Microcins are very small bacteriocins, composed of a relatively few peptides. For this reason, they are distinct from their larger protein cousins. The classic example is microcin V, of E. coli. Subtilosin A is another bacteriocin from Bacillus subtilis. The peptide has a cyclized backbone and forms three cross-links between the sulphurs of Cys13, Cys7 and Cys4 and the alpha-positions of Phe22,Thr28 and Phe31.

It is found that these bacteriocins target and eliminate iron-starved pathogens, which is found specifically in an inflamed gut where the E. Coli strain prefer to thrive. Specifically, the protein targets the pathogens are producing iron-scavenging protein in response to a low iron environment. Researchers found. E. coli Nissle’s microcins killed diarrhea-inducing bacteria called Salmonella Enterica in the guts of infected mice. Microcins also helped Nissle outcompete a different, more virulent of E. coli found in the infected mice's guts.

BACTIBASE database is an open-access database for bacteriocins including microcins.

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