The avermectin derived third-generation doramectin is one of best anti-parasite drug. We constructed an ordered cosmid library of Streptomyces avermitilis and knocked out the bkdF and olmA1 genes to obtain doramectin-producing industrial strains. Further knocking-out other polyketide gene clusters in the genome revealed increasing productivity in most derived strains. Unexpectedly, introduction of the known antibiotics positive-regulatory genes into the industrial strains did not result in increase of duramectin production. We designed a new genomic shuffling method for increasing productivity of doramectin significantly, after several rounds of genomic recombination, and finally reach the level of large-scale industrialization.

We expected to obtain the genetic modified strains with doramectin:avermectin=1:0.3 and fermentation of duramectin 250 mg/L before Dec, 2007, and strains with doramectin:avermectin=1:0.1 and fermentation of duramectin 300 mg/L before Dec, 2008. These strains could be used for large-scale industrialization. We also expected to publish at least five papers including three SCI-sourced, and to apply one patent.