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PubMed2006

The gene cluster for agmatine catabolism of Enterococcus faecalis: study of recombinant putrescine transcarbamylase and agmatine deiminase and a snapshot of agmatine deiminase catalyzing its reaction.

Enterococcus faecalis makes ATP from agmatine in three steps catalyzed by agmatine deiminase (AgDI), putrescine transcarbamylase (PTC), and carbamate kinase (CK). An antiporter exchanges putrescine for agmatine. We have cloned the E. faecalis ef0732 and ef0734 genes of the reported gene cluster for agmatine catabolism, overexpressed them in Escherichia coli, purified the products, characterized them functionally as PTC and AgDI, and crystallized and X-ray diffracted them. The 1.65-Angstroms-resolution structure of AgDI forming a covalent adduct with an agmatine-derived amidine reactional intermediate is described. We provide definitive identification of the gene cluster for agmatine catabolism and confirm that ornithine is a genuine but poor PTC substrate, suggesting that PTC (found here to be trimeric) evolved from ornithine transcarbamylase. N-(Phosphonoacetyl)-putrescine was prepared and shown to strongly (K(i) = 10 nM) and selectively inhibit PTC and to improve PTC crystallization. We find that E. faecalis AgDI, which is committed to ATP generation, closely resembles the AgDIs involved in making polyamines, suggesting the recruitment of a polyamine-synthesizing AgDI into the AgDI pathway. The arginine deiminase (ADI) pathway of arginine catabolism probably supplied the genes for PTC and CK but not those for the agmatine/putrescine antiporter, and thus the AgDI and ADI pathways are not related by a single "en bloc" duplication event. The AgDI crystal structure reveals a tetramer with a five-blade propeller subunit fold, proves that AgDI closely resembles ADI despite a lack of sequence identity, and explains substrate affinity, selectivity, and Cys357-mediated-covalent catalysis. A three-tongued agmatine-triggered gating opens or blocks access to the active center.

Agmatine↗
PubMed1988

Transport of diamines by Enterococcus faecalis is mediated by an agmatine-putrescine antiporter.

Enterococcus faecalis ATCC 11700 is able to use arginine and the diamine agmatine as a sole energy source. Via the highly homologous deiminase pathways, arginine and agmatine are converted into CO2, NH3, and the end products ornithine and putrescine, respectively. In the arginine deiminase pathway, uptake of arginine and excretion of ornithine are mediated by an arginine-ornithine antiport system. The translocation of agmatine was studied in whole cells grown in the presence of arginine, agmatine, or glucose. Rapid uncoupler-insensitive uptake of agmatine was observed only in agmatine-grown cells. A high intracellular putrescine pool was maintained by these cells, and this pool was rapidly released by external putrescine or agmatine but not by arginine or ornithine. Kinetic analysis revealed competitive inhibition for uptake between putrescine and agmatine. Agmatine uptake by membrane vesicles was observed only when the membrane vesicles were preloaded with putrescine. Uptake of agmatine was driven by the outwardly directed putrescine concentration gradient, which is continuously sustained by the metabolic process. Uptake of agmatine and extrusion of putrescine by agmatine-grown cells of E. faecalis appeared to be catalyzed by an agmatine-putrescine antiporter. This transport system functionally resembled the previously described arginine-ornithine antiport, which was exclusively induced when the cells were grown in the presence of arginine.

Agmatine↗
PubMed1988

Cloning and expression of genes encoding pheromone-inducible antigens of Enterococcus (Streptococcus) faecalis.

Fragments, generated by restriction enzyme digestion, of the 58-kilobase Enterococcus (Streptococcus) faecalis tetracycline resistance plasmid pCF10 were cloned and introduced into Escherichia coli and E. faecalis to characterize the pheromone-inducible conjugation system encoded by this plasmid. Western blot (immunoblot) analyses revealed that a 130-kilodalton (kDa) antigen, identical to the Tra130 antigen shown previously to be involved in pCF10-mediated pheromone-inducible surface exclusion, was produced by both bacterial hosts carrying the recombinant plasmid pINY1825 (cloned EcoRI C fragment). Both bacterial hosts carrying pINY1825 also produced various amounts of immunologically related 118- to 125-kDa antigens (designated pre-Tra130) that resembled antigens produced by E. faecalis cells carrying pCF10. An additional 150-kDa antigen, Tra150, probably involved in pheromone-induced cellular aggregation, was produced by Escherichia coli and E. faecalis hosts carrying pINY1801 (cloned EcoRI C and E fragments). The coding sequences for the Tra150 and Tra130 antigens were further localized in the TRA region of pCF10 by transposon insertion mutagenesis. Western blot analyses of the recombinant strains, and of strains carrying derivatives of pCF10 or various recombinant plasmids containing Tn5 or Tn917 insertions, suggested that the portion of pCF10 comprising the tra3 through -6 segments (previously defined by Tn917 insertional mutagenesis) contained several genes that are involved in regulating the synthesis of Tra130 and Tra150.

Antigens, Bacterial↗
PubMed1988

Regulation of the pAD1 sex pheromone response in Enterococcus faecalis: construction and characterization of lacZ transcriptional fusions in a key control region of the plasmid.

Strains carrying the Enterococcus (formerly Streptococcus) faecalis plasmid pAD1 responded to exogenous sex pheromone by inducing a number of gene products which facilitated mating. A 7-kilobase region of pAD1 was identified which contained genes that are important for the regulation of this response. Using the transposon Tn917-lac delivery vector pTV32Ts, we generated a number of fusions that allowed us to examine transcription in this region. At least three transcriptional units were identified by grouping fusions by their phenotype, direction of transcription, and response to pheromone. Transcription from one set of fusions was sensitive to the presence of pheromone. Analysis of the patterns of protein production previously shown to be induced in the presence of pheromone provided more information on the function of the genes of interest. We postulate the existence of two negative regulatory proteins that act coordinately to repress the pheromone response, one of which may be involved in sensing or transmitting the pheromone signal, and at least one positive regulatory protein whose synthesis is dependent on the presence of pheromone. In addition, the isolation of a relatively small deletion mutant capable of producing cAD1. the pheromone specific for pAD1-containing cells, indicates that a factor(s) that is important for the shutdown of endogenous pheromone is also present in this region.

Bacterial Proteins↗
PubMed1988

Conjugative plasmid transfer from Enterococcus faecalis to Escherichia coli.

The possibility of transfer of genetic information by conjugation from gram-positive to gram-negative bacteria was investigated with a pBR322-pAM beta 1 chimeric plasmid, designated pAT191. This shuttle vector, which possesses the tra functions of the streptococcal plasmid pAM beta 1, was conjugatively transferred from Enterococcus faecalis to Escherichia coli with an average frequency of 5 x 10(-9) per donor colony formed after mating.

Conjugation, Genetic↗
PubMed1990

Genetic analysis of the pAD1 hemolysin/bacteriocin determinant in Enterococcus faecalis: Tn917 insertional mutagenesis and cloning.

Thirty-seven nonhemolytic/nonbacteriocinogenic mutations in Enterococcus (Streptococcus) faecalis plasmid pAD1 were generated by Tn917 insertion. All were found to belong to one of two complementation classes. Each class of mutants secreted either hemolysin/bacteriocin (Hly/Bac) component A or L into the culture medium. DNA encoding Hly/Bac was cloned in Escherichia coli in which both components of the hemolysin were expressed individually and collectively. The region encoding components A and L was further defined by deletion analysis and physically mapped. A total of approximately 8.4 kilobases of pAD1 DNA were observed to be required for hemolysin expression. Hly/Bac activity of the wild-type and the inactive L substance was observed to be heat stable. Active Hly/Bac resulting from incubating separately secreted components A and L was also found to be heat stable. The results indicate that component A activates component L and that activated component L possesses the Hly/Bac activity. Component A was also observed to be associated with host immunity to the Hly/Bac.

Bacteriocins↗
PubMed1990

Physiological studies on regulation of glycerol utilization by the phosphoenolpyruvate:sugar phosphotransferase system in Enterococcus faecalis.

In vitro studies with purified glycerol kinase from Enterococcus faecalis have established that this enzyme is activated by phosphorylation of a histidyl residue in the protein, catalyzed by the phosphoenolpyruvate-dependent phosphotransferase system (PTS), but the physiological significance of this observation is not known. In the present study, the regulation of glycerol uptake was examined in a wild-type strain of E. faecalis as well as in tight and leaky ptsI mutants, altered with respect to their levels of enzyme I of the PTS. Glycerol kinase was shown to be weakly repressible by lactose and strongly repressible by glucose in the wild-type strain. Greatly reduced levels of glycerol kinase activity were also observed in the ptsI mutants. Uptake of glycerol into intact wild-type and mutant cells paralleled the glycerol kinase activities in extracts. Glycerol uptake in the leaky ptsI mutant was hypersensitive to inhibition by low concentrations of 2-deoxyglucose or glucose even though the rates and extent of 2-deoxyglucose uptake were greatly reduced. These observations provide strong support for the involvement of reversible PTS-mediated phosphorylation of glycerol kinase in the regulation of glycerol uptake in response to the presence or absence of a sugar substrate of the PTS in the medium. Glucose and 2-deoxyglucose were shown to elicit rapid efflux of cytoplasmic [14C]lactate derived from [14C]glycerol. This phenomenon was distinct from the inhibition of glycerol uptake and was due to phosphorylation of the incoming sugar by cytoplasmic phosphoenolpyruvate. Lactate appeared to be generated by sequential dephosphorylation and reduction of cytoplasmic phosphoenolpyruvate present in high concentrations in resting cells. The relevance of these findings to regulatory phenomena in other bacteria is discussed.

Biological Transport↗
PubMed1990

Regulation of the pAD1 sex pheromone response in Enterococcus faecalis: effects of host strain and traA, traB, and C region mutants on expression of an E region pheromone-inducible lacZ fusion.

Pheromone-induced conjugal transfer of the hemolysin-bacteriocin plasmid pAD1 of Enterococcus faecalis is regulated by a cluster of determinants designated traA, traB, and regions C and E. The E region is believed to include a positive regulator that controls many structural genes related to conjugation. The pheromone-inducible Tn917-lac fusion NR5, located in the E region, is regulated by the products of traA, traB, and the C region. To more closely examine the effects of these genes on the induction of E region products, inserts in each of these genes were combined with the NR5 fusion in a novel approach involving triparental matings with a pAD1 miniplasmid and recombinational mutagenesis. Results indicate that (i) the traA gene product is a key repressor of the pheromone response; (ii) the traB gene product, in cooperation with a gene within or regulated by the E region, controls pheromone shutdown; (iii) a primary function of the C region gene product is in pheromone sensing, with secondary functions in pheromone shutdown and negative regulation; and (iv) the host in which the plasmid resides has a dramatic effect on the regulation of the NR5 fusion in traB and C region mutants. Numerous parallels were observed between the regulation of the NR5 fusion and the regulation of the aggregation and transfer response. These parallels aided in further defining the functions of particular regulatory determinants as well as further establishing the link between the regulation of the E region and the regulation of the aggregation and transfer response.

Cloning, Molecular↗
PubMed1990

A transferable plasmid associated with AS-48 production in Enterococcus faecalis.

Enterococcus faecalis S-48 produces a peptide antibiotic, AS-48, and a bacteriocin, Bc-48. We have isolated mutants that lack these inhibitory characteristics. Further analysis of the mutants indicates that a plasmid of 56 kilobases (pMB2) may harbor the genes for AS-48. In conjugation experiments, pMB2 has been transferred into a plasmid-free OG1X strain of E. faecalis. The OG1X(pMB2) transconjugant produces the antibiotic AS-48 in solid medium, and the MIC of AS-48 for this strain is the same as that of the donor strain.

Anti-Bacterial Agents↗
PubMed1991

Conjugative transfer of Tn916 in Enterococcus faecalis: trans activation of homologous transposons.

Tn916 [carries tet(M)] is a 16.4-kb conjugative transposon that can establish itself in multiple copies in Enterococcus faecalis. To study the interaction of coresident homologous transposons during conjugation, an E. faecalis mutant defective in homologous recombination was utilized for construction of strains harboring Tn916 delta E (a derivative in which erm is substituted for tet) on the chromosome and Tn916 on a nonconjugative plasmid. When these strains were used as donors, the two transposons were able to transfer independently; however, they were found to transfer and become coestablished in the recipient up to 50% of the time. In contrast, cotransfer of a plasmid marker located outside the transposon occurred at a frequency of no greater than 0.5%. Separate experiments showed that mobilization of the nonconjugative plasmids pAM401 and pVA749 by chromosome-borne copies of Tn916 occurred only at low frequencies (generally less than 2% cotransfer). The data imply that the initiation of transposition of Tn916 results in a trans activation that is specific for homologous transposons present in the same cell.

Chromosomes, Bacterial↗
PubMed1991

Molecular and genetic analysis of a region of plasmid pCF10 containing positive control genes and structural genes encoding surface proteins involved in pheromone-inducible conjugation in Enterococcus faecalis.

Exposure of Enterococcus faecalis cells carrying the tetracycline resistance plasmid pCF10 to the heptapeptide pheromone cCF10 results in an increase in conjugal transfer frequency by as much as 10(6)-fold. Pheromone-induced donor cells also express at least two plasmid-encoded surface proteins, the 130-kDa Sec 10 protein, which is involved in surface exclusion, and the 150-kDa Asc10 protein, which has been associated with the formation of mating aggregates. Previous subcloning and transposon mutagenesis studies indicated that the adjacent EcoRI c (7.5 kb) and e (4.5 kb) fragments of pCF10 encode the structural genes for these proteins and that the EcoRI c fragment also encodes at least two regulatory genes involved in activation of the expression of the genes encoding Asc10 and Sec10. In this paper, the results of physical and genetic analysis of this region of pCF10, along with the complete DNA sequences of the EcoRI c and e fragments, are reported. The results of the genetic studies indicate the location of the structural genes for the surface proteins and reveal important features of their transcription. In addition, we provide evidence here and in the accompanying paper (S. B. Olmsted, S.-M. Kao, L. J. van Putte, J. C. Gallo, and G. M. Dunny, J. Bacteriol. 173:7665-7672, 1991) for a role of Asc10 in mating aggregate formation. The data also reveal a complex positive control system that acts at distances of at least 3 to 6 kb to activate expression of Asc10. DNA sequence analysis presented here reveals the positions of a number of specific genes, termed prg (pheromone-responsive genes) in this region of pCF10. The genes mapped include prgA (encoding Sec10) and prgB (encoding Asc10), as well as four putative regulatory genes, prgX, -R, -S, and -T. Although the predicted amino acid sequences of Sec10 and Asc10 have some structural features in common with a number of surface proteins of gram-positive cocci, and the Asc10 sequence is highly similar to that of a similar protein encoded by the pheromone-inducible plasmid pAD1 (D. Galli, F. Lottspeich, and R. Wirth, Mol. Microbiol. 4:895-904, 1990), the regulatory genes show relatively little resemblance to any previously sequenced genes from either procaryotes or eucaryotes.

Amino Acid Sequence↗
PubMed1991

Role of the pheromone-inducible surface protein Asc10 in mating aggregate formation and conjugal transfer of the Enterococcus faecalis plasmid pCF10.

The high transfer frequency of pheromone-inducible conjugative plasmids of Enterococcus faecalis in liquid culture is due in part to the formation of mating aggregates. These aggregates result from the interaction of two surface components, aggregation substance (AS), which is plasmid encoded, and the chromosomally encoded binding substance (BS). In the accompanying paper (S.-M. Kao, S. B. Olmsted, A. S. Viksnins, J.C. Gallo, G. M. Dunny, J. Bacteriol, 173:7650-7664, 1991), the sequence of the prgB gene encoding the AS molecule (Asc10) produced by pheromone-induced cells carrying plasmid pCF10 is presented. Here we report the results of genetic and immunological experiments which define the role of Asc10 in aggregation and plasmid transfer. These data indicate expression of AS on the surface of an E. faecalis cell and its binding to BS expressed on a second cell are required for the formation of a mating pair and the efficient transfer of pCF10 in liquid matings. However, the orientation of the receptors was not critical for transfer; ie., AS expressed on recipient cells could facilitate plasmid transfer via binding to BS on the donor. Our results suggest that additional (as yet unidentified) products are involved in forming the channel that ultimately serves to transfer the DNA, with AS-BS binding serving primarily to generate the initial attachment between cells. The putative prgC gene product, identified by DNA sequencing (data presented in the accompanying paper), could be involved in transfer events occurring subsequent to aggregation.

Antibodies, Monoclonal↗
PubMed1992

Conjugative transfer of Enterococcus faecalis plasmid pAD1: nucleotide sequence and transcriptional fusion analysis of a region involved in positive regulation.

The Enterococcus faecalis plasmid pAD1 undergoes conjugative transfer in response to cAD1, a peptide sex pheromone emitted by potential bacterial recipients. Regulation of pAD1 transfer involves a number of plasmid-encoded determinants:iad, which determines a peptide-competitive inhibitor iAD1; signal sensing and transducing elements; and negative and positive regulators. The key positive regulator(s) of the pheromone response is believed to be encoded within a segment designated the E region of the plasmid. In this study, we analyzed the nucleotide sequence and transcription within the E region. An open reading frame designated traE1 was identified; its inferred protein consists of 118 amino acids. Insertional mutagenesis of traE1 resulted in a complete loss in plasmid transfer capability. Analysis of Tn917-lac insertions giving rise to transcriptional lacZ fusions showed that traE1 is transcribed only under cAD1 inducing conditions. Analysis of additional lacZ fusions within the region provided some insight into the roles of potential regulatory signals within and around the nucleotide sequences reported here. A regulatory role appearing to involve read-through of certain key transcription termination sequences seemed evident.

Amino Acid Sequence↗
PubMed1992

Extracellular and cellular distribution of muramidase-2 and muramidase-1 of Enterococcus hirae ATCC 9790.

A substantial portion of the second peptidoglycan hydrolase (muramidase-2) activity of Enterococcus hirae ATCC 9790 (formerly Streptococcus faecium) is present in the supernatant culture medium. In contrast, nearly all muramidase-1 activity is associated with cells in the latent, proteinase-activatable form. Muramidase-2 activity is produced and secreted throughout growth, with maximal levels attained at or near the end of exponential growth in a rich organic medium. Muramidase-2 activity in the culture medium remained high even during overnight incubations in the absence of proteinase inhibitors. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of supernatant culture medium concentrated by 60% saturated ammonium sulfate precipitation showed the presence of several Coomassie blue-staining bands. One intensely staining protein band, at about 71 kDa, selectively adsorbed to the insoluble peptidoglycan fraction of cell walls of E. hirae, retained muramidase-2 activity, and reacted in Western immunoblots with monoclonal antibodies to muramidase-2. The mobility of extracellular muramidase-2 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis was indistinguishable from that of muramidase-2 extracted with 6 M guanidine hydrochloride from intact bacteria. Muramidase-2 appears to have only a limited number of binding sites on the peptidoglycan of E. hirae cell walls but binds with high affinity. Although high levels of muramidase-2 activity were present in supernatants of stationary-phase cultures, the bacteria were resistant to autolysis. Thus it appears that the peptidoglycan in walls of intact cells of E. hirae is somehow protected from the hydrolytic action of extracellular muramidase-2.

Antibodies, Monoclonal↗
PubMed1992

The cytoplasmic peptidoglycan precursor of vancomycin-resistant Enterococcus faecalis terminates in lactate.

Vancomycin resistance plasmids in enterococci carry the genes vanH and vanA, which encode enzymes catalyzing, respectively, the reduction of 2-keto acids to 2-D-hydroxy acids and the addition of D-hydroxy acids to D-alanine. It has therefore been postulated that resistant cells produce peptidoglycan precursors that terminate in the depsipeptide D-alanine-2-D-hydroxy acid rather than the dipeptide D-alanine-D-alanine, thus preventing vancomycin binding (M. Arthur, C. Molinas, T. D. H. Bugg, G. D. Wright, C. T. Walsh, and P. Courvalin, Antimicrob. Agents Chemother. 36:867-869, 1992). In the present work, a cytoplasmic peptidoglycan precursor was isolated from vancomycin-resistant Enterococcus faecalis and analyzed by mass spectrometry, which suggested the structure UDP-N-acetyl-muramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-lactate.

Amino Acid Sequence↗
PubMed1992

Gene structure of Enterococcus hirae (Streptococcus faecalis) F1F0-ATPase, which functions as a regulator of cytoplasmic pH.

Enterococcus hirae (formerly Streptococcus faecalis) ATCC 9790 has an F1F0-ATPase which functions as a regulator of the cytoplasmic pH but does not synthesize ATP. We isolated four clones which contained genes for c, b, delta, and alpha subunits of this enzyme but not for other subunit genes. It was revealed that two specific regions (upstream of the c-subunit gene and downstream of the gamma-subunit gene) were lost at a specific site in the clones we isolated, suggesting that these regions were unstable in Escherichia coli. The deleted regions were amplified by polymerase chain reaction, and the nucleotide sequences of these regions were determined. The results showed that eight genes for a, c, b, delta, alpha, gamma, beta, and epsilon subunits were present in this order. Northern (RNA) blot analysis showed that these eight genes were transcribed to one mRNA. The i gene was not found in the upper region of the a-subunit gene. Instead of the i gene, this operon contained a long untranslated region (240 bp) whose G + C content was only 30%. There was no typical promoter sequence such as was proposed for E. coli, suggesting that the promoter structure of this species is different from that of E. coli. Deduced amino acid sequences suggested that E. hirae H(+)-ATPase is a typical F1F0-type ATPase but that its gene structure is not identical to that of other bacterial F1F0-ATPases.

Amino Acid Sequence↗
PubMed1992

Tn5381, a conjugative transposon identifiable as a circular form in Enterococcus faecalis.

We have identified two 19-kb conjugative transposons (Tn5381 and Tn5383) in separate strains of multiply resistant Enterococcus faecalis. These transposons confer resistance to tetracycline and minocycline via a tetM gene, are capable of both chromosomal and plasmid integration in a Rec- environment, and transfer between strains in the absence of detectable plasmid DNA at frequencies ranging from < 1 x 10(-9) to 2 x 10(-5) per donor CFU, depending on the donor strain and the growth conditions. Hybridization studies indicate that these transposons are closely related to Tn916. We have identified bands of ca. 19 kb on agarose gel separations of alkaline lysis preparations from E. faecalis strains containing chromosomal copies of Tn5381, which we have confirmed to be a circularized form of this transposon. This phenomenon has previously been observed only when Tn916 has been cloned in Escherichia coli. Overnight growth of donor strains in the presence of subinhibitory concentrations of tetracycline results in an approximately 10-fold increase in transfer frequency of Tn5381 into enterococcal recipients and an increase in the amount of the circular form of Tn5381 as detectable by hybridization. These results suggest that Tn5381 is a Tn916-related conjugative transposon for which the appearance of a circular form and the conjugative-transfer frequency are regulated by a mechanism(s) affected by the presence of tetracycline in the growth medium.

Base Sequence↗
PubMed1992

Evidence that the hemolysin/bacteriocin phenotype of Enterococcus faecalis subsp. zymogenes can be determined by plasmids in different incompatibility groups as well as by the chromosome.

The hemolysin (Hly/Bac) determinant in strains of Enterococcus faecalis was found to be present on plasmids in different incompatibility groups (conferring different sex pheromone responses) as well as on the chromosome. Of 33 Hly/Bac plasmids identified in clinical isolates, the related pheromone for 30 was cAD1; the related pheromone for another two (pYI1 and pYI3) or one (pYI2) was cOB1 or cY12, respectively. The representative Hly/Bac plasmids pAD1, pYI1, pOB1, and pYI2, which responded to pheromones cAD1, cOB1, cOB1, and cYI2, respectively, were compatible with one another. As additions to the incompatibility group IncHly of pAD1, groups for pOB1, pYI1, and pYI2 were designated IncHlyII, IncHlyIII, and IncHlyIV, respectively. Eleven of the 30 plasmids conferring a response to cAD1 were very similar to pAD1 on the basis of their restriction endonuclease profiles. EcoRI fragment D, F, or H containing parts of the Hly/Bac gene(s) of pAD1 hybridized to similar EcoRI fragments from each of the other three representatives of incompatibility groups (i.e., pOB1, pYI1, and pYI2) and to homologous DNA representing the chromosome of the plasmid-free Hly/Bac strain YI6-1.

Bacteriocins↗