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Bacteriocins are proteins or lipopolysaccharides derived from bacterial cell walls producing them. This is adsorbs on the surface of susceptible bacterial cells on specific receptor sites. Bacteriocins acts by inhibiting the growth of other bacterial species.Gratia in 1925, observed the production of a highly specific antibiotic substance by one strain of E.coli which was active against another strain of the same species. The name colicin was given to such substances produced by E.coli and other members of Enterobactericeae family.

With the recognition that colicin like substances were produced by other species of bacteria also, the name ‘bacteriocin’ was proposed for the group of highly specific antibiotic-like substances produced by certain strains of bacteria which are active against other strains of the same or different species.Bacteriocins are given specific names based on the bacterial species of origin, for e.g. colicins from E.coli, warneri from Staphylococcus warneri, pyocins from Pseudomonas pyocyanea (aeruginosa), microcins from Archae, megacins from Bacillus megaterium and diphthericins from Corynebacterium diphtheria.Some of the bacteriocin, especially pyocins, appears like the tail structure of phages. They resemble homicide factors produced by certain yeast and paramecium.

The synthesis of bacteriocin is determined by the presence of colicinogenic factors in bacteria called Col factors. Col factors can be transmitted from cell to another by conjugation or transduction. Certain physical and chemical agents like UV rays, nitrogen, mustard, etc induce colicin production by the cells harboring Col factors.
A cell producing bacteriocin may be immune to it, but may be sensitive to other Bacteriocins. They have a very specific activity on bacteria, being capable of killing some but not all strains of a species. The specificity is made use of in typing certain species such as Shigella sonnei, Proteus sp., Pseudomonas aeruginosa. Bacteriocin kills susceptible cells without lysing them. Lantibotics are bacteriocin that contains lanthionine in their structure.

The production of bacteriocin can be enhanced artificially induced by UV radiation, Mitomycin C, heat shock, etc.

The bacteriocin is classified into different classes namely based on different factors like killing technique, genetic factors, molecular weight, chemical nature and production scheme. They are,
1. Class I bacteriocin; inhibits peptides. E.g. nisin.
2. Class II bacteriocin; makes the target cell more permeable by causing leakage of the cell. It consists of different sub-classes like II a, II b, II c, II d. e.g. pediocin, lactococcin G, enterocin, aureocin, etc.
3. Class III bacteriocin; they cause peptide degradation, cell wall degradation and disturbing the membrane potential resulting in the efflux of ATP. Have sub-classes like III a and III b. e.g. lysostaphin.
4. Class IV bacteriocin; complex molecules containing lipids or carbohydrates.
Overuse of antibiotics may harm the normal flora of the body, so these bacteriocins are of great importance as they are produced by the microbes belonging to the normal microbial flora and prevent the attack of opportunistic pathogens.

Efforts have been made to use bacteriocin for treating cancer, but since their mechanism of action is not known and the uncertainty whether they are capable of killing tumor containing mammalian cells, it is not being used commercially. These can also be modified by bioengineering and thereby make them to be produced inside the body itself.

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