Production of avermectins by Streptomyces avermitilis through solid-state fermentation using agro-industrial waste

The natural products (NPs) avermectins from Streptomyces show exceptional insecticidal activity and become the most widely produced and used biopesticides in the world. Avermectins are produced by submerged fermentation (SmF), generating significant amount of effluent, exhaust gas and solid waste. We therefore endeavored to establish a green and sustainable alternative through solid-state fermentation (SSF) using agro-industrial waste. We determined the optimal culture medium composition and fermentation style through SSF. The maximum concentration of avermectin B1a (3.83 mg/gds) was obtained with a substrate mixture containing wheat bran, corn cob, earthworm cast, sugarcane bagasse, cane molasses, ammonium sulfate and CoCl2 in shallow trays cultivated for 14 days at 28 degrees C by repeated-batch SSF, and the initial moisture content and inoculum size was set as 78.5 % and 25 %, respectively. Economic analysis demonstrated that avermectin production cost generated from the fermentation process by SSF was 8.38 % lower than that by SmF. Moreover, avermectin SSF products could be directly used as microbial pesticides for biological control of underground pests and nematodes. This is the first report on avermectin production via SSF, demonstrating great potential in industrial and agricultural applications. Our work also provides guidance to produce other NPs through SSF in other Streptomyces species.