Characterization of six bioactive compounds from two soil-derived Streptomyces strains, F9 and F4 from Iran

Actinobacteria are highly valuable in the pharmaceutical industry due to their unlimited capacity to produce natural products. In line with the screening of actinomycetes to discover new antibacterial agents, this study isolated and elucidated bioactive compounds from two Streptomyces strains, F9 (99.88% similarity with S. chryseus) and F4 (99.14% similarity with S. rectiviolaceus).

The present study followed a rigorous experimental approach. Previously, two Streptomyces strains, F9 and F4, were isolated and identified. These strains were then selected for the isolation and elucidation of secondary metabolites. The crude extract was semi-purified using Waters, and the active fractions were further purified using Agilent. The structure of the isolated compounds was elucidated through detailed spectroscopic analysis to ensure the accuracy and reliability of the findings.

Four fractions isolated from strain F9 showed antibacterial activity against test microorganisms. HR-ESI-MS, fragmentation pattern, and database search identified chrysomycins B and C. The structure of chrysomycins A and 4'-O-acetylated A was confirmed by 1D and 2D-NMR data. In addition, the findings characterized 2 pigments produced by strain F4 using HR-ESI-MS and fragmentation pattern (ESI-MS/MS), which revealed that major and minor peaks corresponded to butyl-meta-cycloheptylprodiginine and undecylprodiginine, respectively.

Six bioactive compounds, including 4 chrysomycins and 2 pigments, were isolated from 2 Streptomyces strains, F9 and F4. Importantly, this was the first report on isolating chrysomycins A-C and 4'-O-acetylated A from S. chryseus.