and inorganic acids, thus strongly affecting the pH of the environment. Thiobacillus,
for instance, produces significant amounts of sulfuric acid that lowers greatly the pH
of the environment, which in turn causes changes in the composition of the surrounding microbial community. Another example can be the production of lactic
acid by the lactic acid bacteria. That acid production also causes a significant
reduction in the number of microbial species originally present in a given
environment.
Another well-known example of amensalism is the production of ethanol, which
negatively affects many species of microorganisms. For example, production of
ethanol by certain species of yeasts inhibits the growth of many sensitive bacteria.
Bacteriocins, zymocins, mycotoxins as well as antibiotics all belong to the realm of
amensalism.
15.4 Bacteriocins
The term bacteriocin was introduced in 1953 by Jacob and coauthors (Jacob et al.
1953) as denomination for a group of proteins with antibiotic characteristics. These
are the products of certain strains of bacteria and they have lethal effects on other
strains within the same species. The effect of bacteriocins is also dependent on the
presence of specific receptors on the surface of sensitive cells. The receptors are
structures onto which bacteriocins bind and they are located in the bacterial cell wall.
Bacteriocin-producing strains are called bacteriocinogenic strains.
The synthesis of bacteriocins is determined genetically by certain genes. The best
known and the earliest described bacteriocins are the so-called colicins, which are
produced by some strains of Escherichia coli. They affect sensitive bacteria by
various mechanisms. For instance, colicin E2 decomposes the DNA of the attacked
cell, while colicin 3 splits ribosomal RNA. Other colicins bind to the surface
receptors of bacteria and block the flow of nutrients into the cell. Yet another colicin
inhibits bacterial growth by blocking the permeation of ions through the
cytoplasmatic membrane. It is assumed that bacteriocin production gives bacteria a
definitive advantage in their living environment because they thus can eliminate
other microorganisms with which they would otherwise have to compete for nutrition. In a similar fashion, yeasts produce antimicrobial substances akin to bacteriocins, called zymocins. Bacteriocins can also be used for the biological identification
of bacteria of the same species. The names of bacteriocins are derived from the
names of those bacteria which produce them, for example, species of the genus
Proteus form proticins, Pseudomonas aeruginosa produces pyocins and so on.
248
V. Klaban
for instance, produces significant amounts of sulfuric acid that lowers greatly the pH
of the environment, which in turn causes changes in the composition of the surrounding microbial community. Another example can be the production of lactic
acid by the lactic acid bacteria. That acid production also causes a significant
reduction in the number of microbial species originally present in a given
environment.
Another well-known example of amensalism is the production of ethanol, which
negatively affects many species of microorganisms. For example, production of
ethanol by certain species of yeasts inhibits the growth of many sensitive bacteria.
Bacteriocins, zymocins, mycotoxins as well as antibiotics all belong to the realm of
amensalism.
15.4 Bacteriocins
The term bacteriocin was introduced in 1953 by Jacob and coauthors (Jacob et al.
1953) as denomination for a group of proteins with antibiotic characteristics. These
are the products of certain strains of bacteria and they have lethal effects on other
strains within the same species. The effect of bacteriocins is also dependent on the
presence of specific receptors on the surface of sensitive cells. The receptors are
structures onto which bacteriocins bind and they are located in the bacterial cell wall.
Bacteriocin-producing strains are called bacteriocinogenic strains.
The synthesis of bacteriocins is determined genetically by certain genes. The best
known and the earliest described bacteriocins are the so-called colicins, which are
produced by some strains of Escherichia coli. They affect sensitive bacteria by
various mechanisms. For instance, colicin E2 decomposes the DNA of the attacked
cell, while colicin 3 splits ribosomal RNA. Other colicins bind to the surface
receptors of bacteria and block the flow of nutrients into the cell. Yet another colicin
inhibits bacterial growth by blocking the permeation of ions through the
cytoplasmatic membrane. It is assumed that bacteriocin production gives bacteria a
definitive advantage in their living environment because they thus can eliminate
other microorganisms with which they would otherwise have to compete for nutrition. In a similar fashion, yeasts produce antimicrobial substances akin to bacteriocins, called zymocins. Bacteriocins can also be used for the biological identification
of bacteria of the same species. The names of bacteriocins are derived from the
names of those bacteria which produce them, for example, species of the genus
Proteus form proticins, Pseudomonas aeruginosa produces pyocins and so on.
248
V. Klaban