from the L. johnsonii VPI11088 fermentation supernatant using L. helveticus
NCK338 as an indicator organism [151]. Therefore, the lafA gene product, LafA,
is a bacteriocin that kills L. helveticus NCK338. Expansion of the host range to
include L. delbrueckii and Enterococcus faecalis occurs only after the interaction
of LafA and LafX. The need of complementation of two bacteriocins for optimal
activity is reflected in the presence of two bacteriocins encoded in the same
operon and, together with lactococcin M [46], lactacin F [77], plantaricin A [49]
and lactococcin G [128] they are the only class IIB bacteriocins determined on
the genetic level.
Plantaricin A was shown to be dependent on complementation of two almost
identical peptides which differed only in one N-terminal alanine residue [152].
Therefore, plantaricin A was the first known class IIB bacteriocin not to be
encoded by two different adjacent structural bacteriocin genes [134]. When the
plantaricin A gene cluster was genetically analyzed only one structural gene
encoding plantaricin A was detected [134]. Detailed analysis of the plantaricin
A genetic determinants revealed that plantaricin A acts as an inducer peptide of
an agr-like signal transduction system and does not possess any bacteriocinogenic activity [49, 134, 145]. Recent findings confirmed that bacteriocin
activity is most likely encoded by two two-peptide type and one one-peptide
type bacteriocins adjacent to the plnABCD operon [49, 134]. The proteins that
constitute the production and maturation machinery of class IIB bacteriocins
do not differ significantly from the other class II bacteriocins, as deduced from
the lactococcin M and G, and plantaricin A operons [127, 128, 134, 145].
4
Immunity and Resistance Towards Bacteriocins
Three important phenotypes can confer non-sensitivity to bacteriocins: (i) immunity is genetically linked with bacteriocin production and exerts the
strongest level of non-sensitivity, (ii) resistance can occur as the appearance of
spontaneous mutants following selection on the bacteriocin; and (iii) resistance
conferred by a gene that is not genetically linked with bacteriocin production.
These three categories of resistance are likely to be similar for any bacteriocin
[21].
The genetic determinant for nisin immunity has been defined as nisI, the
fifth gene encoded in the nisin operon [92, 101, 153]. The entire NisI protein
showed no significant similarities to other proteins, but its N-terminus strongly
resembles that of signal peptide sequences of lipoproteins from Gram-negative
E. coli and Gram-positive Bacillus and L. lactis [92, 107, 154]. Bacterial lipoproteins are a group of exported proteins that are anchored to the cellular or
outer membrane by lipid moieties. The lipids are covalently linked to the
cysteine residue located at the N-terminus of the secreted protein [92].
Furthermore, the typical consensus sequence of the cleavage site and the tripartite structure of signal peptides is also found in the N-terminus of NisI [92,
107]. NisI therefore is a membrane-bound lipoprotein located on the outside of
the cell membrane [92, 107, 155]. Similar results have been described for the
only other immunity protein reported thus far for a lantibiotic, i.e. PepI, which
36
E. Sablon et al.
NCK338 as an indicator organism [151]. Therefore, the lafA gene product, LafA,
is a bacteriocin that kills L. helveticus NCK338. Expansion of the host range to
include L. delbrueckii and Enterococcus faecalis occurs only after the interaction
of LafA and LafX. The need of complementation of two bacteriocins for optimal
activity is reflected in the presence of two bacteriocins encoded in the same
operon and, together with lactococcin M [46], lactacin F [77], plantaricin A [49]
and lactococcin G [128] they are the only class IIB bacteriocins determined on
the genetic level.
Plantaricin A was shown to be dependent on complementation of two almost
identical peptides which differed only in one N-terminal alanine residue [152].
Therefore, plantaricin A was the first known class IIB bacteriocin not to be
encoded by two different adjacent structural bacteriocin genes [134]. When the
plantaricin A gene cluster was genetically analyzed only one structural gene
encoding plantaricin A was detected [134]. Detailed analysis of the plantaricin
A genetic determinants revealed that plantaricin A acts as an inducer peptide of
an agr-like signal transduction system and does not possess any bacteriocinogenic activity [49, 134, 145]. Recent findings confirmed that bacteriocin
activity is most likely encoded by two two-peptide type and one one-peptide
type bacteriocins adjacent to the plnABCD operon [49, 134]. The proteins that
constitute the production and maturation machinery of class IIB bacteriocins
do not differ significantly from the other class II bacteriocins, as deduced from
the lactococcin M and G, and plantaricin A operons [127, 128, 134, 145].
4
Immunity and Resistance Towards Bacteriocins
Three important phenotypes can confer non-sensitivity to bacteriocins: (i) immunity is genetically linked with bacteriocin production and exerts the
strongest level of non-sensitivity, (ii) resistance can occur as the appearance of
spontaneous mutants following selection on the bacteriocin; and (iii) resistance
conferred by a gene that is not genetically linked with bacteriocin production.
These three categories of resistance are likely to be similar for any bacteriocin
[21].
The genetic determinant for nisin immunity has been defined as nisI, the
fifth gene encoded in the nisin operon [92, 101, 153]. The entire NisI protein
showed no significant similarities to other proteins, but its N-terminus strongly
resembles that of signal peptide sequences of lipoproteins from Gram-negative
E. coli and Gram-positive Bacillus and L. lactis [92, 107, 154]. Bacterial lipoproteins are a group of exported proteins that are anchored to the cellular or
outer membrane by lipid moieties. The lipids are covalently linked to the
cysteine residue located at the N-terminus of the secreted protein [92].
Furthermore, the typical consensus sequence of the cleavage site and the tripartite structure of signal peptides is also found in the N-terminus of NisI [92,
107]. NisI therefore is a membrane-bound lipoprotein located on the outside of
the cell membrane [92, 107, 155]. Similar results have been described for the
only other immunity protein reported thus far for a lantibiotic, i.e. PepI, which
36
E. Sablon et al.