RESUMEN
Pyrolysis mass spectrometry (PyMS) and DNA fingerprinting (RAPD and RSalpha hybridization) were used to characterize soybean inoculant strains and root nodule isolates of bradyrhizobia from the Brazilian Cerrado soils. Most isolates were shown to be derived from the inoculant strains on the basis of genotype comparisons by DNA fingerprinting. Phenotypic analysis (using PyMS) of the strains and separately of the polysaccharides derived from them showed that the nodule isolates differed from the parental strains, suggesting adaptation to the Cerrado soil environment. The extent of the differences between the derivatives and inoculant strains was similar for comparisons made on the basis of whole-cell preparations or from the isolated polysaccharides, indicating that the adaptation was caused by changes in the composition of the polysaccharides produced.
Asunto(s)
Adaptación Fisiológica , Bradyrhizobium/crecimiento & desarrollo , Bradyrhizobium/genética , Glycine max/microbiología , Polisacáridos Bacterianos/química , Microbiología del Suelo , Bradyrhizobium/química , Brasil , Espectrometría de Masas/métodos , Hibridación de Ácido Nucleico , Polisacáridos Bacterianos/genética , Polisacáridos Bacterianos/metabolismo , Técnica del ADN Polimorfo Amplificado AleatorioRESUMEN
Actinomycetes were isolated from soybean rhizosphere soil collected as two field sites in Brazil. All the isolates were identified as Streptomyces species and were screened for streptomycin production and the presence of two genes, strA and strB1, known to be involved in streptomycin biosynthesis in Streptomyces griseus. Antibiotic resistance profiles were determined for 53 isolates from cultivated and uncultivated sites, and approximately half the strains were streptomycin resistance. Clustering by the unweighted pair group method with averages indicated the presence of two major clusters, with the majority of resistant strains from cultivated sites being placed in cluster 1. Only representatives from this cluster contained strA. Streptomycetes containing strA and strB1 were phenotypically diverse, and only half could be assigned to known species. Sequence comparison of 16S rRNA and trpBA (tryptophan synthetase) genes revealed that streptomycin- producing streptomycetes were phylogenetically diverse. It appeared that a population of streptomycetes had colonized the rhizosphere and that a proportion of these were capable of streptomycin production.