bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of White-Opaque Phenotypic Switching in
Candida albicans
by the Efg1p Morphogenetic Regulator
Authors: Sonneborn Anja , Tebarth Bernd , Ernst Joachim F. 
Published: December 2019

ABSTRACT

Phenotypic switching in
Candida albicans
spontaneously generates different cellular morphologies and is manifested in strain WO-1 by the reversible switching between the white and opaque phenotypes. We present evidence that phenotypic switching is regulated by the Efg1 protein, which is known as an essential element of hyphal development (dimorphism). Firstly,
EFG1
is expressed specifically in cells of the white but not the opaque phenotype. During mass conversion from the opaque to the white phenotype, the
EFG1
transcript level correlates with competence of switching of opaque cells to the white form. Secondly, overexpression of
EFG1
by a
PCK1p-EFG1
fusion forces opaque-phase cells to switch to the white form with a high level of efficiency. Thirdly, low-level expression of
EFG1
in strain CAI-8 generates a cellular phenotype similar to that of opaque cells in that cells bud as short rods, which cannot be induced to form hyphae in standard conditions; such cells (unlike authentic opaque cells) lack typical surface “pimples.” Importantly, the opaque-specific
OP4
transcript is induced in the opaque-like cells generated by strain CAI8 as a response to low-level expression of
EFG1
. The results suggest that high
EFG1
expression levels induce and maintain the white cell form while low
EFG1
expression levels induce and maintain the opaque cell form. It is proposed that changes in
EFG1
expression determine or contribute to phenotypic switching events in
C. albicans
.
Genetic Control of Schistosome Infections by the SM1 Locus of the 5q31-q33 Region Is Linked to Differentiation of Type 2 Helper T Lymphocytes
Authors: Rodrigues Virmondes , Piper Karen , Couissinier-Paris Patricia , Bacelar Olivia , Dessein Hélia , Dessein Alain J. 
Published: December 2019

ABSTRACTHuman susceptibility toSchistosoma mansoniinfections is controlled by the SM1 locus on chromosome 5 in q31-q33. This genetic region encodes cytokines which regulate the development of helper T lymphocytes. In the present work, a clonal analysis of CD4+T lymphocytes of homozygous resistant and homozygous susceptible subjects was undertaken to evaluate whether SM1 controls helper T-cell differentiation. Of 121 CD4+T-cell clones (TCC) from three susceptible (S) and three resistant (R) subjects, 68 proliferated when stimulated by parasite antigens. Parasite-specific TCC derived from susceptible subjects (33 STCC) produced 10- to 1,000-fold less interleukin-4 and -5 than TCC from resistant subjects (25 RTCC). Clones from both patient groups produced, however, the same amount of gamma interferon. Parasite-specific STCC were type 1 helper (Th1) or Th0/1, whereas RTCC were either Th2 or Th0/2. These results, together with the localization of SM1 in 5q31-q33, indicate that the SM1 locus controls the differentiation of Th2 lymphocytes.
Identification, Cloning, and Expression of the CAMP factor gene (
cfa
) of Group A Streptococci
Authors: Gase Klaus , Ferretti Joseph J. , Primeaux Charles , McShan W. Michael 
Published: December 2019

ABSTRACT

The CAMP reaction is a synergistic lysis of erythrocytes by the interaction of an extracellular protein (CAMP factor) produced by some streptococcal species with the
Staphylococcus aureus
sphingomyelinase C (beta-toxin). Group A streptococci (GAS [
Streptococcus pyogenes
]) have been long considered CAMP negative, and this reaction commonly has been used to distinguish GAS from
Streptococcus agalactiae
. We here provide evidence that GAS possess this gene and produce an extracellular CAMP factor capable of participating in a positive CAMP reaction. The
S. pyogenes
CAMP factor is specified by a 774-bp open reading frame homologous to the CAMP factor genes from
S. agalactiae
and
Streptococcus uberis
. This gene, designated
cfa
, was isolated on a 1,256-bp fragment and cloned in
Escherichia coli
. Recombinant clones of
E. coli
expressing
cfa
secreted an active CAMP factor. The deduced 28.5-kDa protein encoded by
cfa
consists of 257 amino acids, with a predicted 28-amino-acid signal peptide. The
cfa
gene is widely spread among GAS: 82 of 100 clinical GAS isolates produced a positive CAMP reaction. Of the CAMP-negative strains, 17 of the 18 GAS strains contained the
cfa
gene. Additionally, CAMP activity was detected in streptococci from serogroups C, M, P, R, and U. The
cfa
gene was cloned and actively expressed in
Escherichia coli
and gene fusions were made, placing the β-galactosidase gene (
lacZ
) under control of the
cfa
promoter. These
cfa
promoter-
lacZ
fusions were introduced into
S. pyogenes
via a bacteriophage-derived site-specific integration vector where they showed that the
cfa
gene has a strong promoter that may be subject to as-yet-unidentified regulatory factors. The results presented here, along with previous reports, indicate that the CAMP factor gene is fairly widespread among streptococci, being present at least in groups A, B, C, G, M, P, R, and U.
T-Cell Responses toTreponema pallidumsubsp.pallidumAntigens during the Course of Experimental Syphilis Infection
Authors: Arroll Thomas W. , Centurion-Lara Arturo , Lukehart Sheila A. , Van Voorhis Wesley C. 
Published: December 2019

ABSTRACTIn this study we describe the development of the T-cell response to a panel ofTreponema pallidumantigens over the course of syphilis infection in the rabbit and determine whether these antigens induce the expression of Th1 cytokines. It was determined that the membrane proteins TpN17 and TpN47, as well as the endoflagellar sheath protein TpN37, induce strong proliferation responses through most of syphilis infection; Tromp1 induced only weak proliferative responses. An unexpected drop in proliferative response to these antigens at day 90 of infection, followed by a dramatic increase in response at day 180, suggests that there may be a secondary dissemination ofT. pallidumwhich induces a recall response. Crude epitope mapping of TpN17 and TpN37 showed that multiple epitopes may be present on both antigens, which is likely a contributing factor in the immunodominance of these antigens. The T-cell response to the TpN37 molecule shows acquisition of newly recognized epitopes during the course of infection. SonicatedT. pallidumwas found to induce the expression of interleukin-2 (IL-2) and gamma interferon and not IL-10 mRNA, showing that the general T-cell response toT. pallidumantigens in syphilis infection is biased towards the Th1 phenotype. Of the antigens tested, TpN37 appears to contribute the most to the Th1 cytokine response and therefore may play a key role in the clearance ofT. pallidumfrom lesions.
LcrV ofYersinia pestisEnters Infected Eukaryotic Cells by a Virulence Plasmid-Independent Mechanism
Authors: Fields Kenneth A. , Straley Susan C. 
Published: December 2019

ABSTRACTYersinia pestisis the causative agent of bubonic plague and possesses a set of plasmid-encoded, secretable virulence proteins termed LcrV and Yops which are essential for survival in mammalian hosts. Yops and LcrV are secreted by a type III mechanism (Ysc), and Yops are unidirectionally targeted into the cytosol of associated eukaryotic cells in a tissue culture infection model. LcrV is required for Yops targeting, and recent findings have revealed that it can localize to the bacterial surface; however, its fate in this infection model has not been investigated in detail. In this study, we compared the localization of LcrV to that of the targeted proteins YopE and YopM by immunoblot analysis of fractions ofYersinia-infected HeLa cultures or by laser-scanning confocal microscopy of infected monolayers. Both LcrV and YopE were secreted by contact-activated, extracellularly localized yersiniae and were targeted to the HeLa cell cytosol. Although a significant amount of LcrV partitioned to the culture medium (unlike YopE), this extracellular pool of LcrV was not the source of the LcrV that entered HeLa cells. Unlike targeting of YopE and YopM, targeting of LcrV occurred in the absence of a functional Ysc apparatus and other virulence plasmid (pCD1)-expressed proteins. However, the Ysc is necessary for LcrV to be released into the medium, and our recent work has shown that localization of LcrV on the bacterial surface requires the Ysc. These results indicate that two mechanisms exist for the secretion of LcrV byY. pestis, both of which are activated by contact with eukaryotic cells. LcrV secreted by the Ysc reaches the bacterial surface and the surrounding medium, whereas the second is a novel, Ysc-independent pathway which results in localization of LcrV in the cytosol of infected cells but not the surrounding medium.
Contribution ofSalmonella typhimuriumVirulence Factors to Diarrheal Disease in Calves
Authors: Tsolis Renée M. , Adams L. Garry , Ficht Thomas A. , Bäumler Andreas J. 
Published: December 2019

ABSTRACTLimited knowledge is available about the virulence mechanisms responsible for diarrheal disease caused bySalmonella typhimurium. To assess the contribution to diarrheal disease of virulence determinants identified in models of infection, we tested a collection ofS. typhimuriummutants for their ability to cause enteritis in calves.S. typhimuriumstrains carrying mutations in the virulence plasmid (spvR),Salmonellapathogenicity island 2 (SPI-2) (spiB), or SPI-5 (sopB) caused mortality and acute diarrhea in calves. AnS. typhimurium rfaJmutant, which is defective for lipopolysaccharide outer core biosynthesis, was of intermediate virulence. Mutations in SPI-1 (hilAandprgH) oraroAmarkedly reduced virulence and the severity of diarrhea. Furthermore, histopathological examination of calves infected with SPI-1 oraroAmutants revealed a marked reduction or absence of intestinal lesions. These data suggest that virulence factors, such as SPI-1, which are required during intestinal colonization are more important for pathogenicity in calves than are genes required during the systemic phase ofS. typhimuriuminfection, including SPI-2 or thespvoperon. This is in contrast to the degree of attenuation caused by these mutations in the mouse.
Use of Genetically Manipulated Strains of
Clostridium perfringens
Reveals that Both Alpha-Toxin and Theta-Toxin Are Required for Vascular Leukostasis To Occur in Experimental Gas Gangrene
Authors: Ellemor Darren M. , Baird Rebecca N. , Awad Milena M. , Boyd Richard L. , Rood Julian I. , Emmins John J. 
Published: December 2019

ABSTRACT

A hallmark of gas gangrene (clostridial myonecrosis) pathology is a paucity of leukocytes infiltrating the necrotic tissue. The cause of this paucity most likely relates to the observation of leukocyte aggregates at the border of the area of tissue necrosis, often within the microvasculature itself. Infecting mice with genetically manipulated strains of
Clostridium perfringens
type A (deficient in either alpha-toxin or theta-toxin production) resulted in significantly reduced leukocyte aggregation when alpha-toxin was absent and complete abrogation of leukocyte aggregation when theta-toxin was absent. Thus, both alpha-toxin and theta-toxin are necessary for the characteristic vascular leukostasis observed in clostridial myonecrosis.
Role of Local Cytokines in Increased Gastric Expression of the Secretory Component inHelicobacter pyloriInfection
Authors: Ahlstedt Ingela , Lindholm Catharina , Lönroth Hans , Hamlet Annika , Svennerholm Ann-Mari , Quiding-Järbrink Marianne 
Published: December 2019

ABSTRACTUsing immunohistochemical staining, we examined the presence of secretory component (SC) on epithelial cells in gastric and duodenal biopsy specimens collected fromHelicobacter pylori-infected individuals and healthy controls. Gastric epithelial cells from healthy volunteers expressed low, but detectable, levels of SC. In contrast, significantly higher level of expression of SC (P< 0.001) was observed on epithelial cells in the antra ofH. pylori-infected individuals. The antral SC expression correlated with staining for gamma interferon of intraepithelial and lamina propria lymphocytes (rs= 0.76 and 0.69, respectively,P< 0.001) and correlated weakly with production of tumor necrosis factor alpha (rs= 0.43,P< 0.05), but it did not correlate at all with interleukin-4 production.
Age-Associated Differences in Immunoglobulin G1 (IgG1) and IgG2 Subclass Antibodies to Pneumococcal Polysaccharides following Vaccination
Authors: Lottenbach Kathleen R. , Mink ChrisAnna M. , Barenkamp Stephen J. , Anderson Edwin L. , Homan Sharon M. , Powers Douglas C. 
Published: December 2019

ABSTRACT
Immunoglobulin G (IgG) subclass antibody responses to pneumococcal vaccines were determined for human subjects in four age groups. The ratios of IgG1/IgG2 antibody concentrations declined with advancing age for all five of the serotypes tested. Protein-conjugate vaccines elicited enhanced IgG antibody responses over plain polysaccharide vaccines in infants but not in adult groups.
Coinfection withToxoplasma gondiiInhibits Antigen-Specific Th2 Immune Responses, Tissue Inflammation, and Parasitism in BALB/c Mice Infected withLeishmania major
Authors: Santiago H. C. , Oliveira M. A. P. , Bambirra E. A. , Faria A. M. C. , Afonso L. C. C. , Vieira L. Q. , Gazzinelli R. T. 
Published: December 2019

ABSTRACTLesion size, cellular infiltration, and tissue parasitism in the footpads of BALB/c mice infected withLeishmania majorwere all dramatically inhibited during acute but not chronic infection withToxoplasma gondii. Similarly, acute but not chronic toxoplasmosis at the time of infection withL. majorhad a strong inhibitory effect on development of acquired immune responses mediated by Th2 lymphocytes. In contrast, no major changes inLeishmania-specific Th1-mediated responses were observed in mice coinfected withT. gondii.
Identification of a Third Metalloprotease Toxin Gene in Extraintestinal Isolates of
Bacteroides fragilis
Authors: Chung Gyung-Tae , Franco Augusto A. , Wu Shaoguang , Rhie Gi-Eun , Cheng Rodney , Oh Hee-Bok , Sears Cynthia L. 
Published: December 2019

ABSTRACT

To further understand the epidemiology of enterotoxigenic
Bacteroides fragilis
(ETBF), 89 extraintestinal
B. fragilis
strains from Seoul, Korea, were examined for secretion of
B. fragilis
toxin (BFT) by the HT29/C1 biologic assay and for the
B. fragilis
toxin gene (
bft
) by colony blot hybridization and PCR. Complete agreement between the three techniques was found. Overall, 34
B. fragilis
strains (38%) were identified as ETBF. Eleven of the 34 ETBF strains (32%) expressed a new isoform of BFT (Korea-BFT). This new isoform is more related to BFT-2 than to BFT-1. Like BFT-1 and BFT-2, Korea-BFT cleaves E-cadherin, the zonula adherens protein.
Immune Cells Are Required for Cutaneous Ulceration in a Swine Model of Chancroid
Authors: San Mateo Lani R. , Toffer Kristen L. , Orndorff Paul E. , Kawula Thomas H. 
Published: December 2019

ABSTRACT

Cutaneous lesions of the human sexually transmitted genital ulcer disease chancroid are characterized by the presence of intraepidermal pustules, keratinocyte cytopathology, and epidermal and dermal erosion. These lesions are replete with neutrophils, macrophages, and CD4
+
T cells and contain very low numbers of cells of
Haemophilus ducreyi
, the bacterial agent of chancroid. We examined lesion formation by
H. ducreyi
in a pig model by using cyclophosphamide (CPA)-induced immune cell deficiency to distinguish between host and bacterial contributions to chancroid ulcer formation. Histologic presentation of
H. ducreyi
-induced lesions in CPA-treated pigs differed from ulcers that developed in immune-competent animals in that pustules did not form and surface epithelia remained intact. However, these lesions had significant suprabasal keratinocyte cytotoxicity. These results demonstrate that the host immune response was required for chancroid ulceration, while bacterial products were at least partially responsible for the keratinocyte cytopathology associated with chancroid lesions in the pig. The low numbers of
H. ducreyi
present in lesions in humans and immune-competent pigs have prevented localization of these organisms within skin. However,
H. ducreyi
organisms were readily visualized in lesion biopsies from infected CPA-treated pigs by immunoelectron microscopy. These bacteria were extracellular and associated with necrotic host cells in the epidermis and dermis. The relative abundance of
H. ducreyi
in inoculated CPA-treated pig skin suggests control of bacterial replication by host immune cells during natural human infection.
Glycerol Monolaurate Inhibits Induction of Vancomycin Resistance in
Enterococcus faecalis
Authors: Ruzin Alexey , Novick Richard P. 
Published: December 2019

ABSTRACT

Glycerol monolaurate (GML) is a surfactant that has been found to inhibit the post-exponential phase activation of virulence factor production and the induction of β-lactamase in
Staphylococcus aureus
. It has been suggested that signal transduction is the most probable target for GML (S. J. Projan, S. Brown-Skrobot, P. M. Schlievert, F. Vandenesch, and R. P. Novick, J. Bacteriol. 176:4204–4209, 1994). We found that GML suppresses growth of vancomycin-resistant
Enterococcus faecalis
on plates with vancomycin and blocks the induction of vancomycin resistance, which involves a membrane-associated signal transduction mechanism, either at or before initiation of transcription. Given the surfactant nature of GML and the results of previous experiments, we suggest that GML blocks signal transduction. In contrast, GML has no effect on the induction of erythromycin-inducible macrolide resistance in
S. aureus
, which does not involve signal transduction.
The
leuO
Gene Product Has a Latent Ability To Relieve
bgl
Silencing in
Escherichia coli
Authors: Ueguchi Chiharu , Ohta Tomoko , Seto Chiharu , Suzuki Tomomi , Mizuno Takeshi 
Published: December 2019

ABSTRACT

The
Escherichia coli bgl
operon is of interest, since its expression is silent (phenotypically Bgl
−
), at least under standard laboratory conditions. Here we attempted to identify a
trans
-acting factor(s) that is presumably relevant to the regulation of
bgl
by a random insertion mutagenesis with mini-Tn
10
. These collected mutations, conferring the phenotype of Bgl
+
, were localized in three loci on the genetic map, two of which appeared to be
hns
and
bglJ
, which were previously implicated as the factors affecting the Bgl phenotype. The other locus at 1 to 2 min on the genetic map appeared to be a new one. In this case, the insertion mutation was found to be just in front of the
leuO
gene encoding a putative LysR-like DNA-binding protein. Genetic analyses revealed that overproduction of LeuO in the wild-type cells causes the phenotype of Bgl
+
. A
leuO
deletion mutant was also characterized in terms of expression of
bgl
. From these results, the possible function of LeuO in
bgl
expression will be discussed from an evolutionary and/or ecological point of view.
EpsR Modulates Production of Extracellular Polysaccharides in the Bacterial Wilt Pathogen
Ralstonia
(
Pseudomonas
)
solanacearum
Authors: Chapman Matt R. , Kao C. Cheng 
Published: December 2019

ABSTRACT

Ralstonia solanacearum
is the causal agent of bacterial wilt of many agriculturally important crops. Exopolysaccharide synthesized by products of the
epsI
operon is the major virulence factor for
R. solanacearum
. Expression of
epsI
has been demonstrated to be under the control of several proteins, including several two-component regulators. Overexpression of EpsR was found previously to reduce the amount of synthesis specifically from the
epsI
promoter. Here we present data that a single chromosomal copy of
epsR
activates the
epsI
promoter, suggesting that EpsR is a concentration-dependent effector of
epsI
gene expression. Furthermore, the ability of EpsR to modulate
epsI
expression is dependent on the phosphorylation state of EpsR. Gel mobility shift assays suggest that EpsR can specifically bind the
epsI
promoter and that this binding requires a phosphorylated form of EpsR.
Endonuclease V (
nfi
) Mutant of
Escherichia coli
K-12
Authors: Guo Guangming , Weiss Bernard 
Published: December 2019

ABSTRACT

Endonuclease V (deoxyinosine 3′ endonuclease), the product of the
nfi
gene, has a specificity that encompasses DNAs containing dIMP, abasic sites, base mismatches, uracil, and even untreated single-stranded DNA. To determine its importance in DNA repair pathways,
nfi
insertion mutants and overproducers (strains bearing
nfi
plasmids) were constructed. The mutants displayed a twofold increase in spontaneous mutations for several markers and an increased sensitivity to killing by bleomycin and nitrofurantoin. An
nfi
mutation increased both cellular resistance to and mutability by nitrous acid. This agent should generate potential cleavage sites for the enzyme by deaminating dAMP and dCMP in DNA to dIMP and dUMP, respectively. Relative to that of a wild-type strain, an
nfi
mutant displayed a 12- to 1,000-fold increase in the frequency of nitrite-induced mutations to streptomycin resistance, which are known to occur in A · T base pairs. An
nfi
mutation also enhanced the lethality caused by a combined deficiency of exonuclease III and dUTPase, which has been attributed to unrepaired abasic sites. However, neither the deficiency nor the overproduction of endonuclease V affected the growth of the single-stranded DNA phages M13 or φX174 nor of Uracil-containing bacteriophage λ. These results suggest that endonuclease V has a significant role in the repair of deaminated deoxyadenosine (deoxyinosine) and abasic sites in DNA, but there was no evidence for its cleavage in vivo of single-stranded or uracil-containing DNA.
Cloning of Genes Coding for the Three Subunits of Thiocyanate Hydrolase of
Thiobacillus thioparus
THI 115 and Their Evolutionary Relationships to Nitrile Hydratase
Authors: Katayama Yoko , Matsushita Yasuhiko , Kaneko Miyuki , Kondo Mai , Mizuno Tadayoshi , Nyunoya Hiroshi 
Published: December 2019

ABSTRACT

Thiocyanate hydrolase is a newly found enzyme from
Thiobacillus thioparus
THI 115 that converts thiocyanate to carbonyl sulfide and ammonia (Y. Katayama, Y. Narahara, Y. Inoue, F. Amano, T. Kanagawa, and H. Kuraishi, J. Biol. Chem. 267:9170–9175, 1992). We have cloned and sequenced the
scn
genes that encode the three subunits of the enzyme. The
scnB
,
scnA
, and
scnC
genes, arrayed in this order, contained open reading frames encoding sequences of 157, 126, and 243 amino acid residues, respectively, for the β, α, and γ subunits, respectively. Each open reading frame was preceded by a typical Shine-Dalgarno sequence. The deduced amino-terminal peptide sequences for the three subunits were in fair agreement with the chemically determined sequences. The protein molecular mass calculated for each subunit was compatible with that determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. From a computer analysis, thiocyanate hydrolase showed significant homologies to bacterial nitrile hydratases known to convert nitrile to the corresponding amide, which is further hydrolyzed by amidase to form acid and ammonia. The two enzymes were homologous over regions corresponding to almost the entire coding regions of the genes: the β and α subunits of thiocyanate hydrolase were homologous to the amino- and carboxyl-terminal halves of the β subunit of nitrile hydratase, and the γ subunit of thiocyanate hydrolase was homologous to the α subunit of nitrile hydratase. Comparisons of the catalytic properties of the two homologous enzymes support the model for the reaction steps of thiocyanate hydrolase that was previously presented on the basis of biochemical analyses.