Antimicrobial Activities of Bacteriocin-Like Extracellular Metabolites Produced by Soil Bacteria

Abstract

In an attempt to competitively inhibit other organisms within the same environment, microbial cells produce a wide range of bioactive bacteriocins and bacteriocin-like extracellular metabolites (BLEM). Bacterial species (Bacillus and Pseudomonas) were isolated from soil samples, screened for BLEM production and the crude activity of cell free metabolites determined by agar diffusion assay. Partial purification of metabolites was achieved by protein precipitation with ammonium sulfate and BLEM sensitivities to temperature, pH, surfactant and ultraviolet radiation along with the mode of action of partially purified BLEM on indicator strains and other pathogens were characterized. Bacillus subtilis SF8 and Pseudomonas aeruginosa SF4 produced BLEM inhibitory to closely related strains with partially purified activity units of 768 and 2048AU/mL respectively. BLEMs retained large percentages of their inhibitory activities over a wide range of temperature and pH, 71%, 92% and 80% activity was retained by BLEM from B. subtilis SF8 while 91%, 81% and 89% activity was retained by BLEM from P. aeruginosa SF4 after 60 minutes of BLEM pre-incubation at 900C, pH 4 and 10, respectively. Ultraviolet radiation enhanced BLEM production in P. aeruginosa SF4 but not in B. subtilis SF8. Fourier Transformed Infrared (FTIR) spectroscopy revealed that BLEMs from both B. subtilis SF8 and P. aeruginosa SF4 interfered with cell membrane components of B. macerans SF2 and P. fluorescence BS2 respectively. The BLEM also had a broad inhibitory range on test bacterial and fungal pathogens.