utilizadas em inoculantes comerciais para as duas culturas, pelo seqüenciamento da região do DNA que codifica o gene 16S rRNA, que é suficientemente variável, mas carrega as informações necessárias para permitir a análise filogenética de bactérias. O seqüenciamento permitiu definir que duas das estirpes recomendadas para a cultura da soja, SEMIA 587 e SEMIA 5019 (= 29 w), pertencem à espécie Bradyrhizobium elkanii e as duas outras, SEMIA 5079 (=CPAC 15) e SEMIA 5080 (= CPAC 7), à espécie B. japonicum. Determinou-se, ainda, que a estirpe SEMIA 4080 (=PRF 81), recomendada para o cultura do feijoeiro, pertence à espécie Rhizobium tropici. As seqüências obtidas foram depositadas no banco mundial de genes do National Center for Biotechnology Information.Soybean [Glycine max (L.) Merrill] and common bean (Phaseolus vulgaris L.) crops are of economical and social importance in Brazil; their requirement for nitrogen can be supplied by the symbiosis with bacteria belonging to the order Rhizobiales. However, to guarantee the maximization of the biological nitrogen fixation, seeds must be inoculated with efficient and competitive strains of rhizobia recommended by research. In 2001/2002, 14 million doses of inoculant were sold in Brazil, 99 % of these for soybean and common bean crops. In this study the taxonomic position of the strains used in commercial inoculants for both crops was evaluated by sequencing the DNA region that carries the information for the 16S rRNA gene. Although variable, it codes enough information to allow a phylogenetic analysis of the bacteria. Sequencing determined that two of the strains recommended for the soybean crop, SEMIA 587 and SEMIA 5019 (= 29 w), belong to the Bradyrhizobium elkanii, while the two other, SEMIA 5079 (=CPAC 15) and SEMIA 5080 (=CPAC 7), belong to the B. japonicum species. Strain SEMIA 4080 (=PRF 81), recommended for common bean crop, was identified as member of the species Rhizobium tropici. The sequences were included in the GenBank database of the National Center for Biotechnology Information