ABSTRACT
Phylogenetic analysis was used to evaluate the hypothesis of gene transfer in streptomycetes, many of which are antibiotic producers. The diversity and possible origins of streptomycin-resistance genes was investigated for a population of Streptomyces strains isolated from a site in Brazil where antibiotic production had previously been implicated The analysis provides compelling evidence for the transfer of these genes. Examination of other Streptomyces-type strains also reveals a scattered distribution of streptomycin producers with respect to the overall phylogeny. These results suggest that horizontal gene transfer may be an important factor in the evolution of antibiotic genes in streptomycetes.
Subject(s)
Anti-Bacterial Agents/pharmacology , Soil Microbiology , Streptomyces/genetics , Streptomycin/pharmacology , Anti-Bacterial Agents/biosynthesis , Base Sequence , Blotting, Southern , Brazil , Cloning, Molecular , Conjugation, Genetic , DNA Probes/chemistry , Drug Resistance, Microbial/genetics , Electrophoresis, Agar Gel , Electrophoresis, Gel, Pulsed-Field , Molecular Sequence Data , Phenotype , Phosphotransferases (Alcohol Group Acceptor)/chemistry , Phylogeny , Polymerase Chain Reaction , R Factors/genetics , RNA, Ribosomal, 16S/chemistry , Sequence Alignment , Sequence Analysis, RNA , Streptomyces/classification , Streptomyces/drug effects , Streptomycin/biosynthesis , Tryptophan Synthase/chemistry , Tryptophan Synthase/geneticsABSTRACT
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.
Subject(s)
Soil Microbiology , Streptomyces/isolation & purification , Streptomycin/biosynthesis , Amino Acid Sequence , Bacterial Typing Techniques , Base Sequence , Brazil , DNA, Bacterial/analysis , Molecular Sequence Data , Streptomyces/classification , Streptomyces/metabolismABSTRACT
Actinomycetes have the genetic capability to synthesize many different biologically active secondary metabolites and of these compounds, antibiotics predominate in therapeutic and commercial importance. Intensive research often centres on the use of molecular techniques to investigate the physiology and genetics of antibiotic biosynthesis with a view to improving production. The isolation of clones of Streptomyces hygroscopicus, the producer of geldanamycin, which synthesizes geldanamycin in S. lividans, is reported. Molecular approaches using genes for elongation factors (tuf) were used in attempts to increase the fermentation yield of kirromycin, whilst probes for aphD and sph, genes for streptomycin phosphotransferases, were used to gather information on streptomycin genes in soil. Actinomycete populations in soil and earthworms may help in developing a strategy for discovering additional antimicrobials in soil. The relationship of proline metabolism to the secondary metabolite undecylprodigiosin and the carbon regulation of spiramycin biosynthesis in S. ambofaciens is also reported.
