GFP Transcriptional Fusions Research Articles

Dual Regulation of Phosphatidylserine Decarboxylase Expression by Envelope Stress Responses.

Bacteria adapt to versatile environments by modulating gene expression through a set of stress response regulators, alternative Sigma factors, or two-component systems. Among the central processes that must be finely tuned is membrane homeostasis, including synthesis of phospholipids (PL). However, few genetic regulations of this process have been reported. We have previously shown that the gene coding the first step of PL synthesis is regulated by σE and ppGpp, and that the BasRS (PmrAB) two component system controls the expression of the DgkA PL recycling enzyme. The gene coding for phosphatidylserine decarboxylase, the last step in phosphatidylethanolamine synthesis is another gene in the PL synthesis pathway susceptible of stress response regulation. Indeed, psd appears in transcriptome studies of the σE envelope stress Sigma factor and of the CpxAR two component system. Interestingly, this gene is presumably in operon with mscM coding for a miniconductance mechanosensitive channel. In this study, we dissected the promoter region of the psd-mscM operon and studied its regulation by σE and CpxR. By artificial activation of σE and CpxRA stress response pathways, using GFP transcriptional fusion and western-blot analysis of Psd and MscM enzyme production, we showed that the operon is under the control of two distinct promoters. One is activated by σE, the second is activated by CpxRA and also responsible for basal expression of the operon. The fact that the phosphatidylethanolamine synthesis pathway is controlled by envelope stress responses at both its first and last steps might be important for adaptation of the membrane to envelope perturbations.

A polyketide synthase gene cluster associated with the sexual reproductive cycle of the banana pathogen, Pseudocercospora fijiensis.

Disease spread of Pseudocercospora fijiensis, causal agent of the black Sigatoka disease of banana, depends on ascospores produced through the sexual reproductive cycle. We used phylogenetic analysis to identify P. fijiensis homologs (PKS8-4 and Hybrid8-3) to the PKS4 polyketide synthases (PKS) from Neurospora crassa and Sordaria macrospora involved in sexual reproduction. These sequences also formed a clade with lovastatin, compactin, and betaenone-producing PKS sequences. Transcriptome analysis showed that both the P. fijiensis Hybrid8-3 and PKS8-4 genes have higher expression in infected leaf tissue compared to in culture. Domain analysis showed that PKS8-4 is more similar than Hybrid8-3 to PKS4. pPKS8-4:GFP transcriptional fusion transformants showed expression of GFP in flask-shaped structures in mycelial cultures as well as in crosses between compatible and incompatible mating types. Confocal microscopy confirmed expression in spermagonia in leaf substomatal cavities, consistent with a role in sexual reproduction. A disruption mutant of pks8-4 retained normal pathogenicity on banana, and no differences were observed in growth, conidial production, and spermagonia production. GC-MS profiling of the mutant and wild type did not identify differences in polyketide metabolites, but did identify changes in saturated fatty acid methyl esters and alkene and alkane derivatives. To our knowledge, this is the first report of a polyketide synthase pathway associated with spermagonia.

Positive autoregulation of the flhDC operon in Proteus mirabilis

Using a variety of techniques, we demonstrate the Class I regulator of the flagellar cascade, FlhD4C2, can activate its own expression in Proteus mirabilis. This activation was direct, as the FlhD4C2 protein specifically bound to its promoter region. The expression of bacterial genes under a positive feedback control can exhibit varying levels between cells due to stochastic fluctuations that activate the feedback loop and result in some cells in an “ON” state. Cells containing a chromosomal flhDC::gfp transcriptional fusion exhibited a heterogeneous pattern of expression within the population during growth on agar surfaces and the percentage of cells expressing GFP increased as cells approached swarmer cell differentiation. Disrupting the FlhD4C2 –mediated positive feedback loop significantly reduced the frequency of cells exhibiting GFP expression.

Role in virulence of phospholipases, listeriolysin O and listeriolysin S from epidemic Listeria monocytogenes using the chicken embryo infection model

Most human listeriosis outbreaks are caused by Listeria monocytogenes evolutionary lineage I strains which possess four exotoxins: a phosphatidylinositol-specific phospholipase C (PlcA), a broad-range phospholipase C (PlcB), listeriolysin O (LLO) and listeriolysin S (LLS). The simultaneous contribution of these molecules to virulence has never been explored. Here, the importance of these four exotoxins of an epidemic lineage I L. monocytogenes strain (F2365) in virulence was assessed in chicken embryos infected in the allantoic cavity. We show that LLS does not play a role in virulence while LLO is required to infect and kill chicken embryos both in wild type transcriptional regulator of virulence PrfA (PrfAWT) and constitutively active PrfA (PrfA*) backgrounds. We demonstrate that PlcA, a toxin previously considered as a minor virulence factor, played a major role in virulence in a PrfA* background. Interestingly, GFP transcriptional fusions show that the plcA promoter is less active than the hly promoter in vitro, explaining why the contribution of PlcA to virulence could be observed more importantly in a PrfA* background. Together, our results suggest that PlcA might play a more important role in the infectious lifecycle of L. monocytogenes than previously thought, explaining why all the strains of L. monocytogenes have conserved an intact copy of plcA in their genomes.

Analyzing the Transcriptomes of Two Quorum-Sensing Controlled Transcription Factors, RcsA and LrhA, Important for Pantoea stewartii Virulence.

The Gram-negative proteobacterium Pantoea stewartii subsp. stewartii causes wilt disease in corn plants. Wilting is primarily due to bacterial exopolysaccharide (EPS) production that blocks water transport in the xylem during the late stages of infection. EsaR, the master quorum-sensing (QS) regulator in P. stewartii, modulates EPS levels. At low cell densities EsaR represses or activates expression of a number of genes in the absence of its acyl homoserine lactone (AHL) ligand. At high cell densities, binding of AHL inactivates EsaR leading to derepression or deactivation of its direct targets. Two of these direct targets are the key transcription regulators RcsA and LrhA, which in turn control EPS production and surface motility/adhesion, respectively. In this study, RNA-Seq was used to further examine the physiological impact of deleting the genes encoding these two second-tier regulators. Quantitative reverse transcription PCR (qRT-PCR) was used to validate the regulation observed in the RNA-Seq data. A GFP transcriptional fusion reporter confirmed the existence of a regulatory feedback loop in the system between LrhA and RcsA. Plant virulence assays carried out with rcsA and lrhA deletion and complementation strains demonstrated that both transcription factors play roles during establishment of wilt disease in corn. These efforts further define the hierarchy of the QS-regulated network controlling plant virulence in P. stewartii.

Characterization of five putative aspartate aminotransferase genes in the N2-fixing heterocystous cyanobacterium Anabaena sp. strain PCC 7120

Aspartate and glutamate are two key amino acids used in biosynthesis of many amino acids that play vital role in cellular metabolism. Aspartate aminotransferases (AspATs) are required for channelling nitrogen (N(2)) between Glu and Asp in all life forms. Biochemical and genetic characterization of AspATs have been lacking in N(2)-fixing cyanobacteria. In this report, five putative AspAT genes (alr1039, all2340, alr2765, all4327 and alr4853) were identified in the N(2)-fixing heterocystous cyanobacterium Anabaena sp. PCC 7120. Five recombinant C-terminal hexahistidine-tagged AspATs (AspAT-H(6)) were overexpressed in Escherichia coli and purified to homogeneity. Biochemical analysis demonstrated that these five putative AspATs have authentic AspAT activity in vitro using aspartate as an amino donor. However, the enzymic activities of the five AspATs differed in vitro. Alr4853-H(6) showed the highest AspAT activity, while the enzymic activity for the other four AspATs ranged from 6.5 to 53.7 % activity compared to Alr4853 (100 %). Genetic characterization of the five AspAT genes was also performed by inactivating each individual gene. All of the five AspAT knockout mutants exhibited reduced diazotrophic growth, and alr4853 was further identified to be a Fox gene (requiring fixed N(2) for growth in the presence of oxygen). Four out of five P(aspAT)-gfp transcriptional fusions were constitutively expressed in both diazotrophic and nitrate-dependent growth conditions. Quantitative reverse transcriptase PCR showed that alr4853 expression was increased by 2.3-fold after 24 h of N(2) deprivation. Taken together, these findings add to our understanding of the role of AspATs in N(2)-fixing within heterocystous cyanobacteria.

Histoplasma yeast and mycelial transcriptomes reveal pathogenic-phase and lineage-specific gene expression profiles

BackgroundThe dimorphic fungus Histoplasma capsulatum causes respiratory and systemic disease in mammalian hosts by expression of factors that enable survival within phagocytic cells of the immune system. Histoplasma’s dimorphism is distinguished by growth either as avirulent mycelia or as pathogenic yeast. Geographically distinct strains of Histoplasma differ in their relative virulence in mammalian hosts and in production of and requirement for specific virulence factors. The close similarity in the genome sequences of these diverse strains suggests that phenotypic variations result from differences in gene expression rather than gene content. To provide insight into how the transcriptional program translates into morphological variation and the pathogenic lifestyle, we compared the transcriptional profile of the pathogenic yeast phase and the non-pathogenic mycelial phase of two clinical isolates of Histoplasma.ResultsTo overcome inaccuracies in ab initio genome annotation of the Histoplasma genome, we used RNA-seq methodology to generate gene structure models based on experimental evidence. Quantitative analyses of the sequencing reads revealed 6% to 9% of genes are differentially regulated between the two phases. RNA-seq-based mRNA quantitation was strongly correlated with gene expression levels determined by quantitative RT-PCR. Comparison of the yeast-phase transcriptomes between strains showed 7.6% of all genes have lineage-specific expression differences including genes contributing, or potentially related, to pathogenesis. GFP-transcriptional fusions and their introduction into both strain backgrounds revealed that the difference in transcriptional activity of individual genes reflects both variations in the cis- and trans-acting factors between Histoplasma strains.ConclusionsComparison of the yeast and mycelial transcriptomes highlights genes encoding virulence factors as well as those involved in protein glycosylation, alternative metabolism, lipid remodeling, and cell wall glycanases that may contribute to Histoplasma pathogenesis. These studies lay an essential foundation for understanding how gene expression variations contribute to the strain- and phase-specific virulence differences of Histoplasma.

Expression dynamics of RpoS/Crl-dependent genes in Escherichia coli

The alternative sigma factor RpoS is a central regulator of the stress response in many Proteobacteria, acting both during exponential growth and in stationary phase. The small protein Crl increases the interaction between RpoS and RNA polymerase and thereby activates certain RpoS-dependent promoters. However, the growth-phase dependence of the interaction of Crl with different forms of polymerase remains unknown. We use 41 GFP transcriptional fusions to study the dynamics of gene regulation by RpoS and Crl during growth transition from exponential to stationary phase in Escherichia coli. We confirm that RpoS can regulate gene expression in exponential phase, both positively and negatively. Crl slightly stimulates transcription by RpoS in exponential phase and controls a subset of RpoS-dependent genes in stationary phase. Growth temperature strongly affects induction of specific promoters by RpoS, whereas its impact on gene regulation by Crl is much less significant. In addition, we identify five new genes regulated by Crl (ada, cbpA, glgS, sodC and flgM) and demonstrate that Crl improves promoter binding and opening by RpoS-containing RNA polymerase at the hdeA promoter. Our study also shows that Crl is a cognate enhancer of RpoS activity under different growth conditions, since its deletion has no effect on genes transcribed by other sigma factors.

Amphetamine Activates an Amine-gated Chloride Channel to Generate Behavioral Effects in Caenorhabditis elegans

Amphetamine is a highly addictive psychostimulant, which is thought to generate its effects by promoting release of dopamine through reverse activation of dopamine transporters. However, some amphetamine-mediated behaviors persist in dopamine transporter knock-out animals, suggesting the existence of alternative amphetamine targets. Here we demonstrate the identification of a novel amphetamine target by showing that in Caenorhabditis elegans, a large fraction of the behavioral effects of amphetamine is mediated through activation of the amine-gated chloride channel, LGC-55. These findings bring to light alternative pathways engaged by amphetamine, and urge rethinking of the molecular mechanisms underlying the effects of this highly-addictive psychostimulant.

A multicomponent sugar phosphate sensor system specifically induced in Bacillus cereus during infection of the insect gut

Using a previously developed Bacillus cereus in vivo expression technology (IVET) promoter trap system, we showed that spsA, a gene of unknown function, was specifically expressed in the larval gut during infection. Search for gut-related compounds inducing spsA transcription identified glucose-6-phosphate (G6P) as an activation signal. Analysis of the spsA-related 5-gene cluster indicated that SpsA is part of a new sugar phosphate sensor system composed of a 2-component system (TCS) encoded by spsR and spsK, and 2 additional downstream genes, spsB and spsC. In B. cereus, American Type Culture Collection (ATCC) 14579, spsRK, and spsABC are separate transcriptional units, of which only spsABC was activated by extracellular G6P. lacZ transcriptional fusions tested in mutant and complemented strains showed that SpsRK, SpsA, and SpsB are essential for the transcription of spsABC. Deletion mutant analysis showed that SpsC is essential for the G6P uptake. gfp-transcriptional fusions showed that these genes are required for host-activated expression, as well. This sugar phosphate sensor and transport system is found in pathogenic Bacillus group and Clostridia bacteria and may be important for host adaptation. Our findings provide new insights into the function of 2-component sensor systems in host-pathogen interactions, specifically in the gut.

Single-cell analysis in situ in a Bacillus subtilis swarming community identifies distinct spatially separated subpopulations differentially expressing hag (flagellin), including specialized swarmers

The non-domesticated Bacillus subtilis strain 3610 displays, over a wide range of humidity, hyper-branched, dendritic, swarming-like migration on a minimal agar medium. At high (70 %) humidity, the laboratory strain 168 sfp+ (producing surfactin) behaves very similarly, although this strain carries a frameshift mutation in swrA, which another group has shown under their conditions (which include low humidity) is essential for swarming. We reconcile these different results by demonstrating that, while swrA is essential for dendritic migration at low humidity (30-40 %), it is dispensable at high humidity. Dendritic migration (flagella- and surfactin-dependent) of strains 168 sfp+ swrA and 3610 involves elongation of dendrites for several hours as a monolayer of cells in a thin fluid film. This enabled us to determine in situ the spatiotemporal pattern of expression of some key players in migration as dendrites develop, using gfp transcriptional fusions for hag (encoding flagellin), comA (regulation of surfactin synthesis) as well as eps (exopolysaccharide synthesis). Quantitative (single-cell) analysis of hag expression in situ revealed three spatially separated subpopulations or cell types: (i) networks of chains arising early in the mother colony (MC), expressing eps but not hag; (ii) largely immobile cells in dendrite stems expressing intermediate levels of hag; and (iii) a subpopulation of cells with several distinctive features, including very low comA expression but hyper-expression of hag (and flagella). These specialized cells emerge from the MC to spearhead the terminal 1 mm of dendrite tips as swirling and streaming packs, a major characteristic of swarming migration. We discuss a model for this swarming process, emphasizing the importance of population density and of the complementary roles of packs of swarmers driving dendrite extension, while non-mobile cells in the stems extend dendrites by multiplication.

α-Catulin CTN-1 is required for BK channel subcellular localization in C. elegans body-wall muscle cells

The BK channel, a voltage- and Ca(2+)-gated large-conductance potassium channel with many important functions, is often localized at specific subcellular domains. Although proper subcellular localization is likely a prerequisite for the channel to perform its physiological functions, little is known about the molecular basis of localization. Here, we show that CTN-1, a homologue of mammalian α-catulin, is required for subcellular localization of SLO-1, the Caenorhabditis elegans BK channel α-subunit, in body-wall muscle cells. CTN-1 was identified in a genetic screen for mutants that suppressed a lethargic phenotype caused by expressing a gain-of-function (gf) isoform of SLO-1. In body-wall muscle cells, CTN-1 coclusters with SLO-1 at regions of dense bodies, which are Z-disk analogs of mammalian skeletal muscle. In ctn-1 loss-of-function (lf) mutants, SLO-1 was mislocalized in body-wall muscle but its transcription and protein level were unchanged. Targeted rescue of ctn-1(lf) in muscle was sufficient to reinstate the lethargic phenotype in slo-1(gf);ctn-1(lf). These results suggest that CTN-1 plays an important role in BK channel function by mediating channel subcellular localization.

Suite of novel vectors for ectopic insertion of GFP, CFP and IYFP transcriptional fusions in single copy at the amyE and bglS loci in Bacillus subtilis

We report the development of a suite of six integrative vectors for construction of single copy transcriptional fusions with the gfpmut3, cfp and iyfp reporter genes in Bacillus subtilis. The promoter fusions are constructed using the highly efficient ligation-independent cloning (LIC) technique making them suitable for high-throughput applications. The plasmids insert into the chromosome by a double cross-over event at the amyE or bglS loci and integration at each site can be verified by a plate-based screening assay. The vectors allow expression of two different promoters to be determined in the same strain using the cfp and iyfp reporter genes since CFP and iYFP are spectrally distinct and have comparable half-lives of approximately 2 h in exponentially growing B. subtilis cells. We demonstrate the versatility of these vectors by measuring expression of the tuaA and phoA operons singularly and in combination, during growth in phosphate limiting conditions.

PBaSysBioII: an integrative plasmid generating gfp transcriptional fusions for high-throughput analysis of gene expression in Bacillus subtilis

Plasmid pBaSysBioII was constructed for high-throughput analysis of gene expression in Bacillus subtilis. It is an integrative plasmid with a ligation-independent cloning (LIC) site, allowing the generation of transcriptional gfpmut3 fusions with desired promoters. Integration is by a Campbell-type event and is non-mutagenic, placing the fusion at the homologous chromosomal locus. Using phoA, murAA, gapB, ptsG and cggR promoters that are responsive to phosphate availability, growth rate and carbon source, we show that detailed profiles of promoter activity can be established, with responses to changing conditions being measurable within 1 min of the stimulus. This makes pBaSysBioII a highly versatile tool for real-time gene expression analysis in growing cells of B. subtilis.

Anaerobic Metabolism Occurs in the Substratum of Gonococcal Biofilms and May Be Sustained in Part by Nitric Oxide

Neisseria gonorrhoeae is the etiologic agent of gonorrhea, which has been among the most frequently reported communicable diseases in the United States since 1960. Women frequently do not exhibit symptoms, which can lead to chronic infection. N. gonorrhoeae readily forms biofilms over abiotic surfaces, over primary and transformed cervical epithelial cells, and over cervical tissues in vivo. Biofilms are often associated with chronic infection, which suggests a link between biofilm formation and asymptomatic gonorrhea in women. Proteins involved in anaerobic metabolism and oxidative-stress tolerance are critical for normal biofilm formation of N. gonorrhoeae. Therefore, we examined the spatial profiles of anaerobic respiration in N. gonorrhoeae, using an aniA'-'gfp transcriptional fusion. Nitric oxide (NO) can elicit biofilm dispersal when present at sublethal concentrations in the surrounding medium. Some reports indicate that NO may also encourage biofilm formation at higher, potentially lethal concentrations. NO is produced by polymorphonuclear lymphocytes (PMNs) and cervical endothelial and epithelial cells. Thus, we also examined the effect of NO on N. gonorrhoeae biofilms. We found that anaerobic respiration occurs predominantly in the substratum of gonococcal biofilms and that expression of aniA is induced over time in biofilms. Treatment with high concentrations of a rapid-release NO donor prevents biofilm formation when supplied early in biofilm development but can also enhance biofilm formation once anaerobic respiration is initiated. NO treatment partially restores biofilm formation in an aniA::kan insertion mutant, which suggests that N. gonorrhoeae in biofilms may use NO as a substrate for anaerobic growth but prefer nitrite.

Expression of the Gonococcal Global Regulatory Protein Fur and Genes Encompassing the Fur and Iron Regulon during In Vitro and In Vivo Infection in Women

The ferric uptake regulatory protein, Fur, functions as a global regulatory protein of gene transcription in the mucosal pathogen Neisseria gonorrhoeae. We have shown previously that several N. gonorrhoeae Fur-repressed genes are expressed in vivo during mucosal gonococcal infection in men, which suggests that this organism infects in an iron-limited environment and that Fur is expressed under these conditions. In this study we have demonstrated expression of the gonococcal fur gene in vitro, in human cervical epithelial cells, and in specimens from female subjects with uncomplicated gonococcal infection. In vitro studies confirmed that the expression of the gonococcal fur gene was repressed during growth under iron-replete growth conditions but that a basal level of the protein was maintained. Using GFP transcriptional fusions constructed from specific Fur binding sequences within the fur promoter/operator region, we determined that this operator region was functional during N. gonorrhoeae infection of cervical epithelial cells. Furthermore, reverse transcription-PCR analysis, as well as microarray analysis, using a custom Neisseria Fur and iron regulon microarray revealed that several Fur- and iron-regulated genes were expressed during N. gonorrhoeae infection of cervical epithelial cells. Microarray analysis of specimens obtained from female subjects with uncomplicated gonococcal infection corroborated our in vitro findings and point toward a key role of gonococcal Fur- and iron-regulated genes in gonococcal disease.

The polyhydroxyalkanoate biosynthesis genes are differentially regulated in planktonic- and biofilm-grown Pseudomonas aeruginosa

The planktonic and biofilm growth mode, the presence of polyhydroxyalkanoate (PHA) granules and the nitrogen availability were considered as parameters to study the regulation of genes involved in PHA biosynthesis in Pseudomonas aeruginosa. The transcriptional start point of the phaIF gene cluster, encoding PHA granule-associated proteins with proposed regulatory function, was experimentally verified. Gfp and lacZ transcriptional reporter fusions, respectively, were used to analyse promoter activities. In planktonic growth under nitrogen limitation, the phaC promoter ( PphaC) showed increased induction, while in the PHA-negative mutant the activity of PphaC was reduced to 25% of the wild type and was independent of nitrogen availability. Promoter activity in biofilms was assessed using 2, 0.05 or 0 g/l of NH 4Cl as nitrogen source, respectively. PphaC activity was increased during early biofilm growth, whereas in mature biofilms PphaC activity was preferentially localised to stalks of microcolonies. Nitrogen starvation led to an increased PphaC activity at the biofilm surface. PHA granule formation was confirmed by electron microscopy in planktonic and in biofilm cells. PphaI activity in planktonic cultures was less dependent on the conditions assayed and presented an oscillatory behaviour. In biofilms, PphaI was strongly activated during early stages of biofilm development, but was inactive in mature biofilms. Under nitrogen starvation PphaI activation resembled that of PphaC. These data suggested a differential regulation of PHA biosynthesis genes in planktonic and biofilm cells, as well as an important regulatory function of PhaF, when considering nitrogen availability. Interestingly, in biofilms PHA biosynthesis gene regulation showed a spatial distribution similar to rhamnolipid biosynthesis genes.

Identification of host-induced pathogen genes by differential fluorescence induction reporter systems

The ability to monitor a pathogen's gene expression program in response to the host environment is central to understanding host-microbe interactions. This protocol describes the application of a fluorescence-based promoter trap strategy, termed differential fluorescence induction (DFI), to identify and characterize bacterial genes that are preferentially expressed in infected tissues. In this approach, animals are infected with a library of bacteria expressing random GFP transcriptional gene fusions, and fluorescent bacteria are recovered directly from host tissues using fluorescence-activated cell sorting (FACS). This methodology allows for the identification of bacterial promoters induced in distinct anatomical sites and at different stages of infection. Furthermore, unlike other methodologies, the use of the GFP reporter allows for single cell, temporal and spatial monitoring of pathogen gene expression in infected animals. Library construction, promoter identification and analysis can be done in 4-8 weeks.

Thehedgehog-related genequa-1 is required for molting inCaenorhabditis elegans

The Caenorhabditis elegans genome encodes ten proteins that share similarity with Hedgehog through the C-terminal Hint/Hog domain. While most genes are members of larger gene families, qua-1 is a single copy gene. Here we show that orthologs of qua-1 exist in many nematodes, including Brugia malayi, which shared a common ancestor with C. elegans about 300 million years ago. The QUA-1 proteins contain an N-terminal domain, the Qua domain, that is highly conserved, but whose molecular function is not known. We have studied the expression pattern of qua-1 in C. elegans using a qua-1::GFP transcriptional fusion. qua-1 is mainly expressed in hyp1 to hyp11 hypodermal cells, but not in seam cells. It is also expressed in intestinal and rectal cells, sensilla support cells, and the P cell lineage in L1. The expression of qua-1::GFP undergoes cyclical changes during development in phase with the molting cycle. It accumulates prior to molting and disappears between molts. Disruption of the qua-1 gene function through an internal deletion that causes a frame shift with premature stop in the middle of the gene results in strong lethality. The animals arrest in the early larval stages due to defects in molting. Electron microscopy reveals double cuticles due to defective ecdysis, but no obvious defects are seen in the hypodermis. Qua domain-only::GFP and full-length QUA-1::GFP fusion constructs are secreted and associated with the overlying cuticle, but only QUA-1::GFP rescues the mutant phenotype. Our results suggest that both the Hint/Hog domain and Qua domain are critically required for the function of QUA-1.

DNA Microarray-Based Identification of Genes Associated with Glycopeptide Resistance in Staphylococcus aureus

Six pairs of transcription profiles between glycopeptide-intermediate S. aureus (GISA [or vancomycin-intermediate S. aureus; VISA]) and glycopeptide-susceptible S. aureus (vancomycin-susceptible S. aureus [VSSA], including glycopeptide-susceptible isogenic mutants from VISA) strains were compared using a microarray. Ninety-two open reading frames which were or tended to be increased in transcription in VISA in at least five out of six array combination pairs were evaluated for their effects on glycopeptide susceptibility by introducing these genes one by one into VSSA strain N315 to construct an overexpression library. By screening the library, 17 genes including 8 novel genes were identified as associated with glycopeptide resistance since their experimental overexpression reduced vancomycin and/or teicoplanin susceptibility of N315. The raised MICs of vancomycin and teicoplanin were 1.25 to 3.0 and 1.5 to 6.0 mg/liter, respectively, as compared to 1.0 mg/liter of N315. Three of these genes, namely graF, msrA2, and mgrA, also raised the oxacillin MIC from 8.0 mg/liter for N315 to 64 to approximately 128 mg/liter when they were overexpressed in N315. Their contribution to vancomycin and beta-lactam resistance was further supported by gene knockout and trans-complementation assay. By using a plasmid-based promoter-green fluorescent protein gene (gfp) transcriptional fusion system, graF promoter-activated cells were purified, and subsequent susceptibility tests and Northern blot analysis demonstrated that the cells with up-regulated activity of graF promoter showed reduced susceptibility to vancomycin, teicoplanin, and oxacillin. In addition, cell morphology studies showed that graF and msrA2 overexpression increased cell wall thickness of N315 by factors of 23.91 and 22.27%, respectively, accompanied by glycopeptide MIC increments of 3- to 6-fold, when they were overexpressed in N315. Moreover, extended experiments and analyses indicate that many of the genes identified above are related to the cell wall biosynthetic pathway, including active nutrient transport systems. We propose that the genes which raise glycopeptide resistance in S. aureus function toward altering the cell wall metabolic pathway.