Plasmid transfer in Pediococcus spp.: intergeneric and intrageneric transfer of pIP501

Effect of TraN key residues involved in DNA binding on pIP501 transfer rates in Enterococcus faecalis

Conjugation is a major mechanism that facilitates the exchange of antibiotic resistance genes among bacteria. The broad-host-range Inc18 plasmid pIP501 harbors 15 genes that encode for a type IV secretion system (T4SS). It is a membrane-spanning multiprotein complex formed between conjugating donor and recipient cells. The penultimate gene of the pIP501 operon encodes for the cytosolic monomeric protein TraN. This acts as a transcriptional regulator by binding upstream of the operon promotor, partially overlapping with the origin of transfer. Additionally, TraN regulates traN and traO expression by binding upstream of the PtraNO promoter. This study investigates the impact of nine TraN amino acids involved in binding to pIP501 DNA through site-directed mutagenesis by exchanging one to three residues by alanine. For three traN variants, complementation of the pIP501∆traN knockout resulted in an increase of the transfer rate by more than 1.5 orders of magnitude compared to complementation of the mutant with native traN. Microscale thermophoresis (MST) was used to assess the binding affinities of three TraN double-substituted variants and one triple-substituted variant to its cognate pIP501 double-stranded DNA. The MST data strongly correlated with the transfer rates obtained by biparental mating assays in Enterococcus faecalis. The TraN variants TraN_R23A-N24A-Q28A, TraN_H82A-R86A, and TraN_G100A-K101A not only exhibited significantly lower DNA binding affinities but also, upon complementation of the pIP501∆traN knockout, resulted in the highest pIP501 transfer rates. This confirms the important role of the TraN residues R23, N24, Q28, H82, R86, G100, and K101 in downregulating pIP501 transfer. Although TraN is not part of the mating pair formation complex, TraE, TraF, TraH, TraJ, TraK, and TraM were coeluted with TraN in a pull-down. Moreover, TraN homologs are present not only in Inc18 plasmids but also in RepA_N and Rep_3 family plasmids, which are frequently found in enterococci, streptococci, and staphylococci. This points to a widespread role of this repressor in conjugative plasmid transfer among Firmicutes.

pSK41-like plasmid is necessary for Inc18-like vanA plasmid transfer from Enterococcus faecalis to Staphylococcus aureus in vitro

Vancomycin-resistant Staphylococcus aureus (VRSA) is thought to result from the in vivo conjugative transfer of a vanA plasmid from an Enterococcus sp. to S. aureus. We studied bacterial isolates from VRSA cases that occurred in the United States to identify microbiological factors which may contribute to this plasmid transfer. First, vancomycin-susceptible, methicillin-resistant S. aureus (MRSA) isolates from five VRSA cases were tested for their ability to accept foreign DNA by conjugation in mating experiments with Enterococcus faecalis JH2-2 containing pAM378, a pheromone-response conjugative plasmid. All of the MRSA isolates accepted the plasmid DNA with similar transfer efficiencies (∼10(-7)/donor CFU) except for one isolate, MRSA8, for which conjugation was not successful. The MRSA isolates were also tested as recipients in mating experiments between an E. faecalis isolate with an Inc18-like vanA plasmid that was isolated from a VRSA case patient. Conjugative transfer was successful for 3/5 MRSA isolates. Successful MRSA recipients carried a pSK41-like plasmid, a staphylococcal conjugative plasmid, whereas the two unsuccessful MRSA recipients did not carry pSK41. The transfer of a pSK41-like plasmid from a successful MRSA recipient to the two unsuccessful recipients resulted in conjugal transfer of the Inc18-like vanA plasmid from E. faecalis at a frequency of 10(-7)/recipient CFU. In addition, conjugal transfer could be achieved for pSK41-negative MRSA in the presence of a cell-free culture filtrate from S. aureus carrying a pSK41-like plasmid at a frequency of 10(-8)/recipient CFU. These results indicated that a pSK41-like plasmid can facilitate the transfer of an Inc18-like vanA plasmid from E. faecalis to S. aureus, possibly via an extracellular factor produced by pSK41-carrying isolates.

Utilization of different types of dietary fibres by potential probiotics

A better understanding of the functionality of probiotics and dietary fibres with prebiotic activity is required for the development of improved synbiotic preparations. In this study, utilization of β(2-1) fructans, galactooligosaccharides, and plant polysaccharides as prebiotics by lactobacilli, bifidobacteria, and pediococci was investigated. Our results demonstrate that prebiotics with linear chains consisting of galactose units are better utilized by probiotics than are those consisting of glucose and fructose units, and the ability of probiotic bacteria to utilize prebiotics is strain-specific. In addition, rye fructooligosaccharides represent a prebiotic fibre that supports the growth of a wide range of probiotic cultures and as such has a potential to improve the successfulness of probiotic treatments. This study also demonstrates dietary fibre utilization by pediococci and provides data supporting the possible use of pediococci as a probiotic in synbiotic combinations.

Dissemination of an Enterococcus Inc18-Like vanA plasmid associated with vancomycin-resistant Staphylococcus aureus

Of the 9 vancomycin-resistant Staphylococcus aureus (VRSA) cases reported to date in the literature, 7 occurred in Michigan. In 5 of the 7 Michigan VRSA cases, an Inc18-like vanA plasmid was identified in the VRSA isolate and/or an associated vancomycin-resistant Enterococcus (VRE) isolate from the same patient. This plasmid may play a critical role in the emergence of VRSA. We studied the geographical distribution of the plasmid by testing 1,641 VRE isolates from three separate collections by PCR for plasmid-specific genes traA, repR, and vanA. Isolates from one collection (phase 2) were recovered from surveillance cultures collected in 17 hospitals in 13 states. All VRE isolates from 2 Michigan institutions (n = 386) and between 60 and 70 VRE isolates (n = 883) from the other hospitals were tested. Fifteen VRE isolates (3.9%) from Michigan were positive for an Inc18-like vanA plasmid (9 E. faecalis [12.5%], 3 E. faecium [1.0%], 2 E. avium, and 1 E. raffinosus). Six VRE isolates (0.6%) from outside Michigan were positive (3 E. faecalis [2.7%] and 3 E. faecium [0.4%]). Of all E. faecalis isolates tested, 6.0% were positive for the plasmid, compared to 0.6% for E. faecium and 3.0% for other spp. Fourteen of the 15 plasmid-positive isolates from Michigan had the same Tn1546 insertion site location as the VRSA-associated Inc18-like plasmid, whereas 5 of 6 plasmid-positive isolates from outside Michigan differed in this characteristic. Most plasmid-positive E. faecalis isolates demonstrated diverse patterns by PFGE, with the exception of three pairs with indistinguishable patterns, suggesting that the plasmid is mobile in nature. Although VRE isolates with the VRSA-associated Inc18-like vanA plasmid were more common in Michigan, they remain rare. Periodic surveillance of VRE isolates for the plasmid may be useful in predicting the occurrence of VRSA.

Cloning Vectors Based on Cryptic Plasmids Isolated from Lactic Acid Bacteria:Their Characteristics and Potential Applications in Biotechnology

Lactic acid bacteria (LAB) are Gram positive bacteria, widely distributed in nature, and industrially important as they are used in a variety of industrial food fermentations. The use of genetic engineering techniques is an effective means of enhancing the industrial applicability of LAB. However, when using genetic engineering technology, safety becomes an essential factor for the application of improved LAB to the food industry. Cloning and expression systems should be derived preferably from LAB cryptic plasmids that generally encode genes for which functions can be proposed, but no phenotypes can be observed. However, some plasmid-encoded functions have been discovered in cryptic plasmids originating from Lactobacillus, Streptococcus thermophilus, and Pediococcus spp. and can be used as selective marker systems in vector construction. This article presents information concerning LAB cryptic plasmids, and their structures, functions, and applications. A total of 134 cryptic plasmids collated are discussed.

Evidence for Plasmid Linkage of Raffinose Utilization and Associated alpha-Galactosidase and Sucrose Hydrolase Activity in Pediococcus pentosaceus

The ability to ferment the trisaccharide raffinose was linked with the presence of plasmid DNA in three strains of Pediococcus pentosaceus. Parental strains showed associated inducible alpha-galactosidase and sucrose hydrolase activities when grown in alpha-galactosides and sucrose, respectively. Derivative strains of PPE1.0, PPE2.0, and PPE5.0, which had lost 30-, 28-, and 23-megadalton plasmids, respectively, had no alpha-galactosidase or sucrose hydrolase activity.

Conjugative Plasmid in Corynebacterium flaccumfaciens subsp. oortii That Confers Resistance to Arsenite, Arsenate, and Antimony(III)

Gene transfer systems for phytopathogenic corynebacteria have not been reported previously. In this paper we describe a conjugative 46-megadalton plasmid (pDG101) found in Corynebacterium flaccumfaciens subsp. oortii CO101 that mediates resistance to arsenite, arsenate, and antimony(III). Transfer of the plasmid from CO101 to four other strains from the C. flaccumfaciens group occurred between cells immobilized on nitrocellulose filters or on agar surfaces. Transconjugant strains expressed the same levels of metal resistance as the donor strain and were able to act as donor strains in subsequent matings. The physical presence of the plasmid was detected by agarose gel electrophoresis. Arsenite-sensitive derivatives of the donor and transconjugant strains were obtained after heat treatment; these were cured of pDG101.

pEOC01: A plasmid from Pediococcus acidilactici which encodes an identical streptomycin resistance (aadE) gene to that found in Campylobacter jejuni

The complete nucleotide sequence of pEOC01, a plasmid (11,661 bp) from Pediococcus acidilactici NCIMB 6990 encoding resistance to clindamycin, erythromycin, and streptomycin was determined. The plasmid, which also replicates in Lactococcus and Lactobacillus species contains 16 putative open reading frames (ORFs), including regions annotated to encode replication, plasmid maintenance and multidrug resistance functions. Based on an analysis the plasmid replicates via a theta replicating mechanism closely related to those of many larger Streptococcus and Enterococcus plasmids. Interestingly, genes homologous to a toxin/antitoxin plasmid maintenance system are present and are highly similar to the omega-epsilon-zeta operon of Streptococcus plasmids. The plasmid contains two putative antibiotic resistance homologs, an ermB gene encoding erythromycin and clindamycin resistance, and a streptomycin resistance gene, aadE. Of particular note is the aadE gene which holds 100% identity to an aadE gene found in Campylobacter jejuni plasmid but which probably originated from a Gram-positive source. This observation is significant in that it provides evidence for recent horizontal transfer of streptomycin resistance from a lactic acid bacterium to a Gram-negative intestinal pathogen and as such infers a role for such plasmids for dissemination of antibiotic resistance genes possibly in the human gut.

Worst-case scenarios for horizontal gene transfer from Lactococcus lactis carrying heterologous genes to Enterococcus faecalis in the digestive tract of gnotobiotic mice

Since genetically modified (GM) lactic acid bacteria (LAB) might be released in open environments for future nutritional and medical applications, the purpose of this study was to determine an upper limit for the horizontal gene transfer (HGT) in the digestive tract (DT) from Lactococcus lactis carrying heterologous genes (lux genes encoding a bacterial luciferase) to Enterococcus faecalis. Two enterococcal wide host-range conjugative model systems were used: (i) a system composed of a mobilizable plasmid containing the heterologous lux genes and a native conjugative helper plasmid; and (ii) a Tn916-lux transposon. Both systems were tested under the most transfer-prone conditions, i.e. germfree mice mono-associated with the recipient E. faecalis. No transfer was observed with the transposon system. Transfers of the mobilizable plasmid carrying heterologous genes were below 10(2) transconjugants per g of faeces for a single donor dose and reached between 10(3) and 10(4) transconjugants per g of faeces when continuous inoculation of the donor strain was used. Once established in mice, transconjugants persisted at low levels in the mouse DT.

Intergeneric transfer of the Enterococcus faecalis plasmid pIP501 to Escherichia coli and Streptomyces lividans and sequence analysis of its tra region

The nucleotide sequence of the transfer (tra) region of the multiresistance broad-host-range Inc18 plasmid pIP501 was completed. The 8629-bp DNA sequence encodes 10 open reading frames (orf), 9 of them are possibly involved in pIP501 conjugative transfer. The putative pIP501 tra gene products show highest similarity to the respective ORFs of the conjugative Enterococcus faecalis plasmids pRE25 and pAMbeta1, and the Streptococcus pyogenes plasmid pSM19035, respectively. ORF7 and ORF10 encode putative homologues of type IV secretion systems involved in transport of effector molecules from pathogens to host cells and in conjugative plasmid transfer in Gram-negative (G-) bacteria. pIP501 mobilized non-selftransmissible plasmids such as pMV158 between different E. faecalis strains and from E. faecalis to Bacillus subtilis. Evidence for the very broad-host-range of pIP501 was obtained by intergeneric conjugative transfer of pIP501 to a multicellular Gram-positive (G+) bacterium, Streptomyces lividans, and to G- Escherichia coli. We proved for the first time pIP501 replication, expression of its antibiotic resistance genes as well as functionality of the pIP501 tra genes in S. lividans and E. coli.

Development of a thermally regulated broad-spectrum promoter system for use in pathogenic gram-positive species

Selectively regulating gene expression is an essential molecular tool that is lacking for many pathogenic gram-positive bacteria. In this report, we describe the evaluation of a series of promoters regulated by the bacteriophage P1 temperature-sensitive C1 repressor in Enterococcus faecium, Enterococcus faecalis, and Staphylococcus aureus. Using the lacZ gene to monitor gene expression, we examined the strength, basal expression, and induced expression of synthetic promoters carrying C1 operator sites. The promoters exhibited extremely low basal expression and, under inducing conditions, gave high levels of expression (100- to 1,000-fold induction). We demonstrate that the promoter system could be modulated by temperature and showed rapid induction and that the mechanism of regulation occurred at the level of transcription. Controlled expression with the same constructs was also demonstrated in the gram-negative bacterium Escherichia coli. However, low basal expression and the ability to achieve derepression were dependent on both the number of mismatches in the C1 operator sites and the promoter driving c1 expression. Since the promoters were designed to contain conserved promoter elements from gram-positive species and were constructed in a broad-host-range plasmid, this system will provide a new opportunity for controlled gene expression in a variety of gram-positive bacteria.

Discovering lactic acid bacteria by genomics

This review summarizes a collection of lactic acid bacteria that are now undergoing genomic sequencing and analysis. Summaries are presented on twenty different species, with each overview discussing the organisms fundamental and practical significance, environmental habitat, and its role in fermentation, bioprocessing, or probiotics. For those projects where genome sequence data were available by March 2002, summaries include a listing of key statistics and interesting genomic features. These efforts will revolutionize our molecular view of Gram-positive bacteria, as up to 15 genomes from the low GC content lactic acid bacteria are expected to be available in the public domain by the end of 2003. Our collective view of the lactic acid bacteria will be fundamentally changed as we rediscover the relationships and capabilities of these organisms through genomics.

Analysis of the genetic determinant for production of the pediocin P of Pediococcus pentosaceus Pep1

Pediococcus pentosaceus Pep1 is a vacuum-packaged Turkish sausage isolate which produces a potentially novel bacteriocin of the pediocin (anti-Listeria) family of peptides designated as pediocin P. Curing experiments and plasmid profile analysis indicated that both bacteriocin immunity and production determinants were linked and encoded by 9.0 MDa plasmid, pHD1.0. Attempts to transform purified plasmid pHD1.0 into recipient Escherichia coli JM109 cells by electroporation were successful but none of the E. coli JM109 cells were able to express and/or release pediocin P. However, P. pentosaceus PC, a plasmid-cured variant of P. pentosaceus Pep1 was successfully transformed with pHD1.0 by electroporation and Bac-Bacs P. pentosaceus PC cells restarted to express and/or release pediocin P again as indicated by the presence of zone of growth inhibition of L. plantarum NCDO 955 around colonies.

Molecular characterization of the replicon of the Pediococcus pentosaceus 43200 pediocin A plasmid pMD136

The pediocin A-encoding plasmid of Pediococcus pentosaceus 43200, pMD136, was characterized by restriction enzyme analysis. Analysis of its replicon was facilitated by the construction of a probe vector consisting of the Escherichia coli plasmid pSP72 and the cat gene from Staphylococcus aureus plasmid pC194. The replication region of pMD136 was localized on a 1.6-kb EcoRI/BglII fragment. Sequencing analysis revealed a non-coding region, repA, spanning the first 440 bp, followed by an open reading frame, repB, encoding a putative protein of 390 amino acids. The non-coding region contained two sets of 6-bp and two sets of 22-bp direct repeats and two sets of inverted repeats upstream of the open reading frame. Strong homology of the isolated replicon was found to theta-type replicons of Lactococcus lactis plasmids. Segregational stability assay suggested at least two regions as potentially involved in the stabilization of pMD136. The plasmid's strong homology to other theta-type replicons and its relatively high stability suggest that pMD136 belongs to the widespread family of theta-replication plasmids.

Phenotypic and genetic characterization of the bacteriophage abortive infection mechanism AbiK from Lactococcus lactis

The natural plasmid pSRQ800 isolated from Lactococcus lactis subsp. lactis W1 conferred strong phage resistance against small isometric phages of the 936 and P335 species when introduced into phage-sensitive L. lactis strains. It had very limited effect on prolate phages of the c2 species. The phage resistance mechanism encoded on pSRQ800 is a temperature-sensitive abortive infection system (Abi). Plasmid pSRQ800 was mapped, and the Abi genetic determinant was localized on a 4.5-kb EcoRI fragment. Cloning and sequencing of the 4.5-kb fragment allowed the identification of two large open reading frames. Deletion mutants showed that only orf1 was needed to produce the Abi phenotype. orf1 (renamed abiK) coded for a predicted protein of 599 amino acids (AbiK) with an estimated molecular size of 71.4 kDa and a pI of 7.98. DNA and protein sequence alignment programs found no significant homology with databases. However, a database query based on amino acid composition suggested that AbiK might be in the same protein family as AbiA. No phage DNA replication nor phage structural protein production was detected in infected AbiK+ L. lactis cells. This system is believed to act at or prior to phage DNA replication. WHen cloned into a high-copy vector, AbiK efficiency increased 100-fold. AbiK provides another powerful tool that can be useful in controlling phages during lactococcal fermentations.

Production of pediocin AcH by Lactobacillus plantarum WHE 92 isolated from cheese

Among 1,962 bacterial isolates from a smear-surface soft cheese (Munster cheese) screened for activity against Listeria monocytogenes, six produced antilisterial compounds other than organic acids. The bacterial strain WHE 92, which displayed the strongest antilisterial effect, was identified at the DNA level as Lactobacillus plantarum. The proteinaceous nature, narrow inhibitory spectrum, and bactericidal mode of action of the antilisterial compound produced by this bacterium suggested that it was a bacteriocin. Purification to homogeneity and sequencing of this bacteriocin showed that it was a 4.6-kDa, 44-amino-acid peptide, the primary structure of which was identical to that of pediocin AcH produced by different Pediococcus acidilactici strains. We report the first case of the same bacteriocin appearing naturally with bacteria of different genera. Whereas the production of pediocin AcH from P. acidilactici H was considerably reduced when the final pH of the medium exceeded 5.0, no reduction in the production of pediocin AcH from L. plantarum WHE 92 was observed when the pH of the medium was up to 6.0. This fact is important from an industrial angle. As the pH of dairy products is often higher than 5.0, L. plantarum WHE 92, which develops particularly well in cheeses, could constitute an effective means of biological combat against L. monocytogenes in this type of foodstuff.

Cloning and sequencing of LlaDCHI [corrected] restriction/modification genes from Lactococcus lactis and relatedness of this system to the Streptococcus pneumoniae DpnII system

The natural 7.8-kb plasmid pSRQ700 was isolated from Lactococcus lactis subsp. cremoris DCH-4. It encodes a restriction/modification system named LlaDCHI [corrected]. When introduced into a phage-sensitive L. lactis strain, pSRQ700 confers strong phage resistance against the three most common lactococcal phage species, namely, 936, c2, and P335. The LlaDCHI [corrected] endonuclease was purified and found to cleave the palindromic sequence 5'-GATC-3'. It is an isoschizomer of Streptococcus pneumoniae DpnII. The plasmid pSRQ700 was mapped, and the genetic organization of LlaDCHI [corrected] was localized. Cloning and sequencing of the entire LlaDCHI [corrected] system allowed the identification of three open reading frames. The three genes (llaIIA, llaIIB, and llaIIC) overlapped and are under one putative promoter. A putative terminator was found at the end of llaIIC. The genes llaIIA and llaIIB coded for m6A methyltransferases, and llaIIC coded for an endonuclease. The LlaDCHI [corrected] system shares strong genetic similarities with the DpnII system. The deduced amino acid sequence of M.LlaIIA was 75% identical with that of M.DpnII, whereas M.LlaIIB was 88% identical with M.DpnA. However, R.LlalII shared only 31% identity with R.DpnII.

Efficient plasmid mobilization by pIP501 in Lactococcus lactis subsp. lactis

pIP501 is a streptococcal conjugative plasmid which can be transmitted among numerous gram-positive strains. To identify a minimal mobilization (mob) locus of pIP501, DNA fragments of pIP501 were cloned into nonconjugative target plasmids and tested for mobilization by pIP501. We show that nonmobilizable plasmids containing a specific fragment of pIP501 are transmitted at high frequencies between Lactococcus lactis subsp. lactis strains if transfer (tra) functions are provided in trans by a pIP501 derivative. Independent transfer of the mobilized plasmid was observed in up to 44% of transconjugants. A 2.2-kb segment containing mob was sequenced. This DNA segment is characterized by three palindromes (palI, palII, and palIII) and a 202-amino-acid open reading frame (ORFX) of unknown function. The smallest DNA fragment conferring high frequency mobilization was localized to a 1.0-kb region (extending from pIP501 coordinates 3.60 to 4.60 on the 30.2-kb map) which contains palI (delta G = -27 kcal/mol [ca. -110,000 J/mol]). A 26-bp sequence identical to palI is present on pIP501, upstream of the plasmid copy control region. Further homologies with the palI sequence are also found with the related Enterococcus faecalis conjugative plasmid pAM beta 1. The region containing mob maps outside the previously described segment mediating pIP501 conjugation. Our results with recA strains indicate that the mob site is a hot spot for cointegrate formation.

RepR protein expression on plasmid pIP501 is controlled by an antisense RNA-mediated transcription attenuation mechanism

Expression of the rate-limiting initiator protein RepR of plasmid pIP501 is controlled by the antisense RNAIII. Mutational alteration of individual G residues within the single-stranded loops of RNAIII led to an increase in copy number. In contrast to the G-rich single-stranded loops, two smaller AT-rich loops of RNAIII were found to be dispensable for its inhibitory function. Reciprocal mutations in the same loop compensated for each other's effect, and a destabilization of the major stem structure of RNAIII also resulted in an increased copy number. These data were consistent with the idea that the interaction of RNAIII with its target starts with the formation of a kissing complex between the single-stranded loops of both molecules. The repR mRNA leader sequence, which includes the target of RNAIII, is able to assume two alternative structures due to the presence of two inverted repeats the individual sequences of which are mutually complementary. In the presence of the antisense RNAIII, one of these inverted repeats (IR2) is forced to fold into a transcriptional terminator structure that prevents transcription of the repR gene. In the absence of RNAIII, formation of the transcriptional terminator is prevented and expression of the essential repR gene can proceed normally. This antisense RNA-driven transcriptional attenuation mechanism was supported by extensive deletional analysis and direct evidence that IR2 functions as a transcriptional terminator.

Antimicrobial susceptibility of Pediococcus spp. and genetic basis of macrolide resistance in Pediococcus acidilactici HM3020

We determined the MICs of 28 antimicrobial agents against 36 clinical strains of Pediococcus spp. (25 P. acidilactici, 9 P. pentosaceus, and 2 P. urinaeequi strains). Penicillin G, imipenem, gentamicin, netilmicin, erythromycin, clindamycin, rifampin, chloramphenicol, daptomycin, and ramoplanin were the most active. All strains of P. acidilactici were susceptible to novobiocin, whereas all isolates of P. pentosaceus were resistant. Novobiocin could therefore be helpful for differentiation of these two closely related species. P. acidilactici HM3020 was inducibly resistant to macrolide, lincosamide, and streptogramin B-type (MLS) antibiotics. Resistance was due to a determinant homologous to ermAM and carried by a nontransferable 46-kb plasmid, pVM20. This plasmid was structurally distinct from two enterococcal MLS resistance plasmids, pIP819 and pAM beta 1. The 34 strains of P. acidilactici and P. pentosaceus were resistant to tetracycline, and total DNA of these strains did not hybridize to probes specific for tetK, tetL, tetM, and tetO.

Characterization of the minimal origin required for replication of the streptococcal plasmid pIP501 in Bacillus subtilis

By using deletional analysis the origin of replication, oriR, of the streptococcal plasmid pIP501 in Bacillus subtilis has been mapped at a position immediately downstream of the repR gene. Determination of both the right and left border of oriR allowed the definition of a sequence of a maximum of 52 nucleotides which theoretically constitutes the minimal origin of replication. Recently, the start point of leading-strand synthesis of the closely related plasmid pAM beta 1 has been mapped at a position which is located exactly in the middle of this sequence (Bruand et al., 1991). The function of oriR did not depend on its location downstream of the repR gene. Translocation of oriR-containing fragments to other regions of the plasmid proved to be possible. The smallest translocated fragment that still reconstituted autonomous replication was 72bp in size. This fragment was also active in directing the replication of an Escherichia coli plasmid in B. subtilis when the RepR protein was supplied in trans from a repR gene integrated into the host chromosome. The transformation efficiency of plasmids carrying translocated oriR fragments showed a certain dependence on the fragment length and orientation. The DNA sequence of oriR included an inverted repeat, both branches of which appeared to be essential for oriR function. The repeats of oriR shared sequence similarity with a repeat located upstream of promoter pII, which has been suggested to be involved in autoregulation of repR expression.

The amount of RepR protein determines the copy number of plasmid pIP501 in Bacillus subtilis

To prove the hypothesis that the amount of RepR protein is the rate-limiting factor for replication of plasmid pIP501 in Bacillus subtilis, the repR gene was placed under control of the inducible promoter pspac. The plasmid copy number of the pIP501 derivative pRS9 could be deliberately adjusted between approximately 1 and 50 to 100 molecules per cell by varying the concentration of the inducer isopropyl-beta-D-thiogalactopyranoside. Construction of a repR-lacZ fusion proved that the increase in copy number was due to a proportional increase in the amount of RepR protein.

Cloning, expression, and nucleotide sequence of genes involved in production of pediocin PA-1, and bacteriocin from Pediococcus acidilactici PAC1.0

The production of pediocin PA-1, a small heat-stable bacteriocin, is associated with the presence of the 9.4-kbp plasmid pSRQ11 in Pediococcus acidilactici PAC1.0. It was shown by subcloning of pSRQ11 in Escherichia coli cloning vectors that pediocin PA-1 is produced and, most probably, secreted by E. coli cells. Deletion analysis showed that a 5.6-kbp SalI-EcoRI fragment derived from pSRQ11 is required for pediocin PA-1 production. Nucleotide sequence analysis of this 5.6-kbp fragment indicated the presence of four clustered open reading frames (pedA, pedB, pedC, and pedD). The pedA gene encodes a 62-amino-acid precursor of pediocin PA-1, as the predicted amino acid residues 19 to 62 correspond entirely to the amino acid sequence of the purified pediocin PA-1. Introduction of a mutation in pedA resulted in a complete loss of pediocin production. The pedB and pedC genes, encoding proteins of 112 and 174 amino acid residues, respectively, are located directly downstream of the pediocin structural gene. Functions could not be assigned to their gene products; mutation analysis showed that the PedB protein is not involved in pediocin PA-1 production. The mutation analysis further revealed that the fourth gene, pedD, specifying a relatively large protein of 724 amino acids, is required for pediocin PA-1 production in E. coli. The predicted pedD protein shows strong similarities to several ATP-dependent transport proteins, including the E. coli hemolysin secretion protein HlyB and the ComA protein, which is required for competence induction for genetic transformation in Streptococcus pneumoniae.(ABSTRACT TRUNCATED AT 250 WORDS)

Copy number control of the streptococcal plasmid pIP501 occurs at three levels

Transcriptional analysis of the replication region of plasmid pIP501 has revealed three active promoters. The repR gene which is essential for pIP501 replication was transcribed from promoter pII. A small antisense RNA (136 nt, RNAIII) generated from promoter pIII was complementary to the leader region of the repR mRNA. Introduction of either point mutations or deletions into promoter pIII or RNAIII resulted in a 5-20fold increased plasmid copy number suggesting a negative regulatory function for RNAIII. The copR gene, the complete DNA and amino acid sequence of which is reported, was dispensable for pIP501 replication. However, deletion of the copR promoter pI and/or the copR coding sequence led to a 10-20fold increase in plasmid copy number. This effect was also observed when a -1 frameshift mutation was introduced into the CopR coding region. Mutations in copR and pIII/RNAIII were not additive. It is, therefore, proposed that both components act at the same level of copy number control most likely in a sequential way. A second level of copy number control was found to involve an inverted repeat structure upstream of and overlapping with promoter pII. Destruction of this repeat sequence by deletion caused an increase in copy number 2-3fold higher than that observed for either RNAIII or copR mutations. A working model is proposed how different components of pIP501 interact to regulate its copy number.

Identification of a region that influences host range of the streptococcal conjugative plasmid pIP501

pIP501 is a member of a group of conjugative plasmids that are self-transmissible to a wide variety of streptococci as well as to other gram-positive bacteria. Several pIP501 restriction fragment deletion derivatives have been isolated and characterized. In this paper we describe one such derivative (pVA1702) which was conjugally proficient but had a limited host range. The loss of host range ability was seen as decreased conjugal transfer from Enterococcus faecalis to Streptococcus sanguis and was coincident with the deletion of a 4.5-kb DNA fragment. Transformation of pVA1702 into S. sanguis also was dramatically reduced as compared to its progenitor, suggesting the 4.5-kb fragment encoded a factor(s) necessary for stable maintenance in this host but not in E. faecalis. These observations suggest that pIP501 employs specific mechanisms enabling its maintenance in certain gram-positive bacteria.

In vivo genetic systems in lactic acid bacteria

A review of in vivo genetic systems covers the key features of transduction and conjugation but emphasises the intramolecular and intermolecular DNA interactions that are often associated with these processes. As well as the transfer of many lactose plasmids, conjugal transfer of nisin genes and the use of conjugation to construct bacteriophage-resistant dairy starter cultures are discussed. The discovery and characterization of insertion sequences in Lactobacillus and Lactococcus and the exploitation of heterologous conjugation and transposition systems in the lactic acid bacteria are described.

Clinical and microbiologic characteristics of pediococci

Over a 43-month period, 23 separate isolates of nonenterococcal alpha- and nonhemolytic streptococci were reported by our clinical microbiology laboratory to be resistant to vancomycin. This constituted 0.32% of nonenterococcal alpha- and nonhemolytic streptococci reported and 4.4% of such streptococci upon which susceptibility testing was performed. Of 13 isolates which were available for further study, all were highly resistant to vancomycin (MIC greater than or equal to 1,024 micrograms/ml), but none were actually streptococci. Three were clearly gram-positive rods by Gram stain and were found to be homofermentative lactobacilli. Two strains with elongated gram-positive cocci from colonies on agar showed small gram-positive rods when grown in thioglycolate broth and were physiologically identified as Lactobacillus confusus. Two isolates with lenticular gram-positive cocci appeared to be Leuconostoc mesenteroides subsp. mesenteroides. Six gram-positive isolates with round cells from growth on agar and from broth were arranged in tetrads in broth and closely resembled Pediococcus acidilactici. Twelve additional strains of pediococci that were not of human origin were also found to be highly resistant to vancomycin. These findings confirm published reports of clinical isolation of organisms resembling pediococci and suggest that clinically isolated, vancomycin-resistant bacteria which superficially resemble streptococci are probably other lactic acid bacteria.

Genetic analysis of the conjugal transfer determinants encoded by the streptococcal broad-host-range plasmid pIP501

pIP501 is a 30.2-kilobase (kb) broad-host-range conjugative streptococcal plasmid which encodes chloramphenicol and erythromycin resistance. A smaller conjugation-proficient derivative of pIP501 has been constructed and designated pVA1702. pVA1702 is 25.2 kb, encodes only kanamycin resistance, and confers conjugative ability in an Enterococcus faecalis mating system. The temperature-sensitive transposon delivery vectors pTV1ts and pTV32 carrying Tn917 and Tn917lac, respectively, were used to create insertion mutants of pVA1702 in E. faecalis. These insertions enabled us to localize the determinants conferring conjugation to two separate regions of pVA1702: the 7.5-kb region A and the 8.8-kb region B. A nested set of deletions of the 7.5-kb region was subcloned in Escherichia coli, and the expression of these deletions was examined in an E. coli minicell system. The genes for three conjugal proteins have been located and designated cnjA, cnjB, and cnjC (for conjugation). Two other peptides that are transcribed in a divergent direction from the cnj genes were encoded in the A region, but it is not known whether they are involved in conjugation. These studies indicate that the conjugation genes of pIP501 are arranged in multiple transcriptional units.

In vivo transfer of pAM beta 1 from Lactobacillus reuteri to Enterococcus faecalis

Trials were conducted to determine the in vivo transferability of plasmid-mediated antibiotic resistance between two strains of enteric Gram-positive bacteria. Germ-free mice were associated with the donor Lactobacillus reuteri DSM 20016 strain, carrying the broad host range pAM beta 1 plasmid, and with the Enterococcus faecalis JH2SS recipient strain. Analysis of faecal content of associated mice demonstrated that the in vivo transfer of this plasmid did occur and that frequencies of conjugation were affected by the presence of subtherapeutic levels of antibiotic in the diet.

Evidence for the conjugal transfer of the broad host range plasmid pIP501 into strains of Lactobacillus helveticus

The conjugative broad host range plasmid pIP501 was transferred from Streptococcus faecalis to a series of strains of lactic streptococci used commercially as dairy starter cultures. With these transconjugants as donors the plasmid was exconjugated to two strains of Lactobacillus helveticus and a commercially used strain of Strep. thermophilus. There was evidence that the plasmid could transfer between isogenic derivatives of one of the strains of Lact. helveticus. Transfer from Lact. helveticus to Strep. faecalis was also detected but at a low frequency. There was no evidence for the conjugal transfer of plasmid pIP501 into a strain of Lact. bulgaricus by exconjugation from either lactic streptococci or Lactobacillus sp.

Conjugal transfer of group B streptococcal plasmids and comobilization of Escherichia coli-Streptococcus shuttle plasmids to Lactobacillus plantarum

The antibiotic resistance group B streptococcal plasmids, pIP501 and pVA797, were conjugally transferred from Streptococcus faecalis to Lactobacillus plantarum. The Escherichia coli-Streptococcus shuttle plasmids, pVA838 and pSA3, were mobilized from S. sanguis to L. plantarum by pVA797 via cointegrate formation. pVA838 readily resolved from pVA797 and was present in L. plantarum as deletion derivatives. The pVA797::pSA3 cointegrate failed to resolve in L. plantarum.

Plasmid-Associated Bacteriocin Production and Sucrose Fermentation in Pediococcus acidilactici

Production of bacteriocin activity designated pediocin PA-1 was associated with the presence of a 6.2-megadalton plasmid in Pediococcus acidilactici PAC1.0. The bacteriocin exhibited activity against P. acidilactici, P. pentosaceus, Lactobacillus plantarum, L. casei, L. bifermentans, and Leuconostoc mesenteroides subsp. dextranicum. Partial characterization of pediocin PA-1 is described. The molecular weight of pediocin PA-1 was ca. 16,500. Additionally, strain PAC1.0 was found to contain a 23-megadalton plasmid associated with sucrose-fermenting ability.

Plasmids in Leuconostoc oenos

A new procedure was used to isolate 11 plasmids from eight Leuconostoc oenos strains. Plasmid DNA was not detected in 34 other strains of this species. Plasmid sizes ranged from 2.47 to 4.61 kilobase pairs. This is the first report of extrachromosomal elements in L. oenos.

Pediococci and biotechnology

Nomenclature changes of pediococci postdate the publication of Bergey's Manual. Pediococci possess both a "group" and a "type" antigen. They are gram positive, asporogenous, nonmotile, generally catalase negative, but may possess catalase-like activity. The pediococci may have either a cytochrome or a flavoprotein enzyme system. Anaerobically they are homofermentative using the PEP:PTS and the EMP pathway. Catalase positive strains utilize glucose aerobically and anaerobically while lactose and glycerol are only used aerobically. Some pentoses are fermented to lactate and acetate. Absolute requirement for folinic acid and nearly all amino acids is observed. Pediococci grow luxuriously in All Purpose Tween (APT) broth and are isolated on Rogosa SL agar. Detection can be done by electrical impedance and fluorescent antibody techniques. The Arrhenius concept was utilized in selecting metabolically efficient strains. Antibiotics, antioxidants, some chloride salts and some spices are detrimental to the pediococci. On the other hand, some chloride salts, manganese, and some spices are stimulant. Dialysis-fermentation and immobilization of pediococcal cells were recorded. Some strains decarboxylate histidine to histamine. The resting cell metabolism and the production of bacteriocin have been utilized in antibiosis. An intra and intergeneric genetic transfer system of plasmids from pediococci was by a conjugation-like mechanism. Formation of bacteriocin and fermentation of carbohydrates were linked to plasmids. Lytic bacteriophages to pediococci have not yet been identified. Industrial cultures are mainly frozen concentrates. Linear equations were developed to model the fermentative activity of pediococci and the effects of environmental factors.

Conjugal plasmid transfer (pAM beta 1) in Lactobacillus plantarum

The streptococcal plasmid pAM beta 1 (erythromycin resistance) was transferred via conjugation from Streptococcus faecalis to Lactobacillus plantarum and was transferred among L. plantarum strains. Streptococcus sanguis Challis was transformed with pAM beta 1 isolated from these transconjugants, and transformants harboring intact pAM beta 1 could conjugate the plasmid back to L. plantarum.

Involvement of a Plasmid in Production of Ropiness (Mucoidness) in Milk Cultures by Streptococcus cremoris MS

Curing and genetic transfer experiments showed that lactose-fermenting ability (Lac + ) and the ability to produce mucoidness in milk cultures (Muc + ) in Streptococcus cremoris MS were coded on plasmids. The Lac + phenotype was associated with a 75.8-megadalton plasmid, pSRQ2201. The Muc + phenotype was associated with a 18.5-megadalton plasmid, pSRQ2202. The Lac plasmid, pSRQ2201, was first conjugatively transferred from S. cremoris MS to Lac − S. lactis ML-3/2.2. Later, the Muc plasmid, pSRQ2202, was conjugatively transferred from Lac − Muc + S. cremoris MS04 to Lac + nonmucoid S. lactis transconjugant ML-3/2.201. Subsequently, pSRQ2201 and pSRQ2202 were cotransferred from Lac + Muc + S. lactis transconjugant ML-3/2.202 to Lac − , nonmucoid, malty S. lactis 4/4.2 and S. lactis subsp. diacetylactis SLA3.25. Transconjugants showing pSRQ2201 were Lac + ; those containing pSRQ2202 were Muc + . With the transfer of pSRQ2202, the transconjugants S. lactis ML-3/2.202 and S. lactis subsp. diacetylactis SLA3.2501 not only acquired the Muc + phenotype but also resistance to bacteriophages, which were lytic to the respective parent strains S. lactis ML-3/2.201 and S. lactis subsp. diacetylactis SLA3.25.

Highly efficient protoplast transformation system for Streptococcus faecalis and a new Escherichia coli-S. faecalis shuttle vector

A highly efficient protoplast transformation system for Streptococcus faecalis has been developed by systematically optimizing different parameters. Up to 10(6) transformants per micrograms of DNA were consistently obtained within 3 days, and cell wall regeneration of protoplasts was virtually 100%. A systematic search for useful vectors showed that the broad-host-range plasmid pIP501 could transform S. faecalis at a high frequency (6.3 X 10(4) transformants per microgram). By combining a high-copy-number derivative of pIP501, designated pGB354, with the Escherichia coli vector pACYC184, we constructed a new E. coli-S. faecalis shuttle vector (pAM401) having nine unique restriction sites. In a shotgun cloning experiment, we ligated a tetracycline resistance determinant from Streptococcus sanguis chromosomal DNA into pAM401 by direct transformation of S. faecalis, establishing the utility of the protoplast transformation system and of the new shuttle vector.

Association of a 13.6-Megadalton Plasmid in Pediococcus pentosaceus with Bacteriocin Activity

Pediococcus pentosaceus FBB61 and L7230, isolated from cucumber fermentations, produced a bacteriocin, designated pediocin A, which had identical activity spectra against species of Pediococcus, Clostridium, Staphylococcus , and Streptococcus . Both strains possessed a 13.6-megadalton plasmid (pMD136). Plasmid curing experiments suggested that both bacteriocin immunity and production determinants were encoded by pMD136. Use of pediocin-producing strains in food fermentations is discussed.

Images

Plasmid DNA in Strains of Pediococcus cerevisiae and Pediococcus pentosaceus

Five parental strains of Pediococcus were examined for plasmid content. Each strain contained three to six resident plasmids, ranging in size from 4.5 to 39.5 megadaltons. A bacteriocin-like substance produced by Pediococcus cerevisiae FBB63 was tentatively linked to a 10.5-megadalton plasmid after being cured with novobiocin.

Images

Transfer of Sucrose-Fermenting Ability and Nisin Production Phenotype among Lactic Streptococci

Transfer of sucrose fermentation ability, nisin production, and nisin resistance from Streptococcus lactis to S. lactis and Streptococcus lactis subsp. diacetylactis occurred between cells immobilized on nitrocellulose filters in the presence of DNase. Transconjugants were able to act as donors to transfer the Suc-Nis phenotype in subsequent mating. No changes in sensitivity to lytic phage c2 were noted in S. lactis transconjugants. However, temperature-independent restriction of lytic phage 18-16 was noted in transconjugants of S. lactis subsp. diacetylactis 18-16. Adsorption studies with phage-resistant transconjugants showed that resistance was not due to lack of adsorption by the lytic phage. Physical evidence for the presence of introduced plasmid DNA was not found in lysates of transconjugants.