Antimicrobial Potential of a Rare Actinomycete Isolated from Soil: Crossiella sp.-EK18

Abstract

Aim: The aim of this work was to screen for important broad-spectrum antimicrobial metabolites-producing species of Actinomycetes from the uncultivated soil of Ekiti State, Southwestern,            Nigeria. Methodology: Ten uncultivated or barren soil samples each of 20 g were collected across Ekiti state between April and June 2014 for the isolation of Actinomycetes. The isolate was identified culturally as well as molecularly using 16S rDNA analysis. The influence of production parameters on antimicrobial activity was performed using standard method. The antimicrobial metabolites were produced by submerged fermentation. Partial purification was carried out by column chromatography. Chemical characteristics of the metabolites were determined by Fourier transformed infra-red spectrometer (FTIR) and gas chromatography coupled with mass spectrometer. The antimicrobial activity was carried out by agar well diffusion and macro broth dilution. Results: Out of ten actinomycetes isolated, Isolate EK18 possessed broad-spectrum antimicrobial activity and it was identified to be a strain of Crossiella based on its 16S rDNA gene sequence (KU934250). The best antimicrobial activity against indicator strains was observed at pH 7.0, at 28 degree Celsius after 15 days of incubation, in a medium that contained starch, casein+KNO3 supplemented with sodium chloride of 0.6% (w/v). Unsaturated aliphatic alkene, carboxylic acids, amides, hydroxyl, and carbonyls were functional groups detected in the synthesized antimicrobial metabolites by the strain while eleven antimicrobial metabolites were identified and characterized. The Minimum Inhibitory Concentration (MIC) against indicator strains was between 3.12 mg/L to 12.5 mg/L while Minimum Bactericidal Concentration (MBC) ranged between 12.5 mg/L and 25.0 mg/L. Crossiella sp.-EK18 exhibited broad-spectrum activity against indicator strains. Conclusion: The results indicated that potential broad-spectrum antimicrobial metabolites-producing strains of Actinomycetes could be isolated from the soil of southwestern Nigeria. These strains could be used in the production of antimicrobials that may find usefulness in combating emergent and re-emerging pathogens.