Enhancing colistin efficacy against Salmonella infections with a quinazoline-based dual therapeutic strategy.

Colistin remains one of the last-resort therapies for combating infections caused by multidrug-resistant (MDR) Enterobacterales, despite its adverse nephro- and neuro-toxic effects. This study elucidates the mechanism of action of a non-antibiotic 4-anilinoquinazoline-based compound that synergistically enhances the effectiveness of colistin against Salmonella enterica. The quinazoline sensitizes Salmonella by deactivating intrinsic, mutational, and transferable resistance mechanisms that enable Salmonella to counteract the antibiotic impact colistin, together with an induced disruption to the electrochemical balance of the bacterial membrane. The attenuation of colistin resistance via the combined treatment approach also proves efficacious against E. coli, Klebsiella, and Acinetobacter strains. The dual therapy reduces the mortality of Galleria mellonella larvae undergoing a systemic Salmonella infection when compared to individual drug treatments. Overall, our findings unveil the potential of the quinazoline-colistin combined therapy as an innovative strategy against MDR bacteria.

Metagenomic approach to infer rumen microbiome derived traits of cattle.

Ruminants enable the conversion of indigestible plant material into animal consumables, including dairy products, meat, and valuable fibers. Microbiome research is gaining popularity in livestock species because it aids in the knowledge of illnesses and efficiency processes in animals. In this study, we use WGS metagenomic data to thoroughly characterize the ruminal ecosystem of cows to infer positive and negative livestock traits determined by the microbiome. The rumen of cows from Argentina were described by combining different gene biomarkers, pathways composition and taxonomic information. Taxonomic characterization indicated that the two major phyla were Bacteroidetes and Firmicutes; in third place, Proteobacteria was highly represented followed by Actinobacteria; Prevotella, and Bacteroides were the most abundant genera. Functional profiling of carbohydrate-active enzymes indicated that members of the Glycoside Hydrolase (GH) class accounted for 52.2 to 55.6% of the total CAZymes detected, among them the most abundant were the oligosaccharide degrading enzymes. The diversity of GH families found suggested efficient hydrolysis of complex biomass. Genes of multidrug, macrolides, polymyxins, beta-lactams, rifamycins, tetracyclines, and bacitracin resistance were found below 0.12% of relative abundance. Furthermore, the clustering analysis of genera and genes that correlated to methane emissions or feed efficiency, suggested that the cows analysed could be regarded as low methane emitters and clustered with high feed efficiency reference animals. Finally, the combination of bioinformatic analyses used in this study can be applied to assess cattle traits difficult to measure and guide enhanced nutrition and breeding methods.

Intranasal trans-sialidase-based vaccine against Trypanosoma cruzi triggers a mixed cytokine profile in the nasopharynx-associated lymphoid tissue and confers local and systemic immunogenicity.

Trypanosoma cruzi, the agent of Chagas disease, can infect through conjunctive or oral mucosas. Therefore, the induction of mucosal immunity by vaccination is relevant not only to trigger local protection but also to stimulate both humoral and cell-mediated responses in systemic sites to control parasite dissemination. In a previous study, we demonstrated that a nasal vaccine based on a Trans-sialidase (TS) fragment plus the mucosal STING agonist c-di-AMP, was highly immunogenic and elicited prophylactic capacity. However, the immune profile induced by TS-based nasal vaccines at the nasopharyngeal-associated lymphoid tissue (NALT), the target site of nasal immunization, remains unknown. Hence, we analyzed the NALT cytokine expression generated by a TS-based vaccine plus c-di-AMP (TSdA+c-di-AMP) and their association with mucosal and systemic immunogenicity. The vaccine was administered intranasally, in 3 doses separated by 15 days each other. Control groups received TSdA, c-di-AMP, or the vehicle in a similar schedule. We demonstrated that female BALB/c mice immunized intranasally with TSdA+c-di-AMP boosted NALT expression of IFN-γ and IL-6, as well as IFN-ß and TGF-ß. TSdA+c-di-AMP increased TSdA-specific IgA secretion in the nasal passages and also in the distal intestinal mucosa. Moreover, T and B-lymphocytes from NALT-draining cervical lymph nodes and spleen showed an intense proliferation after ex-vivo stimulation with TSdA. Intranasal administration of TSdA+c-di-AMP provokes an enhancement of TSdA-specific IgG2a and IgG1 plasma antibodies, accompanied by an increase IgG2a/IgG1 ratio, indicative of a Th1-biased profile. In addition, immune plasma derived from TSdA+c-di-AMP vaccinated mice exhibit in-vivo and ex-vivo protective capacity. Lastly, TSdA+c-di-AMP nasal vaccine also promotes intense footpad swelling after local TSdA challenge. Our data support that TSdA+c-di-AMP nasal vaccine triggers a NALT mixed pattern of cytokines that were clearly associated with an evident mucosal and systemic immunogenicity. These data are useful for further understanding the immune responses elicited by the NALT following intranasal immunization and the rational design of TS-based vaccination strategies for prophylaxis against T. cruzi.

Redundant potassium transporter systems guarantee the survival of Enterococcus faecalis under stress conditions.

Enterococcus is able to grow in media at pH from 5.0 to 9.0 and a high concentration of NaCl (8%). The ability to respond to these extreme conditions requires the rapid movement of three critical ions: proton (H+), sodium (Na+), and potassium (K+). The activity of the proton F0F1 ATPase and the sodium Na+ V0V1 type ATPase under acidic or alkaline conditions, respectively, is well established in these microorganisms. The potassium uptake transporters KtrI and KtrII were described in Enterococcus hirae, which were associated with growth in acidic and alkaline conditions, respectively. In Enterococcus faecalis, the presence of the Kdp (potassium ATPase) system was early established. However, the homeostasis of potassium in this microorganism is not completely explored. In this study, we demonstrate that Kup and KimA are high-affinity potassium transporters, and the inactivation of these genes in E. faecalis JH2-2 (a Kdp laboratory natural deficient strain) had no effect on the growth parameters. However, in KtrA defective strains (ΔktrA, ΔkupΔktrA) an impaired growth was observed under stress conditions, which was restored to wild type levels by external addition of K+ ions. Among the multiplicity of potassium transporters identify in the genus Enterococcus, Ktr channels (KtrAB and KtrAD), and Kup family symporters (Kup and KimA) are present and may contribute to the particular resistance of these microorganisms to different stress conditions. In addition, we found that the presence of the Kdp system in E. faecalis is strain-dependent, and this transporter is enriched in strains of clinical origin as compared to environmental, commensal, or food isolates.

Genomic analysis revealed conserved acid tolerance mechanisms from native micro-organisms in fermented feed.

AIMS: Fermented feed is an agricultural practice used in many regions of the world to improve the growth performance of farm animals. This study aimed to identify and evaluate the lactic acid bacteria and yeast involved in the production of fermented feed. METHODS AND RESULTS: We isolated and described two micro-organisms from autochthonous microbiota origin present in a regional feed product, Lactobacillus paracasei IBR07 (Lacticaseibacillus paracasei) and Kazachstania unispora IBR014 (Saccharomyces unisporum). Genome sequence analyses were performed to characterize both micro-organisms. Potential pathways involved in the acid response, tolerance and persistence were predicted in both genomes. Although L. paracasei and K. unispora are considered safe for animal feed, we analysed the presence of virulence factors, antibiotic resistance and pathogenicity islands. Furthermore, the Galleria mellonella model was used to support the safety of both isolates. CONCLUSIONS: We conclude that IBR07 and IBR014 strains are good candidates to be used as starter cultures for feed fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: The data presented here will be helpful to explore other biotechnological aspects and constitute a starting point for further studies to establish the consumption benefit of fermented feed in farm animal production.

Diversity of volatile organic compound production from leucine and citrate in Enterococcus faecium.

Enterococcus faecium is frequently isolated from fermented food; in particular, they positively contribute to the aroma compound generation in traditional cheese. Citrate fermentation is a desirable property in these bacteria, but this feature is not uniformly distributed among E. faecium strains. In the present study, three selected E. faecium strains, IQ110 (cit-), GM70 (cit+ type I), and Com12 (cit+ type II), were analyzed in their production of aroma compounds in milk. End products and volatile organic compounds (VOCs) were determined by solid-phase micro-extraction combined with gas chromatography mass spectrometry (SPME-GC-MS). Principal component analysis (PCA) of aroma compound profiles revealed a different VOC composition for the three strains. In addition, resting cell experiments of E. faecium performed in the presence of leucine, citrate, or pyruvate as aroma compound precursors allowed us to determine metabolic differences between the studied strains. GM70 (cit+ type I) showed an active citrate metabolism, with increased levels of diacetyl and acetoin generation relative to Com12 or to citrate defective IQ110 strains. In addition, in the experimental conditions tested, a defective citrate-fermenting phenotype for the Com12 strain was found, while its leucine degradation and pyruvate metabolism were conserved. In conclusion, rational selection of E. faecium strains could be performed based on genotypic and phenotypic analyses. This would result in a performing strain, such as GM70, that could positively contribute to flavor, with typical notes of diacetyl, acetoin, 3-methyl butanal, and 3-methyl butanol in an adjuvant culture.

Implications of the expression of Enterococcus faecalis citrate fermentation genes during infection.

Citrate is an ubiquitous compound in nature. However, citrate fermentation is present only in a few pathogenic or nonpathogenic microorganisms. The citrate fermentation pathway includes a citrate transporter, a citrate lyase complex, an oxaloacetate decarboxylase and a regulatory system. Enterococcus faecalis is commonly present in the gastro-intestinal microbiota of warm-blooded animals and insect guts. These bacteria can also cause infection and disease in immunocompromised individuals. In the present study, we performed whole genome analysis in Enterococcus strains finding that the complete citrate pathway is present in all of the E. faecalis strains isolated from such diverse habitats as animals, hospitals, water, milk, plants, insects, cheese, etc. These results indicate the importance of this metabolic preservation for persistence and growth of E. faecalis in different niches. We also analyzed the role of citrate metabolism in the E. faecalis pathogenicity. We found that an E. faecalis citrate fermentation-deficient strain was less pathogenic for Galleria mellonella larvae than the wild type. Furthermore, strains with deletions in the oxaloacetate decarboxylase subunits or in the α-acetolactate synthase resulted also less virulent than the wild type strain. We also observed that citrate promoters are induced in blood, urine and also in the hemolymph of G. mellonella. In addition, we showed that citrate fermentation allows E. faecalis to grow better in blood, urine and G. mellonella. The results presented here clearly indicate that citrate fermentation plays an important role in E. faecalis opportunistic pathogenic behavior.

Safety assessment and functional properties of four enterococci strains isolated from regional Argentinean cheese.

The members of the Enterococcus genus are widely distributed in nature. Its strains have been extensively reported to be present in plant surfaces, soil, water and food. In an attempt to assess their potential application in food industry, four Enterococcus faecium group-strains recently isolated from Argentinean regional cheese products were evaluated using a combination of whole genome analyses and in vivo assays. In order to identify these microorganisms at species level, in silico analyses using their newly reported sequences were conducted. The average nucleotide identity (ANI), in silico DNA-DNA hybridization, and phylogenomic trees constructed using core genome data allowed IQ110, GM70 and GM75 strains to be classified as E. faecium while IQ23 strain was identified as E. durans. Besides their common origin, the strains showed differences in their genetic structure and mobile genetic element content. Furthermore, it was possible to determine the absence or presence of specific features related to growth in milk, cheese ripening, probiotic capability and gut adaptation including sugar, amino acid, and peptides utilization, flavor compound production, bile salt tolerance as well as biogenic amine production. Remarkably, all strains encoded for peptide permeases, maltose utilization, bile salt tolerance, diacetyl and tyramine production genes. On the other hand, some variability was observed regarding citrate and lactose utilization, esterase, and cell wall-associated proteinase. In addition, while strains were predicted to be non-human pathogens by the in silico inspection of pathogenicity and virulence factors, only the GM70 strain proved to be non-virulent in Galleria mellonella model. In conclusion, we propose that, in order to improve the rational selection of strains for industrial applications, a holistic approach involving a comparative genomic analysis of positive and negative features as well as in vivo evaluation of virulence behavior should be performed.

Enzymes Required for Maltodextrin Catabolism in Enterococcus faecalis Exhibit Novel Activities.

Maltose and maltodextrins are formed during the degradation of starch or glycogen. Maltodextrins are composed of a mixture of maltooligosaccharides formed by α-1,4- but also some α-1,6-linked glucosyl residues. The α-1,6-linked glucosyl residues are derived from branching points in the polysaccharides. In Enterococcus faecalis, maltotriose is mainly transported and phosphorylated by a phosphoenolpyruvate:carbohydrate phosphotransferase system. The formed maltotriose-6″-phosphate is intracellularly dephosphorylated by a specific phosphatase, MapP. In contrast, maltotetraose and longer maltooligosaccharides up to maltoheptaose are taken up without phosphorylation via the ATP binding cassette transporter MdxEFG-MsmX. We show that the maltose-producing maltodextrin hydrolase MmdH (GenBank accession no. EFT41964) in strain JH2-2 catalyzes the first catabolic step of α-1,4-linked maltooligosaccharides. The purified enzyme converts even-numbered α-1,4-linked maltooligosaccharides (maltotetraose, etc.) into maltose and odd-numbered (maltotriose, etc.) into maltose and glucose. Inactivation of mmdH therefore prevents the growth of E. faecalis on maltooligosaccharides ranging from maltotriose to maltoheptaose. Surprisingly, MmdH also functions as a maltogenic α-1,6-glucosidase, because it converts the maltotriose isomer isopanose into maltose and glucose. In addition, E. faecalis contains a glucose-producing α-1,6-specific maltodextrin hydrolase (GenBank accession no. EFT41963, renamed GmdH). This enzyme converts panose, another maltotriose isomer, into glucose and maltose. A gmdH mutant had therefore lost the capacity to grow on panose. The genes mmdH and gmdH are organized in an operon together with GenBank accession no. EFT41962 (renamed mmgT). Purified MmgT transfers glucosyl residues from one α-1,4-linked maltooligosaccharide molecule to another. For example, it catalyzes the disproportionation of maltotriose by transferring a glucosyl residue to another maltotriose molecule, thereby forming maltotetraose and maltose together with a small amount of maltopentaose.IMPORTANCE The utilization of maltodextrins by Enterococcus faecalis has been shown to increase the virulence of this nosocomial pathogen. However, little is known about how this organism catabolizes maltodextrins. We identified two enzymes involved in the metabolism of various α-1,4- and α-1,6-linked maltooligosaccharides. We found that one of them functions as a maltose-producing α-glucosidase with relaxed linkage specificity (α-1,4 and α-1,6) and exo- and endoglucosidase activities. A third enzyme, which resembles amylomaltase, exclusively transfers glucosyl residues from one maltooligosaccharide molecule to another. Similar enzymes are present in numerous other Firmicutes, such as streptococci and lactobacilli, suggesting that these organisms follow the same maltose degradation pathway as E. faecalis.

Enterococcus faecalis Uses a Phosphotransferase System Permease and a Host Colonization-Related ABC Transporter for Maltodextrin Uptake.

Maltodextrin is a mixture of maltooligosaccharides, which are produced by the degradation of starch or glycogen. They are mostly composed of α-1,4- and some α-1,6-linked glucose residues. Genes presumed to code for the Enterococcus faecalis maltodextrin transporter were induced during enterococcal infection. We therefore carried out a detailed study of maltodextrin transport in this organism. Depending on their length (3 to 7 glucose residues), E. faecalis takes up maltodextrins either via MalT, a maltose-specific permease of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), or the ATP binding cassette (ABC) transporter MdxEFG-MsmX. Maltotriose, the smallest maltodextrin, is primarily transported by the PTS permease. A malT mutant therefore exhibits significantly reduced growth on maltose and maltotriose. The residual uptake of the trisaccharide is catalyzed by the ABC transporter, because a malT mdxF double mutant no longer grows on maltotriose. The trisaccharide arrives as maltotriose-6″-P in the cell. MapP, which dephosphorylates maltose-6'-P, also releases Pi from maltotriose-6″-P. Maltotetraose and longer maltodextrins are mainly (or exclusively) taken up via the ABC transporter, because inactivation of the membrane protein MdxF prevents growth on maltotetraose and longer maltodextrins up to at least maltoheptaose. E. faecalis also utilizes panose and isopanose, and we show for the first time, to our knowledge, that in contrast to maltotriose, its two isomers are primarily transported via the ABC transporter. We confirm that maltodextrin utilization via MdxEFG-MsmX affects the colonization capacity of E. faecalis, because inactivation of mdxF significantly reduced enterococcal colonization and/or survival in kidneys and liver of mice after intraperitoneal infection.IMPORTANCE Infections by enterococci, which are major health care-associated pathogens, are difficult to treat due to their increasing resistance to clinically relevant antibiotics, and new strategies are urgently needed. A largely unexplored aspect is how these pathogens proliferate and which substrates they use in order to grow inside infected hosts. The use of maltodextrins as a source of carbon and energy was studied in Enterococcus faecalis and linked to its virulence. Our results demonstrate that E. faecalis can efficiently use glycogen degradation products. We show here that depending on the length of the maltodextrins, one of two different transporters is used: the maltose-PTS transporter MalT, or the MdxEFG-MsmX ABC transporter. MdxEFG-MsmX takes up longer maltodextrins as well as complex molecules, such as panose and isopanose.

Draft Genome Sequence of Lactococcus lactis subsp. lactis bv. diacetylactis CRL264, a Citrate-Fermenting Strain.

We report the draft genome sequence of Lactococcus lactis subsp. lactis bv. diacetylactis CRL264, a natural strain isolated from artisanal cheese from northwest Argentina. L. lactis subsp. lactis bv. diacetylactis is one of the most important microorganisms used as starter culture around the world. The CRL264 strain constitutes a model microorganism in the studies on the generation of aroma compounds (diacetyl, acetoin, and 2,3-butanediol) by lactic acid bacteria. Our genome analysis shows similar genetic organization to other available genomes of L. lactis bv. diacetylactis strains.

Draft Genome Sequences of Four Enterococcus faecium Strains Isolated from Argentine Cheese.

We report the draft genome sequences of four Enterococcus faecium strains isolated from Argentine regional cheeses. These strains were selected based on their technological properties, i.e., their ability to produce aroma compounds (diacetyl, acetoin, and 2,3-butanediol) from citrate. The goal of our study is to provide further genetic evidence for the rational selection of enterococci strains based on their pheno- and genotype in order to be used in cheese production.

Functional Analysis of the Citrate Activator CitO from Enterococcus faecalis Implicates a Divalent Metal in Ligand Binding.

The regulator of citrate metabolism, CitO, from Enterococcus faecalis belongs to the FCD family within the GntR superfamily. In the presence of citrate, CitO binds to cis-acting sequences located upstream of the cit promoters inducing the expression of genes involved in citrate utilization. The quantification of the molecular binding affinities, performed by isothermal titration calorimetry (ITC), indicated that CitO has a high affinity for citrate (K D = 1.2 ± 0.2 µM), while it did not recognize other metabolic intermediates. Based on a structural model of CitO where a putative small molecule and a metal binding site were identified, it was hypothesized that the metal ion is required for citrate binding. In agreement with this model, citrate binding to CitO sharply decreased when the protein was incubated with EDTA. This effect was reverted by the addition of Ni(2+), and Zn(2+) to a lesser extent. Structure-based site-directed mutagenesis was conducted and it was found that changes to alanine in residues Arg97 and His191 resulted in decreased binding affinities for citrate, as determined by EMSA and ITC. Further assays using lacZ fusions confirmed that these residues in CitO are involved in sensing citrate in vivo. These results indicate that the molecular modifications induced by a ligand and a metal binding in the C-terminal domain of CitO are required for optimal DNA binding activity, and consequently, transcriptional activation.

Aroma compounds generation in citrate metabolism of Enterococcus faecium: Genetic characterization of type I citrate gene cluster.

Enterococcus is one of the most controversial genera belonging to Lactic Acid Bacteria. Research involving this microorganism reflects its dual behavior as regards its safety. Although it has also been associated to nosocomial infections, natural occurrence of Enterococcus faecium in food contributes to the final quality of cheese. This bacterium is capable of fermenting citrate, which is metabolized to pyruvate and finally derives in the production of the aroma compounds diacetyl, acetoin and 2,3 butanediol. Citrate metabolism was studied in E. faecium but no data about genes related to these pathways have been described. A bioinformatic approach allowed us to differentiate cit(-) (no citrate metabolism genes) from cit(+) strains in E. faecium. Furthermore, we could classify them according to genes encoding for the transcriptional regulator, the oxaloacetate decarboxylase and the citrate transporter. Thus we defined type I organization having CitI regulator (DeoR family), CitM cytoplasmic soluble oxaloacetate decarboxylase (Malic Enzyme family) and CitP citrate transporter (2-hydroxy-carboxylate transporter family) and type II organization with CitO regulator (GntR family), OAD membrane oxaloacetate decarboxylase complex (Na(+)-transport decarboxylase enzyme family) and CitH citrate transporter (CitMHS family). We isolated and identified 17 E. faecium strains from regional cheeses. PCR analyses allowed us to classify them as cit(-) or cit(+). Within the latter classification we could differentiate type I but no type II organization. Remarkably, we came upon E. faecium GM75 strain which carries the insertion sequence IS256, involved in adaptative and evolution processes of bacteria related to Staphylococcus and Enterococcus genera. In this work we describe the differential behavior in citrate transport, metabolism and aroma generation of three strains and we present results that link citrate metabolism and genetic organizations in E. faecium for the first time.

Genomic comparative analysis of the environmental Enterococcus mundtii against enterococcal representative species.

BACKGROUND: Enterococcus mundtii is a yellow-pigmented microorganism rarely found in human infections. The draft genome sequence of E. mundtii was recently announced. Its genome encodes at least 2,589 genes and 57 RNAs, and 4 putative genomic islands have been detected. The objective of this study was to compare the genetic content of E. mundtii with respect to other enterococcal species and, more specifically, to identify genes coding for putative virulence traits present in enterococcal opportunistic pathogens. RESULTS: An in-depth mining of the annotated genome was performed in order to uncover the unique properties of this microorganism, which allowed us to detect a gene encoding the antimicrobial peptide mundticin among other relevant features. Moreover, in this study a comparative genomic analysis against commensal and pathogenic enterococcal species, for which genomic sequences have been released, was conducted for the first time. Furthermore, our study reveals significant similarities in gene content between this environmental isolate and the selected enterococci strains (sharing an "enterococcal gene core" of 805 CDS), which contributes to understand the persistence of this genus in different niches and also improves our knowledge about the genetics of this diverse group of microorganisms that includes environmental, commensal and opportunistic pathogens. CONCLUSION: Although E. mundtii CRL1656 is phylogenetically closer to E. faecium, frequently responsible of nosocomial infections, this strain does not encode the most relevant relevant virulence factors found in the enterococcal clinical isolates and bioinformatic predictions indicate that it possesses the lowest number of putative pathogenic genes among the most representative enterococcal species. Accordingly, infection assays using the Galleria mellonella model confirmed its low virulence.

Expression of the agmatine deiminase pathway in Enterococcus faecalis is activated by the AguR regulator and repressed by CcpA and PTS(Man) systems.

Although the agmatine deiminase system (AgDI) has been investigated in Enterococcus faecalis, little information is available with respect to its gene regulation. In this study we demonstrate that the presence of exogenous agmatine induces the expression of agu genes in this bacterium. In contrast to the homologous and extensively characterized AgDI system of S. mutants, the aguBDAC operon in E. faecalis is not induced in response to low pH. In spite of this, agmatine catabolism in this bacterium contributes by neutralizing the external medium while enhancing bacterial growth. Our results indicate that carbon catabolic repression (CCR) operates on the AgDI system via a mechanism that involves interaction of CcpA and P-Ser-HPr with a cre site found in an unusual position considering the aguB promoter (55 nt upstream the +1 position). In addition, we found that components of the mannose phosphotransferase (PTS(Man)) system also contributed to CCR in E. faecalis since a complete relief of the PTS-sugars repressive effect was observed only in a PTS(Man) and CcpA double defective strain. Our gene context analysis revealed that aguR is present in oral and gastrointestinal microorganisms. Thus, regulation of the aguBDAC operon in E. faecalis seems to have evolved to obtain energy and resist low pH conditions in order to persist and colonize gastrointestinal niches.

Enterococcus faecalis utilizes maltose by connecting two incompatible metabolic routes via a novel maltose 6'-phosphate phosphatase (MapP).

Similar to Bacillus subtilis, Enterococcus faecalis transports and phosphorylates maltose via a phosphoenolpyruvate (PEP):maltose phosphotransferase system (PTS). The maltose-specific PTS permease is encoded by the malT gene. However, E. faecalis lacks a malA gene encoding a 6-phospho-α-glucosidase, which in B. subtilis hydrolyses maltose 6'-P into glucose and glucose 6-P. Instead, an operon encoding a maltose phosphorylase (MalP), a phosphoglucomutase and a mutarotase starts upstream from malT. MalP was suggested to split maltose 6-P into glucose 1-P and glucose 6-P. However, purified MalP phosphorolyses maltose but not maltose 6'-P. We discovered that the gene downstream from malT encodes a novel enzyme (MapP) that dephosphorylates maltose 6'-P formed by the PTS. The resulting intracellular maltose is cleaved by MalP into glucose and glucose 1-P. Slow uptake of maltose probably via a maltodextrin ABC transporter allows poor growth for the mapP but not the malP mutant. Synthesis of MapP in a B. subtilis mutant accumulating maltose 6'-P restored growth on maltose. MapP catalyses the dephosphorylation of intracellular maltose 6'-P, and the resulting maltose is converted by the B. subtilis maltose phosphorylase into glucose and glucose 1-P. MapP therefore connects PTS-mediated maltose uptake to maltose phosphorylase-catalysed metabolism. Dephosphorylation assays with a wide variety of phospho-substrates revealed that MapP preferably dephosphorylates disaccharides containing an O-α-glycosyl linkage.

Biochemical and genetic characterization of the Enterococcus faecalis oxaloacetate decarboxylase complex.

Enterococcus faecalis encodes a biotin-dependent oxaloacetate decarboxylase (OAD), which is constituted by four subunits: E. faecalis carboxyltransferase subunit OadA (termed Ef-A), membrane pump Ef-B, biotin acceptor protein Ef-D, and the novel subunit Ef-H. Our results show that in E. faecalis, subunits Ef-A, Ef-D, and Ef-H form a cytoplasmic soluble complex (termed Ef-AHD) which is also associated with the membrane. In order to characterize the role of the novel Ef-H subunit, coexpression of oad genes was performed in Escherichia coli, showing that this subunit is vital for Ef-A and Ef-D interaction. Diminished growth of the oadA and oadD single deletion mutants in citrate-supplemented medium indicated that the activity of the complex is essential for citrate utilization. Remarkably, the oadB-deficient strain was still capable of growing to wild-type levels but with a delay during the citrate-consuming phase, suggesting that the soluble Ef-AHD complex is functional in E. faecalis. These results suggest that the Ef-AHD complex is active in its soluble form, and that it is capable of interacting in a dynamic way with the membrane-bound Ef-B subunit to achieve its maximal alkalinization capacity during citrate fermentation.

Draft genome sequence of Enterococcus mundtii CRL1656.

We report the draft genome sequence of Enterococcus mundtii CRL1656, which was isolated from the stripping milk of a clinically healthy adult Holstein dairy cow from a dairy farm of the northwestern region of Tucumán (Argentina). The 3.10-Mb genome sequence consists of 450 large contigs and contains 2,741 predicted protein-coding genes.

CcpA represses the expression of the divergent cit operons of Enterococcus faecalis through multiple cre sites.

BACKGROUND: In Enterococcus faecalis the genes encoding the enzymes involved in citrate metabolism are organized in two divergent operons, citHO and oadHDB-citCDEFX-oadA-citMG (citCL locus). Expression of both operons is specifically activated by adding citrate to the medium. This activation is mediated by binding of the GntR-like transcriptional regulator (CitO) to the cis-acting sequences located in the cit intergenic region. Early studies indicated that citrate and glucose could not be co-metabolized suggesting some form of catabolite repression, however the molecular mechanism remained unknown. RESULTS: In this study, we observed that the citHO promoter is repressed in the presence of sugars transported by the Phosphoenolpyruvate:carbohydrate Phosphotranserase System (PTS sugars). This result strongly suggested that Carbon Catabolic Repression (CCR) impedes the expression of the activator CitO and the subsequent induction of the cit pathway. In fact, we demonstrate that CCR is acting on both promoters. It is partially relieved in a ccpA-deficient E. faecalis strain indicating that a CcpA-independent mechanism is also involved in regulation of the two operons. Furthermore, sequence analysis of the citH/oadH intergenic region revealed the presence of three putative catabolite responsive elements (cre). We found that they are all active and able to bind the CcpA/P-Ser-HPr complex, which downregulates the expression of the cit operons. Systematic mutation of the CcpA/P-Ser-HPr binding sites revealed that cre1 and cre2 contribute to citHO repression, while cre3 is involved in CCR of citCL. CONCLUSION: In conclusion, our study establishes that expression of the cit operons in E. faecalis is controlled by CCR via CcpA-dependent and -independent mechanisms.