This study investigates the activity of gut-derived nisin-like lantibiotics against human gut pathogens and commensals. Six novel class I lantibiotics, four of which are newly identified, were discovered through bioinformatic analysis of gut microbial genomes. These lantibiotics were produced and purified using an improved expression platform, and their minimal inhibitory concentrations (MICs) against Gram-positive human pathogens and gut commensals were determined. Structure-activity relationship (SAR) studies revealed key regions and residues that influence antimicrobial properties. The findings suggest that these lantibiotics could be valuable for developing new therapeutics and food preservatives. The study also explores the mechanisms of lantibiotic resistance in pathogens and commensals, including cell wall modifications, efflux pumps, and other resistance mechanisms. SAR studies of blauticin and nisin O, as well as Lan-P49.1 and Lan-P49.2, highlight the importance of specific regions, such as the hinge region, in determining antimicrobial activity. These results indicate that the hinge region plays a critical role in the efficacy of nisin-like lantibiotics, and that certain residues can significantly impact antimicrobial activity depending on their context. The study demonstrates that nisin-like lantibiotics do not require full dehydration for their antimicrobial activity, and that mixed dehydration states are representative of naturally produced compounds. The findings provide insights into the potential of lantibiotics as antimicrobial agents and highlight the importance of understanding their interactions with the human gut microbiome. The research underscores the need for further investigation into the mechanisms of lantibiotic resistance and the development of more effective lantibiotic-based therapeutics and food preservatives.This study investigates the activity of gut-derived nisin-like lantibiotics against human gut pathogens and commensals. Six novel class I lantibiotics, four of which are newly identified, were discovered through bioinformatic analysis of gut microbial genomes. These lantibiotics were produced and purified using an improved expression platform, and their minimal inhibitory concentrations (MICs) against Gram-positive human pathogens and gut commensals were determined. Structure-activity relationship (SAR) studies revealed key regions and residues that influence antimicrobial properties. The findings suggest that these lantibiotics could be valuable for developing new therapeutics and food preservatives. The study also explores the mechanisms of lantibiotic resistance in pathogens and commensals, including cell wall modifications, efflux pumps, and other resistance mechanisms. SAR studies of blauticin and nisin O, as well as Lan-P49.1 and Lan-P49.2, highlight the importance of specific regions, such as the hinge region, in determining antimicrobial activity. These results indicate that the hinge region plays a critical role in the efficacy of nisin-like lantibiotics, and that certain residues can significantly impact antimicrobial activity depending on their context. The study demonstrates that nisin-like lantibiotics do not require full dehydration for their antimicrobial activity, and that mixed dehydration states are representative of naturally produced compounds. The findings provide insights into the potential of lantibiotics as antimicrobial agents and highlight the importance of understanding their interactions with the human gut microbiome. The research underscores the need for further investigation into the mechanisms of lantibiotic resistance and the development of more effective lantibiotic-based therapeutics and food preservatives.