Saprophyticin S: A Novel Saposin-like, Leaderless Bacteriocin Produced by Staphylococcus saprophyticus P1CEA4 of Porcine Origin.

With antimicrobial resistance (AMR) posing a major global threat, largely driven by antibiotic overuse, the search for alternative antimicrobial strategies has become increasingly urgent. Bacteriocins, due to their specificity and limited impact on host microbiota, are gaining attention as viable substitutes. Here, we report the identification and characterization of a novel bacteriocin produced by Staphylococcus saprophyticus P1CEA4, a strain isolated from meat-producing pigs. This strain exhibited potent direct and extracellular antimicrobial activity. Whole-genome sequencing (WGS) enabled the identification of multiple gene clusters encoding putative bacteriocins and secondary metabolites. Among them, a gene encoding a novel leaderless bacteriocin was functionally validated through in vitro cell-free protein synthesis (IV-CFPS) and purification from the cell-free supernatant. The bacteriocin, named saprophyticin S (SapS), is a 51-amino-acid, highly cationic peptide (pI 10.08) with a mass range of 6047.8-6110.5 Da, due to N-terminal formylation and oxidation states. Structurally, it resembles other class IIc saposin-like bacteriocins such as epidermicin NI01 and aureocin A53. SapS displayed broad antimicrobial activity against pathogenic species of clinical, veterinary, and food safety relevance, including vancomycin-resistant Enterococcus (VRE) and methicillin-resistant Staphylococcus aureus (MRSA). SapS was inactive against Gram-negative strains on its own, but displayed synergy with microcins and colicins against Escherichia coli.