Antibacterial and cytotoxic potency of thermophilic Streptomyces werraensis MI?S.24?3 isolated from an Egyptian extreme environment

The need for novel and active antibiotics specially from actinomycetes is essential due to new and drug-resistant pathogens.
In this study, 87 actinomycetes were isolated, and 18 strains among them characterized as thermophilic actinomycetes.
Further fractionation and preliminary antibacterial activities indicated that one strain, coded as MI-S.24-3, showed good
antibacterial activity. Based on the phenotypic, genomic, phylogenetic, and biochemical analyses, MI-S.24-3 was identified as
Streptomyces werraensis. Results demonstrated that the ethyl acetate active fraction showed maximum antibacterial activity
against Staphylococcus aureus and Escherichia coli with MIC (12.7 ± 0.1 and 18.3 ± 0.2 mg/mL), and MBC (96.5 ± 1.4 and
91.5 ± 0.7 mg/mL), respectively, with determination of time kill kinetics assay. The active fraction showed moderate-to-weak
cytotoxic effects against human lung carcinoma (A549 cells), breast cancer cell line (MCF-7), and human cervical carcinoma
(HELA cells) with a IC50
of (23.8 ± 1.2, 54 ± 1.8, 96.4 ± 3.2 μg/mL, respectively). Active components were characterised by
different chemically volatile, ester, and lactone compounds, determined by GC–MS coupled with daughter ions of (GC–MS/
MS). Notably, erucic acid and reynosin identified compounds are rare metabolites produced by Streptomyces werraensis.
Our findings demonstrated that the MI-S.24-3 strain could be a potential source for active compounds of biomedical and
pharmaceutical interest.