Physico-chemical Characterization of Indigenous Streptomyces and Influence of pH on Antimicrobial Activity

Background: Emergence of multi-drug resistant pathogens has afflicted the population of developing countries like Bangladesh in recent years for which a sustainable holistic combating approach is required. Since Streptomyces is a source of numerous bioactive molecules, the study was aimed at physico-chemical characterization of 8 indigenous Streptomyces isolates of Bangladesh. Methods: Tolerance of Streptomyces isolates to different growth conditions was assessed at temperature range 4 °C to 60 °C, pH range 3 to 11 and salinity up to 15% of NaCl concentration. Ability of isolates in utilizing different carbohydrates was checked through media of single sugar as sole carbon and energy source. The antimicrobial activity of the isolates against four pathogens was assayed with culture supernatant obtained from 5 different pH levels. The data was analyzed statistically by software R version 3.4.1. Results: All the isolates grew optimally in the temperature range of 20- 40 °C, pH range of 5- 9 and salinity of 1% NaCl concentration although certain isolates tolerated up to 60 °C and 10% of salinity. Based on the sugar profiles, the isolates were allocated into different biotypes and their relatedness was found with S. mutabilis (Ca), S. subrutilis(Cb1) and S. mirabilis (Cb2) as positioned at same clusters in the dendrogram. The antimicrobial molecules produced by the Streptomyces isolates were not heat stable and denatured by ethanol, hence presumed as protein. The maximum antagonism was recorded against E. coli by isolate B-5 at pH 6 (18 mm), against S. typhimurium by A- 9 at pH 9 (20 mm), against S. aureus by B-7 at pH 5 (18 mm) and against B. cereus by B- 7 at pH 8 and 9 (18 mm) as well as by D-5 at pH 7 (18 mm). It was also deduced that the pH as a growth condition significantly influenced the production of pathogen specific antimicrobial compounds by the Streptomyces isolates. Conclusion: The ability of the Streptomyces isolates in tolerating wide range of growth conditions would be of special advantage and the influence of pH in pathogen specific antimicrobial production could enhance the chances of obtaining diverse antimicrobials.