bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nickel Resistance Determinants in
Bradyrhizobium
Strains from Nodules of the Endemic New Caledonia Legume
Serianthes calycina
Authors: Chaintreuil Clémence , Rigault Frédéric , Moulin Lionel , Jaffré Tanguy , Fardoux Joël , Giraud Eric , Dreyfus Bernard , Bailly Xavier 
Published: October 2007

ABSTRACT

Bradyrhizobium
strains, isolated in New Caledonia from nodules of the endemic legume
Serianthes calycina
growing in nickel-rich soils, were able to grow in the presence of 15 mM NiCl
2
. The genomes of these strains harbored two Ni resistance determinants, the
cnr
and
nre
operons. By constructing a
cnrA
mutant, we demonstrated that the
cnr
operon determines the high nickel resistance in
Bradyrhizobium
strains.
Mat Formation in
Saccharomyces cerevisiae
Requires Nutrient and pH Gradients
Authors: Reynolds Todd B. , Jansen An , Peng Xin , Fink Gerald R. 
Published: October 2007

ABSTRACT

The ability of
Saccharomyces cerevisiae
to form morphologically complex colony-like structures called mats requires expression of the cell surface glycoprotein Flo11p and growth on a semisolid surface. As the mat grows, it forms two visually distinct populations called the rim (edge of the mat) and the hub (interior of the mat), which can be physically separated from one another based on their agar adherence properties. Here, we show that growth of the mat on a semisolid agar surface creates concentric glucose and pH gradients in the medium that are required for the differentiation of the hub and rim. Disruption of the pathways that respond to changing levels of glucose block mat formation by decreasing
FLO11
expression. However, in wild-type cells, Flo11p is expressed in both portions of the structure. The difference in adherence between the rim and hub appears to be a consequence of the reduced adherence of Flo11p at the elevated pH of the rim.
Genome-Wide Transcriptional Profiling of the Cyclic AMP-Dependent Signaling Pathway during Morphogenic Transitions of
Candida albicans
Authors: Bahn Yong-Sun , Molenda Matthew , Staab Janet F. , Lyman Courtney A. , Gordon Laura J. , Sundstrom Paula 
Published: October 2007

ABSTRACT

Candida albicans
is an opportunistic human fungal pathogen that causes systemic candidiasis as well as superficial mucosal candidiasis. In response to the host environment,
C. albicans
transitions between yeast and hyphal forms. In particular, hyphal growth is important in facilitating adhesion and invasion of host tissues, concomitant with the expression of various hypha-specific virulence factors. In previous work, we showed that the cyclic AMP (cAMP) signaling pathway plays a crucial role in morphogenic transitions and virulence of
C. albicans
by studying genes encoding adenylate cyclase-associated protein (
CAP1
) and high-affinity phosphodiesterase (
PDE2
) (Y. S. Bahn, J. Staab, and P. Sundstrom, Mol. Microbiol.
50:
391-409, 2003; and Y. S. Bahn and P. Sundstrom, J. Bacteriol.
183:
3211-3223, 2001). However, little is known about the downstream targets of the cAMP signaling pathway that are responsible for morphological transitions and the expression of virulence factors. Here, microarrays were probed with RNA from strains with hypoactive (
cap1/cap1
null mutant), hyperactive (
pde2/pde2
null mutant), and wild-type cAMP signaling pathways to provide insight into the molecular mechanisms of virulence that are regulated by cAMP and that are related to the morphogenesis of
C. albicans
. Genes controlling metabolic specialization, cell wall structure, ergosterol/lipid biosynthesis, and stress responses were modulated by cAMP during hypha formation. Phenotypic traits predicted to be regulated by cAMP from the profiling results correlated with the relative strengths of the mutants when tested for resistance to azoles and subjected to heat shock stress and oxidative/nitrosative stress. The results from this study provide important insights into the role of the cAMP signaling pathway not only in morphogenic transitions of
C. albicans
but also for adaptation to stress and for survival during host infections.
cis
-Acting Elements within the
Candida albicans ERG11
Promoter Mediate the Azole Response through Transcription Factor Upc2p
Authors: Oliver Brian G. , Song Jia L. , Choiniere Jake H. , White Theodore C. 
Published: October 2007

ABSTRACT

The azole antifungal drugs are used to treat infections caused by
Candida albicans
and other fungi. These drugs interfere with the biosynthesis of ergosterol, the major sterol in fungal cells, by inhibiting an ergosterol biosynthetic enzyme, lanosterol 14 α-demethylase, encoded by the
ERG11
gene. In vitro, these drugs as well as other ergosterol biosynthesis inhibitors increase
ERG11
mRNA expression by activation of the
ERG11
promoter. The signal for this activation most likely is the depletion of ergosterol, the end product of the pathway. To identify
cis
-acting regulatory elements that mediate this activation,
ERG11
promoter fragments have been fused to the luciferase reporter gene from
Renilla reniformis
. Promoter deletions and linker scan mutations localized the region important for azole induction to a segment from bp −224 to −251 upstream of the start codon, specifically two 7-bp sequences separated by 13 bp. These sequences form an imperfect inverted repeat. The region is recognized by the transcription factor Upc2p and functions as an enhancer of transcription, as it can be placed upstream of a heterologous promoter in either direction, resulting in the azole induction of that promoter. The promoter constructs are not azole inducible in the
upc2/upc2
homozygous deletion, demonstrating that Upc2p controls the azole induction of
ERG11
. These results identify an azole-responsive enhancer element (ARE) in the
ERG11
promoter that is controlled by the Upc2p transcription factor. No other ARE is present in the promoter. Thus, this ARE and Upc2p are necessary and sufficient for azole induction of
ERG11
.
Ssk2 Mitogen-Activated Protein Kinase Kinase Kinase Governs Divergent Patterns of the Stress-Activated Hog1 Signaling Pathway in
Cryptococcus neoformans
Authors: Bahn Yong-Sun , Geunes-Boyer Scarlett , Heitman Joseph 
Published: October 2007

ABSTRACT

The stress-activated p38/Hog1 mitogen-activated protein kinase (MAPK) pathway is structurally conserved in many diverse organisms, including fungi and mammals, and modulates myriad cellular functions. The Hog1 pathway is uniquely specialized to control differentiation and virulence factors in a majority of clinical
Cryptococcus neoformans
serotype A and D strains. Here, we identified and characterized the Ssk2 MAPKKK that functions upstream of the MAPKK Pbs2 and the MAPK Hog1 in
C. neoformans
. The
SSK2
gene was identified as a potential component responsible for the difference in Hog1 phosphorylation between the serotype D f1 sibling strains B-3501 and B-3502 through comparative analysis of meiotic maps showing their meiotic segregation patterns of Hog1-dependent sensitivity to the antifungal drug fludioxonil. Ssk2 is the only component of the Hog1 MAPK cascade that is polymorphic between the two strains, and the B-3501 and B-3502
SSK2
alleles were distinguished by two coding sequence changes. Supporting this finding,
SSK2
allele exchange completely interchanged the Hog1-controlled signaling patterns, related phenotypes, and virulence levels of strains B-3501 and JEC21. In the serotype A strain H99, disruption of the
SSK2
gene enhanced capsule and melanin biosynthesis and mating efficiency, similar to
pbs2
and
hog1
mutations. Furthermore,
ssk2
Δ,
pbs2
Δ, and
hog1
Δ mutants were hypersensitive to a variety of stresses and resistant to fludioxonil. In agreement with these results, Hog1 phosphorylation was abolished in the
ssk2
Δ mutant, similar to what occurred in the
pbs2
Δ mutant. Taken together, these findings indicate that Ssk2 is a critical interface connecting the two-component system and the Pbs2-Hog1 MAPK pathway in
C. neoformans
.
Fibrotic Response as a Distinguishing Feature of Resistance and Susceptibility to Pulmonary Infection with
Mycobacterium tuberculosis
in Mice
Authors: Marquis Jean-François , Nantel André , LaCourse Ronald , Ryan Lynn , North Robert J. , Gros Philippe 
Published: October 2007

ABSTRACT

The differential susceptibility of inbred mouse strains DBA/2J (susceptible) and C57BL/6J (resistant) to pulmonary tuberculosis following aerosol infection is under complex genetic control. In this report, transcriptional profiling with RNAs from
Mycobacterium tuberculosis
-infected lungs was used to investigate the physiological response, cell type, and biochemical pathways underlying differential susceptibility to infection. Statistical analysis of cDNA-based microarrays revealed that 1,097 transcripts showed statistically significant changes in abundance (changes of ≥1.5-fold) in at least one of four experimental group comparisons (C57BL/6J [day 0] versus DBA/2J [day 0] mice, C57BL/6J [day 90] versus DBA/2J [day 90] mice, C57BL/6J [day 90] versus C57BL/6J [day 0] mice, or DBA/2J [day 90] versus DBA/2J [day 0] mice). A group of genes showing very high degrees of significance (changes of ≥2.0-fold) displayed enrichment for transcripts associated with tissue remodeling and the fibrotic response. The differential expression of fibrotic response genes (
Sparc
,
Col1a1
,
Col1a2
,
Col4a1
, and
Col4a2
) in the infected lungs of the two mouse strains was validated by another microarray platform (Affymetrix oligonucleotide chips) and by reverse transcription-PCR. Furthermore, the differential expression of additional genes known to be associated with fibrosis (
Mmp2
,
Timp1
, and
Arg1
) was also validated by these approaches. Overall, these results identify the differential fibrotic response as a pathological basis for the high susceptibility of DBA/2J mice to pulmonary tuberculosis.
Impairment of Infectivity and Immunoprotective Effect of a
LYT1
Null Mutant of
Trypanosoma cruzi
Authors: Zago M. Paola , Barrio Alejandra B. , Cardozo Rubén M. , Duffy Tomás , Schijman Alejandro G. , Basombrío Miguel A. 
Published: October 2007

ABSTRACT

Trypanosoma cruzi
infection of host cells is a complex process in which many proteins participate but only a few of these proteins have been identified experimentally. One parasite factor likely to be involved is the protein product of
LYT1
, a single-copy gene cloned, sequenced, and characterized by Manning-Cela et al. (Infect. Immun. 69:3916-3923, 2001). This gene was potentially associated with infectivity, since the deletion of both
LYT1
alleles in the CL Brenner strain (the wild type [WT]) resulted in a null mutant
T. cruzi
clone (L16) that shows an attenuated phenotype in cell culture models. The aim of this work was to characterize the infective behavior of L16 in the insect vector and murine models. The infection of adult Swiss mice with 10
3
trypomastigotes of both clones revealed a significant reduction in infective behavior of L16, as shown by direct parasitemia, spleen index, and quantitation of tissue parasite burden, suggesting the loss of virulence in the null mutant clone. Although L16 blood counts were almost undetectable, blood-based PCRs indicated the presence of latent and persistent infection during all of the study period and epimastigotes were reisolated from hemocultures until 12 months postinfection. Nevertheless, virulence was not restored in L16 by serial passages in mice, and reisolated parasites lacking the
LYT1
gene and bearing the antibiotic resistance genes revealed the stability of the genetic manipulation. Histopathological studies showed a strong diminution in the muscle inflammatory response triggered by L16 compared to that triggered by the WT group, consistent with a lower tissue parasite load. A strong protection against a virulent challenge in both L16- and WT-infected mice was observed; however, the immunizing infection by the genetically modified parasite was highly attenuated.
Essential Role of Chitinase in the Development of the Filarial Nematode
Acanthocheilonema viteae
Authors: Tachu Babila , Pillai Smitha , Lucius Richard , Pogonka Thomas 
Published: October 2007

ABSTRACT

Chitinases of pathogens have been proposed as potential targets of vaccines or specific inhibitors. We studied the genomic organization, transcript levels, developmental expression, and biological function of chitinases in the rodent filarial nematode
Acanthocheilonema viteae
, a model organism for human-pathogenic filarial worms. Characterization of nine genomic clones from an
A. viteae
phage library and Southern blot experiments revealed the existence of three different chitinase genes, two of which could theoretically yield functional transcripts. The deduced proteins of these genes had the common modular organization of family 18 chitinases. Northern blot experiments and rapid amplification of cDNA ends-PCR with adult worms and larval stages showed that only one gene is expressed, with high variation in transcript levels, as determined by real-time PCR. Chitinase transcript levels were lowest in the late male stage 4 larva (L4) and peaked in the stage 3 larva (L3), which was corroborated by Western blotting. RNA interference (RNAi) experiments showed that treatment of L3 and adult female worms with double-stranded RNA of chitinase inhibited molting of L3 worms and hatching of microfilariae. RNAi also led to the death of 50% of female worms, revealing the essential role of chitinase in the life cycle of filarial nematodes.
Mechanisms of Dexamethasone-Mediated Inhibition of Toll-Like Receptor Signaling Induced byNeisseria meningitidisandStreptococcus pneumoniae
Authors: Mogensen Trine H. , Berg Randi S. , Paludan Søren R. , Østergaard Lars 
Published: October 2007

ABSTRACTExcessive inflammation contributes to the pathogenesis of bacterial meningitis, which remains a serious disease despite treatment with antibiotics. Therefore, anti-inflammatory drugs have important therapeutic potential, and clinical trials have revealed that early treatment with dexamethasone significantly reduces mortality and morbidity from bacterial meningitis. Here we investigate the molecular mechanisms behind the inhibitory effect of dexamethasone upon the inflammatory responses evoked byNeisseria meningitidisandStreptococcus pneumoniae, two of the major causes of bacterial meningitis. The inflammatory cytokine response was dependent on Toll-like receptor signaling and was strongly inhibited by dexamethasone. Activation of the NF-κB pathway was targeted at several levels, including inhibition of IκB phosphorylation and NF-κB DNA-binding activity as well as upregulation of IκBα synthesis. Our data also revealed that the timing of steroid treatment relative to infection was important for achieving strong inhibition, particularly in response toS. pneumoniae. Altogether, we describe important targets of dexamethasone in the inflammatory responses evoked byN. meningitidisandS. pneumoniae, which may contribute to our understanding of the clinical effect and the importance of timing with respect to corticosteroid treatment during bacterial meningitis.
Interaction ofBrucella suisandBrucella abortusRough Strains with Human Dendritic Cells
Authors: Billard Elisabeth , Dornand Jacques , Gross Antoine 
Published: October 2007

ABSTRACTBrucellais a facultative intracellular pathogen of various mammals and the etiological agent of brucellosis. We recently demonstrated that dendritic cells (DCs), which are critical components of adaptive immunity, are highly susceptible toBrucellainfection. Furthermore,Brucellaprevented the infected DCs from engaging in maturation processes and impaired their capacity to present antigen to naive T cells and to secrete interleukin-12 (IL-12). The lipopolysaccharide (LPS) phenotype is largely associated with the virulence ofBrucella. Depending on whether they express the O-side chain of LPS or not, the bacteria display a smooth or rough phenotype. RoughBrucellamutants are attenuated and induce a potent protective T-cell-dependent immune response. Due to the essential role of DCs in the initiation of T-cell-dependent adaptive immune responses, it seemed pertinent to study the interaction between roughBrucellastrains and human DCs. In the present paper, we report that, in contrast to smooth bacteria, infection of DCs with rough mutants ofBrucella suisorBrucella abortusleads to both phenotypic and functional maturation of infected cells. Rough mutant-infected DCs then acquire the capacity to produce IL-12 and to stimulate naive CD4+T lymphocytes. Experiments with rough and smooth purified LPS ofBrucellasupported the hypothesis of an indirect involvement of the O-side chain. These results provide new data concerning the role of LPS inBrucellavirulence strategy and illuminate phenomena contributing to immune protection conferred by rough vaccine strains.
Phagocytosis ofBorrelia burgdorferi, the Lyme Disease Spirochete, Potentiates Innate Immune Activation and Induces Apoptosis in Human Monocytes
Authors: Cruz Adriana R. , Moore Meagan W. , La Vake Carson J. , Eggers Christian H. , Salazar Juan C. , Radolf Justin D. 
Published: October 2007

ABSTRACTWe have previously demonstrated that phagocytosedBorrelia burgdorferiinduces activation programs in human peripheral blood mononuclear cells that differ qualitatively and quantitatively from those evoked by equivalent lipoprotein-rich lysates. Here we report that ingestedB. burgdorferiinduces significantly greater transcription of proinflammatory cytokine genes than do lysates and that liveB. burgdorferi, but notB. burgdorferilysate, is avidly internalized by monocytes, where the bacteria are completely degraded within phagolysosomes. In the course of these experiments, we discovered that liveB. burgdorferialso induced a dose-dependent decrease in monocytes but not a decrease in dendritic cells or T cells and that the monocyte population displayed morphological and biochemical hallmarks of apoptosis. Particularly noteworthy was the finding that apoptotic changes occurred predominantly in monocytes that had internalized spirochetes. Abrogation of phagocytosis with cytochalasin D prevented the death response. Heat-killedB. burgdorferi, which was internalized as well as live organisms, induced a similar degree of apoptosis of monocytes but markedly less cytokine production. Surprisingly, opsonophagocytosis ofTreponema pallidumdid not elicit a discernible cell death response. Our combined results demonstrate thatB. burgdorfericonfined to phagolysosomes is a potent inducer of cytosolic signals that result in (i) production of NF-κB-dependent cytokines, (ii) assembly of the inflammasome and activation of caspase-1, and (iii) induction of programmed cell death. We propose that inflammation and apoptosis represent mutually reinforcing components of the immunologic arsenal that the host mobilizes to defend itself against infection with Lyme disease spirochetes.
α-Enolase Resides on the Cell Surface of
Mycoplasma fermentans
and Binds Plasminogen
Authors: Yavlovich Amichai , Rechnitzer Hagai , Rottem Shlomo 
Published: October 2007

ABSTRACT

Plasminogen (Plg) binding to the cell surface of
Mycoplasma fermentans
results in a marked increase in the maximal adherence of the organism to HeLa cells, enhanced Plg activation by the urokinase-type Plg activator, and the induction of the internalization of
M. fermentans
by eukaryotic host cells (A. Yavlovich, A. Katzenell, M. Tarshis, A. A. Higazi, and S. Rottem, Infect. Immun. 72:5004-5011, 2004). In this study, the
M. fermentans
Plg binding protein was isolated by affinity chromatography of Triton X-100-solubilized
M. fermentans
membranes by utilizing a column of a Plg-biotin complex attached to avidin that was eluted with ε-aminocaproic acid. The eluted ∼50-kDa protein was identified by mass spectrometric techniques as α-enolase. The possibility that α-enolase, a key cytoplasmatic glycolytic enzyme, resides also on the cell surface of
M. fermentans
was supported by an immunoblot analysis using polyclonal anti-α-enolase antiserum, which showed that α-enolase was present in a purified
M. fermentans
membrane preparation, as well as by immunochemical criteria and by immunoelectron microscopy analysis. Our observation that Plg blocked the binding of anti-α-enolase antibodies to a 50-kDa polypeptide band resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of
M. fermentans
membrane or soluble preparations further supports our notion that mycoplasmal surface α-enolase is a major Plg binding protein of
M. fermentans
.
Flagellin Suppresses the Inflammatory Response and Enhances Bacterial Clearance in a Murine Model ofPseudomonas aeruginosaKeratitis
Authors: Kumar Ashok , Hazlett Linda D. , Yu Fu-Shin X. 
Published: October 2007

ABSTRACTPseudomonas aeruginosais a common organism associated with bacterial keratitis, especially in extended-wear contact lens users. In the present study, we determined that pretreatment of cultured human corneal epithelial cells with flagellin isolated from theP. aeruginosaPAO1 strain attenuated cytokine production when the cells were challenged with a cytotoxic strain (ATCC 19660), suggesting a potential use of bacterial flagellin to downregulate infection-associated inflammation in vivo. Administration of flagellin via the subconjunctival and intraperitoneal routes 24 h prior toPseudomonasinoculation significantly improved the disease outcome, preserved structural integrity and transparency, and thus maintained vision in otherwise perforated corneas of C57BL/6 (B6) mice. The flagellin pretreatment resulted in suppression of polymorphonuclear leukocyte infiltration at a late stage of infection but not at an early stage of infection, decreased the expression of proinflammatory cytokine genes (genes encoding interleukin-1β [IL-1β], macrophage inflammatory protein 2, IL-12, and gamma interferon), and greatly enhanced bacterial clearance in the corneas of B6 mice probably through induced expression of the cathelicidin-related antimicrobial peptide and inducible nitric oxide synthase. This is the first report that describes the protective mechanisms induced by a Toll-like receptor agonist that not only curbs the host inflammatory response but also eliminates invading bacteria in the B6 mouse cornea.