Modification of Starch-Ammonium Sulfate Concentration To Enhance the Antibacterial Activity of Marine Streptomyces Aureofaciens A3.

This study is the first to report an enhancement in the antibacterial activity of Streptomyces aureofaciens A3 when cultured in an artificial seawater-based ISP4A medium. The primary objective was to evaluate both the antibacterial activity and metabolite profile of S. aureofaciens A3 cultured in ISP4A medium with varying concentrations of starch and ammonium sulfate, designated as C1, C2, C3, N1, N2, and N3. The activated inoculum (10%, v/v) was fermented for 14 days at 28 °C with agitation at 150 rpm, then extracted with methanol to obtain a methanol extract. The antibacterial activity of the extract was tested using the Kirby-Bauer method. The results showed that the methanol extract from the N2 medium produced the largest inhibition zones, with diameters of 20.80 mm against E. coli and 11.41 mm against B. subtilis. Furthermore, the methanol extracts from both N2 and C1 media exhibited the highest inhibition zones against S. aureus (18.90 mm) and P. aeruginosa (14.80 mm). GC/MS analysis of these extracts identified several major compounds, including hexadecanoic acid, methyl stearate, pyrrolo[1,2-a] pyrazine-1,4-dione, bis(2-ethylhexyl) phthalate, and benzene-propanoic acid. These findings suggest that an optimal concentration of starch and ammonium sulfate enhances the broad-spectrum antibacterial activity of S. aureofaciens A3.