Supplementary Figure 10: Validation of newly identified acrB mutations for improved solvent and antibiotic tolerance.

a) On the left a global overview of AcrB efflux pump. Substrates enter the pump through the openings in the periplasmic space and are extruded via the AcrB/AcrA/TolC complex across the outer membrane and into the extracellular space. Library targeted residues are highlighted by blue spheres for reference and the red dot indicates the region where many of the enriched variants clustered. On the right is a blow up of the loop-helix motif abutting the central funnel where enriched mutations in isobutanol were identified (red and teal spheres), presumably affecting solute transport from the periplasmic space. Mutants targeting the T60 position (teal spheres) was also enriched in the presence of erythromycin b) Confirmation of N70D and D73L mutations for tolerance to isobutanol. The N70D mutation in particular appears to improve the final OD to a significant degree. Reconstructed strains were measured for final OD in capped 1.5 mL eppendorf tubes following 48 hours incubation. Error bars are derived from N=3 trials and p-values derived from a one-tailed T-test. c) Improved growth of the AcrB T60N mutant was observed in inhibitory concentrations of erythromycin (200 μg/mL) and isobutanol (1.2%) in shaking 96 well plate, indicating that this mutation may enhance the efflux activity of this pump towards many compounds. For these experiments, CREATE cassette designs were individually synthesized, cloned and sequence verified before recombineering into E. coli MG1655 to reconstruct the mutations and the genomic modifications were sequence verified by colony PCR to confirm the genotype-phenotype association.