<p style="text-align:justify"><strong><strong>The varied performance of genetic circuits based on host environment, termed as the ‘chassis effect,’ creates uncertainty in synthetic biology applications. However, the underlying factors governing this effect are not clearly understood. Researchers from Norway and the United Kingdom have now demonstrated that genetic inverter circuit performance was directly related to physiological attributes, and not phylogenomic relatedness, in six engineered Gammaproteobacteria species. Their findings establish host physiology as a robust predictor of genetic circuit performance. </strong></strong></p>