Isolation Optimization and Characterization of Antimicrobial Peptide Producing Bacteria from Soil

In this study, soil bacteria were isolated and characterized including its antimicrobial peptide. For this, soil samples were collected from agriculture lands. Soil samples were diluted and cultured in nutrient agar plates to obtain the isolated bacterial colonies. Antimicrobial peptide producers were screened by stab overlay, agar well diffusion, cross streaking and lacuna assay methods. The isolated strains were identified through morphological, cultural and biochemical properties. Isolates with significant antimicrobial peptide producing potential, which inhibited the growth of sensitive strains in all applied assays have been identified as pseudomonas luteola with 98 % similarity index by API kit. Maximum antimicrobial activity of the isolated strain was observed at pH 7, 18 h incubation at 35 ̊C in brain heart infusion agar (BHI). Under optimized growth conditions, inhibitory zone was 34-36 mm, almost 20 folds higher than the initial and further increased after particle purification with 60 % ammonium sulfate precipitation. Estimated molecular size of the peptide produced by the isolates was less than 20 kda. These antimicrobial peptides lost antibacterial activity after treating with protinease K. Antimicrobial peptide obtained from producer strain was active against Shigella, Salmonella, Staphylococcus aureus, E. coli. Furthermore, this study suggests that clinically and industrially important peptide antibacterial compounds can be obtained from unexplored ecological niches.