Protective effect of microbisporicin (NAI-107) against vancomycin resistant Enterococcus faecium infection in a Galleria mellonella model

Increasing antimicrobial resistance in Enterococcus faecium necessitates the search for novel treatment agents, such as bacteriocins. In this study, we conducted an in vivo assessment of five bacteriocins, namely Lacticin Z, Lacticin Q, Garvicin KS (ABC), Aureocin A53 and Microbisporicin (NAI-107), against vanB-resistant Enterococcus faecium using a Galleria mellonella model. Our in vitro experiments demonstrated the efficacy of all five bacteriocins against vanB-resistant E. faecium with only NAI-107 demonstrating in vivo efficacy. Notably, NAI-107 exhibited efficacy across a range of tested doses, with the highest efficacy observed at a concentration of 16 µg/mL. Mortality rates in the group treated with 16 µg/mL NAI-107 were lower than those observed in the linezolid-treated group. These findings strongly suggest that NAI-107 holds promise as a potential alternative therapeutic agent for treating infections caused by resistant E. faecium and warrants further investigation.

Microbisporicin (NAI-107) protects Galleria mellonella from infection with Neisseria gonorrhoeae

IMPORTANCE

We screened 66 bacteriocins to see if they exhibited anti-gonococcal activity. We found 12 bacteriocins with anti-gonococcal effects, and 4 bacteriocins showed higher anti-gonococcal activity. Three bacteriocins, lacticin Z, lacticin Q, and Garvicin KS (ABC), showed in vitro anti-gonococcal activity but no in vivo inhibitory effects against the Neisseria gonorrhoeae (WHO-P) isolate. On the other hand, NAI-107 showed in vivo anti-gonococcal activity. The findings suggest that NAI-107 is a promising alternative to treat gonorrhea infections.

Enhancing the antibacterial function of probiotic Escherichia coli Nissle: when less is more

Probiotic bacteria confer multiple health benefits, including preventing the growth, colonization, or carriage of harmful bacteria in the gut. Bacteriocins are antibacterial peptides produced by diverse bacteria, and their production is tightly regulated and coordinated at the transcriptional level. A popular strategy for enhancing the antibacterial properties of probiotic bacteria is to retrofit them with the ability to overproduce heterologous bacteriocins. This is often achieved from non-native constitutive promoters or in response to host or pathogen signal from synthetic promoters. How the dysregulated overproduction of heterologous bacteriocins affects the fitness and antibacterial efficacy of the retrofitted probiotic bacteria is often overlooked. We have conferred the prototypical probiotic Escherichia coli strain Nissle (EcN) the ability to produce microcin C (McC) from the wild-type promoter and two mutant promoters that allow, relative to the wild-type promoter, high and low amounts of McC production. This was done by introducing specific changes to the sequence of the wild-type promoter driving transcription of the McC operon while ensuring that the modified promoters respond to native regulation. By studying the transcriptomic responses and antibacterial efficacy of the retrofitted EcN bacteria in a Galleria mellonella infection model of enterohemorrhagic E. coli, we show that EcN bacteria that produce the lowest amount of McC display the highest antibacterial efficacy with little-to-none undesired collateral impact on their fitness. The results highlight considerations researchers may take into account when retrofitting probiotic bacteria with heterogenous gene products for therapeutic, prophylactic, or diagnostic applications. Bacteria that resist killing by antibiotics are a major risk to modern medicine. The use of beneficial "probiotic" bacteria to make antibiotic-like compounds at the site of infection in the body is emerging as a popular alternative to the use of conventional antibiotics. A potential drawback of engineering probiotic bacteria in this way is that producing antibiotic-like compounds could impart undesired side effects on the performance of such bacteria, thereby compromising their intended use. This study highlights considerations researchers may take into account when engineering probiotic bacteria for therapeutic, prophylactic, or diagnostic applications.

Selective Bacteriocins: A Promising Treatment for Staphylococcus aureus Skin Infections Reveals Insights into Resistant Mutants, Vancomycin Resistance, and Cell Wall Alterations

The emergence of antibiotic-resistant S. aureus has become a major public health concern, necessitating the discovery of new antimicrobial compounds. Given that the skin microbiome plays a critical role in the host defence against pathogens, the development of therapies that target the interactions between commensal bacteria and pathogens in the skin microbiome offers a promising approach. Here, we report the discovery of two bacteriocins, cerein 7B and cerein B4080, that selectively inhibit S. aureus without affecting S. epidermidis, a commensal bacterium on the skin. Our study revealed that exposure of S. aureus to these bacteriocins resulted in mutations in the walK/R two-component system, leading to a thickening of the cell wall visible by transmission electron microscopy and subsequent decreased sensitivity to vancomycin. Our findings prompt a nuanced discussion of the potential of those bacteriocins for selective targeting of S. aureus on the skin, given the emergence of resistance and co-resistance with vancomycin. The idea put forward implies that by preserving commensal bacteria, selective compounds could limit the emergence of resistance in pathogenic cells by promoting competition with remaining commensal bacteria, ultimately reducing chronical infections and limiting the spread of antibiotic resistance.

Deletion of QDR genes in a bioethanol-producing yeast strain reduces propagation of contaminating lactic acid bacteria

Bacterial contaminations in yeast fermentation tanks are a recurring problem for the bioethanol production industry. Lactic acid bacteria (LAB), particularly of the genus Lactobacillus, are the most common contaminants. Their proliferation can reduce fermentation efficiency or even impose premature shutdown for cleaning. We have previously reported that laboratory yeast strains naturally excrete amino acids via transporters of the Drug: H⁺ Antiporter-1 (DHA1) family. This excretion allows yeast to cross-feed LAB, which are most often unable to grow without an external amino acid supply. Whether industrial yeast strains used in bioethanol production likewise promote LAB proliferation through cross-feeding has not been investigated. In this study, we first show that the yeast strain Ethanol Red used in ethanol production supports growth of Lactobacillus fermentum in an amino-acid-free synthetic medium. This effect was markedly reduced upon homozygous deletion of the QDR3 gene encoding a DHA1-family amino acid exporter. We further show that cultivation of Ethanol Red in a nonsterile sugarcane-molasses-based medium is associated with an increase in lactic acid due to LAB growth. When Ethanol Red lacked the QDR1, QDR2, and QDR3 genes, this lactic acid production was not observed and ethanol production was not significantly reduced. Our results indicate that Ethanol Red cultivated in synthetic or molasses medium sustains LAB proliferation in a manner that depends on its ability to excrete amino acids via Qdr transporters. They further suggest that using mutant industrial yeast derivatives lacking DHA1-family amino acid exporters may be a way to reduce the risk of bacterial contaminations during fermentation.

In vitro and in vivo production and split-intein mediated ligation (SIML) of circular bacteriocins

Circular bacteriocins are antimicrobial peptides produced by bacteria that after synthesis undergo a head-to-tail circularization. Compared to their linear counterparts, circular bacteriocins are, in general, very stable to temperature and pH changes and more resistant to proteolytic enzymes, being considered as one of the most promising groups of antimicrobial peptides for their potential biotechnological applications. Up to now, only a reduced number of circular bacteriocins have been identified and fully characterized, although many operons potentially coding for new circular bacteriocins have been recently found in the genomes of different bacterial species. The production of these peptides is very complex and depends on the expression of different genes involved in their synthesis, circularization, and secretion. This complexity has greatly limited the identification and characterization of these bacteriocins, as well as their production in heterologous microbial hosts. In this work, we have evaluated a synthetic biology approach for the in vitro and in vivo production combined with a split-intein mediated ligation (SIML) of the circular bacteriocin garvicin ML (GarML). The expression of one single gene is enough to produce a protein that after intein splicing, circularizes in an active peptide with the exact molecular mass and amino acid sequence as native GarML. In vitro production coupled with SIML has been validated with other, well described and not yet characterized, circular bacteriocins. The results obtained suggest that this synthetic biology tool holds great potential for production, engineering, improving and testing the antimicrobial activity of circular bacteriocins.

Promising Antimicrobial Activity and Synergy of Bacteriocins Against Mycobacterium tuberculosis

In this study, we assessed the potential of bacteriocins and their in vitro synergistic effects in combination with anti-tuberculosis drugs against Mycobacterium tuberculosis. We evaluated the in vitro activity of chemically synthesized bacteriocins in combination with rifampicin (RIF), ofloxacin, and moxifloxacin against the reference M. tuberculosis H37Rv and a clinical-resistant strain. We first screened the bacteriocin PARAGEN collection and found active bacteriocins. We then determined their minimal inhibitory concentration (MIC), minimal bactericidal concentration, and their fractional inhibitory index by the checkerboard microdilution assay. Remarkably, we identified four bacteriocins with interesting antimycobacterial activity alone and in combinations with RIF, ofloxacin, and moxifloxacin, with significant reduction of the MIC that showed impressive synergistic effects against the susceptible and resistant clinical strains. In conclusion, our preliminary results show promising bacteriocins candidate used in a synergistic combination with anti-tuberculosis drugs and emphasize the need for combined therapy as a new strategy to enhance the activity of existing drugs, which may confer very promising therapeutic benefits against M. tuberculosis.

In the Age of Synthetic Biology, Will Antimicrobial Peptides be the Next Generation of Antibiotics?

Antibiotics have changed human health and revolutionised medical practice since the Second World War. Today, the use of antibiotics is increasingly limited by the rise of antimicrobial-resistant strains. Additionally, broad-spectrum antibiotic activity is not adapted to maintaining a balanced microbiome essential for human health. Targeted antimicrobials could overcome these two drawbacks. Although the rational design of targeted antimicrobial molecules presents a formidable challenge, in nature, targeted genetically encoded killing molecules are used by microbes in their natural ecosystems. The use of a synthetic biology approach allows the harnessing of these natural functions. In this commentary article we illustrate the potential of applying synthetic biology towards bacteriocins to design a new generation of antimicrobials.

PARAGEN 1.0: A Standardized Synthetic Gene Library for Fast Cell-Free Bacteriocin Synthesis

The continuous emergence of microbial resistance to our antibiotic arsenal is widely becoming recognized as an imminent threat to global human health. Bacteriocins are antimicrobial peptides currently under consideration as real alternatives or complements to common antibiotics. These peptides have been much studied, novel bacteriocins are regularly reported and several genomic databases on these peptides are currently updated. Despite this, to our knowledge, a physical collection of bacteriocins that would allow testing and comparing them for different applications does not exist. Rapid advances in synthetic biology in combination with cell-free protein synthesis technologies offer great potential for fast protein production. Based on the amino acid sequences of the mature peptide available in different databases, we have built a bacteriocin gene library, called PARAGEN 1.0, containing all the genetic elements required for in vitro cell-free peptide synthesis. Using PARAGEN 1.0 and a commercial kit for cell-free protein synthesis we have produced 164 different bacteriocins. Of the bacteriocins synthesized, 54% have shown antimicrobial activity against at least one of the indicator strains tested, including Gram-positive and Gram-negative bacteria representing commonly used lab strains, industrially relevant microorganisms, and known pathogens. This bacteriocin collection represents a streamlined pipeline for selection, production, and screening of bacteriocins as well as a reservoir of ready-to-use antimicrobials against virtually any class of relevant bacteria.

Mobilization of Microbiota Commensals and Their Bacteriocins for Therapeutics

With the specter of resurgence of pathogens due to the propagation of antibiotic-resistance genes, innovative antimicrobial strategies are needed. In this review, we summarize the beneficial aspects of bacteriocins, a set of miscellaneous peptide-based bacterium killers, compared with classical antibiotics, and emphasize their use in cocktails to curb the emergence of new resistance. We highlight that their prey spectrum, their molecular malleability, and their multiple modes of production might lead to specific and personalized treatments to prevent systemic disorders. Complementarily, we discuss how we might exploit prevailing bacterial commensals, such as Streptococcus salivarius, and deliberately mobilize their bacteriocin arsenal 'on site' to cure multiresistant infections or finely reshape the endogenous microbiota for prophylaxis purposes.

Alpha-fetoprotein controls female fertility and prenatal development of the gonadotropin-releasing hormone pathway through an antiestrogenic action

It has been shown previously that female mice homozygous for an alpha-fetoprotein (AFP) null allele are sterile as a result of anovulation, probably due to a defect in the hypothalamic-pituitary axis. Here we show that these female mice exhibit specific anomalies in the expression of numerous genes in the pituitary, including genes involved in the gonadotropin-releasing hormone pathway, which are underexpressed. In the hypothalamus, the gonadotropin-releasing hormone gene, Gnrh1, was also found to be down-regulated. However, pituitary gene expression could be normalized and fertility could be rescued by blocking prenatal estrogen synthesis using an aromatase inhibitor. These results show that AFP protects the developing female brain from the adverse effects of prenatal estrogen exposure and clarify a long-running debate on the role of this fetal protein in brain sexual differentiation.

Alpha-fetoprotein protects the developing female mouse brain from masculinization and defeminization by estrogens

Two clearly opposing views exist on the function of alpha-fetoprotein (AFP), a fetal plasma protein that binds estrogens with high affinity, in the sexual differentiation of the rodent brain. AFP has been proposed to either prevent the entry of estrogens or to actively transport estrogens into the developing female brain. The availability of Afp mutant mice (Afp(-/-)) now finally allows us to resolve this longstanding controversy concerning the role of AFP in brain sexual differentiation, and thus to determine whether prenatal estrogens contribute to the development of the female brain. Here we show that the brain and behavior of female Afp(-/-) mice were masculinized and defeminized. However, when estrogen production was blocked by embryonic treatment with the aromatase inhibitor 1,4,6-androstatriene-3,17-dione, the feminine phenotype of these mice was rescued. These results clearly demonstrate that prenatal estrogens masculinize and defeminize the brain and that AFP protects the female brain from these effects of estrogens.

Alpha-fetoprotein, the major fetal serum protein, is not essential for embryonic development but is required for female fertility

The alpha-fetoprotein gene (Afp) is a member of a multigenic family that comprises the related genes encoding albumin, alpha-albumin, and vitamin D binding protein. The biological role of this major embryonic serum protein is unknown although numerous speculations have been made. We have used gene targeting to show that AFP is not required for embryonic development. AFP null embryos develop normally, and individually transplanted homozygous embryos can develop in an AFP-deficient microenvironment. Whereas mutant homozygous adult males are viable and fertile, AFP null females are infertile. Our analyses of these mice indicate that the defect is caused by a dysfunction of the hypothalamic/pituitary system, leading to anovulation.

Stimulation of the alpha-fetoprotein promoter by unliganded thyroid hormone receptor in association with protein deacetylation

alpha-Fetoprotein (AFP) is a serum protein expressed during fetal life, the expression of which is shut off after birth. The activity of the mouse Afp gene promoter region comprised between -80 and -38 bp is regulated by the thyroid hormone receptor (T3R): negatively in the presence of T3 and positively in the absence of T3. The stimulating effect of unliganded T3R is, unexpectedly, antagonized by cofactors that have histone-acetyl-transferase activity, or by sodium butyrate, which inhibits histone acetylases (HDACs). The unliganded T3R stimulating activity effect is thus associated with protein deacetylation, contrary to the usual situation. In combination with previous results, our observations suggest that T3-mediated down regulation of the Afp promoter is due to T3-induced protein acetylation leading to loss of a nucleosomal structure (required for promoter activity) and chromatin opening.

Identification of KLF13 and KLF14 (SP6), novel members of the SP/XKLF transcription factor family

Using the sequence of the SP1 zinc-finger DNA-binding domain as a probe to screen a mouse EST database, we identified two novel members of the SP/XKLF transcription factor family, KLF13 and KLF14. The mouse Klf13 cDNA (1310 bp in length) contains a single open reading frame of 288 amino acids with a DNA-binding domain closely related to that of the human RFLAT-1 protein and a putative transactivator N-terminal domain rich in proline and alanine residues. The mouse Klf13 gene seems to be the homologue of the human RFLAT1 gene. The mouse Klf14 sequence is homologous to a human genomic sequence from chromosome 17 that is believed to code for a protein with three zinc fingers at the end of its C-terminal domain. Using reverse transcription-polymerase chain reaction, we showed ubiquitous expression of Klf13 and Klf14 in adult mice. A third member of this family was also identified in a human EST database; this sequence was found to be identical to KLF11 (TIEG2), recently identified by Cook et al. (1998, J. Biol. Chem. 273: 25929-25936). The corresponding mouse cDNA was isolated and sequenced. The three genes were localized in the human and the rat: chromosomes 15 (human KLF13), 17q21.3-q22 (human KLF14; HGMW-approved symbol SP6), and 2p25 (human KLF11) and chromosomes 1q31-q32 (rat Klf13), 10q31-q32.1 (rat Klf14) (SP6), and 6q16-q21 (rat Klf11).

Identification of an enhancer and an alternative promoter in the first intron of the alpha-fetoprotein gene

In this study we have characterized a positive regulatory region located in the first intron of the alpha-fetoprotein (AFP) gene. We show that the enhancer activity of the region depends on a 44 bp sequence centered on a CACCC motif. The sequence is the target of the two zinc fingers transcription factors BKLF and YY1. The introduction of a mutation destroying the CACCC box impairs the binding of BKLF but improves that of YY1. Moreover, the mutated sequence behaves as a negative control element, suggesting that BKLF behaves as a positive factor and that YY1 is a negative one. We also demonstrate the existence of a novel, tissue-specific AFP mRNA isoform present in the yolk sac and fetal liver which initiates from an alternative promoter located approximately 100 bp downstream of the enhancer element. The transcriptional start site controlled by this new promoter (called P2), was mapped to 66 bp downstream of a TATA box. A putative AUG translation site in-frame with exon 2 of the classical gene was found 295 bp downstream of the transcription start site. Like the traditional AFP promoter (P1), the P2 promoter is active in the yolk sac and fetal liver. Embryonic stem cells with an AFP knock-in gene containing either the P2 promoter or deleted for it were isolated and comparative analysis of embryonic bodies derived from these cells suggests that the P2 promoter contributes to early expression of the AFP gene.

New positive selection system based on the parD (kis/kid) system of the R1 plasmid

The use of vectors that are designed to allow positive selection of recombinants facilitates cloning experiments in E. coli. Using kid, a lethal gene of the R1 plasmid parD locus, we generated pKID vectors leading to high selective efficiency of recombinants (greater than 90%). The E. coli bacterial host used to propagate these vectors produces the Kis protein, the natural antagonist of Kid. This new positive-selection system exhibits the same efficiency as the original ccdB-based selection vectors, pKIL (4). We also show that the ccdB and kid systems are independent. This property increases the potential of plasmidic poison-antidote systems for genetic applications and opens the door to a generation of new vectors containing the two selection systems.

Rat Chromosome 2: assignment of the genes encoding cyclin B1, interleukin 6 signal transducer, and proprotein convertase 1 to the Mcs1-containing region and identification of new microsatellite markers

The rat Chromosome (Chr) 2 harbors several genes controlling tumor growth or development, blood pressure, and non-insulin-dependent diabetes mellitus. We report that the region (2q1) containing the mammary susceptibility cancer gene Mcs1 also harbors the genes encoding cyclin B1, interleukin 6 signal transducer (gp130), and proprotein convertase 1. We also generated 13 new anonymous microsatellite markers from Chr 2-sorted DNA. These markers, as well as a microsatellite marker in the cyclin B1 gene, were genetically mapped in combination with known markers. A cyclin B1-related gene was also cytogenetically assigned to rat Chr 11q22-q23.

Positive selection vectors to generate fused genes for the expression of his-tagged proteins

Epitope tagging simplifies detection, characterization and purification of proteins. Gene fusion to combine the coding region of a well-characterized epitope with the coding region for a protein of interest generally requires several subcloning steps. Alternatively, a PCR strategy can be used to generate such a chimeric gene. In addition to its simplicity, this approach allows one to limit the size of the multiple cloning sites present in conventional expression vectors, thus reducing the introduction of artifactual amino-acid sequences into the fused protein. In this communication, we describe new vectors that allow PCR cloning and selection of chimeric genes coding for N- or C-terminal His-tagged proteins. These vectors are based on the control of cell death CcdB direct selection technology and are well adapted to the cloning of blunt-ended PCR products that were generated by using thermostable polymerases that provide proofreading activity.

Direct selection cloning vectors adapted to the genetic analysis of gram-negative bacteria and their plasmids

A range of specific and unusual biological pathways are found in Gram-negative bacteria. It is possible to express the genes involved in these processes in Escherichia coli, however, some genes prove lethal when cloned into high copy number vectors in common usage. Conversely, various genetic functions remain silent in E. coli and require to be transferred into their original host for expression and subsequent analysis. To facilitate the cloning and the characterisation of bacterial genes, we have constructed CcdB 'positive-selection' vectors that possess one or more of the following properties: (i) low or medium copy number; (ii) narrow or broad replication host range; (iii) conjugational mobilisation. In this communication, we illustrate the use of these new cloning tools and analyse the CcdB toxicity in different bacterial species.

Bifunctional lacZ alpha-ccdB genes for selective cloning of PCR products

The use of PCR-amplified DNA-fragments is a classical approach to generate recombinant DNA. To facilitate the cloning of PCR products, we have constructed two new pKIL vectors that allow selection of recombinants. The multiple cloning sites (MCS) of these plasmids contain two adjacent Aspel sites and a unique HindII site. Cleavage of these vectors with Aspel produce linearized molecules with a single thymidine nucleotide at the 3' ends allowing TA cloning of Taq-amplified fragments. On the other hand, cleavage with HindII can be used for the cloning of blunt-ended PCR products generated by other DNA polymerases. The LacZ alpha-CcdB fusion protein produced by these plasmids has retained both the CcdB killer activity and the ability to alpha-complement the truncated LacZ delta M15. This bifunctionality allowed us to show that small PCR products (< 1000 bp) that do not disrupt lacZ alpha efficiently do inactivate CcdB, which demonstrates that the CcdB-based selection is well adapted for cloning of PCR products, especially for small size fragments.

Molecular analysis of RepHI1B, a replicon specific to IncHI1 plasmids

RepHI1B is one of the replicons that is specific to IncHI1 multireplicon plasmids. Its general organization resembles that of several replicons that control their copy number by an iteron mechanism. The RepHI1B replicon (2.4 kb) contains: (i) an 882 bp repA gene coding for a 32 kDa replication protein (RepA), sharing significant similarity with the initiator proteins of other replicons belonging to various incompatibility (Inc) groups, including P1 (IncY), Rts1 (IncT), RepFIB (IncFI), and RepHI1A (IncHI1); (ii) two sets of 17 bp DNA repeats (iterons), one upstream and one downstream from repA. By complementation testing, we identified the replication origin (ori) of RepHI1B in a 223 bp locus upstream from repA. By primer extension we mapped two promoters of repA (Pr1 and Pr2) in the ori sequence. We used repA::lacZ transcriptional fusions to study regulation of the repA gene. This analysis showed that repA is transcriptionally autoregulated. Gel mobility shift assays demonstrated that RepA binds specifically to the origin and to iterons overlapping the Pr1 and Pr2 promoters. A G to A transition at nucleotide position 13 of the iteron located in Pr2 (repeat 5) drastically decreases autoregulation of repA by inhibiting binding of RepA.

Negative regulation of the alpha-foetoprotein gene in fibroblasts: identification and characterization of cis and trans elements

The alpha-foetoprotein (AFP) gene is extinguished in hybrids formed between hepatoma cells (expressing cells) and fibroblasts (non-expressing cells). Transfection experiments with constructions containing segments from the promoter region of the AFP-gene, placed upstream of an ubiquitously expressed promoter (the Herpes virus thymidine kinase gene promoter), showed that the AFP gene-derived sequence contains at least one negative element active in fibroblasts (while this sequence behaves as an enhancer in hepatoma cells). We identified such a fibroblast negative region, localized between nucleotide positions -80 to -38 (FNE1). Gel retardation experiments showed that FNE1 specifically binds fibroblast nuclear proteins, generating three complexes. The sequence from -57 to -43 was shown to be responsible for both the formation of these complexes and the negative activity of FNE1. These results suggest that the binding of nuclear factors to the AFP promoter region contributes to silencing the AFP gene in non-expressing cells, such as fibroblasts, and thus to establishing lineage-specific expression of the AFP gene.

Molecular analysis of the replication elements of the broad-host-range RepA/C replicon

RepA/C is a replicon specific to the IncA/C incompatibility group of plasmids and was isolated recently from plasmid RA1. The sequence of this autoreplicative region was established; it contains 13 repeats, suggesting that the replicon uses iterons to control its copy number. The sequence contains two ORFs, one potentially coding for a 33-kDa protein (ORF1) and a second potentially coding for a 14-kDa protein (ORF2) (Llanes et al., 1994b). In this work, using an in vitro transcription/translation system, we detected a polypeptide whose size corresponded well to that of the deduced product of ORF1. Deletion and insertion mutation analysis showed that ORF1 is essential for replication; it encodes an initiator protein (called RepA). ORF2 was not essential for replication in Escherichia coli and its function remains to be determined. Using complementation experiments, the replication origin (ori) of RepA/C was defined. The ori was located in a 600-bp fragment downstream from repA, containing 10 direct repeats. To study the control of repA expression, a transcriptional fusion PrepA::lacZ was constructed. Its analysis showed that repA is transcriptionally autoregulated as are most repA genes of replicons controlled by iterons.

Positive-selection vectors using the F plasmid ccdB killer gene

Plasmids pKIL18/19 are positive-selection cloning vectors containing an active cytotoxic ccdB gene under the control of the lacP promoter. They are derivatives of high-copy-number pUC18/19 plasmids in which the ccdB killer gene has been fused in phase downstream from the lacP MCS18 and MCS19 multiple cloning sites. When an Escherichia coli wild-type gyrA+ strain is transformed by such vectors, the ccdB gene product blocks bacterial growth. However, if ccdB is inactivated by insertion of a foreign DNA fragment, this recombinant plasmid no longer interferes with host viability. The positive selection of recombinant clones is highly efficient and bench manipulations are simplified to the utmost: E. coli transformants are plated on rich medium and only cells containing recombinant plasmids give rise to colonies. The CcdB protein is a potent poison of gyrase and the gyrA462 mutation confers total resistance to CcdB [Bernard and Couturier, J. Mol. Biol. 226 (1992) 735-745]. Therefore, pKIL18/19 vectors can be amplified and prepared in large quantities in a gyrA462 host. Like pUC vectors, pKIL vectors are designed for general cloning/sequencing procedures.

Cloning and characterization of the Inc A/C plasmid RA1 replicon

The Inc A/C plasmids, like Inc P and Inc Q plasmids, have a broad host range. However, their maintenance functions remain to be studied. An autoreplicative region of 2.79 kb named RepA/C, able to replicate both in the family Enterobacteriaceae and in Pseudomonas spp., was isolated and sequenced. The stability, copy number, and incompatibility expression of this replicon were determined. RepA/C and a nonautoreplicative fragment of 16 kb of this replicon were used as probes and showed specific hybridizations with the Inc P3-A/C plasmids from Pseudomonas spp. and members of the Enterobacteriaceae. These probes could be used as tools for identification of the plasmids of this epidemiologically important Inc group.

Nucleotide sequence and replication characteristics of RepHI1B: a replicon specific to the IncHI1 plasmids

The IncHI1 plasmids are multireplicon plasmids. They contain at least three autoreplicative regions, one of which is closely related to the RepFIA replicon of F. Two other IncHI1-specific replicons, RepHI1A and RepHI1B, have been recently isolated and mapped on the R27 (IncHI1) genome (P. Gabant, P. Newnham, D. Taylor, and M. Couturier, J. Bacteriol. 175, 7697-7701, 1993). In the present work, the DNA sequence of RepHI1B was determined. It reveals DNA repeats of 17 base pairs located upstream and downstream from a gene coding for a 32 kilodalton protein (RepA) required for replication. Interestingly, RepA presents significant homology with other Rep proteins encoded by plasmids belonging to different incompatibility groups: P1 (IncY), Rts1 (IncT), RepFIB (IncFI) and RepHI1A (IncHI1). All these results provide strong evidence that the RepHI1B replicon of the IncHI1 subgroup belongs to the group of plasmids which control their copy number by an iteron mechanism.

Isolation and location on the R27 map of two replicons and an incompatibility determinant specific for IncHI1 plasmids

Two replicons were isolated independently from different IncHI1 plasmids. One was isolated from R27, and a second was isolated from pIP522. We demonstrate, by DNA-DNA hybridization experiments, that these maintenance regions are different and that they are specific to, and carried by, all IncHI1 plasmids tested. In view of this specificity we decided to designate the replicon isolated from R27 as RepHI1A and the replicon isolated from pIP522 as RepHI1B. These two autoreplicative regions are not related to a third replicon present in all IncHI1 plasmids that bears homology with RepFIA and that expresses the characteristic incompatibility of IncHI1 subgroup plasmids toward F factor (D. Saul, D. Lane, and P. L. Bergquist, Mol. Microbiol. 2:219-225, 1988; D. E. Taylor, R. W. Hedges, and P. L. Bergquist, J. Gen. Microbiol. 131:1523-1530, 1985). These results demonstrate that all IncHI1 plasmids tested contain at least three replicons. An incompatibility (Inc) region that hybridizes specifically to all the IncHI1 plasmids was previously isolated (M. Couturier, F. Bex, P. L. Bergquist, and W. K. Maas, Microbiol. Rev. 52:375-395, 1988). Although this Inc locus is not located in an autoreplicative region of IncHI1 plasmids, we observed that this locus stabilizes a low-copy-number replicon. This Inc locus is probably a component of an active partition locus involved in the maintenance of IncHI1 plasmids. The nucleotide sequence of the Inc region contains direct repeats of 31 bp. In addition, this incompatibility determinant hybridizes specifically with IncHI1 plasmids but expresses incompatibility toward plasmids of both IncHI subgroups (IncHI1 and IncHI2). In this communication, we present the mapping of these maintenance elements on the R27 genome.