216 ◾ Fundamental Food Microbiology
bacteriocins (e.g., pediocin AcH is produced by many Ped. acidilactici strains, but sakacin A
and sakacin P are produced by different strains of Lab. sake).
◾ Strains from different species and genera can produce the same bacteriocins (e.g., pediocin
AcH is produced by strains of Ped. acidilactici, Ped. pentosaceus, Ped. parvulus, Lab. plantarum, Bacillus coagulans).
◾ Strains from different subspecies can produce different bacteriocins (e.g., different Lac. lactis
ssp. lactis produce nisin A and lacticin 481).
◾ Different species from a genus can produce different bacteriocins (e.g., enterococcin EFS2
and enterocin 900 are produced by strains of Ent. faecalis and Ent. faecium, respectively).
◾ Natural variants of the same bacteriocin can be produced by different strains and species
(e.g., nisin A and Z by Lac. lactis strains; pediocin AcH and coagulin by Ped. acidilactici and
Bac. coagulans, respectively).
◾ Many bacteriocins named differently before their amino acid sequences are determined to be
the same (e.g., pediocin AcH and pediocin PA of Ped. acidilactici strains). 9,10
Characteristics of Bacteriocins 10–16
Although isolation of a large number of bacteriocins of lactic acid bacteria has been reported in the
literature, for most the amino acid sequences have not been determined. Amino acid sequencing
studies have shown that some of the bacteriocins that were initially given different names have
the same amino acid sequences. Some examples are pediocin AcH and pediocin PA-1, curvacin A
and sakacin A, and sakacin P and bavaricin A. In general, they contain less than 60 amino acids,
but their bactericidal efficiency is not related to the number of amino acids in the molecule. They
are cationic, and the net positive charge is higher at low pH. Because of their hydrophobic nature,
the molecules have a tendency to aggregate, especially when stored in the liquid state and at high
concentrations. The bactericidal property is higher at lower pH, relatively stable at high temperature, and not affected by organic solvents. Anions in high concentrations can reduce bactericidal
efficiency of some cationic bacteriocins by competitive exclusion. Different proteolytic enzymes
can hydrolyze these peptides, leading to a loss of activity. They are fairly stable at frozen and refrigerated storage, but some with methionine can be oxidized to methionine sulfoxide, which reduces
the potency (e.g., pediocin AcH). The monomers, especially with disulfide bonds, can form dimers
and trimers by bond exchange but retain their bactericidal efficiency.
Bacteriocins of lactic acid bacteria are characterized as ribosomally synthesized peptides as they
undergo very little structural change following translation. In general, a molecule, as translated,
is designated as prebacteriocin, which contains an N-terminus leader peptide and a C-terminus
probacteriocin. The leader peptide is removed during transportation of the molecules from the
cytoplasm side to outside through the membrane-bound ABC transporter; the ABC transporter,
acting as an endopeptidase, excises the leader peptide. Although many bacteriocins have one peptide chain, some have two peptide chains. The function of the leader peptide is to direct the transport of a molecule through the ABC transporter. Once the bacteriocin molecules are released into
the environment, depending on the pH, they either remain bound with the anionic molecules on
the cell surface or are released into the environment. Recent studies have shown that some bacteriocins can be transported by the sec-dependent secretory system, whereas a few do not have the
leader sequence.
Bacteriocin molecules, based on the molecular structures, are subdivided into several groups.
Broadly, they are grouped as Class I, which contains lanthionine rings, and Class II, which lacks
bacteriocins (e.g., pediocin AcH is produced by many Ped. acidilactici strains, but sakacin A
and sakacin P are produced by different strains of Lab. sake).
◾ Strains from different species and genera can produce the same bacteriocins (e.g., pediocin
AcH is produced by strains of Ped. acidilactici, Ped. pentosaceus, Ped. parvulus, Lab. plantarum, Bacillus coagulans).
◾ Strains from different subspecies can produce different bacteriocins (e.g., different Lac. lactis
ssp. lactis produce nisin A and lacticin 481).
◾ Different species from a genus can produce different bacteriocins (e.g., enterococcin EFS2
and enterocin 900 are produced by strains of Ent. faecalis and Ent. faecium, respectively).
◾ Natural variants of the same bacteriocin can be produced by different strains and species
(e.g., nisin A and Z by Lac. lactis strains; pediocin AcH and coagulin by Ped. acidilactici and
Bac. coagulans, respectively).
◾ Many bacteriocins named differently before their amino acid sequences are determined to be
the same (e.g., pediocin AcH and pediocin PA of Ped. acidilactici strains). 9,10
Characteristics of Bacteriocins 10–16
Although isolation of a large number of bacteriocins of lactic acid bacteria has been reported in the
literature, for most the amino acid sequences have not been determined. Amino acid sequencing
studies have shown that some of the bacteriocins that were initially given different names have
the same amino acid sequences. Some examples are pediocin AcH and pediocin PA-1, curvacin A
and sakacin A, and sakacin P and bavaricin A. In general, they contain less than 60 amino acids,
but their bactericidal efficiency is not related to the number of amino acids in the molecule. They
are cationic, and the net positive charge is higher at low pH. Because of their hydrophobic nature,
the molecules have a tendency to aggregate, especially when stored in the liquid state and at high
concentrations. The bactericidal property is higher at lower pH, relatively stable at high temperature, and not affected by organic solvents. Anions in high concentrations can reduce bactericidal
efficiency of some cationic bacteriocins by competitive exclusion. Different proteolytic enzymes
can hydrolyze these peptides, leading to a loss of activity. They are fairly stable at frozen and refrigerated storage, but some with methionine can be oxidized to methionine sulfoxide, which reduces
the potency (e.g., pediocin AcH). The monomers, especially with disulfide bonds, can form dimers
and trimers by bond exchange but retain their bactericidal efficiency.
Bacteriocins of lactic acid bacteria are characterized as ribosomally synthesized peptides as they
undergo very little structural change following translation. In general, a molecule, as translated,
is designated as prebacteriocin, which contains an N-terminus leader peptide and a C-terminus
probacteriocin. The leader peptide is removed during transportation of the molecules from the
cytoplasm side to outside through the membrane-bound ABC transporter; the ABC transporter,
acting as an endopeptidase, excises the leader peptide. Although many bacteriocins have one peptide chain, some have two peptide chains. The function of the leader peptide is to direct the transport of a molecule through the ABC transporter. Once the bacteriocin molecules are released into
the environment, depending on the pH, they either remain bound with the anionic molecules on
the cell surface or are released into the environment. Recent studies have shown that some bacteriocins can be transported by the sec-dependent secretory system, whereas a few do not have the
leader sequence.
Bacteriocin molecules, based on the molecular structures, are subdivided into several groups.
Broadly, they are grouped as Class I, which contains lanthionine rings, and Class II, which lacks