bluuebunny/crossref_metadata_2025_split huggingface dataset:
Real-Time PCR Investigation of Potential Vectors, Reservoirs, and Shedding Patterns of Feline Hemotropic Mycoplasmas
Authors: Willi Barbara , Boretti Felicitas S. , Meli Marina L. , Bernasconi Marco V. , Casati Simona , Hegglin Daniel , Puorger Maria , Neimark Harold , Cattori Valentino , Wengi Nicole , Reusch Claudia E. , Lutz Hans , Hofmann-Lehmann Regina 
Published: April 2007

ABSTRACTThree hemotropic mycoplasmas have been identified in pet cats:Mycoplasma haemofelis, “CandidatusMycoplasma haemominutum,” and “CandidatusMycoplasma turicensis.” The way in which these agents are transmitted is largely unknown. Thus, this study aimed to investigate fleas, ticks, and rodents as well as saliva and feces from infected cats for the presence of hemotropic mycoplasmas, to gain insight into potential transmission routes for these agents. DNA was extracted from arthropods and from rodent blood or tissue samples from Switzerland and from salivary and fecal swabs from two experimentally infected and six naturally infected cats. All samples were analyzed with real-time PCR, and some positive samples were confirmed by sequencing. Feline hemotropic mycoplasmas were detected in cat fleas and in a fewIxodessp. andRhipicephalussp. ticks collected from animals but not in ticks collected from vegetation or from rodent samples, although the latter were frequentlyMycoplasma coccoidesPCR positive. When shedding patterns of feline hemotropic mycoplasmas were investigated, “Ca. Mycoplasma turicensis” DNA was detected in saliva and feces at the early but not at the late phase of infection.M. haemofelisand “Ca. Mycoplasma haemominutum” DNA was not amplified from saliva and feces of naturally infected cats, despite high hemotropic mycoplasma blood loads. Our results suggest that besides an ostensibly indirect transmission by fleas, direct transmission through saliva and feces at the early phase of infection could play a role in the epizootiology of feline hemotropic mycoplasmas. Neither the investigated tick nor the rodent population seems to represent a major reservoir for feline hemotropic mycoplasmas in Switzerland.
Flux Analysis of Central Metabolic Pathways in
Geobacter metallireducens
during Reduction of Soluble Fe(III)-Nitrilotriacetic Acid
Authors: Tang Yinjie J. , Chakraborty Romy , Martín Héctor García , Chu Jeannie , Hazen Terry C. , Keasling Jay D. 
Published: April 2007

ABSTRACT

We analyzed the carbon fluxes in the central metabolism of
Geobacter metallireducens
strain GS-15 using
13
C isotopomer modeling. Acetate labeled in the first or second position was the sole carbon source, and Fe-nitrilotriacetic acid was the sole terminal electron acceptor. The measured labeled acetate uptake rate was 21 mmol/g (dry weight)/h in the exponential growth phase. The resulting isotope labeling pattern of amino acids allowed an accurate determination of the in vivo global metabolic reaction rates (fluxes) through the central metabolic pathways using a computational isotopomer model. The tracer experiments showed that
G. metallireducens
contained complete biosynthesis pathways for essential metabolism, and this strain might also have an unusual isoleucine biosynthesis route (using acetyl coenzyme A and pyruvate as the precursors). The model indicated that over 90% of the acetate was completely oxidized to CO
2
via a complete tricarboxylic acid cycle while reducing iron. Pyruvate carboxylase and phosphoenolpyruvate (PEP) carboxykinase were present under these conditions, but enzymes in the glyoxylate shunt and malic enzyme were absent. Gluconeogenesis and the pentose phosphate pathway were mainly employed for biosynthesis and accounted for less than 3% of total carbon consumption. The model also indicated surprisingly high reversibility in the reaction between oxoglutarate and succinate. This step operates close to the thermodynamic equilibrium, possibly because succinate is synthesized via a transferase reaction, and the conversion of oxoglutarate to succinate is a rate-limiting step for carbon metabolism. These findings enable a better understanding of the relationship between genome annotation and extant metabolic pathways in
G. metallireducens
.
Using the
Ralstonia solanacearum
Tat Secretome To Identify Bacterial Wilt Virulence Factors
Authors: González Enid T. , Brown Darby G. , Swanson Jill K. , Allen Caitilyn 
Published: April 2007

ABSTRACT

To identify secreted virulence factors involved in bacterial wilt disease caused by the phytopathogen
Ralstonia solanacearum
, we mutated
tatC
, a key component of the
t
win-
a
rginine
t
ranslocation (Tat) secretion system. The
R. solanacearum tatC
mutation was pleiotropic; its phenotypes included defects in cell division, nitrate utilization, polygalacturonase activity, membrane stability, and growth in plant tissue. Bioinformatic analysis of the
R. solanacearum
strain GMI1000 genome predicted that this pathogen secretes 70 proteins via the Tat system. The
R. solanacearum tatC
strain was severely attenuated in its ability to cause disease, killing just over 50% of tomato plants in a naturalistic soil soak assay where the wild-type parent killed 100% of the plants. This result suggested that elements of the Tat secretome may be novel bacterial wilt virulence factors. To identify contributors to
R. solanacearum
virulence, we cloned and mutated three genes whose products are predicted to be secreted by the Tat system: RSp1521, encoding a predicted AcvB-like protein, and two genes, RSc1651 and RSp1575, that were identified as upregulated in planta by an in vivo expression technology screen. The RSc1651 mutant had wild-type virulence on tomato plants. However, mutants lacking either RSp1521, which appears to be involved in acid tolerance, or RSp1575, which encodes a possible amino acid binding protein, were significantly reduced in virulence on tomato plants. Additional bacterial wilt virulence factors may be found in the Tat secretome.
Sensitivity of
Escherichia albertii
, a Potential Food-Borne Pathogen, to Food Preservation Treatments
Authors: Sharma Manan , Kniel Kalmia E. , Derevianko Alexandra , Ling Jason , Bhagwat Arvind A. 
Published: April 2007

ABSTRACT

Escherichia albertii
is a potential food-borne pathogen because of its documented ability to cause diarrheal disease by producing attachment and effacement lesions. Its tolerances to heat (56°C), acid (pH 3.0), and pressure (500 MPa [5 min]) were evaluated and found to be significantly less than those of wild-type
E. coli
O157:H7.
Functional Characterization of Spliceosomal Introns and Identification of U2, U4, and U5 snRNAs in the Deep-Branching Eukaryote
Entamoeba histolytica
Authors: Davis Carrie A. , Brown Michael P. S. , Singh Upinder 
Published: April 2007

ABSTRACT

Pre-mRNA splicing is essential to ensure accurate expression of many genes in eukaryotic organisms. In
Entamoeba histolytica
, a deep-branching eukaryote, approximately 30% of the annotated genes are predicted to contain introns; however, the accuracy of these predictions has not been tested. In this study, we mined an expressed sequence tag (EST) library representing 7% of amoebic genes and found evidence supporting splicing of 60% of the testable intron predictions, the majority of which contain a GUUUGU 5′ splice site and a UAG 3′ splice site. Additionally, we identified several splice site misannotations, evidence for the existence of 30 novel introns in previously annotated genes, and identified novel genes through uncovering their spliced ESTs. Finally, we provided molecular evidence for the
E. histolytica
U2, U4, and U5 snRNAs. These data lay the foundation for further dissection of the role of RNA processing in
E. histolytica
gene expression.
Molecular Basis for Preferential Protective Efficacy of Antibodies Directed to the Poorly Acetylated Form of Staphylococcal Poly-
N
-Acetyl-β-(1-6)-Glucosamine
Authors: Cerca Nuno , Jefferson Kimberly K. , Maira-Litrán Tomas , Pier Danielle B. , Kelly-Quintos Casie , Goldmann Donald A. , Azeredo Joana , Pier Gerald B. 
Published: May 2007

ABSTRACT

Poly-
N
-acetyl-glucosamine (PNAG) is a staphylococcal surface polysaccharide influencing biofilm formation that is also under investigation for its vaccine potential. Antibodies that bind to PNAG with either low (<15%) or high (>90%) levels of acetate are superior at opsonic and protective activity compared with antibodies that bind to PNAG with only high levels (>70%) of acetate. PNAG is synthesized by four proteins encoded within the intercellular adhesin (
ica
) locus
icaADBC
. In
Staphylococcus epidermidis
,
icaB
encodes a deacetylase needed for the surface retention of PNAG and optimal biofilm formation. In this study, we confirmed that
icaB
plays a similar role in
Staphylococcus aureus
and found that an
icaB
mutant of
S. aureus
expressed significantly less surface-associated PNAG, was highly susceptible to antibody-independent opsonic killing that could not be enhanced with antibody raised against deacetylated PNAG (dPNAG), and had reduced survival capacity in a murine model of bacteremia. In contrast, an
icaB
-overexpressing strain produced primarily surface-associated PNAG, was more susceptible to opsonophagocytosis with antibody to dPNAG, and had increased survival in a murine bacteremia model. The highly acetylated secreted PNAG was more effective at blocking opsonic killing mediated by a human monoclonal antibody (mAb) to native PNAG than it was at blocking killing mediated by a human mAb to dPNAG, which by itself was a more effective opsonin. Retention of dPNAG on the surface of
S. aureus
is key to increased survival during bacteremia and also provides a molecular mechanism explaining the superior opsonic and protective activity of antibody to dPNAG.
Inhibition of Dendritic Cell Maturation by Malaria Is Dose Dependent and Does Not RequirePlasmodium falciparumErythrocyte Membrane Protein 1
Authors: Elliott Salenna R. , Spurck Timothy P. , Dodin Joelle M. , Maier Alexander G. , Voss Till S. , Yosaatmadja Francisca , Payne Paul D. , McFadden Geoffrey I. , Cowman Alan F. , Rogerson Stephen J. , Schofield Louis , Brown Graham V. 
Published: May 2007

ABSTRACTRed blood cells infected withPlasmodium falciparum(iRBCs) have been shown to modulate maturation of human monocyte-derived dendritic cells (DCs), interfering with their ability to activate T cells. Interaction betweenPlasmodium falciparumerythrocyte membrane protein 1 (PfEMP1) and CD36 expressed by DCs is the proposed mechanism, but we show here that DC modulation does not require CD36 binding, PfEMP1, or contact between DCs and infected RBCs and depends on the iRBC dose. iRBCs expressing a PfEMP1 variant that binds chondroitin sulfate A (CSA) but not CD36 were phagocytosed, inhibited lipopolysaccharide (LPS)-induced phenotypic maturation and cytokine secretion, and abrogated the ability of DCs to stimulate allogeneic T-cell proliferation. CD36- and CSA-binding iRBCs showed comparable inhibition.P. falciparumlines rendered deficient in PfEMP1 expression by targeted gene knockout or knockdown also inhibited LPS-induced phenotypic maturation, and separation of DCs and iRBCs in transwells showed that inhibition was not contact dependent. Inhibition was observed at an iRBC:DC ratio of 100:1 but not at a ratio of 10:1. High doses of iRBCs were associated with apoptosis of DCs, which was not activation induced. Lower doses of iRBCs stimulated DC maturation sufficient to activate autologous T-cell proliferation. In conclusion, modulation of DC maturation byP. falciparumis dose dependent and does not require interaction between PfEMP1 and CD36. Inhibition and apoptosis of DCs by high-dose iRBCs may or may not be physiological. However, our observation that low-dose iRBCs initiate functional DC maturation warrants reevaluation and further investigation of DC interactions with blood-stageP. falciparum.
Marginal Zone B-Cell Depletion Impairs Murine Host Defense againstBorrelia burgdorferiInfection
Authors: Belperron Alexia A. , Dailey Catherine M. , Booth Carmen J. , Bockenstedt Linda K. 
Published: May 2007

ABSTRACTMarginal zone B (MZB) cells are a B-cell subset that produces T-cell-independent antibodies to blood-borne antigens. In this study, we examined the effects of MZB cell depletion on the immune response to the Lyme disease spirocheteBorrelia burgdorferi, an extracellular pathogen for which T-cell-independent antibody is an important host defense. MZB cell depletion of C3H/HeJ mice using monoclonal antibody to LFA-1 and α4β1integrins reducedB. burgdorferi-specific immunoglobulin M (IgM) titers, enhanced pathogen burden, and led to more severe arthritis assessed within the first 2 weeks of infection. In addition, MZB cell-depleted mice had reduced levels ofB. burgdorferi-specific IgG, which correlated with diminished splenic CD4+T-cell-activation, proliferation, and cytokine production. Passive transfer of immune mouse serum from infected control mice into infected MZB cell-depleted mice reduced pathogen burden but did not alter the expression of T-cell activation markers on splenic CD4+T cells. These findings demonstrate that MZB cells not only are a source of pathogen-specific IgM important for limiting spirochete burden and pathology but also play a prominent role in the priming of splenic T-cell responses to a blood-borne pathogen.
Characterization of aPseudomonas putidaRough Variant Evolved in a Mixed-Species Biofilm withAcinetobactersp. Strain C6
Authors: Hansen Susse Kirkelund , Haagensen Janus A. J. , Gjermansen Morten , Jørgensen Thomas Martini , Tolker-Nielsen Tim , Molin Søren 
Published: April 2007

ABSTRACTGenetic differentiation by natural selection is readily observed among microbial populations, but a more comprehensive understanding of evolutionary forces, genetic causes, and resulting phenotypic advantages is not often sought. Recently, a surface population ofPseudomonas putidabacteria was shown to evolve rapidly by natural selection of better-adapted variants in a mixed-species biofilm consortium (S. K. Hansen, P. B. Rainey, J. A. Haagensen, and S. Molin, Nature 445:533-536, 2007). Adaptation was caused by mutations in awapHhomolog (PP4943) involved in core lipopolysaccharide biosynthesis. Here we investigate further the biofilm physiology and the phenotypic characteristics of the selectedP. putidarough colony variants. The coexistence of theP. putidapopulation in a mixed-species biofilm withAcinetobactersp. strain C6 is dependent on the benzoate excreted fromAcinetobacterduring the catabolism of benzyl alcohol, the sole carbon source. Examination of biofilm development and the dynamics of the wild-type consortium revealed that the biofilm environment became oxygen limited, possibly with low oxygen concentrations aroundAcinetobactermicrocolonies. In contrast toP. putidawild-type cells, which readily dispersed from the mixed-species biofilm in response to oxygen starvation, the rough variant cells displayed a nondispersal phenotype. However, in monospecies biofilms proliferating on benzoate, the rough variant (like the wild-type population) dispersed in response to oxygen starvation. A key factor explaining this conditional, nondispersal phenotype is likely to be the acquired ability of the rough variant to coaggregate specifically withAcinetobactercells. We further show that theP. putidarough variant displayed enhanced production of a cellulose-like polymer as a consequence of the mutation inwapH. The resulting phenotypic characteristics of theP. putidarough variant explain its enhanced fitness and ability to form tight structural associations withAcinetobactermicrocolonies.
Roles of
rapH
and
rapG
in Positive Regulation of Rapamycin Biosynthesis in
Streptomyces hygroscopicus
Authors: Kuščer Enej , Coates Nigel , Challis Iain , Gregory Matt , Wilkinson Barrie , Sheridan Rose , Petković Hrvoje 
Published: April 2007

ABSTRACT

Rapamycin is an important macrocyclic polyketide produced by
Streptomyces hygroscopicus
and showing immunosuppressive, antifungal, and antitumor activities as well as displaying anti-inflammatory and neuroregenerative properties. The immense pharmacological potential of rapamycin has led to the production of an array of analogues, including through genetic engineering of the rapamycin biosynthetic gene cluster. This cluster contains several putative regulatory genes. Based on DNA sequence analysis, the products of genes
rapH
and
rapG
showed high similarities with two different families of transcriptional activators, LAL and AraC, respectively. Overexpression of either gene resulted in a substantial increase in rapamycin biosynthesis, confirming their positive regulatory role, while deletion of both from the chromosome of
S. hygroscopicus
resulted in a complete loss of antibiotic production. Complementation studies indicated an essential role of the RapG regulator for rapamycin biosynthesis and a supportive role of RapH. A direct effect of
rapH
and
rapG
gene products on the promoter of the rapamycin polyketide synthase operon,
rapA
-
rapB
, was observed using the chalcone synthase gene
rppA
as a reporter system.
A Novel Cell Surface-Anchored Cellulose-Binding Protein Encoded by the
sca
Gene Cluster of
Ruminococcus flavefaciens
Authors: Rincon Marco T. , Cepeljnik Tadej , Martin Jennifer C. , Barak Yoav , Lamed Raphael , Bayer Edward A. , Flint Harry J. 
Published: April 2007

ABSTRACT

Ruminococcus flavefaciens
produces a cellulosomal enzyme complex, based on the structural proteins ScaA, -B, and -C, that was recently shown to attach to the bacterial cell surface via the wall-anchored protein ScaE. ScaA, -B, -C, and -E are all cohesin-bearing proteins encoded by linked genes in the
sca
cluster. The product of an unknown open reading frame within the
sca
cluster, herein designated CttA, is similar in sequence at its C terminus to the corresponding region of ScaB, which contains an X module together with a dockerin sequence. The ScaB-XDoc dyad was shown previously to interact tenaciously with the cohesin of ScaE. Likewise, avid binding was confirmed between purified recombinant fragments of the CttA-XDoc dyad and the ScaE cohesin. In addition, the N-terminal regions of CttA were shown to bind to cellulose, thus suggesting that CttA is a cell wall-anchored, cellulose-binding protein. Proteomic analysis showed that the native CttA protein (∼130 kDa) corresponds to one of the three most abundant polypeptides binding tightly to insoluble cellulose in cellulose-grown
R. flavefaciens
17 cultures. Interestingly, this protein was also detected among cellulose-bound proteins in the related strain
R. flavefaciens
007C but not in a mutant derivative, 007S, that was previously shown to have lost the ability to grow on dewaxed cotton fibers. In
R. flavefaciens
, the presence of CttA on the cell surface is likely to provide an important mechanism for substrate binding, perhaps compensating for the absence of an identified cellulose-binding module in the major cellulosomal scaffolding proteins of this species.
Bacillus subtilisPellicle Formation Proceeds through Genetically Defined Morphological Changes
Authors: Kobayashi Kazuo 
Published: April 2007

ABSTRACTBiofilms are structured multicellular communities of bacteria that form through a developmental process. In standing culture, undomesticated strains ofBacillus subtilisproduce a floating biofilm, called a pellicle, with a distinct macroscopic architecture. Here we report on a comprehensive analysis ofB. subtilispellicle formation, with a focus on transcriptional regulators and morphological changes. To date, 288 known or putative transcriptional regulators encoded by theB. subtilisgenome have been identified or assigned based on similarity to other known proteins. The genes encoding these regulators were systematically disrupted, and the effects of the mutations on pellicle formation were examined, resulting in the identification of 19 regulators involved in pellicle formation. In addition, morphological analysis revealed that pellicle formation begins with the formation of cell chains, which is followed by clustering and degradation of cell chains. Genetic and morphological evidence showed that each stage of morphological change can be defined genetically, based on mutants of transcriptional regulators, each of which blocks pellicle formation at a specific morphological stage. Formation and degradation of cell chains are controlled by down- and up-regulation of σD- and σH-dependent autolysins expressed at specific stages during pellicle formation. Transcriptional analysis revealed that the transcriptional activation ofsigHdepends on the formation of cell clusters, which in turn activates transcription of σH-dependent autolysin in cell clusters. Taken together, our results reveal relationships between transcriptional regulators and morphological development during pellicle formation byB. subtilis.
Identification of the Missing
trans
-Acting Enoyl Reductase Required for Phthiocerol Dimycocerosate and Phenolglycolipid Biosynthesis in
Mycobacterium tuberculosis
Authors: Siméone Roxane , Constant Patricia , Guilhot Christophe , Daffé Mamadou , Chalut Christian 
Published: April 2007

ABSTRACT

Phthiocerol dimycocerosates (DIM) and phenolglycolipids (PGL) are functionally important surface-exposed lipids of
Mycobacterium tuberculosis
. Their biosynthesis involves the products of several genes clustered in a 70-kb region of the
M. tuberculosis
chromosome. Among these products is PpsD, one of the modular type I polyketide synthases responsible for the synthesis of the lipid core common to DIM and PGL. Bioinformatic analyses have suggested that this protein lacks a functional enoyl reductase activity domain required for the synthesis of these lipids. We have identified a gene, Rv2953, that putatively encodes an enoyl reductase. Mutation in Rv2953 prevents conventional DIM formation and leads to the accumulation of a novel DIM-like product. This product is unsaturated between C-4 and C-5 of phthiocerol. Consistently, complementation of the mutant with a functional
pks15/1
gene from
Mycobacterium bovis
BCG resulted in the accumulation of an unsaturated PGL-like substance. When an intact Rv2953 gene was reintroduced into the mutant strain, the phenotype reverted to the wild type. These findings indicate that Rv2953 encodes a
trans
-acting enoyl reductase that acts with PpsD in phthiocerol and phenolphthiocerol biosynthesis.
Intracellular Parasitism of Chlamydiae: Specific Infectivity of Chlamydiaphage Chp2 in
Chlamydophila abortus
Authors: Skilton R. J. , Cutcliffe L. T. , Pickett M. A. , Lambden P. R. , Fane B. A. , Clarke I. N. 
Published: April 2007

ABSTRACT
The obligate intracellular nature of chlamydiae presents challenges to the characterization of its phages, which are potential tools for a genetic transfer system. An assay for phage infectivity is described, and the infectious properties of phage Chp2 were determined.