220 ◾ Fundamental Food Microbiology
Genetics and Gene Organization
The limited available information has revealed that the structural genes encoding prebacteriocin
molecules of lactic acid bacteria can be encoded in a plasmid (e.g., pediocin AcH or PA-1), in the
genome (e.g., sakacin P), or in a genome-integrated transposon (e.g., nisin A) of a producer strain.
With plasmid-encoded bacteriocins, several variations are observed: A single plasmid can encode
only one bacteriocin (e.g., pediocin AcH or PA-1) or more than one bacteriocin (e.g., lactococcin
A, B, and M); the same bacteriocin can be encoded in different-size plasmids in the same species
(e.g., lactococcin A in three separate strains of Lac. lactis) or different species (e.g., pediocin AcH
in Ped. acidilactici, Ped. pentosaceus, Ped. purvulus, and Lab. plantarum); or a strain producing
more than one bacteriocin that can be encoded in different plasmids (e.g., carnobacteriocin A and
carnobacteriocin B1 and B2 are encoded in two plasmids in a Car. piscicola strain).
In addition to the structural gene encoding for a bacteriocin, the DNA (plasmid or genome)
also encodes several other genes related to its production (Figure 17.2). Some of them are quite
simple (e.g., pediocin AcH), whereas others can be very complex (e.g., nisin A). There are many
other differences in the organization of the genes associated with bacteriocin production in lactic
acid bacteria. The genes could present in a single operon (e.g., in pediocin AcH and nisin A) or in
more than one operon (sakacin P), and all genes are arranged in the same direction (e.g., sakacin
P) or in opposite directions (e.g., leucocin A). In some, one or more genes can overlap (e.g., nisin A
and leucocin A). The gene organization in the simplest form, as observed for pediocin AcH or PA-1
production, consists of an operon, with the promoter located upstream, and four genes, encoding
for four proteins: pap or pedA for prepediocin, pap or pedB for immunity protein (PapB or PedB
confer immunity against pediocin), pap or pedC for helper protein (PapC or PedC necessary for
the efficient transport of pediocin), and pap or pedD (PapD or PedD for the ABC-transporter
protein). Almost similar gene expressions, but with two promoters, are present in the production
of leucocin A. In nisin A production, the genetic expression is quite different. Eleven genes, nisABTCIPRKFEG, are present in the operon with the promoter located upstream and nisA encoding
for prenisin (Figure 17.2). The functions of the other proteins from the other genes are as follows:
Nisin A
A
B
T
C
I
P
Transposon
C
C
D
D
K
F
E
G
Plasmid
Plasmid
R
A
A
B
B
E
ORF1
ORF1
ORF2 ORF3 ORF4
I
I
A
A
K
K
R
R
T
T
E
E
Pediocin AcH
Leucocin A
Sakacin A
Sakacin P
Figure 17.2 organization of several well-characterized bacteriocin gene clusters. Structural
genes are shown as shaded arrows, promoters as black arrowheads, and rho-independent terminators as lollipop symbols. Genes of unknown functions are designated oRFs.
Genetics and Gene Organization
The limited available information has revealed that the structural genes encoding prebacteriocin
molecules of lactic acid bacteria can be encoded in a plasmid (e.g., pediocin AcH or PA-1), in the
genome (e.g., sakacin P), or in a genome-integrated transposon (e.g., nisin A) of a producer strain.
With plasmid-encoded bacteriocins, several variations are observed: A single plasmid can encode
only one bacteriocin (e.g., pediocin AcH or PA-1) or more than one bacteriocin (e.g., lactococcin
A, B, and M); the same bacteriocin can be encoded in different-size plasmids in the same species
(e.g., lactococcin A in three separate strains of Lac. lactis) or different species (e.g., pediocin AcH
in Ped. acidilactici, Ped. pentosaceus, Ped. purvulus, and Lab. plantarum); or a strain producing
more than one bacteriocin that can be encoded in different plasmids (e.g., carnobacteriocin A and
carnobacteriocin B1 and B2 are encoded in two plasmids in a Car. piscicola strain).
In addition to the structural gene encoding for a bacteriocin, the DNA (plasmid or genome)
also encodes several other genes related to its production (Figure 17.2). Some of them are quite
simple (e.g., pediocin AcH), whereas others can be very complex (e.g., nisin A). There are many
other differences in the organization of the genes associated with bacteriocin production in lactic
acid bacteria. The genes could present in a single operon (e.g., in pediocin AcH and nisin A) or in
more than one operon (sakacin P), and all genes are arranged in the same direction (e.g., sakacin
P) or in opposite directions (e.g., leucocin A). In some, one or more genes can overlap (e.g., nisin A
and leucocin A). The gene organization in the simplest form, as observed for pediocin AcH or PA-1
production, consists of an operon, with the promoter located upstream, and four genes, encoding
for four proteins: pap or pedA for prepediocin, pap or pedB for immunity protein (PapB or PedB
confer immunity against pediocin), pap or pedC for helper protein (PapC or PedC necessary for
the efficient transport of pediocin), and pap or pedD (PapD or PedD for the ABC-transporter
protein). Almost similar gene expressions, but with two promoters, are present in the production
of leucocin A. In nisin A production, the genetic expression is quite different. Eleven genes, nisABTCIPRKFEG, are present in the operon with the promoter located upstream and nisA encoding
for prenisin (Figure 17.2). The functions of the other proteins from the other genes are as follows:
Nisin A
A
B
T
C
I
P
Transposon
C
C
D
D
K
F
E
G
Plasmid
Plasmid
R
A
A
B
B
E
ORF1
ORF1
ORF2 ORF3 ORF4
I
I
A
A
K
K
R
R
T
T
E
E
Pediocin AcH
Leucocin A
Sakacin A
Sakacin P
Figure 17.2 organization of several well-characterized bacteriocin gene clusters. Structural
genes are shown as shaded arrows, promoters as black arrowheads, and rho-independent terminators as lollipop symbols. Genes of unknown functions are designated oRFs.