Evaluation of the Cytotoxicity of Secondary Bioactive Compounds Produced by Streptomyces in Soil against a Colon Cancer Cell Line.

Colorectal cancer is one of the most serious malignancies affecting humans. In this study, Streptomyces bioactive chemicals extracted from soil were analyzed for their anti-colorectal-cancer and antibacterial properties. A total of 100 soil samples were collected from Kerman-Iran, incubated in SCA media and the antimicrobial properties were tested using the cross-streak method. Three strains were cultured in ISP4 medium to obtain secondary bioactive compounds. After studying the effects of the bioactive compounds on the HT29 and human foreskin fibroblast (HFF) cell lines, the expression of the p53, p21, BAX, BCL2, Casp3 and Casp8 genes was analyzed by real-time PCR and flow cytometry to detect the presence of apoptosis.The isolates show high degree of identification with Streptomyces rochei, Streptomyces fungicidicus and Streptomyces maritimus due to 16SrDNA sequence homology. Compared to HT-29 cells, Streptomyces extracts had lower cytotoxicity against normal cells (SI=5.88), followed by HFF (SI=4.14). The cell lines demonstrated a dose-dependent significant increase in DNA fragmentation, an increase in the proportion of cells in sub-G1 phase and caused G2/M cell cycle arrest in HT-29 and HFF cells.The bacterial extracts obtained displayed strong antibacterial properties and inhibited the proliferation of HT-29 and HFF cell lines. The treated cells exhibited morphological changes caused by the activation of caspase and p53/p21 proteins. This confirms that Streptomyces-induced apoptosis is mediated by the activation of p21/p53. Anti-apoptotic Bcl-2 gene expression was downregulated by treatment with the extracts. Further studies are needed to understand the antimicrobial properties of Streptomyces.