Revealing the chassis-effect on a broad-host-range genetic switch and its concordance with interspecies bacterial physiologies

Broad-host-range synthetic biology is an emerging frontier that aims to expand our current engineerable domain of microbial hosts for biodesign applications. As more novel species are brought to "model status", synthetic biologists are discovering that identically engineered genetic circuits can exhibit different performances depending on the organism it operates within, an observation referred to as the "chassis-effect". It remains a major challenge to uncover which genome encoded and physiological biological determinants will underpin chassis effects that govern the performance of engineered genetic devices. In this study, we compared model and novel bacterial hosts to ask whether phylogenomic relatedness or similarity in host physiology is a better predictor of toggle switch performance. This was accomplished using comparative framework based on multivariate statistical approaches to systematically demonstrate the chassis-effect and characterize the performance dynamics of a genetic toggle switch operating within six Gammaproteobacteria. Our results solidify the notion that genetic devices are significantly impacted by host-context. Furthermore, we formally determined that hosts exhibiting more similar metrics of growth and molecular physiology also exhibit more similar toggle switch performance, indicating that specific bacterial physiology underpins measurable chassis effects. The result of this study contributes to the field of broad-host-range synthetic biology by lending increased predictive power to the implementation of genetic devices in less-established microbial hosts.