## 4 Discussion  
The global increase in antibiotic-resistant bacteria poses a serious threat to public health, with approximately 1.27 million deaths attributed to antimicrobial resistance in 2019 [40]. While the development of synthetic antibiotics remains important, there is renewed interest in natural sources. Among these, the genus _Streptomyces_ has contributed over two-thirds of clinically used antibiotics and continues to serve as a rich source of bioactive compounds [41]. Researchers are actively investigating new strains, particularly from understudied or extreme environments, to discover novel antimicrobial agents [42]. As part of these ongoing efforts, we explored microbial resources from Vietnam, a region known for its rich biodiversity. We successfully isolated _Streptomyces_ sp. CH6, which showed strong antibacterial activity against both Gram-positive and Gram-negative bacteria. In addition, the CH6 crude extract displayed antioxidant and anticancer activity. The 16S rRNA analysis revealed that the _Streptomyces_ sp. CH6 strain is most closely related to _S. evansiae_ DSM 41979\({}^{\text{T}}\), _S. harenosi_ PRKS01-65\({}^{\text{T}}\), and _S. caelestis_ NRRL 2418\({}^{\text{T}}\) with 98.9%, 98.1%, and 98.0% sequence similarity, respectively. Although these levels of similarity typically suggest a close taxonomic relationship, it is well recognized that 16S rRNA gene sequences can lack sufficient resolution to distinguish between closely related _Streptomyces_ species. To clarify the genomic relationship and facilitate genome mining, we conducted a whole-genome comparison using ANI. The ANI between CH6 and _S. evansiae_ DSM 41979 (GCA_031845585.1) was found to be 92.6%, which is below the generally accepted species boundary of 95-96% [43]. This result strongly suggests that _Streptomyces_ sp. CH6 represents a genomically distinct species. In support of these results, the dDDH between _Streptomyces_ sp. CH6 and _S. evansiae_ DSM 41979T, _S. kunimgensis_ DSM 41681T, and _S. roseofulvus_ JCM 4334 are 45.8%, 23.2%, and 23.1%, respectively, which are well below the 70% threshold typically used to define bacterial species boundaries. Our next experiments will focus on comparing the phenotypic, biochemical, and metabolic characteristics of the CH6 strain with those of its closest relatives, such as _S. evansiae_ DSM 41979\({}^{\text{T}}\), in order to provide further evidence that the CH6 strain represents a novel _Streptomyces_ species. The whole-genome sequencing and bioinformatics analysis of _Streptomyces_ sp. CH6 strain revealed 13 BGCs for secondary metabolite biosynthesis with similarities ranging from 13.2% to 80.7% to known clusters (Table 3). Among them, nine clusters showed moderate similarity (50-80%), suggesting the potential to produce known or related bioactive compounds. The totopotensamide cluster (54.1%) has been reported to exhibit cytotoxic activity, reinforcing the strain's therapeutic potential [44]. The genome of the CH6 strain also contains the detoxin S1 biosynthetic cluster (30.6%), which is associated with a natural product originally identified in _Streptomyces_ sp. NRRL S-325. However, the biological functions of detoxin S1 remain largely uncharacterized [45]. Supporting the extract's antioxidant activity, the isorenieratene cluster (56.7%) encodes carotenoids known for free radical scavenging [46], while the ectoine cluster (80.7%) produces an osmoprotectant that stabilizes cells under oxidative stress [47]. In addition, some of the identified clusters, such as kinamycin (13.2%) and julichrome Q3-3 (16.5%), showed very low similarity to known reference clusters, suggesting that _Streptomyces_ sp. CH6 may have the potential to produce novel secondary metabolites. Collectively, these clusters suggest a strong genetic basis for the production of bioactive metabolites in the CH6 strain. To validate this biosynthetic potential, in vitro assays were conducted to evaluate the antioxidant and anticancer activities of the CH6 crude extract.