The genes involved in production of and immunity to sakacin A, a bacteriocin from Lactobacillus sake Lb706

Antimicrobial peptides of lactic acid bacteria: mode of action, genetics and biosynthesis

A survey is given of the main classes of bacteriocins, produced by lactic acid bacteria: I. lantibiotics II. small heat-stable non-lanthionine containing membrane-active peptides and III. large heat-labile proteins. First, their mode of action is detailed, with emphasis on pore formation in the cytoplasmatic membrane. Subsequently, the molecular genetics of several classes of bacteriocins are described in detail, with special attention to nisin as the most prominent example of the lantibiotic-class. Of the small non-lanthionine bacteriocin class, the Lactococcus lactococcins, and the Lactobacillus sakacin A and plantaricin A-bacteriocins are discussed. The principles and mechanisms of immunity and resistance towards bacteriocins are also briefly reported. The biosynthesis of bacteriocins is treated in depth with emphasis on response regulation, post-translational modification, secretion and proteolytic activation of bacteriocin precursors. To conclude, the role of the leader peptides is outlined and a conceptual model for bacteriocin maturation is proposed.

Environmentally regulated genes of Streptococcus suis: identification by the use of iron-restricted conditions in vitro and by experimental infection of piglets

The identification of environmentally regulated genes of Streptococcus suis by the use of iron-restricted conditions in vitro and by experimental infection of piglets is described. Eighteen unique iron-restriction-induced (iri) genes and 22 unique in-vivo-selected (ivs) genes of Strep. suis were found. None of the ivs genes was exclusively expressed in vivo. Four iri genes were identical to four clones selected in piglets. Two ivs genes were similar to genes for putative virulence factors. One of these ivs genes was identical to the epf gene of virulent Strep. suis serotype 2 strains and the other showed homology to a gene encoding a fibronectin-binding protein of Streptococcus gordonii. Two additional ivs genes showed homology to environmentally regulated genes previously identified by using an in vivo expression technology (IVET) selection system in other bacterial species. One of these showed similarity to the agrA gene of Staphylococcus aureus, a key locus involved in the regulation of numerous virulence proteins. The promoter selection system described in this paper has been successfully used for the identification of many environmentally regulated genes potentially involved in the pathogenesis of Strep. suis infections in piglets.

Engineering increased stability in the antimicrobial peptide pediocin PA-1

Pediocin PA-1 is a food grade antimicrobial peptide that has been used as a food preservative. Upon storage at 4 degrees C or room temperature, pediocin PA-1 looses activity, and there is a concomitant 16-Da increase in the molecular mass. It is shown that the loss of activity follows first-order kinetics and that the instability can be prevented by replacing the single methionine residue (Met31) in pediocin PA-1. Replacing Met by Ala, Ile, or Leu protected the peptide from oxidation and had only minor effects on bacteriocin activity (for most indicator strains 100% activity was maintained). Replacement of Met by Asp was highly deleterious for bacteriocin activity.

Class II antimicrobial peptides from lactic acid bacteria

Strains of lactic acid bacteria (LAB) produce a wide variety of antibacterial peptides. More than fifty of these so-called peptide bacteriocins have been isolated in the last few years. They contain 20-60 amino acids, and are cationic and hydrophobic in nature. Several of these bacteriocins consist of two complementary peptides. The peptide bacteriocins of LAB are inhibitory at concentrations in the nanomolar range, and cause membrane permeabilization and leakage of intracellular components in sensitive cells. The inhibitory spectrum is limited to gram-positive bacteria, and in many cases to bacteria closely related to the producing strain. Among the target organisms are food spoilage bacteria and pathogens such as Listeria, so that many of these antimicrobial peptides could have a potential as food preservatives as well as in medical applications.

Genetic transformation in Streptococcus mutans requires a peptide secretion-like apparatus

Competence for genetic transformation in Streptococcus pneumoniae and Streptococcus gordonii involves the ComAB secretion apparatus, which is thought to export the competence-stimulating peptide. Homologous secretory systems are also used for the export of certain bacteriocins and bacteriocin-like peptides. In this study, a similar secretory apparatus was found in the Streptococcus mutans genome, and its role in transformation was investigated. Gene inactivation resulted in a mutant deficient in transformability. We suggest that secretion of a peptide, possibly the competence-stimulating peptide itself, is involved in competence induction also in S. mutans.

The synthesis of the bacteriocin sakacin A is a temperature-sensitive process regulated by a pheromone peptide through a three-component regulatory system

Sakacin A is a bacteriocin produced by Lactobacillus sakei Lb706. The gene cluster (sap) encompasses a regulatory unit composed of three consecutive genes, orf4 and sapKR. sapKR encode a histidine protein kinase and a response regulator, while orf4 encodes the putative precursor of a 23-amino-acid cationic peptide (termed Sap-Ph). The authors show that Sap-Ph serves as a pheromone regulating bacteriocin production. Lb706 produced bacteriocin when the growth temperature was kept at 25 or 30 degrees C, but production was reduced or absent at higher temperatures (33.5-35 degrees C). Production was restored by lowering the growth temperature to 30 degrees C, but at temperatures of 33-34 degrees C also by adding exogenous Sap-Ph to the growth medium. A knock-out mutation in orf4 abolished sakacin A production. Exogenously added Sap-Ph complemented this mutation, unambiguously showing the essential role of this peptide for bacteriocin production. Another sakacin A producer, Lactobacillus curvatus LTH1174, had a similar response to temperature and exogenously added Sap-Ph.

Functional analysis of promoters involved in quorum sensing-based regulation of bacteriocin production in Lactobacillus

Bacteriocin production in Lactobacillus sake LTH673 involves at least four operons: a regulatory operon (sppIPKR); two operons encoding bacteriocins and their immunity proteins (sppAiA and orfX); and an operon needed for secretion (sppTE). We show here that the response regulator encoded by sppR in L. sake LTH673, as well as the homologous response regulators encoded by plnC and plnD in Lactobacillus plantarum C11, bind to characteristic repeats found in the -80 to -40 regions of spp operons. The promoters controlling bacteriocin operons are strictly regulated, and their activity is increased more than 1000-fold upon activation. Constitutive expression for the regulatory and transport operons is driven, at least in part, by promoters upstream of the -80 to -40 regions. Peak promoter activity of the regulatory and transporter operons precedes that of the two bacteriocin operons. The results reveal how promoters involved in quorum sensing-based regulation of bacteriocin production in Lactobacillus differ in strength, leakiness and timing of their activity.

A C-terminal disulfide bridge in pediocin-like bacteriocins renders bacteriocin activity less temperature dependent and is a major determinant of the antimicrobial spectrum

Several lactic acid bacteria produce so-called pediocin-like bacteriocins that share sequence characteristics, but differ in activity and target cell specificity. The significance of a C-terminal disulfide bridge present in only a few of these bacteriocins was studied by site-directed mutagenesis of pediocin PA-1 (which naturally contains the bridge) and sakacin P (which lacks the bridge). Introduction of the C-terminal bridge into sakacin P broadened the target cell specificity of this bacteriocin, as illustrated by the fact that the mutants were 10 to 20 times more potent than the wild-type toward certain indicator strains, whereas the potency toward other indicator strains remained essentially unchanged. Like pediocin PA-1, disulfide-containing sakacin P mutants had the same potency at 20 and 37 degrees C, whereas wild-type sakacin P was approximately 10 times less potent at 37 degrees C than at 20 degrees C. Reciprocal effects on target cell specificity and the temperature dependence of potency were observed upon studying the effect of removing the C-terminal disulfide bridge from pediocin PA-1 by Cys-->Ser mutations. These results clearly show that a C-terminal disulfide bridge in pediocin-like bacteriocins contributes to widening of the antimicrobial spectrum as well as to higher potency at elevated temperatures. Interestingly, the differences between sakacin P and pediocin PA-1 in terms of the temperature dependency of their activities correlated well with the optimal temperatures for bacteriocin production and growth of the bacteriocin-producing strain.

Characterization of the genetic locus responsible for production and immunity of carnobacteriocin A: the immunity gene confers cross-protection to enterocin B

Carnobacteriocin A (CbnA) is a regulated bacteriocin produced by Carnobacterium piscicola LV17A that is encoded on a 72 kb plasmid. A 10.0 kb fragment from this plasmid that contained information necessary for bacteriocin production and immunity was cloned and sequenced. Genetic analysis showed the presence of the previously sequenced structural gene for CbnA, as well as genes encoding proteins homologous to dedicated bacteriocin transport proteins and proteins of three-component signal transduction systems. The induction factor (CbnX) was chemically synthesized and induced CbnA production at 10(-11) M or higher in a C. piscicola LV17A culture that had lost the ability to produce bacteriocin as a result of dilution. The gene cbiA for the immunity protein is not located in typical close proximity to the structural gene for CbnA and is encoded in the opposite orientation. CbiA has homology with EniB, the immunity protein for enterocin B that is also encoded in the opposite orientation to the bacteriocin gene. CbiA and EniB cross-protected against the corresponding bacteriocins.

Cloning and expression of the genes involved in the production of and immunity against the bacteriocin lacticin RM

The production of lacticin RM, a novel bacteriocin produced by Lactococcus lactis subsp. lactis EZ26, is associated with the presence of a 6-kb plasmid, pHU1. The information necessary for lacticin RM production and immunity was localized to a 2.5-kb SalI-Eco47III fragment. Sequencing analysis of this fragment revealed the presence of six open reading frames (ORFs). Deletion and mutation analyses showed that orfX and orfY are not required for lacticin RM production or immunity, whereas the other ORFs (lacA, lacF, lacG and lacI) are necessary for the bacteriocin's production. Transcription analysis indicated that lacA, lacF and lacG are organized in an operon. lacA is probably the lacticin RM structural gene. It putatively encodes a 134-amino acid peptide, and it does not share homology with known bacteriocins. The deduced LacG protein is hydrophobic and consists of six potential trans-membrane helices. lacF encodes a conserved ATP-binding domain homologous to ABC transporters known in bacteriocin immunity systems. LacF and LacG may form an active ABC transporter. Gene-disruption mutations indicated that both are required for immunity against lacticin RM. lacI encodes a small cationic protein, which is required for the production of and immunity to lacticin RM. Protection was obtained only when lacF, lacG and lacI were present together.

A gene cluster encoding plantaricin 1.25beta and other bacteriocin-like peptides in Lactobacillus plantarum TMW1.25

Plantaricin 1.25beta is a thermostable class two bacteriocin produced by Lactobacillus plantarum TMW1.25 isolated from sausage fermentation. It is co-produced with several other bacteriocin-like peptides. Using oligonucleotides derived from previously determined peptide sequences, a 3.8 kb DNA fragment could be amplified. A neighboring 1.8 kb fragment was amplified using ligation-anchored single-specific-primer PCR. Sequencing of the complete 5.6 kb stretch revealed that the structural gene for plantaricin 1.25beta, plnB, was located downstream of another bacteriocin gene, plnC. Seven other open reading frames were detected, including plnK encoding a bacteriocin-like peptide, but not including any putative immunity genes. Interestingly, the gene cluster contained an IS30-like insertion sequence, designated IS125, as well as an ISS1 homolog.

Class IIa bacteriocins: biosynthesis, structure and activity

In the last decade, a variety of ribosomally synthesized antimicrobial peptides or bacteriocins produced by lactic acid bacteria have been identified and characterized. As a result of these studies, insight has been gained into fundamental aspects of biology and biochemistry such as producer self protection, membrane-protein interactions, and protein modification and secretion. Moreover, it has become evident that these peptides may be developed into useful antimicrobial additives. Class IIa bacteriocins can be considered as the major subgroup of bacteriocins from lactic acid bacteria, not only because of their large number, but also because of their activities and potential applications. They have first attracted particular attention as listericidal compounds and are now believed to be the next in line if more bacteriocins are to be approved in the future. The present review attempts to provide an insight into general knowledge available for class IIa bacteriocins and discusses common features and recent findings concerning these substances.

A nisin bioassay based on bioluminescence

A Lactococcus lactis subsp. lactis strain that can sense the bacteriocin nisin and transduce the signal into bioluminescence was constructed. By using this strain, a bioassay based on bioluminescence was developed for quantification of nisin, for detection of nisin in milk, and for identification of nisin-producing strains. As little as 0.0125 ng of nisin per ml was detected within 3 h by this bioluminescence assay. This detection limit was lower than in previously described methods.

Mutational analysis and membrane topology of ComP, a quorum-sensing histidine kinase of Bacillus subtilis controlling competence development

ComP is a sensor histidine kinase of Bacillus subtilis required for the signal transduction pathway that initiates the development of competence for genetic transformation. It is believed that ComP senses the presence of ComX, a modified extracellular peptide pheromone, and donates a phosphate to ComA, thereby activating this transcription factor for binding to the srfA promoter. In the present study, fusions to the Escherichia coli proteins PhoA and LacZ and analysis of its susceptibility to the protease kallikrein were used to probe the membrane topology of ComP. These data suggest that ComP contains six or eight membrane-spanning segments and two large extracytoplasmic loops in its N-terminal membrane-associated domain. Deletions were introduced involving the large extracellular loops to explore the role of the N-terminal domain of ComP in signal transduction. The absence of the second loop conferred a phenotype in which ComP was active in the absence of ComX. The implications of these data are discussed.

Purification and partial amino acid sequence of plantaricin 1.25 alpha and 1.25 beta, two bacteriocins produced by Lactobacillus plantarum TMW1.25

Two bacteriocins produced by Lactobacillus plantarum TMW1.25 have been purified by a four-step purification procedure, including ammonium sulphate precipitation and cation-exchange chromatography followed by hydrophobic-interaction chromatography on octyl sepharose. The final purification was performed by repeated reversed-phase chromatography steps which yielded two bacteriocin fractions designated plantaricin 1.25 alpha and plantaricin 1.25 beta. The molecular masses of the peptides in these fractions were 5979 and 5203 Da, respectively. Combination of the fractions did not have any synergistic effects on bacteriocin activity, indicating that they each contain a one-peptide bacteriocin. The major peptide in the alpha fraction was blocked at its N-terminus, and a partial sequence (25 residues) could only be obtained after cleavage with CNBr. This sequence did not show clear homologies with known bacteriocins. The beta peptide has been sequenced almost completely and consists, presumably, of 53 residues. This peptide displayed strong homology to the known N-terminal part of brevicin 27 produced by Lactobacillus brevis SB27. The results showed that the beta peptide contains as many as six consecutive lysine residues at the N-terminus.

Evidence for production of a new lantibiotic (butyrivibriocin OR79A) by the ruminal anaerobe Butyrivibrio fibrisolvens OR79: characterization of the structural gene encoding butyrivibriocin OR79A

The ruminal anaerobe Butyrivibrio fibrisolvens OR79 produces a bacteriocin-like activity demonstrating a very broad spectrum of activity. An inhibitor was isolated from spent culture fluid by a combination of ammonium sulfate and acidic precipitations, reverse-phase chromatography, and high-resolution gel filtration. N-terminal analysis of the isolated inhibitor yielded a 15-amino-acid sequence (G-N/Q-G/P-V-I-L-X-I-X-H-E-X-S-M-N). Two different amino acid residues were detected in the second and third positions from the N terminus, indicating the presence of two distinct peptides. A gene with significant homology to one combination of the determined N-terminal sequence was cloned, and expression of the gene was confirmed by Northern blotting. The gene (bvi79A) encoded a prepeptide of 47 amino acids and a mature peptide, butyrivibriocin OR79A, of 25 amino acids. Significant sequence homology was found between this peptide and previously reported lantibiotics containing the double-glycine leader peptidase processing site. Immediately downstream of bvi79A was a second, partial open reading frame encoding a peptide with significant homology to proteins which are believed to be involved in the synthesis of lanthionine residues. These findings indicate that the isolated inhibitory peptides represent new lantibiotics. Results from both total and N-terminal amino acid sequencing indicated that the second peptide was identical to butyrivibriocin OR79A except for amino acid substitutions in positions 2 and 3 of the mature lantibiotic. Only a single coding region was detected when restriction enzyme digests of total DNA were probed either with an oligonucleotide based on the 5' region of bvi79A or with degenerate oligonucleotides based on the predicted sequence of the second peptide.

Alignment and structure prediction of divergent protein families: periplasmic and outer membrane proteins of bacterial efflux pumps

Broad-specificity efflux pumps have been implicated in multidrug-resistant strains of Pseudomonas aeruginosa and other Gram-negative bacteria. Most Gram-negative pumps of clinical relevance have three components, an inner membrane transporter, an outer membrane channel protein, and a periplasmic protein, which together coordinate efflux from the cytoplasmic membrane across the outer membrane through an unknown mechanism. The periplasmic efflux proteins (PEPs) and outer membrane efflux proteins (OEPs) are not obviously related to proteins of known structure, and understanding the structure and function of these proteins has been hindered by the difficulty of obtaining reasonable multiple alignments. We present a general strategy for the alignment and structure prediction of protein families with low mutual sequence similarity using the PEP and OEP families as detailed examples. Gibbs sampling, hidden Markov models, and other analysis techniques were used to locate motifs, generate multiple alignments, and assign PEP or OEP function to hypothetical proteins in several species. We also developed an automated procedure which combines multiple alignments with structure prediction algorithms in order to identify conserved structural features in protein families. This process was used to identify a probable alpha-helical hairpin in the PEP family and was applied to the detection of transmembrane beta-strands in OEPs. We also show that all OEPs contain a large tandem duplication, and demonstrate that the OEP family is unlikely to adopt a porin fold, in contrast to previous predictions.

Characterization and heterologous expression of the genes encoding enterocin a production, immunity, and regulation in Enterococcus faecium DPC1146

Enterocin A is a small, heat-stable, antilisterial bacteriocin produced by Enterococcus faecium DPC1146. The sequence of a 10, 879-bp chromosomal region containing at least 12 open reading frames (ORFs), 7 of which are predicted to play a role in enterocin biosynthesis, is presented. The genes entA, entI, and entF encode the enterocin A prepeptide, the putative immunity protein, and the induction factor prepeptide, respectively. The deduced proteins EntK and EntR resemble the histidine kinase and response regulator proteins of two-component signal transducing systems of the AgrC-AgrA type. The predicted proteins EntT and EntD are homologous to ABC (ATP-binding cassette) transporters and accessory factors, respectively, of several other bacteriocin systems and to proteins implicated in the signal-sequence-independent export of Escherichia coli hemolysin A. Immediately downstream of the entT and entD genes are two ORFs, the product of one of which, ORF4, is very similar to the product of the yteI gene of Bacillus subtilis and to E. coli protease IV, a signal peptide peptidase known to be involved in outer membrane lipoprotein export. Another potential bacteriocin is encoded in the opposite direction to the other genes in the enterocin cluster. This putative bacteriocin-like peptide is similar to LafX, one of the components of the lactacin F complex. A deletion which included one of two direct repeats upstream of the entA gene abolished enterocin A activity, immunity, and ability to induce bacteriocin production. Transposon insertion upstream of the entF gene also had the same effect, but this mutant could be complemented by exogenously supplied induction factor. The putative EntI peptide was shown to be involved in the immunity to enterocin A. Cloning of a 10.5-kb amplicon comprising all predicted ORFs and regulatory regions resulted in heterologous production of enterocin A and induction factor in Enterococcus faecalis, while a four-gene construct (entAITD) under the control of a constitutive promoter resulted in heterologous enterocin A production in both E. faecalis and Lactococcus lactis.

Membrane topology of the lactococcal bacteriocin ATP-binding cassette transporter protein LcnC. Involvement of LcnC in lactococcin a maturation

Many non-lantibiotic bacteriocins of lactic acid bacteria are produced as precursors with N-terminal leader peptides different from those present in preproteins exported by the general sec-dependent (type II) secretion pathway. These bacteriocins utilize a dedicated (type I) secretion system for externalization. The secretion apparatus for the lactococcins A, B, and M/N (LcnA, B, and M/N) from Lactococcus lactis is composed of the two membrane proteins LcnC and LcnD. LcnC belongs to the ATP-binding cassette transporters, whereas LcnD is a protein with similarities to other accessory proteins of type I secretion systems. This paper shows that the N-terminal part of LcnC is involved in the processing of the precursor of LcnA. By making translational fusions of LcnC to the reporter proteins beta-galactosidase (LacZ) and alkaline phosphatase (PhoA*), it was shown that both the N- and C-terminal parts of LcnC are located in the cytoplasm. As the N terminus of LcnC is required for LcnA maturation and is localized in the cytoplasm, we conclude that the processing of the bacteriocin LcnA to its mature form takes place at the cytosolic side of the cytoplasmic membrane.

A system for heterologous expression of bacteriocins in Lactobacillus sake

A system for efficient heterologous expression of class II bacteriocins is described that is based on introducing two plasmids in a bacteriocin-negative Lactobacillus sake strain. The first plasmid (pSAK20) contains the genes necessary for transcriptional activation of the Sakacin A promoter as well as export and processing of bacteriocin precursors. The second plasmid (a pLPV111 derivative) contains the structural and immunity genes for the bacteriocin of interest fused to the sakacin A promoter. Using this system, various bacteriocins were produced at levels equal to or higher than those obtained with the corresponding wild-type producer strains.

Divercin V41, a new bacteriocin with two disulphide bonds produced by Carnobacterium divergens V41: primary structure and genomic organization

Divercin V41 is a new bacteriocin produced by Carnobacterium divergens V41, a lactic acid bacterium isolated from fish viscera. The amino acid sequence of divercin V41 showed high homologies with pediocin PA-1 and enterocin A. Two disulphide bonds were present in the hydrophilic N-terminal domain and in the highly variable hydrophobic C-terminal domain, respectively. A DNA probe designed from the N-terminal sequence of the purified peptide was used to locate the structural gene of divercin V41. A 6 kb chromosomal fragment containing the divercin V41 structural gene (dvnA) was cloned and sequenced. The results indicate that divercin V41 is synthesized as a pre-bacteriocin of 66 amino acids. The 23-residue N-terminal extension is cleaved off to yield the mature 43-amino-acid divercin V41. In addition, the fragment encodes putative proteins commonly found within bacteriocin operons, including an ATP-dependent transporter, two immunity-like proteins and the two components of a lantibiotic-type signal-transducing system. The genetic organization of the fragment suggested important gene rearrangements.

Two-component signal-transducing systems involved in stress responses and vancomycin susceptibility in Lactobacillus sakei

Fragments of five rrp genes encoding response regulators (RRs) in Lactobacillus sakei were amplified by PCR using degenerate oligonucleotide primers. The five rrp genes were part of distinct loci that also comprised hpk genes encoding histidine protein kinases (HPKs). The putative RRs belonged to the OmpR-PhoB subclass of response regulators that consist of N-terminal receiver and C-terminal DNA-binding domains. The putative HPKs were members of the EnvZ-NarX family of orthodox histidine protein kinases which possess two transmembrane segments in a non-conserved N-terminal domain and a C-terminal cytoplasmic kinase domain. Insertional inactivation of the rrp genes indicated that the RRs are implicated in susceptibility to the glycopeptide antibiotic vancomycin, and to extreme pH, temperature and oxidative conditions.

Heterologous expression of the bacteriocin mesentericin Y105 using the dedicated transport system and the general secretion pathway

Two different N-terminal extensions have been identified within class II bacteriocin precursors. The first one is a two-glycine-type leader peptide associated with a dedicated ATP-binding cassette transporter. The second is a signal peptide which directs the bacteriocin precursor to the general secretion machinery. Mesentericin Y105 is a class II anti-Listeria bacteriocin produced by Leuconostoc mesenteroides Y105 via a dedicated transport system (DTS). To investigate heterologous expression systems capable of producing mesentericin Y105 in various hosts, two different secretion vectors were constructed. One of them, containing the mesentericin Y105 structural gene fused to the segment encoding the divergicin A signal peptide, was introduced into Escherichia coli, Leuconostoc subsp. and Lactococcus subsp. In E. coli, mesentericin Y105 production was linked to a putative periplasmic toxicity. To take advantage of this secretion system, the mesentericin Y105 precursor was also produced in E. coli. It was demonstrated that this pre-bacteriocin exhibited some antagonistic activity against Listeria. To allow for a comparison between the two different transport systems, mesentericin Y105 production using the vector containing the mesentericin Y105 structural gene and its DTS transporter operon was examined. The production of mesentericin Y105 was monitored by a new fast purification method followed by MS analysis. It was shown that, in Leuconostoc, the production of mesentericin Y105 is enhanced via the DTS compared to the general secretion pathway.

Comparative studies of class IIa bacteriocins of lactic acid bacteria

Four class IIa bacteriocins (pediocin PA-1, enterocin A, sakacin P, and curvacin A) were purified to homogeneity and tested for activity toward a variety of indicator strains. Pediocin PA-1 and enterocin A inhibited more strains and had generally lower MICs than sakacin P and curvacin A. The antagonistic activity of pediocin-PA1 and enterocin A was much more sensitive to reduction of disulfide bonds than the antagonistic activity of sakacin P and curvacin A, suggesting that an extra disulfide bond that is present in the former two may contribute to their high levels of activity. The food pathogen Listeria monocytogenes was among the most sensitive indicator strains for all four bacteriocins. Enterocin A was most effective in inhibiting Listeria, having MICs in the range of 0.1 to 1 ng/ml. Sakacin P had the interesting property of being very active toward Listeria but not having concomitant high levels of activity toward lactic acid bacteria. Strains producing class IIa bacteriocins displayed various degrees of resistance toward noncognate class IIa bacteriocins; for the sakacin P producer, it was shown that this resistance is correlated with the expression of immunity genes. It is hypothesized that variation in the presence and/or expression of such immunity genes accounts in part for the remarkably large variation in bacteriocin sensitivity displayed by lactic acid bacteria.

The yvsA-yvqA (293 degrees-289 degrees) region of the Bacillus subtilis chromosome containing genes involved in metal ion uptake and a putative sigma factor

The region between yvsA (293 degrees) and yvqA (289 degrees) of the Bacillus subtilis chromosome has been sequenced within the framework of the B. subtilis 168 international sequencing programme. A primary analysis of the 42 ORFs identified in this 43 kb region is presented. The region included a high proportion of genes that did not show homology with genes in other bacteria. The identified ORFs showed homology to proteins involved in the transport of metal ions, two-component signal transducers, ATP-binding-cassette-type transporters and a sigma factor.

Molecular analysis of the locus responsible for production of plantaricin S, a two-peptide bacteriocin produced by Lactobacillus plantarum LPCO10

A 4.5-kb region of chromosomal DNA carrying the locus responsible for the production of plantaricin S, a two-peptide bacteriocin produced by Lactobacillus plantarum LPCO10 (R. Jiménez-Díaz, J. L. Ruiz-Barba, D. P. Cathcart, H. Holo, I. F. Nes, K. H. Sletten, and P. J. Warner, Appl. Environ. Microbiol. 61:4459-4463, 1995), has been cloned, and the nucleotide sequence has been elucidated. Two genes, designated plsA and plsB and encoding peptides alpha and beta, respectively, of plantaricin S, plus an open reading frame (ORF), ORF2, were found to be organized in an operon. Northern blot analysis showed that these genes are cotranscribed, giving a ca. 0.7-kb mRNA, whose transcription start point was determined by primer extension. Nucleotide sequences of plsA and plsB revealed that both genes are translated as bacteriocin precursors which include N-terminal leader sequences of the double-glycine type. The role of ORF2 is unknown at the moment, although it might be expected to encode an immunity protein of the type described for other bacteriocin operons. In addition, several other potential ORFs have been found, including some which may be responsible for the regulation of bacteriocin production. Two of them, ORF8 and ORF14, show strong homology with histidine protein kinase and response regulator genes, respectively, which have been found to be involved in the regulation of the production of other bacteriocins from lactic acid bacteria. A third ORF, ORF5, shows homology with gene agrB from Staphylococcus aureus, which is involved in the mechanism of regulation of the virulence phenotype in this species. Thus, an agr-like regulatory system for the production of plantaricin S is postulated.

An exported inducer peptide regulates bacteriocin production in Enterococcus faecium CTC492

Production of the bacteriocins enterocin A and enterocin B in Enterococcus faecium CTC492 was dependent on the presence of an extracellular peptide produced by the strain itself. This induction factor (EntF) was purified, and amino acid sequencing combined with DNA sequencing of the corresponding gene identified it as a peptide of 25 amino acids. The gene encodes a prepeptide of 41 amino acids, including a 16-amino-acid leader peptide of the double-glycine type. Environmental factors influenced the level of bacteriocin production in E. faecium CTC492. The optimal pH for bacteriocin production was 6.2. At pH 5.5, growth was slow, and very little bacteriocin was formed. The presence of NaCl or ethanol (EtOH) was also inhibitory to bacteriocin production, and at high concentrations of these solutes, no bacteriocin production was observed. The induction factor induced its own synthesis, and by dilution of the culture 106 times or more, nonproducing cultures were obtained. Bacteriocin production was induced in these cultures by addition of EntF. The response was linear, and low bacteriocin production could be induced by about 10(-17) M EntF. This response was attenuated by low pH or the presence of high concentrations of NaCl or EtOH, and 300 times more EntF was needed to induce detectable bacteriocin production in the presence of 6.5% NaCl. High levels of bacteriocin production in cultures grown at low pH or in the presence of high concentrations of NaCl or EtOH were obtained by addition of sufficient amounts of EntF.

The DevBCA exporter is essential for envelope formation in heterocysts of the cyanobacterium Anabaena sp. strain PCC 7120

The gene devA of the filamentous heterocyst-form-ing cyanobacterium Anabaena sp. strain PCC 7120 encodes a protein with high similarity to ATP-binding cassettes of ABC transporters. Mutant M7 defective in the devA gene is arrested in the development of heterocysts at an early stage and is not able to fix N2 under aerobic conditions. The devA gene is differentially expressed in heterocysts. To gain a better understanding of the structural components of this putative ABC transporter, we determined the complete nucleotide sequence of the entire gene cluster. The two additional genes, named devB and devC, encode proteins with similarities to membrane fusion proteins (DevB) of several ABC exporters and to membrane-spanning proteins (DevC) of ABC transporters in general. Site-directed mutations in each of the three genes resulted in identical phenotypes. Heterocyst-specific glycolipids forming the laminated layer of the envelope were identified in lipid extracts of M7 and in the site-directed mutants. However, transmission electron microscopy revealed unequivocally that the glycolipid layer is missing in mutant M7. Ultrastructural analysis also confirmed a developmental block at an early stage of differentiation. The results of this study suggest that the devBCA operon encodes an exporter of glycolipids or of an enzyme that is necessary for the formation of the laminated layer. The hypothesis is proposed that an intact envelope could be required for further heterocyst differentiation.

Biochemical and genetic characterization of enterocin P, a novel sec-dependent bacteriocin from Enterococcus faecium P13 with a broad antimicrobial spectrum

Enterocin P is a new bacteriocin produced by Enterococcus faecium P13 isolated from a Spanish dry-fermented sausage. Enterocin P inhibited most of tested spoilage and food-borne gram-positive pathogenic bacteria, such as Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens, and Clostridium botulinum. Enterocin P is produced during growth in MRS broth from 16 to 45 degrees C; it is heat resistant (60 min at 100 degrees C; 15 min at 121 degrees C) and can withstand exposure to pH between 2.0 and 11.0, freeze-thawing, lyophilization, and long-term storage at 4 and -20 degrees C. The bacteriocin was purified to homogeneity by ammonium sulfate precipitation, gel filtration, cation-exchange, hydrophobic-interaction, and reverse-phase liquid chromatography. The sequence of 43 amino acids of the N terminus was obtained by Edman degradation. DNA sequencing analysis of a 755-bp region revealed the presence of two consecutive open reading frames (ORFs). The first ORF encodes a 71-amino-acid protein containing a hydrophobic N-terminal sec-dependent leader sequence of 27 amino acids followed by the amino acid sequence corresponding to the purified and sequenced enterocin P. The bacteriocin is apparently synthesized as a prepeptide that is cleaved immediately after the Val-Asp-Ala residues (positions -3 to -1), resulting in the mature bacteriocin consisting of 44 amino acids, and with a theoretical molecular weight of 4,493. A second ORF, encoding a putative immunity protein composed of 88 amino acids with a calculated molecular weight of 9,886, was found immediately downstream of the enterocin P structural gene. Enterocin P shows a strong antilisterial activity and has the consensus sequence found in the pediocin-like bacteriocins; however, enterocin P is processed and secreted by the sec-dependent pathway.

Plasmids in Lactobacillus

This review describes Lactobacillus plasmids on distribution, structure, function, vector construction, vector stability, application, and prospective. About 38% of species of the genus Lactobacillus were found to contain plasmids with different sizes (from 1.2 to 150 kb) and varied numbers (1 or more). Some Lactobacillus plasmids with small sizes were highly similar to those of single strand plasmids from other Gram-positive bacteria. The extensive sequence homologies of plus origins, replication initiation proteins, minus origins, cointegration sites, and the presence of single strand intermediates supported the fact that these small Lactobacillus plasmids replicate with a rolling-circle replication mechanism. Some Lactobacillus plasmid replicons were of broad host range that could function in other Gram-positive bacteria, and even in Escherichia coli, while replicons of other Gram-positive bacteria also function in Lactobacillus. Although most Lactobacillus plasmids are cryptic, some plasmid-encoded functions have been discovered and applied to vector construction and Lactobacillus identification, detection, and modification.

Characterization of a locus from Carnobacterium piscicola LV17B involved in bacteriocin production and immunity: evidence for global inducer-mediated transcriptional regulation

Mutational, nucleotide sequence, and transcriptional analyses of a 10-kb fragment (carnobacteriocin locus) from the 61-kb plasmid of Carnobacterium piscicola LV17B demonstrated the presence of two gene clusters (cbnXY and cbnSKRTD) upstream of the previously sequenced carnobacteriocin B2 structural and immunity genes (cbnB2 and cbiB2). Deduced products of cbnK and cbnR have sequence similarity to proteins of Agr-type two-component signal transduction systems, and those of cbnT and cbnD have sequence similarity to proteins of signal sequence-independent secretion systems. Deduced products of cbnX, cbnY, and cbnS are class II-type bacteriocin precursors with potential leader peptides containing double-glycine cleavage sites. Genetic analysis indicated that the 10-kb locus contains information required for the production of, and immunity to, the plasmid-encoded carnobacteriocin B2 and the chromosomally encoded carnobacteriocin BM1. In addition, this locus is involved in the production of at least one additional antimicrobial compound and an inducer factor that plays a role in the regulation of carnobacteriocin B2. Transcription analysis indicated that the operons cbnXY, cbnB2-cbiB2, and cbnBM1-cbiBM1 (with the latter encoding carnobacteriocin BM1 and its immunity protein on the chromosome) and two small transcripts containing cbnS are transcribed only in induced cultures. These transcripts are coregulated and subject to inducer-mediated transcriptional control. Similar regulation of the cbn operons is mirrored by the similarity in the nucleotide sequence of their promoter regions, all of which contain two imperfect direct repeats resembling those in Agr-like regulated promoters upstream of the transcription start sites.

A model assay to demonstrate how intrinsic factors affect diffusion of bacteriocins

A rapid and simple method to elucidate how intrinsic factors in a given food product affect bacteriocin diffusion and efficacy is described. The basic idea of this assay is to help predict which bacteriocin or other inhibitory substance to select for a given product, where increased security towards specific microorganisms is wanted. In an agar plate model system the effect of five factors (number of indicator cells, pH and concentration of NaCl, agar and soy oil) on the diffusion of the bacteriocins sakacin A, sakacin P, pediocin PA-1, piscicolin 61 and nisin was studied. An experimental design permitting simultaneous evaluation of the effect of all factors was used. The results indicated that each bacteriocin has a characteristic intrinsic factor effect profile. However, pH and load of indicator cells affect all the bacteriocins.

Cloning and characterization of the haemocin immunity gene of Haemophilus influenzae

The bacteriocin haemocin is produced by most type b strains of Haemophilus influenzae, including strains of diverse genetic lineage, and is toxic to virtually all nontypeable H. influenzae strains. An H. influenzae transformant bearing a plasmid with a 1.5-kbp chromosomal fragment capable of conferring haemocin immunity on a haemocin-susceptible H. influenzae mutant was selected by using partially purified haemocin. Deletional and site-directed mutagenesis localized the haemocin immunity gene to the 3' open reading frame (ORF) within this chromosomal fragment. Subcloning of this ORF demonstrated that it was sufficient to confer haemocin immunity on wild-type haemocin-susceptible H. influenzae strains as well as haemocin-susceptible strains of Escherichia coli. This ORF, designated hmcl, encodes a 105-amino-acid protein with an estimated molecular mass of 12.6 kDa. Primer extension analysis revealed a putative transcriptional start site 34 bp upstream of the start codon, and the presence of a promoter immediately upstream of hmcI was confirmed by cloning the gene into a promoterless chloramphenicol acetyltransferase vector. To characterize the hmcI gene product, a His-HmcI fusion protein was constructed.

Effect of amino acid substitutions on the activity of carnobacteriocin B2. Overproduction of the antimicrobial peptide, its engineered variants, and its precursor in Escherichia coli

Carnobacteriocin B2, a 48-amino acid antimicrobial peptide containing a YGNGV motif that is produced by the lactic acid bacterium Carnobacterium piscicola LV17B, was overexpressed as fusion with maltose-binding protein in Escherichia coli. This fusion protein was cleaved with Factor Xa to allow isolation of the mature bacteriocin that was identical in all respects to that obtained from C. piscicola. Similar methodology permitted production of the precursor precarnobacteriocin B2 (CbnB2P), which has an 18-amino acid leader, as well as six mutants of the mature peptide: CbnF3 (Tyr3 --> Phe), CbnS33 (Phe33 --> Ser), CbnI34 (Val34 --> Ile), CbnI37 (Val37 --> Ile), CbnG46 (Arg46 --> Gly), and Cbn28 (truncated frameshift mutation: (carnobacteriocin B2 1-28) + ELTHL). Examination of these compounds for antimicrobial activity showed that although CbnI34, CbnI37, and CbnG46 were fully active, CbnB2P, CbnF3, CbnS33, Cbn28, and all of the fusion proteins had greatly reduced or no antimicrobial activity. Expression of the immunity protein that protects against the action of the parent carnobacteriocin B2 in a previously sensitive organism also protects against the active mutants. Because carnobacteriocin B2 also acts as an inducer of bacteriocin production in C. piscicola, the ability of the precursor CbnB2P and the mutants to exert this effect was examined. All were able to induce Bac- cultures and reestablish the Bac+ phenotype except for the truncated Cbn28. The results demonstrate that very minor changes in the peptide sequence may drastically alter antimicrobial activity but that the induction of bacteriocin production is much more tolerant of structural modification, especially at the N terminus.

Functional analysis of the gene encoding immunity to lactacin F, lafI, and its use as a Lactobacillus-specific, food-grade genetic marker

Lactacin F is a two-component class II bacteriocin produced by Lactobacillus johnsonii VPI 11088. The laf operon is composed of the bacteriocin structural genes, lafA and lafX, and a third open reading frame, ORFZ. Two strategies were employed to study the function of ORFZ. This gene was disrupted in the chromosome of NCK64, a lafA729 lafX ORFZ derivative of VPI 11088. A disruption cassette consisting of ORFZ interrupted with a cat gene was cloned into pSA3 and introduced into NCK64. Manipulation of growth temperatures and antibiotic selection resulted in homologous recombination which disrupted the chromosomal copy of ORFZ with the cat gene. This ORFZ mutation resulted in loss of immunity to lactacin F but had little effect on production of LafX, which is not bactericidal without LafA. Expression of ORFZ in this ORFZ- background rescued the immune phenotype. Expression of ORFZ in a bacteriocin-sensitive derivative of VPI 11088 also reestablished immunity. These data indicate that ORFZ, renamed lafI, encodes the immunity factor for the lactacin F system. The sensitivity of various Lactobacillus strains to lactacin F was further evaluated. Lactacin F inhibited 11 strains including several members of the A1, A2, A3, A4, B1, and B2 L. acidophilus homology groups. Expression of lafI in bacteriocin-sensitive strains L. acidophilus ATCC 4356, L. acidophilus NCFM/N2, L. fermentum NCDO1750, L. gasseri ATCC 33323, and L. johnsonii ATCC 33200 provided immunity to lactacin F. Furthermore, it was shown that lactacin F production by VPI 11088 could be used to select for L. fermentum NCDO1750 transformants containing the recombinant plasmid encoding LafI. The data demonstrate that lafI is functional in heterologous hosts, suggesting that it may be a suitable food-grade genetic marker for use in lactobacillus species.

Expression of the antimicrobial peptide carnobacteriocin B2 by a signal peptide-dependent general secretory pathway

Carnobacteriocin B2 is a well-characterized class II bacteriocin produced by a 61-kb plasmid from Carnobacterium piscicola LV17. Export of this bacteriocin is dependent on specific ABC (ATP-binding cassette) secretion proteins. Divergicin A is a strongly hydrophobic narrow-spectrum bacteriocin produced by a 3.4-kb plasmid from Carnobacterium divergens LV13. Predivergicin A contains a signal peptide and utilizes the general secretary pathway for export (R. W. Worobo, M. J. van Belkum, M. Sailer, K. L. Roy, J. C. Vederas, and M. E. Stiles, J. Bacteriol. 177:3143-3149, 1995). Fusion of the carnobacteriocin B2 structural gene (devoid of its natural leader peptide) behind the signal peptide of divergicin A in the expression vector pMG36e permitted production and export of active carnobacteriocin B2 in the absence of the specific secretion genes. N-terminal sequencing of purified carnobacteriocin B2 established that correct processing of the prebacteriocin occurred beyond the Ala-Ser-Ala cleavage site of the signal peptide. Carnobacteriocin B2 was produced by the wild-type strain of C. divergens, LV13, and in C. piscicola LV17C, the nonbacteriocinogenic, plasmidless variant of the original carnobacteriocin B2 producer strain. The corresponding immunity gene was included immediately downstream of the structural gene. Both of the host strains are sensitive to the bacteriocin, and both acquired immunity when they were transformed with the construct. C. divergens LV13 containing the divergicin A signal peptide-carnobacteriocin B2 fusion construct produces both divergicin A and carnobacteriocin B2 and demonstrates the first example of multiple-bacteriocin expression via the general secretory pathway. The small amount of genetic material required for independent bacteriocin expression has implications for the development of a food-grade multiple-bacteriocin expression vector for use in lactic acid bacteria.

Characterisation of the pvdE gene which is required for pyoverdine synthesis in Pseudomonas aeruginosa

Pseudomonas aeruginosa (Pa) strain PAO synthesises a siderophore, pyoverdine (Pvd), when grown under conditions of iron starvation. Pvd consists of a dihydroxyquinoline group attached to an 8-amino-acid-residue peptide. DNA spanning at least 78 kb of the chromosome is required for Pvd synthesis, but to date only three genes involved in this process have been characterised. We report the characterisation of a fourth Pa gene, pvdE, which we show to be required for Pvd synthesis. The deduced amino acid sequence of PvdE indicates that the protein is a member of the ATP-binding-cassette (ABC) family of membrane transporter proteins, and this is the first example of the involvement of an ABC-type protein in siderophore synthesis.

Biopreservation by lactic acid bacteria

Biopreservation refers to extended storage life and enhanced safety of foods using the natural microflora and (or) their antibacterial products. Lactic acid bacteria have a major potential for use in biopreservation because they are safe to consume and during storage they naturally dominate the microflora of many foods. In milk, brined vegetables, many cereal products and meats with added carbohydrate, the growth of lactic acid bacteria produces a new food product. In raw meats and fish that are chill stored under vacuum or in an environment with elevated carbon dioxide concentration, the lactic acid bacteria become the dominant population and preserve the meat with a "hidden' fermentation. The same applies to processed meats provided that the lactic acid bacteria survive the heat treatment or they are inoculated onto the product after heat treatment. This paper reviews the current status and potential for controlled biopreservation of foods.

Biosynthesis of bacteriocins in lactic acid bacteria

A large number of new bacteriocins in lactic acid bacteria (LAB) has been characterized in recent years. Most of the new bacteriocins belong to the class II bacteriocins which are small (30-100 amino acids) heat- stable and commonly not post-translationally modified. While most bacteriocin producers synthesize only one bacteriocin, it has been shown that several LAB produce multiple bacteriocins (2-3 bacteriocins). Based on common features, some of the class II bacteriocins can be divided into separate groups such as the pediocin-like and strong anti-listeria bacteriocins, the two-peptide bacteriocins, and bacteriocins with a sec-dependent signal sequence. With the exception of the very few bacteriocins containing a sec-dependent signal sequence, class II bacteriocins are synthesized in a preform containing an N-terminal double-glycine leader. The double-glycine leader-containing bacteriocins are processed concomitant with externalization by a dedicated ABC-transporter which has been shown to possess an N-terminal proteolytic domain. The production of some class II bacteriocins (plantaricins of Lactobacillus plantarum C11 and sakacin P of Lactobacillus sake) have been shown to be transcriptionally regulated through a signal transduction system which consists of three components: an induction factor (IF), histidine protein kinase (HK) and a response regulator (RR). An identical regulatory system is probably regulating the transcription of the sakacin A and carnobacteriocin B2 operons. The regulation of bacteriocin production is unique, since the IF is a bacteriocin-like peptide with a double-glycine leader processed and externalized most probably by the dedicated ABC-transporter associated with the bacteriocin. However, IF is not constituting the bacteriocin activity of the bacterium, IF is only activating the transcription of the regulated class II bacteriocin gene(s). The present review discusses recent findings concerning biosynthesis, genetics, and regulation of class II bacteriocins.

Characterization of the locus responsible for the bacteriocin production in Lactobacillus plantarum C11

Lactobacillus plantarum C11 secretes a small cationic peptide, plantaricin A, that serves as induction signal for bacteriocin production as well as transcription of plnABCD. The plnABCD operon encodes the plantaricin A precursor (PlnA) itself and determinants (PlnBCD) for a signal transducing pathway. By Northern (RNA) and sequencing analyses, four new plantaricin A-induced operons were identified. All were highly activated in concert with plnABCD upon bacteriocin induction. Two of these operons (termed plnEFI and plnJKLR) each encompass a gene pair (plnEF and plnJK, respectively) encoding two small cationic bacteriocin-like peptides with double-glycine-type leaders. The open reading frames (ORFs) encoding the bacteriocin-like peptides are followed by ORFs (plnI and -L, respectively) encoding cationic hydrophobic proteins resembling bacteriocin immunity proteins. On the third operon (termed plnMNOP), a similar bacteriocin-like ORF (plnN) and a putative immunity ORF (either plnM or -P) were identified as well. These findings suggest that two bacteriocins of two-peptide type (mature PlnEF and PlnJK) and a bacteriocin of one-peptide type (mature PlnN) could be responsible for the observed bacteriocin activity. The last operon (termed plnGHSTUV) contains two ORFs (plnGH) apparently encoding an ABC transporter and its accessory protein, respectively, known to be involved in processing and export of peptides with precursor double-glycine-type leaders. Promoter structure was established. A conserved regulatory-like box encompassing two direct repeats was identified in the promoter regions of all five plantaricin A-induced operons. These repeats may serve as regulatory elements for gene expression.

Cloning and genetic organization of the bacteriocin 31 determinant encoded on the Enterococcus faecalis pheromone-responsive conjugative plasmid pYI17

The conjugative plasmid pYI17 (57.5 kb) isolated from Enterococcus faecalis YI717 confers a pheromone response on the host and encodes the bacteriocin 31 gene. Bacteriocin 31 is active against E. hirae 9790, E. faecium, and Listeria monocytogenes. pYI17 was mapped physically by restriction enzyme analysis and the relational clone method. Deletion mutant and sequence analyses of the EcoRI fragment B cloned from pYl17 revealed that a 1.0-kb fragment contained the bacteriocin gene (bacA) and an immunity gene (bacB). This fragment induced bacteriocin activity in E. faecalis OG1X and E. hirae 9790. The bacA gene is located on the pYI17 physical map between 3.37 and 3.57 kb, and bacB is located between 3.59 kb and 3.87 kb, bacA encodes 67 amino acids, and bacB encodes 94 amino acids. The deduced amino acid sequence of the bacA protein contained a series of hydrophobic residues typical of a signal sequence at its amino terminus. The predicted mature bacA protein (43 amino acids) showed sequence homology with the membrane-active class II bacteriocins of lactic acid bacteria. Analysis of Tn5 insertion mutants and the resulting transcripts indicated that these genes are transcribed as an operon composed of bacA, bacB, and an open reading frame located downstream of bacB designated ORF3.

Analysis of the sakacin P gene cluster from Lactobacillus sake Lb674 and its expression in sakacin-negative Lb. sake strains

Sakacin P is a small, heat-stable, ribosomally synthesized peptide produced by certain strains of Lactobacillus sake. It inhibits the growth of several Gram-positive bacteria, including Listeria monocytogenes. A 7.6 kb chromosomal DNA fragment from Lb. sake Lb674 encompassing all genes responsible for sakacin P production and immunity was sequenced and introduced into Lb. sake strains Lb790 and Lb706X which are bacteriocin-negative and sensitive to sakacin P. The transformants produced sakacin P in comparable amounts to the parental strain, Lb674. The sakacin P gene cluster comprised six consecutive genes: sppK, sppR, sppA, spiA, sppT and sppE, all transcribed in the same direction. The deduced proteins SppK and SppR resembled the histidine kinase and response regulator proteins of bacterial two-component signal transducing systems of the AgrB/AgrA-type. The genes sppA and spiA encoded the sakacin P preprotein and the putative immunity protein, respectively. The predicted proteins SppT and SppE showed strong similarities to the proposed transport proteins of several other bacteriocins and to proteins implicated in the signal-sequence-independent export of Escherichia coli haemolysin A. Deletion and frameshift mutation analyses showed that sppK, sppT and sppE were essential for sakacin P production in Lb706X. The putative SpiA peptide was shown to be involved in immunity to sakacin P. Analogues of sppR and spiA were found on the chromosomes of Lb. sake Lb706X and Lb790, indicating the presence of an incomplete spp gene cluster in these strains.

Primary metabolite kinetics of bacteriocin biosynthesis by Lactobacillus amylovorus and evidence for stimulation of bacteriocin production under unfavourable growth conditions

To optimize bacteriocin production processes, the relationships between growth, bacteriocin production and factors affecting the occurrence and intensity of the activity peak during the growth cycle must be understood. Amylovorin L471, a bacteriocin produced by Lactobacillus amylovorus DCE 471, displays primary metabolite kinetics with a peak activity during the midexponential phase. Because of this growth association, only conditions favouring a drastic increase in biomass improve the volumetric bacteriocin titre. Specific bacteriocin production is enhanced under unfavourable growth conditions such as low temperatures (30°), and the presence of potentially toxic compounds such as ethanol (1.0%, v/v) and oxygen (80%, v/v, air saturation). Whereas volumetric biomass formation and growth-associated bacteriocin production are dependent on the amount of glucose and nitrogen supplied, slow growth rates stimulate specific bacteriocin production. Bacteriocin inactivation can be ascribed to protein aggregation and adsorption phenomena. It may be overcome by switching the pH to 2.0 during the fermentation run after having reached the peak activity. Thus, manipulation of the cell environment can stimulate bacteriocin production. The latter can be induced by unfavourable growth conditions, so-called stress factors. The specific growth rate seems to play an important role in the control of bacteriocin production.

Induction of bacteriocin production in Lactobacillus sake by a secreted peptide

Lactobacillus sake LTH673 is known to produce a bacteriocin called sakacin P. Production of and immunity to sakacin P were found to depend on the presence of a protease-sensitive component that is produced by L. sake LTH673 itself. This component (called inducing factor [IF]) was purified from culture supernatants and shown to be a basic, nonbacteriocin peptide consisting of 19 amino acids, which in principle is capable of forming a highly amphiphilic helical structure. Circular dichroism studies showed that IF indeed could adopt a helical structure, but only in membrane-mimicking environments. Both purified IF and chemically synthesized IF induced expression of the structural gene for sakacin P and concomitant secretion of the gene product. In addition, IF induced its own production and immunity to sakacin P and related bacteriocins. These results indicate that bacteriocin production by L. sake LTH673 is controlled by an autoinduction pathway in which IF may function as a cell density signal.

Divergicin 750, a novel bacteriocin produced by Carnobacterium divergens 750

Divergicin 750, a bacteriocin produced by Carnobacterium divergens 750, preferentially inhibited the growth of strains of Carnobacterium and Enterococcus. Selected strains of Listeria monocytogenes and Clostridium perfringens were also inhibited. The bacteriocin was purified to homogeneity by ammonium sulfate precipitation and sequential S-Sepharose, hydrophobic interaction and reversed phase chromatography. The complete amino acid sequence was determined by Edman degradation. The peptide consisted of 34 amino acid residues. The calculated M(r) from the peptide sequence, 3447.7, agreed well with that obtained by mass spectrometry. Divergicin 750 did not show any sequence similarities to other known bacteriocins. The plasmid-located structural gene encoding divergicin 750 (dvn750) was cloned and sequenced. The gene encoded a primary translation product of 63 amino acids with a deduced M(r) = 6789.4 which is cleaved between amino acid residues 29 and 30 to yield the mature bacteriocin.