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Background In the present study, adaptive laboratory evolution was used to stimulate antibiotic production in a Streptomyces strain JB140 (wild-type) exhibiting very little antimicrobial activity against bacterial pathogens. The seven different competition experiments utilized three serial passages (3 cycles of adaptation-selection of 15 days each) in which Streptomyces strain (wild-type) was challenged repeatedly to one (bi-culture) or two (tri-culture) or three (quadri-culture) target pathogens. The study demonstrates a simple laboratory model to study the adaptive potential of evolved phenotypes and genotypes in Streptomyces to induce antibiotic production. Results Competition experiments resulted in the evolution of the wild-type Streptomyces strain JB140 into the seven unique mutant phenotypes that acquired the ability to constitutively exhibit increased antimicrobial activity against three bacterial pathogens Salmonella Typhi (NCIM 2051), Staphylococcus aureus (NCIM 2079), and Proteus vulgaris (NCIM 2027). The mutant phenotypes not only effectively inhibited the growth of the tested pathogens but were also observed to exhibit improved antimicrobial responses against one clinical multidrug-resistant (MDR) uropathogenic Escherichia coli (UPEC 1021) isolate. In contrast to the adaptively evolved mutants, only a weak antimicrobial activity was detected in the wild-type parental strain. To get molecular evidence of evolution, RAPD profiles of the wild-type Streptomyces and its evolved mutants were compared which revealed significant polymorphism among them. Conclusion The competition-based adaptive laboratory evolution method can constitute a platform for evolutionary engineering to select improved phenotypes (mutants) with increased antibacterial profiles against targeted pathogens.

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The efficacy of an actinomycete strain JB66 recovered from a sand dune soil from the Bikaner district of the Thar desert in inhibiting the growth of various bacterial pathogens was studied. The type strains Staphylococcus aureus, Shigella flexneri, Klebsiella pneumoniae and the clinical isolates Escherichia coli, multidrug-resistant S. aureus and P. vulgaris were included in the antimicrobial assays. Polyphasic characterization of JB66 isolate revealed its identity as Streptomyces (MH762010). It showed 88.99-89.24% sequence similarity with the other members of this genus and share the maximum (88.89%) similarity with Streptomyces sp. ATSC13. The strain JB66 was found to produce a high amount of extracellular L-asparaginase, catalase, gelatinase, protease, tyrosinase and urease enzymes. The partial chemical categorization of the methanolic crude extract of the JB66 strain led to the preliminary identification of various metabolic compounds. The thin-layer chromatography fractionation revealed the presence of prodigiosin pigment or chandramycin, cephalosporin or zeatin, daidzein, demethoxy rapamycin, 4,6-dihydroxy-7-methoxyisoflavone, munumbicins and amiclenomycin like compounds. Bio-autography revealed that the metabolites localized at the Rf values of 0.40, 0.46 and 0.53 in TLC profile had the actual bioactive fractions. UV-VIS spectrum absorbance maxima at 288 nm revealed the presence of an aromatic nucleus.