Enhanced production of avermectin by deletion of type III polyketide synthases biosynthetic cluster rpp in Streptomyces avermitilis.

UNLABELLED: The rpp biosynthetic gene cluster (sav7130-7131) in Streptomyces avermitilis contains a type III polyketide synthases (PKSs) and a cytochrome P450 and was reportedly involved in producing a diffusible brown pigment. Since the same precursor malonyl-CoA was used as substrate for the type I PKSs and type III PKSs, there might be a competition for precursor between rpp gene cluster and avermectin biosynthetic cluster. In this work, rpp biosynthetic gene cluster deletion mutants were constructed to improve avermectin production. In an industrial strain AV-LP, rpp deletion improved avermectin production from 1024 to 1262 mg l-1 without any effect on the cell growth. In the same way, the production of an industrial overproducer increased from 3582 to 4450 mg l-1 . Transcriptional analysis suggested that the deletion of rpp gene cluster stimulated transcription of aveR, leading to increased transcription of biosynthetic gene aveA1 and a consequent increase in avermectin production.

SIGNIFICANCE AND IMPACT OF THE STUDY: Because of the wide use of avermectins, many efforts have been made to improve the productivity via conventional genetic engineering technique. However, due to the lack of the molecular and genetic basis underlying such a yield enhancement after iterative rounds of mutagenesis and selection, it is often difficult to improve the titre in overproducers. Here, we report knocking out rpp biosynthetic gene cluster improved the production of an industrial overproducer by 24%. This work enriched the strategy to improve the production of antibiotics in industrial strains and may help further understanding of the interaction between type III polyketide synthases and other types.