Production of a polypeptide Antimicrobial Compound by Lactic Acid Bacteria Isolated from Rhizospheric Soil of Egyptian Organic Farms
Publication Date : 05/03/2019
Abstract The current study aimed to isolation of lactic acid bacteria (LAB) showing antimicrobial activity mainly against some fungal and bacterial pathogens. A total of 41 LAB strains were isolated from the rhizosphere of healthy and diseased tomato and phaseolus plants using MRS agar medium supplemented with bromocresol green as an indicator of lactic acid production. The isolated bacterial strains were screened for antimicrobial activity against Staphylococcus aureus ATCC 2913 (G +ve), Pseudomonas aeruginosa ATCC 27953 (G -ve) and Mucor racemosus (phytopathogenic fungus). Among the tested LAB isolates, 32 of them showed antimicrobial activity against the tested pathogens with variable potency. However, LAB isolate No.38 exhibited the highest antimicrobial activity against the indicator strains and was the only strain showing antifungal activity against Mucor racemosus. According to 16S rDNA sequence and phylogenetic analysis, strain No.38 showed the highest similarity (98%) with Enterococcus faecium and was designed as Enterococcus faecium MN 38 (accession No.MK280754). Investigation of the effect of various physiological parameters revealed production of the bioactive agents by E. faecium MN 38 at temperature range 30-37 °C, pH range 4-7. In addition, strain MN 38 was able to tolerate NaCl concentration up to 4%. Finally, the precipitation of the bioactive compound from the culture filtrate by 60-80% ammonium sulphate, suggested the proteinaceous nature of the bioactive agent produced by E. faecium MN 38. The results indicated that plant rhizosphere is a promising source of antimicrobial agents producing LAB with potential application in biocontrol of phytopathogens and soil-born pathogenic bacteria and fungi.
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