Characterization of a LAL-type regulator NemR in nemadectin biosynthesis and its application for increasing nemadectin production in Streptomyces cyaneogriseus

Nemadectin, a macrocyclic lactone antibiotic, is produced by Streptomyces cyaneogriseus ssp. noncyanogenus. A methoxime derivative of nemadectin, moxdectin, has been widely used to control insect and helminth in animal health. Despite the importance of nemadectin, little attention has been paid to the regulation of nemadectin biosynthesis, which has hindered efforts to improve nemadectin production via genetic manipulation of regulatory genes. Here, we characterize the function of nemR, the cluster-situated regulatory gene encoding a LAL-family transcriptional regulator, in the nemadectin biosynthesis gene cluster of S. cyaneogriseus ssp. noncyanogenus NMWT1. NemR is shown to be essential for nemadectin production and found to directly activate the transcription of nemA1-1/A1-2/A2, nemC and nemA4/A3/E/D operons, but indirectly activate that of nemG and nemF. A highly conserved sequence 5'-TGGGGTGKATAGGGGGTA-3' (K=T/G) is verified to be essential for NemR binding. Moreover, four novel targets of NemR, including genes encoding an SsgA-like protein (TU94_12730), a methylmalonyl-CoA mutase (TU94_19950), a thioesterase of oligomycin biosynthesis (TU94_22425) and a MFS family transporter (TU94_24835) are identified. Overexpression of nemR significantly increased nemadectin production by 79.9%, in comparison with NMWT1, suggesting that nemR plays an important role in the nemadectin biosynthesis.