Proteomics reveals the key molecular players in Escherichia coli exposed to the antimicrobial cationic polymer 6-6 polyionene.

Polyionenes are polymers with antibacterial properties that hold great promise for the development of applications aiming to preserve against microbial surface contamination. In this study, the effect of 6-6 polyionene (PI 6-6) on a model Gram-negative bacterium, Escherichia coli, was deciphered using next-generation, label-free shotgun proteomics. Cells were exposed to two sub-minimum inhibitory concentrations (MIC) of the polymer before performing comprehensive proteomic analysis. Under these conditions, the abundance of up to 30 % of the proteins detected was significantly modulated compared to untreated controls. The most strongly impacted biological processes were central metabolism and cellular information processing. Exposure to PI 6-6 induced the production of reactive oxygen species depending on the PI 6-6 concentration. At 0.5x MIC, enzymes involved in hydrogen peroxide detoxification, polyamine and hydrogen sulfide biosynthesis, and sulfur metabolism, were up-modulated. At 0.75x MIC, a higher level of oxidized methionine was detected than in controls. Up-modulation of CspA RNA chaperone alongside other proteins linked to RNA metabolism and ribosome biogenesis was also observed. A large fraction of proteins was also down-modulated under both concentration conditions, with the majority of the top ten down-modulated proteins overlapping between the two treatments. These proteins primarily participate in the glyoxylate/dicarboxylate metabolism and propanoate metabolic pathways, which are both key routes for energy production and carbohydrate metabolism.