Jae Kyung Sohng

Production, isolation and biological activity of nargenicin from Nocardia sp. CS682

Culture broth of an actinomycete isolate, Nocardia sp. CS682 showed specifically higher antibacterial activity against methicilin resistant Staphylococcus aureus (MRSA). Purified substance from the organism, CS-682, which is active against MRSA and Micrococcus leuteus, is a C28H37NO8 (M+H+, observed: 516.83) and identified as an unusual macrolide antibiotic, nargenicin. The chemical structure of CS-682 was identified by FT-IR, 1H-NMR, 13C-NMR, and (1H-1H and 1H-13H) COSY. The anti-MRSA activity of CS-682 was stronger than that of oxacillin, vancomycin, monensin, erythromycin, and spiramycin. Phylogenetic analysis showed that strain CS682 is closely related to Nocardia tenerifensis DSM 44704T (98.7% sequence similarity), followed by N. brasiliensis ATCC 19296T (98.4% sequence similarity). The ability of Nocardia sp. CS682 to produce nargenicin was unique.

Paired-termini Antisense RNA Mediated Inhibition of DoxR in Streptomyces peucetius ATCC 27952

Our previous study provided an insight into DoxR as a negative regulator of doxorubicin production in Streptomyces peucetius ATCC 27952. Streptomyces hosts are advantageous in terms of producing a number of pharmaceuticals in low titer. Antisense RNAs (asRNAs) silencing strategy acts as an alternative tool for metabolic engineering of microorganisms for construction of an efficient cell factory. In this study, a paired-termini antisense RNAs (PTasRNAs) silencing strategy was employed for inhibition of DoxR to enhance doxorubicin production. To continue this endeavor, we designed and constructed the piBR702 vector for the expression of PTasRNAs in monocistronic mode. Further, two variants of asRNA, adoxR and bdoxR were designed and cloned into piBR702. All the rDNAs were transformed into S. peucetius to generate engineered strains. The engineered strains, S. peucetius A and S. peucetius B produced enhanced titers of doxorubicin, daunorubicin, and e-rhodomycinone; however, no such change was seen in S. peucetius AB. Moreover, RT-PCR analysis of doxR from S. peucetius A and S. peucetius B, together with the higher production from S. peucetius A, confirmed adoxR as a better asRNA than bdoxR. The reason behind this could be due to the simple secondary structure and low binding free energy of adoxR (−419 kcal/mol) than bdoxR (−358.8 kcal/mol). Our study demonstrated that antibiotic production was enhanced significantly by inhibiting DoxR, a negative regulator in S. peucetius using PTasRNAs. In addition, this study further provides an insight into PTasRNAs as an effective tool for gene silencing in Streptomyces and its use as an effective tool for metabolic engineering.