Aspiculamycin

The alarming rise in antibiotic-resistant pathogens has coincided with a decline in the supply of new antibiotics. It is therefore of great importance to find and create new antibiotics. Nucleoside antibiotics are a large family of natural products with diverse biological functions. Their biosynthesis is a complex process through multistep enzymatic reactions and is subject to hierarchical regulation. Genetic and biochemical studies of the biosynthetic machinery have provided the basis for pathway engineering and combinatorial biosynthesis to create new or hybrid nucleoside antibiotics. Dissection of regulatory mechanisms is leading to strategies to increase the titer of bioactive nucleoside antibiotics.

Nikkomycins and gougerotin are peptidyl nucleoside antibiotics with broad biological activities. The nikkomycin biosynthetic gene cluster comprises one pathway-specific regulatory gene (sanG) and 21 structural genes, whereas the gene cluster for gougerotin biosynthesis includes one putative regulatory gene, one major facilitator superfamily transporter gene, and 13 structural genes. In the present study, we introduced sanG driven by six different promoters into Streptomyces ansochromogenes TH322. Nikkomycin production was increased significantly with the highest increase in engineered strain harboring hrdB promoter-driven sanG. In the meantime, we replaced the native promoter of key structural genes in the gougerotin (gou) gene cluster with the hrdB promoters. The heterologous producer Streptomyces coelicolor M1146 harboring the modified gene cluster produced gougerotin up to 10-fold more than strains carrying the unmodified cluster. Therefore, genetic manipulations of genes involved in antibiotics biosynthesis with the constitutive hrdB promoter present a robust, easy-to-use system generally useful for the improvement of antibiotics production in Streptomyces.

Gougerotin, a peptidyl nucleoside antibiotic, possesses antitumor, antiviral, antibacterial, antimycoplasma, anthelmintic, and acaricidal activities. Here, we report the cloning of a complete gougerotin biosynthetic gene cluster from Streptomyces graminearus and heterologous production of gougerotin in Streptomyces coelicolor. Sequence analysis of a 28.7 kb DNA fragment indicated that the cluster consists of 25 open reading frames (ORFs). Gene disruption and genetic complementation experiments revealed that 15 of the 25 ORFs are required for gougerotin biosynthesis. A gougerotin biosynthetic pathway was proposed based on the analyses of bioinformatics and intermediates accumulated in selected gene inactivation mutants. These studies substantially promoted our understanding of gougerotin biosynthesis and provide "building blocks" for combinatorial biosynthesis using genes encoding different enzymes in nucleoside antibiotics.