Abstract：Spinosad is a kind of bio-insecticide showing advantages such as high-efficiency and low-toxicity, which is wildly used in pesticide, veterinary drug, sanitary field, etc. However, industrial production of spinosad still has not been implement in China, because of relatively late and undeveloped study on spinosad high-yield strain breeding and relative fermentation process. Previously, a spinosad high-yield strain, Saccharopolyspora spinosa ASAGF73, was obtained through multiple rounds mutagenesis. In this study, we focused on analysing spinosyn biosynthetic gene cluster(spn) expression profile and comparing the difference between wide-type strain ATCC49460 and high-yield ASAGF73 during fermentation process, and preliminarily elucidated the rate-limiting step for spinosad synthesis. Bioinformatic analysis revealed that spn gene cluster contained 9 transcripts, and their expressions were detected using RT-PCR with primers designed inside each transcript. The results showed that the high production of ASAGF73 strain could be due to the high expression of some transcripts in spn cluster, the expression of genes coding for polyketide synthase(PKS) and cross-bridging in ASAGF73 was higher than those in ATCC49460. spnG, which coded rhamnosyltransferase, showed high expression in ASAGF73 strain at the beginning of the fermentation but decreased to a quite low level later, which was not ideal for spinosad high production and might be the rate-limiting step for spinosad synthesis. The present study was the comprehensive and comparative expression analysis of spinosad biosynthetic gene cluster and genes for rhamnose biosynthesis in the 2 S. spinosa strains during fermentation, provided some clues to understand the molecular mechanisms which can lead to the increasing of spinosad production yield.
