Cloning natural product biosynthetic gene clusters from cultured or uncultured sources and their subsequent expression by genetically tractable heterologous hosts is an essential strategy for the elucidation and characterisation of novel microbial natural products. The availability of suitable expression hosts is a critical aspect of this workflow. In this work, we mutagenised five endogenous biosynthetic gene clusters from Streptomyces albus S4, which reduced the complexity of chemical extracts generated from the strain and eliminated antifungal and antibacterial bioactivity. We showed that the resulting quintuple mutant can express foreign biosynthetic gene clusters by heterologously producing actinorhodin, cinnamycin and prunustatin. We envisage that our strain will be a useful addition to the growing suite of heterologous expression hosts available for exploring microbial secondary metabolism. Keywords Streptomyces Á Streptomyces albus Á Secondary metabolites Á Natural products Á Heterologous expression Asif Fazal and Divya Thankachan have contributed equally to this work.

15Cloning natural product biosynthetic gene clusters from cultured or uncultured sources and 16 their subsequent expression by genetically tractable heterologous hosts is an essential strategy for the 17 elucidation and characterisation of novel microbial natural products. The availability of suitable 18 expression hosts is a critical aspect of this workflow. In this work, we mutagenised five endogenous 19 biosynthetic gene clusters from Streptomyces albus S4, which reduced the complexity of chemical 20 extracts generated from the strain and eliminated antifungal and antibacterial bioactivity. We showed 21 that the resulting quintuple mutant can express foreign BGCs by heterologously producing 22 actinorhodin, cinnamycin and prunustatin. We envisage that our strain will be a useful addition to the 23 growing suite of heterologous expression hosts available for exploring microbial secondary 24 metabolism. 25