Stability and effects on the colonic microbiota of microcins, antimicrobial peptides produced by enterobacteria 
 Séverine Zirah1, Sabrine Naimi2,3, Sylvie Rebuffat1, Ismail Fliss2

1     Molécules de Communication et Adaptation des Microorganismes, UMR 7245 CNRS-MNHN, CP 54, 57 rue Cuvier, 75005 Paris, France
2     Département Sciences des aliments, Université Laval, Quebec, Canada

Microcins are bacteriocins produced by enterobacteria. The remarkable diversity of structures and mechanisms of action of several microcins is determined by complex post-translational modifications1. They have a relatively narrow spectrum of antibacterial activity and are a promising alternative to antibiotics in view of the emergence and spread of multi-resistance. Microcin J25 (MccJ25), a 21 amino acid peptide produced by Escherichia coli has a high antibacterial activity against Escherichia and Salmonella strains by inhibiting RNA polymerase. Its structure includes an N-terminal macrolactam ring, into which the C-terminal tail bends and is trapped by steric constraints, forming a loop over the ring. We evaluated the stability of MccJ25 and its impact on the colon microbiota in vitro, using the TIM-1 dynamic simulator of the digestive tract2 and the PolyFermS colic fermentation system3. Samples were extracted and analyzed using liquid chromatography coupled to mass spectrometry analysis (LC-MS).  Multivariate analysis of LC-MS data and generation of molecular networks from LC-MS/MS data were carried out. Obtained results showed that microcin J25 is relatively stable under gastric conditions but is degraded quickly in the compartment mimicking the duodenum. The identification of degradation products formed revealed that the loop underwent multiple hydrolysis. The comparison of the impact of the MCCJ25 and the rifampicin, an antibiotic of the rifamycin family and also an inhibitor of RNA polymerase, on the colonic microbiota showed that the rifampicin had a considerable impact on the metabolome with an accumulation of amino acids linked to inhibition of protein synthesis, whereas metabolic perturbations caused by the action of microcin J25 are short-lived.

1.  Tehlig S., Ben Said L., Zirah S., Fliss I., Rebuffat S. Front. Microbiol. 11:586433, 2020.
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3.  Tanner S.A., Berner A.Z., Rigozzi E., Grattepanche F., Chassard C., Lacroix C., PloS One 9:e94123, 2014.