The presence of latent bacteria is a serious problem in plant tissue cultures. While endophytes are generally beneficial to plants in situ, they may affect culture growth under the modified conditions in vitro. The present study was undertaken to identify and characterize endophytic bacteria associated with the medicinal plant Echinacea in tissue culture. Based on classical microbiological tests and 16S rRNA analyses, it was found that endophytic bacteria associated with aseptically micropropagated Echinacea plantlets are representatives of several genera, Acinetobacter, Bacillus, Pseudomonas, Wautersia (Ralstonia) and Stenotrophomonas. Based on TLC and HPLC analyses, we found that Pseudomonas stutzeri P3 strain produces plant hormone, auxin (indole-3-acetic acid, IAA). Antibiotic resistance was also assessed as a virulence factor. The majority of endophytic bacteria were resistant to the antibiotic kanamycin, but susceptible to chloramphenicol. Recommendations for propagating Echinacea in vitro cultures involve the addition of chloramphenicol, tetracycline, and ampicillin, antibiotics that cause no side effects on these plant species.Abbreviations: IAA -indole-3-acetic acid; MS -Murashige and Skoog medium; NA -nutrient agar; NBnutrient broth; TSA -tryptic soy agar
This study aimed to evaluate the antibacterial, leishmanicidal, and cytotoxic potential of metabolites produced by bacteria isolated from rhizosphere soil samples. The bacterium was identified by molecular techniques as Streptomyces kronopolitis. A preliminary screening was carried for the antimicrobial activity of S. kronopolitis, demonstrating activity against Staphylococcus aureus ATCC 6538, Corynebacterium diphtheriae ATCC 27010, C. diphtheriae ATCC 27012, and Mycobacterium abscessus, with inhibition halos of sizes 25, 36, 29, and 33 mm, respectively. To obtain secondary metabolites, the bacteria was subjected to submerged fermentation, and the metabolites were extracted using the liquid-liquid method with ethyl acetate. There was a similar MIC for M. abscessus and the two strains of C. diphtherium, reaching a concentration of 0.125 mg/mL, while that of S. aureus was 0.048 mg/mL. Assays for leishmanicidal activity and cytotoxicity against HEp-2 cells and red blood cells were performed. The metabolite showed IC50 of 9.0 ± 0.9 µg/mL and CC50 of 226.2 µg/ ml. This metabolite does not have hemolytic activity and is more selective for parasites than for mammalian cells, with a selectivity index of 24.85. Thus, the studied metabolite may be a strong candidate for the development of less-toxic drugs to treat diseases caused by pathogens.
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