Fig. 1: Host-guest interactions between macrocycles and bacterial homoserine lactones selective for HSLs with prolonged acyl chains.

a Schematic of the interaction between macrocyclic “hosts” with HSL “guests”. b The molecular structures, abbreviated names and bacterial species of all QS HSLs used in this study. c Schematic representation of HSL quorum sensing in Gram-negative bacteria (left), along with a virulence inhibition approach (right). In short, HSLs produced by select individuals diffuse freely through the outer and inner membranes and get sensed by intracellular receptor proteins in other community members, promoting the production of isogenic HSL and a synchronized regulation of activities. Applied virulence inhibition strategy, where the interaction between the HSLs and macrocyclic host prevents the recognition of HSLs by its cognate receptor. d Screening for the interaction between HSLs as seen in (b) and a set of macrocycles reveals several combinations where the macrocycle interacts with the HSL and where the growth rate in E. coli (I₁/I₀ OD₆₀₀) remains mostly unaffected (threshold, grey dashed lines, ±20%). The interaction is detected through a HSL biosensor, where the cognate receptor is expressed, and the promotor binding region is fused to GFP. Interactions between macrocycles and HSLs are observed through a decrease in affinity (I₁/I₀). e Concentration-dependent effects of the strongest interacting macrocycle, P[5]a, on the fluorescent expression in E. coli for each of the six HSLs, indicates increased affinity towards HSLs with longer acyl chains. The data represent average values of biological replicates ± s.d (n = 3 per group). f Effect of P[5]a on the growth rate and viability of E. coli. E. coli incubated with highest tested concentration of P[5]a, 2.5 mM, shows a standard growth curve, including lag, log and stationary phase. A BacLight bacterial viability assessment shows cell viability in all tested concentrations of P[5]a after 24 h of exposure and no concentration-dependent cell death. The data represent average values of biological replicates ± s.d (n = 3 per group).