Bacterial cell fate under stress: lipid remodeling and antimicrobial peptide attack

Dynamic changes in lipid membrane composition are a common response to stress, often involving shifts in key lipid molecules. Phosphatidic acid (PA), a central precursor in lipid biosynthesis, accumulates when anionic phospholipid synthesis is blocked-lipids that are typically primary targets of membrane-active antimicrobial peptides (AMPs). This raises the question of how cationic AMPs adapt to such lipid remodeling, which is especially relevant given their promise as novel therapeutics against escalating antimicrobial resistance. Their killing mechanism is often unclear. To identify ongoing processes clearly linked to bacterial cell death, six assays targeting membrane integrity and cell viability were performed alongside bactericidal measurements. These assays were conducted on Escherichia coli and a mutant depleted of anionic phospholipids, treated with the cationic peptides melittin and LL-37. Correlation of assays generated characteristic antimicrobial profiles, providing insight into the peptides' mechanisms. LL-37 acted independently of membrane composition, while melittin showed increased activity in the absence of anionic phospholipids. This study confirmed specific interactions with PA, but their action suggests targets beyond the membrane, as bacteria remained viable during membrane disruption but failed to form colonies. Overall, these findings indicate that both peptides can effectively handle lipid remodeling and uncover processes driving bacterial cell death.