Cationic Polymers Enable Internalization of Negatively Charged Chemical Probe into Bacteria

The bacterial cell envelope provides a protective barrier that is challenging for small molecules and biomolecules to cross. Given the anionic nature of both Gram-positive and Gramnegative bacterial cell envelopes, negatively charged molecules are particularly difficult to deliver into these organisms. Many strategies have been employed to penetrate bacteria ranging from reagents such as cell-penetrating peptides, enzymes, and metal-chelating compounds, to physical perturbations. While cationic polymers are known antimicrobial agents, their ability to permeabilize bacterial cells without causing high levels of toxicity and cell lysis has not been demonstrated. Here, we evaluate the ability of four cationic polymers, two linear and two micellar (from self-assembled amphiphilic block copolymers), to facilitate the internalization of an anionic ATP-based chemical probe into Escherichia coli and Bacillus subtilis. Not only did we observe the permeabilization of these organisms, but also found that labeled cells were able to continue to grow and divide. In particular, the micelle-based polymers yielded effective internalization of the negatively charged chemical probe better than their linear analogues.