Microcins are very small

bacteriocin Bacteriocins are proteinaceous or peptide, peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally ...

s, composed of relatively few

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s. For this reason, they are distinct from their larger

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

cousins. The classic example is microcin V, of ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

''. Subtilosin A is another bacteriocin from ''

Bacillus subtilis ''Bacillus subtilis'' (), known also as the hay bacillus or grass bacillus, is a gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacill ...

''. The

peptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty am ...

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. Microcins produced by

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

''E. coli'' strains target and eliminate enteric pathogens such as ''

Salmonella enterica ''Salmonella enterica'' (formerly ''Salmonella choleraesuis'') is a rod-shaped, flagellate, facultative anaerobic, Gram-negative bacterium and a species of the genus ''Salmonella''. It is divided into six subspecies, arizonae (IIIa), diarizonae ...

'' by mimicking the siderophores the pathogens use for iron scavenging. Microcins also help commensal strains of ''E. coli'' outcompete pathogenic strains. BACTIBASE database is an open-access database for bacteriocins including microcins.

References

Bacterial toxins Peripheral membrane proteins {{Bacteria-stub