Production of Multiple Variants of the Antimicrobial Sactipeptide Gnavucin D by the Human Gut Isolate Mediterraneibacter gnavus HB038.

While several bacteriocins have been identified from gut-isolated cultures, there remains a need for the discovery of bacteriocins with varying inhibition spectra for strain applications such as microbiome editing, pathogen elimination and colonization resistance. With this in mind, here we describe a new antibacterial sactipeptide gnavucin D, produced by Mediterraneibacter gnavus HB038 isolated from a healthy 2-year-old child. Gnavucin D has activity against the pathogens Clostridium perfringens, Streptococcus agalactiae, Bacillus cereus, and vancomycin-resistant Enterococcus. The gene cluster includes five structural genes in tandem that encode for three different core peptides (29 amino acids each) with molecular masses of 2704.21 (D1), 2734.23 (D2/D3), and 2732.21 (D4/D5) Da. The nearest relative to these bacteriocins was found to be another sactipeptide thurincin H produced by Bacillus thuringiensis with which it shares 30% identity. Although the amino acids encoding the gnavucin and thurincin are similar with regard to putative functions, their homology to each other is low, varying from 30% to 55%. Interestingly, all these bacteriocins had short leader peptides of only 9 amino acids. Gnavucin D was found to be extremely stable to temperature, pH and proteolysis which is possibly a reflection of the sulfur to carbon post-translational modifications. The observed molecular masses of the 3 different peptides correspond to four modifications, yielding a structurally restricted, most likely double-hairpin conformation which is characteristic of such sactipeptides. Consequently, gnavucin D can be a promising candidate for selective antibacterial activity against human pathogens.