Additional file 1: Table S1. Strains used in this study. Table S2. Oligos used. Figure S1. Structure of terminator sequences. A selected set of terminator transcript sequences from the compilation of 582 terminator sequences characterised by Chen et al. by their termination efficiency (Te) [3].The calculated free energy of the secondary structure is shown below each transcript sequence. Figure S2. Efficiency of fimA mutagenesis with Cas12a. A 10/10 E. coli colonies isolated after cotransformation with crRNA1 and the donor oligonucleotide carrying homology arms to introduce a 97 bp fimA deletion tested positive (lanes 1–10) for a mutation as detected by colony PCR using primers F1 and R1. B 3/10 E. coli colonies isolated after co-transformation with crRNA1 and the donor oligonucleotide carrying homology arms to insert a 57 bp terminator beside the 97 bp fimA deletion at position 75 of the fimA (ΔfimA75::L3S2P56) gene tested positive (lanes 1, 5 and 7 marked with *) as detected by colony PCR using primers F1 and R1. C 1/10 E. coli colonies isolated after co-transformation with crRNA1 and the donor oligonucleotide carrying homology arms to insert a 57 bp terminator sequence beside the 172 bp fimA deletion at position 1 of the fimA (ΔfimA1::L3S2P56) gene tested positive (lane 5, marked with *) as detected by colony PCR using primers F2 and R2. Lane 11 shows a PCR product on WT E. coli DNA template as detected with primers F1 and R1. Lanes labeled as L were loaded with a double-stranded DNA ladder containing fragments of different lengths in base pairs (bp). Figure S3. Atomic force microscopy (AFM) of bacteria grown in static cultures. A AFM imaging of E. coli cells with the ΔfimA75 allele carrying the empty vector pSU19. A E. coli cell showing no type 1 fimbriae is shown in the inset. B AFM imaging of the ΔfimA75 mutant E. coli carrying a plasmid containing a fimA+ allele for transcomplementation. A E. coli cell showing type 1 fimbriae is shown in the inset. Scale bars: A, B 4 μm. A, B insets 2 μm. Figure S4. Thermodynamic properties of terminator sequences. Correlation of the efficiency of mutagenesis and the following thermodynamic parameters: A free energy for the closure of the hairpin loop (∆GL). B free energy of the hairpin folding (ΔGH). C Free energy of the extended hairpin (∆GA). D Free energy of the base of the stem (∆GB). E Free energy of the U-tract (∆GU), F length (bp).