Isolation and screening of actinomycetes producing antimicrobial substances from an extreme Moroccan biotope

Abstract

Introduction: this study was carried out to isolate and screen actinomycetes from soil of two salterns in Taza-Morocco, for the production of antimicrobial compounds against a set of target bacteria. Also, it aims to highlight some practices in order to isolates actinomycetes and screen for their ability to produce antibacterial compounds. Methods: soil samples were analyzed for physical and chemical parameters including pH, electrical conductivity, and salinity. The actinomycetes were isolated on Casein Starch Agar (CSA) medium and purified on International Streptomyces Project 2 (ISP-2) medium. Antimicrobial activity of actinomycete isolates was evaluated by measuring the inhibition zone. These activities were tested against Dickeya solani IP2222, Pectobacterium brasiliensis 13471a, Escherichia coli K12, Proteus mirabilis, Pseudomonas aeruginosa CECT118, Listeria innocua CECT4030, Staphylococcus aureus CECT976, Bacillus subtilis DSM 347 and Candida alibicans, using three different culture media (CSA, Bennett and Mueller Hinton) and at two temperatures of incubation (30°C and 37°C). Results: physical and chemical analysis of soil samples showed that both sites are alkaline. Also, with regards to salinity, the second site showed to contain high salt concentration compared the first site. The abundance of bacteria isolated on CSA medium from both sites showed correlation with the physical-chemical properties of the sampling soils. Incubation temperature of 30°C resulted in a high number of actinomycetes (18/22) isolates with antimicrobial effect relative to the temperature of 37°C (4/22). Some actinomycetes isolates show antimicrobial effect on only one culture medium, which shows a special nutritional requirement to express their antimicrobial effect. On the other hand, some isolates, they express their antimicrobial effect on the three media at the same time. Additionally, some isolates of actinomycetes inhibit the growth of several microorganisms at once. While others inhibit the growth of only one microorganism tested which reflects a possible specificity of antimicrobial substances. Conclusion: growth conditions including, media composition, temperature of incubation and the spectrum of test strain tailors the behavior of the antimicrobial screening.