Abstract
The objective of this study was to optimize the nutritional and cultural conditions of Streptomyces strain ERI-1, ERI-3 and ERI-26 for the production of antimicrobial metabolites under shake-flask conditions. Effect of eight fermentation medium, different temperature, pH, incubation time, different carbon and nitrogen sources and different concentration of sodium chloride on production of antimicrobial metabolites were studied. Antimicrobial activity of the fermentation medium was evaluated by cup plate method by measuring the zone of inhibition. Nutritional and cultural conditions for the production of antimicrobial metabolites by Streptomyces strain ERI-1, ERI-3 and ERI-26 under shake-flask conditions have been optimized. Modified nutrient medium was found to be good base for fermentation. Glucose and ammonium nitrate were identified as best carbon and nitrogen sources, respectively for growth and production of more antimicrobial compounds. Similarly, initial production medium pH of 7.0, incubation temperature of 30°C and incubation time of 96 h was found to be optimal. Optimization of medium and cultural conditions resulted in better antibacterial and antifungal activity. The zone of inhibition of ERI-26 against Aspergillus niger was 25 and 20 mm for Curvularia lunata, respectively. It is clear that novel Stretomyces strains ERI-1, ERI-3 and ERI-26 produced extra cellular antimicrobial metabolites effective against pathogenic bacteria and fungi, moreover the medium and cultural conditions for better antimicrobial metabolites production have been optimized. Key words: Streptomyces, antimicrobial activity, nutritional requirements, cultural conditions, optimized media.
Highlights
IntroductionAmong 10000 known antibiotics, 45-55% is produced by Streptomycetes (Demain, 2006; Lazzarini et al., 2000)
Streptomycetes are potent producers of secondary metabolites
Considering that any screening program of microbial natural products can handle a limited number of fermentations, applying many growth conditions to each strain may critically restrict the number of strains and the diversity of biosynthetic pathways included in the screening
Summary
Among 10000 known antibiotics, 45-55% is produced by Streptomycetes (Demain, 2006; Lazzarini et al., 2000). A common strategy, widely applied in industrial screening programs, consists of the application of several growth conditions (including variables such as production media, incubation time and other factors) to different strains which has been studied (Vilella et al, 2000). Considering that any screening program of microbial natural products can handle a limited number of fermentations, applying many growth conditions to each strain may critically restrict the number of strains and the diversity of biosynthetic pathways included in the screening. The production of antibiotics is increased by the presence of a non preferred carbon source, or by other nutrients (Mohd et al, 2012). The source and availability of nitrogen can influence the production of secondary metabolites (Arasu et al, 2008; Arasu et al, 2009)
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