Determining the location of some Antibiotic- Coding Genes in Streptomyces spp


Twelve isolates belonging to the species streptomyces antibioticus(3), S. albus (2), S. streptovaticillium(1), and S. purpureus (5) were checked for their ability to resist different antibiotics. The results showed variation in their pattern of antibiotic resistance. The antibiotic production ability of these isolates was tested and it was found that five of them are antibiotic producers while the rest were not. Two methods were used to determine the location of genes encoding antibiotics, conjugation and plasmid curing. Conjugation between each of the isolates of streptomyces as donars and the laboratory strain E. coli JM83 as a recipient produced no transconjugant colonies capable of antibiotic production .Treating the original donar isolates with ethidium bromide (25µg/ml), showed that 40% of the isolate (4) lost their ability to produce antibiotics. This result suggests that the genes encoding antibiotic production are located on the plasmid DNA.Failure of curing colonies towards antibiotic production in the isolates 1,8 may indicate that antibiotic resistant trait is located on the chromosomal DNA in these isolates.