Soil-dwelling Antagonistic Streptomycetes; Isolation coupled with functional and molecular screening

Abstract

Abstract One of the most challenging medical concerns is treating diseases caused by resistant bacteria. It is hence inevitable to explore sources of new antimicrobial derivatives. Calcium dependent antibiotics (CDAs) are lipopeptide antibiotics produced by Streptomycetes. CDAs are synthesized by a genes cluster which includes many pathway-specific regulatory genes. The gene cdaR can be utilized as a marker of CDA production. Micrococcus luteus has been employed as indicator to probe the production of lipopeptide antibiotics. This study was designed to yield domestic soil bacteria capable of producing antibacterial products and probe whether they are of lipopeptide nature. Soil samples were collected from Baft County, southern Iran. Chalky appearance of colonies on a semi-differentiative solid medium, FZmsn, was used to isolate representative Streptomycetes. Genomic DNA of isolates was extracted utilizing RIMA ® Kit and PCR products were run on gel electrophoresis and visualized by ethidium bromide under UV light. Molecular identity of the isolates was probed by PCR using a Streptomyces-specific primer pair. Evaluation of the isolates’ antibacterial effects against six indicator bacteria was carried out by using a pen-assay cross-streak culture method. The isolates were also investigated for the presence of the regulatory gene cdaR. Twelve illustrative Streptomycetes were isolated and characterized. Pen-assay experiments resulted in four isolates effective against S. aureus, S. epidermidis, and B. subtilis. Three of these were antagonistic against E. coli and two against M. luteus. No isolate was found to counter the growth of P. aeruginosa. The method proved to be facile in yielding domestic Streptomycetes active against pathogenic bacteria. Further research is being done on the isolates and properties of their products.