Fig. 2

Galactose biosensors based on anti-CRISPR proteins. a Upon induction with galactose, an anti-CRISPR protein of the AcrIIA family is produced. An increase in fluorescence is detected if the anti-CRISPR is able to prevent the dSpCas9-Mxi1:gRNA system from binding the Tsynth8_pCYC1noTATA synthetic promoter. b Galactose biosensor performance. Main values of the ON/OFF ratio were calculated over at least 3 independent experiments for each circuit. The symbol “*” indicates a working biosensor i.e. there is a statistically significant difference between the mean fluorescence of the ON and OFF state (two-sided Welch’s t-test, p-value < 0.05). A detailed statistical comparison of the relative fluorescence of these ten anti-CRIPSR-based constructs is given in Additional file 1: Figure S3. c Viability test. The viability coefficients of five YES gates presenting slow growth rate underline the presence of only moderate toxic effects. The control strain (A5-RGR grown in glucose-supplied synthetic medium) is associated with a viability coefficient, equal to 0.98, significantly higher in statistical terms than all the other viability coefficients calculated in this test (as denoted by the symbol “**”). A further statistical analysis on these results is reported in Additional file 1: Figure S8