Optimising the production of dsRNA biocontrols in microbial systems using multiple transcriptional terminators.

Crop pests and pathogens annually cause over $100 billion in global crop damage, with insects consuming 5-20% of major grain crops. Current crop pest and disease control strategies rely on insecticidal and fungicidal sprays, plant genetic resistance, transgenes and agricultural practices. dsRNA is emerging as a novel sustainable method of plant protection as an alternative to traditional chemical pesticides. Successful commercialisation of dsRNA based biocontrols requires the economical production of large quantities of dsRNA combined with suitable delivery methods to ensure RNAi efficacy against the target pest. In this study, we have optimised the design of plasmid DNA constructs to produce dsRNA biocontrols in E. coli, by employing a wide range of alternative synthetic transcriptional terminators prior to measurement of dsRNA yield. We demonstrate that a 7.8-fold increase of dsRNA was achieved using triple synthetic transcriptional terminators within a dual T7 dsRNA production system compared to the absence of transcriptional terminators. Moreover, our data demonstrates that batch fermentation production dsRNA using multiple transcriptional terminators is scalable and generates significantly higher yields of dsRNA generated in the absence of transcriptional terminators at both small-scale batch culture and large-scale fermentation. In addition, we show that application of these dsRNA biocontrols expressed in E. coli cells results in increased insect mortality. Finally, novel mass spectrometry analysis was performed to determine the precise sites of transcriptional termination at the different transcriptional terminators providing important further mechanistic insight.