BACTERIOCIN

Introduction

Bacteriocins are proteinaceous toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are typically considered to be narrow spectrum antibiotics, though this has been debated They are phenomenologically analogous to yeast and paramecium killing factors, and are structurally, functionally, and ecologically diverse. Bacteriocins were first discovered by A. Gratia in 1925. He was involved in the process of searching for ways to kill bacteria, which also resulted in the development of antibiotics and the discovery of bacteriophage, all within a span of a few years. He called his first discovery a colicine because it killed E. coli.

Classification of bacteriocins

Bacteriocins are categorized in several ways, including producing strain, common resistance mechanisms, and mechanism of killing. There are several large categories of bacteriocin which are only phenomenologically related. These include the bacteriocins from gram-positive bacteria, the , the microcins, and the bacteriocins from Archaea. The bacteriocins from E. coli are called colicins (formerly called 'colicines,' meaning 'coli killers'). They are the longest studied bacteriocins. They are a diverse group of bacteriocins and do not include all the bacteriocins produced by E. coli. For example the bacteriocins produced by Staphylococcus warneri, are called as warnerin [5] or warnericin. In fact, one of the oldest known so-called colicins was called colicin V and is now know as microcin V. It is much smaller and produced and secreted in a different manner than the classic colicins. The bacteriocins of lactic acid-fermenting bacteria are called lantibiotics. This naming system is problematic for a

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number of reasons. First, naming bacteriocins by what they putatively kill would be more accurate if their killing spectrum were contiguous with genus or species designations. The bacteriocins frequently possess spectra that exceed the bounds of their named taxa and almost never kill the majority of the taxa for which they are named. Further, the original naming is generally derived not from the sensitive strain the bacteriocin kills, but instead the organism that produces the bacteriocin. This makes the use of this naming system a problematic basis for theory; thus the alternative classification systems.

Methods classification

Alternative methods of classification include: method of killing (pore forming, dnase, nuclease, murein production inhibition, etc), genetics (large plasmids, small plasmids, chromosomal), molecular weight and chemistry (large protein, polypeptide, with/without sugar moiety, containing atypical amino acids like lanthionine) and method of production (ribosomal, post ribosomal modifications, non-ribosomal).

One method of classification fits the bacteriocins into Class I, Class IIa/b/c, and Class III.

Class I bacteriocins

The class I bacteriocins are small peptide inhibitors and include nisin.

Class II bacteriocins

The class II bacteriocins are small heat-stable proteins. The action of Class IIa bacteriocins seems to involve disruption of mannose transport into target cells. Class IIb bacteriocins form

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pores in the membranes of target cells and disrupt the proton gradient of target cells. Other bacteriocins can be grouped together as Class IIc. These have a wide range of effects on membrane permeability, cell wall formation and pheromone actions of target cells.

Class III bacteriocins

Large, heat-labile protein bacteriocins.

Databases

Two databases of bacteriocins are available: BAGEL and BACTIBASE.

Medical significance

Bacteriocins are of interest in medicine because they are made by non-pathogenic bacteria that normally colonize the human body. Loss of these harmless bacteria following antibiotic use may allow opportunistic pathogenic bacteria to invade the human body.

Bacteriocins have also been suggested as a cancer treatmentThey have shown distinct promise as a diagnostic agent for some cancers, but their status as a form of therapy remains experimental and outside the main thread of cancer research. Partly this is due to questions about their mechanism of action and the presumption that anti-bacterial agents have no obvious connection to killing mammalian tumor cells. Some of these questions have been addressed, at least in part

In the long quest for medical applications, bacteriocins have also been tested as AIDS drugs

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Production

There are many ways to demonstrate bacteriocin production, depending on the sensitivity and labor intensiveness desired. To demonstrate their production, technicians stab inoculate multiple strains on separate multiple nutrient agar Petri dishes, incubate at 30 °C for 24 h., overlay each plate with one of the strains (in soft agar), incubate again at 30 °C for 24 h. After this process, the presence of bacteriocins can be inferred if there are zones of growth inhibition around stabs. This is the simplest and least sensitive way. It will often mistake phage for bacteriocins. Some methods prompt production with UV radiation, Mitomycin C, or heat shock. UV radiation and Mitomycin C are used because the DNA damage they produce stimulates the SOS response. Cross streaking may be substituted for lawns. Similarly, production in broth may be followed by dripping the broth on a nascent bacterial lawn, or even filtering it. Precipitation (ammonium sulfate) and some purification (e.g. column or HPLC) may help exclude lysogenic and lytic phage from the assay.

Bacteriocins by class

Class I

Class IIa

Class IIb

Class IIc

Class III

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Bacteriocins by name

agrocin alveicin carnocin colicin curvaticin divercin enterocin enterolysin epidermin erwiniocin glycinecin halocin lactococin lacticin leucoccin mesentericin nisin pediocin plantaricin sakacin subtilin sulfolobicin vibriocin warnerin

Chemistry of bacteriocin

Bacteriocins are proteinaceous toxins given off by bacteria to inhibit the growth of similar bacterial strain(s). E. coli bacteriocins are called colicins.

The bacteriocins of lactic acid-fermenting bacteria are well studied because of the commercial use of these bacteria in the food industry for making dairy products such as cheese. Bacteriocins are classified according to their extent of posttranslational modification. The lantibiotics are a class of more extensively modified bacteriocins, also called Class I. Bacteriocins for which disulfide bonds are the only modification to the peptide are Class II bacteriocins. Most bacteriocins are biologically active single-chain peptides. Some are only active as partners with a second peptide (see Class IIb, below).

Nisin and epidermin are members of a family of lantibiotics that bind to a cell wall precursor lipid component of target bacteria and disrupt cell wall production. The duramycin family of lantibiotics binds phosphoethanolamine in the membranes of its target cells and seem to disrupt several physiological functions.

The action of Class IIa bacteriocins seems to involve disruption of mannose transport into target cells. Class IIb bacteriocins form pores in the membranes of target cells and disrupt the proton gradient of target cells. Other bacteriocins can be grouped together as Class IIc. These have a wide range of effects on membrane permeability, cell wall formation and pheromone actions of target cells.

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Bacteriocins are of interest in medicine because they are made by non-pathogenic bacteria that normally colonize the human body. Loss of these harmless bacteria following antibiotic use may allow oportunistic pathogenic bacteria to invade the human body.

To demonstrate their production, technicians stab inoculate multiple strains on separate multiple nutrient agar Petri dishes, incubate at 30 °C for 24 h., overlay each plate with one of the strains (in soft agar), incubate again at 30 °C for 24 h. After this process, the presence of bacteriocins can be inferred if there are zones of growth inhibition around stabs.

Class II bacteriocins are a class of small peptides that inhibit the growth of various bacteria.

Many Gram-positive bacteria produce ribosomally synthesized antimicrobial peptides, termed bacteriocins. One important and well studied class of bacteriocins is the class IIa or pediocin-like bacteriocins produced by lactic acid bacteria. All class IIa bacteriocins are produced by food-associated strains, isolated from a variety of food products of industrial and natural origins, including meat products, dairy products and vegetables. Class IIa bacteriocins are all cationic, display anti-Listeria activity, and kill target cells by permeabilizing the cell membrane [1] [2] [3] .

Class IIa bacteriocins contain between 37 and 48 residues[4]. Based on their primary structures, the peptide chains of class IIa bacteriocins may be divided roughly into two regions: a hydrophilic, cationic and highly conserved N-terminal region, and a less conserved hydrophobic/amphiphilic C-terminal region. The N-terminal region contains the conserved Y-G-N-G-V/L 'pediocin box' motif and two conserved cysteine residues joined by a disulfide bridge. It forms a three-stranded antiparallel beta-sheet supported by the conserved disulfide bridge. This cationic N-terminal beta-sheet domain mediates binding of the class IIa

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bacteriocin to the target cell membrane. The C-terminal region forms a hairpin-like domain that penetrates into the hydrophobic part of the target cell membrane, thereby mediating leakage through the membrane. The two domains are joined by a hinge, which enables movement of the domains relative to each other.

Some proteins known to belong to the class IIa bacteriocin family are listed below:

Pediococcus acidilactici pediocin PA-1.

Leuconostoc mesenteroides mesentericin Y105.

Carnobacterium piscicola carnobacteriocin B2.

Lactobacillus sakei sakacin P.

Enterococcus faecium enterocin A.

Enterococcus faecium enterocin P.

Leuconostoc gelidum leucocin A.

Lactobacillus curvatus curvacin A.

Listeria innocua listeriocin 743A.

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REFERENCES

1. Ennahar S, Sonomoto K, Ishizaki A (1999). "Class IIa bacteriocins from lactic acid bacteria: antibacterial activity and food preservation". J. Biosci. Bioeng. 87

2. Farkas-Himsley H (1980). "Bacteriocins--are they broad-spectrum antibiotics?". J. Antimicrob. Chemother. 6 (4): 424–6. doi:10.1093/jac/6.4.424. PMID 7430010.

3. Gratia A (1925). "Sur un remarquable example d'antagonisme entre deux souches de colibacille". Compt. Rend. Soc. Biol. 93: 1040–2.

4. Gratia JP (October 2000). "André Gratia: a forerunner in microbial and viral genetics". Genetics 156 (2): 471–6. PMID 11014798. http://www.genetics.org/cgi/pmidlookup?view=long&pmid=11014798.

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