bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-Phase Transport in PEM Fuel Cell Cathodes
Authors: Gurau Vladimir , Zawodzinski Thomas A. , Mann J. Adin
Published: April 2008

To date, multiphase computational fluid dynamics models for proton exchange membrane (PEM) fuel cells failed to provide even a qualitative depiction of the fuel cell water management. This was primarily due to the inability to capture two-phase phenomena in the cathode catalyst layer and the water saturation equilibrium at the interface between the fuel cell components. A model without the cathode catalyst layer cannot capture dominant mechanisms of water transfer and cannot explain correctly the fuel cell performance. We propose a multifluid, multiphase model consisting of separate transport equations for each phase. The model accounts for gas- and liquid-phase momentam and species transport in the cathode channel, gas diffusion layer (GDL), and catalyst layer and for the current density, ionomer-phase potential, and water content in the catalyst coated membrane. The model considers water produced at cathode by (I) electrochemical reaction, (II) change of phase, and (III) parallel, competing mechanisms of water transfer between the ionomer distributed in the catalyst layer and the catalyst layer pores. Liquid water is transported in the GDL and the catalyst layer due to liquid pressure gradient and in the channel due to gravity and two-phase drag. We have developed a transport equation for the water content. The source/sink terms of the transport equation represent the parallel, competing mechanisms of water transfer between the ionomer phase and the catalyst layer pores. They are (I) sorption/desorption at nonequilibrium and (II) electro-osmotic drag by the secondary current. Another distinguishing feature of this model is the capability to capture water saturation equilibrium at channel-GDL and GDL–catalyst layer interfaces. The computational results are used to study the dynamics of water transport within and between the fuel cell components and the impact of the GDL and catalyst layer properties on the amount of water retained in the fuel cell components during operation. A new dominant mechanism of water transfer between the ionomer distributed in the catalyst layer and the catalyst layer pores is identified. The amount of water retained in GDL is determined by GDL permeability and its pore size at the interface with the channel. The amount of water retained in the cathode catalyst layer is determined by the saturation equilibrium at the interface with the GDL. Models based on the two-phase mixture model are not applicable to PEM fuel cell electrodes.
Flow, Transport, and Reactions in a Thin Layer Flow Cell
Authors: Fuhrmann Jürgen , Zhao Hong , Holzbecher Ekkehard , Langmach Hartmut
Published: April 2008

The performance of fuel cells depends on the rate parameters of the kinetic reactions between the involved species, among other conditions. The determination of these parameters is crucial for the understanding of the functionality of fuel cells. Differential electrochemical mass spectroscopy in thin layer flow cells is used as a tool to gain improved understanding of the heterogeneous catalytic reactions taking place in fuel cell catalytic layers. In this paper, we focus on the description of thin layer cells by numerical models based on partial differential equations and the extraction of kinetics parameters by inverse modeling. For the model setup, various software tools are used. The simulation of laminar free flow is performed by the commercial code COMSOL. A finite volume code is used for the simulation of the reactive transport. The latter is coupled with a Levenberg–Marquardt algorithm for the determination of kinetic constants. Two designs of thin layer flow cells are considered: a cylindrical and a rectangular design. A drawback of the cylindrical cell design is the highly inhomogeneous velocity field leading to spatial variations of the conditions for electrode reactions. In contrast, the rectangular cell design shows a homogeneous flow field in the vicinity of the catalyst. The rectangular cell design has the additional advantage that flow is essentially two dimensional and can be computed analytically, which simplifies the numerical approach. The inverse modeling procedure is demonstrated for a hydrogen-carbon monoxide system.
Bifurcation Analysis of a Two-Phase PEMFC Model
Authors: Grötsch Markus , Hanke-Rauschenbach Richard , Mangold Michael
Published: April 2008

A major issue of polymer-electrolyte-membrane (PEM) fuel cell operation is the water management of the cells. This article tries to contribute to an improved understanding of flooding/drying out effects by performing a analysis for a rigorous two-phase PEM fuel cell model. The model is examined by means of a bifurcation analysis. This investigation is performed numerically with parameter continuation methods. The nonlinear behavior is qualified and possible instabilities are detected. A steady state multiplicity is found. The multiplicity is physically explained and the influence of selected fuel cell parameters is investigated. The multiplicity is finally verified in a dynamic simulation. The future work aims at a model reduction of the analyzed fuel cell model to gain a low order model suitable for model-based control strategies.
Daptomycin Is Effective in Treatment of Experimental Endocarditis Due to Methicillin-Resistant and Glycopeptide-Intermediate
Staphylococcus aureus
Authors: Marco Francesc , García de la Mària Cristina , Armero Yolanda , Amat Eurídice , Soy Dolors , Moreno Asunción , del Río Ana , Almela Manel , Mestres Carlos A. , Gatell José M. , Jiménez de Anta María Teresa , Miró José M.
Published: April 2008

Daptomycin is a lipopeptide antibiotic with potent in vitro activity against gram-positive cocci, including
Staphylococcus aureus
. This study evaluated the in vitro and in vivo efficacies of daptomycin against two clinical isolates: methicillin-resistant
S. aureus
(MRSA) 277 (vancomycin MIC, 2 μg/ml) and glycopeptide-intermediate
S. aureus
(GISA) ATCC 700788 (vancomycin MIC, 8 μg/ml). Time-kill experiments demonstrated that daptomycin was bactericidal in vitro against these two strains. The in vivo activity of daptomycin (6 mg/kg of body weight every 24 h) was evaluated by using a rabbit model of infective endocarditis and was compared with the activities of a high-dose (HD) vancomycin regimen (1 g intravenously every 6 h), the recommended dose (RD) of vancomycin regimen (1 g intravenously every 12 h) for 48 h, and no treatment (as a control). Daptomycin was significantly more effective than the vancomycin RD in reducing the density of bacteria in the vegetations for the MRSA strains (0 [interquartile range, 0 to 1.5] versus 2 [interquartile range, 0 to 5.6] log CFU/g vegetation;
P
= 0.02) and GISA strains (2 [interquartile range, 0 to 2] versus 6.6 [interquartile range, 2.0 to 6.9] log CFU/g vegetation;
P
< 0.01) studied. In addition, daptomycin sterilized more MRSA vegetations than the vancomycin RD (13/18 [72%] versus 7/20 [35%];
P
= 0.02) and sterilized more GISA vegetations than either vancomycin regimen (12/19 [63%] versus 4/20 [20%];
P
< 0.01). No statistically significant difference between the vancomycin HD and the vancomycin RD for MRSA treatment was noted. These results support the use of daptomycin for the treatment of aortic valve endocarditis caused by GISA and MRSA.
Systemic Expression of Cytokine Production in Patients with Severe Pneumococcal Pneumonia: Effects of Treatment with a β-Lactam versus a Fluoroquinolone
Authors: Calbo Esther , Alsina Montserrat , Rodríguez-Carballeira Mónica , Lite Josep , Garau Javier
Published: April 2008

Bacterial alveolar invasion is followed by an inflammatory response. A systemic extension of the compartmentalized immune response has been described in patients with severe pneumonia. The data suggest that some antimicrobials may induce a differential release of cytokines. We conducted a prospective, randomized study in adult patients with severe pneumococcal pneumonia to measure the effects of ceftriaxone and levofloxacin in the systemic cytokine expression over time. Demographic, clinical characteristics, and severity scores were recorded. The serum concentrations of tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), IL-6, IL-8, IL-10, and IL-1 receptor agonist were measured at 0, 24, 72, and 120 h. A total of 32 patients were included in the study. Both groups were homogeneous in terms of age, comorbidities, severity of disease, and corticosteroid or statin use. With the single exception of IL-1β, all cytokines were detected in venous blood. All of the cytokines studied showed a similar pattern of progressive decrease over time. No significant differences in the concentrations of any of the cytokines studied were found, with the exception of TNF-α, for which lower concentrations were obtained at 120 h in the levofloxacin group (
P
= 0.014). Basal oxygen saturation (
P
= 0.034) and heart rate (
P
= 0.029) returned to normal values earlier in the levofloxacin arm. We demonstrated that in patients with severe pneumococcal pneumonia pro- and anti-inflammatory responses could be detected in venous blood, representing a systemic extension of the compartmentalized response. Treatment with a β-lactam agent or a fluoroquinolone has different effects on cytokine production and its systemic expression, impacting the clinical course of the disease.
Activities and Ultrastructural Effects of Antifungal Combinations against Simulated
Candida
Endocardial Vegetations
Authors: Pai Manjunath P. , Samples Marie L. , Mercier Renee-Claude , Spilde Michael N.
Published: April 2008

In vitro pharmacodynamic model (PDM) simulation of serum antifungal concentrations may predict the value of combination antifungal regimens against
Candida
sp. endocarditis. We investigated the effects of combinations of flucytosine (5FC), micafungin (Mica), and voriconazole (Vor) against
Candida
-infected human platelet-fibrin clots, used as simulated endocardial vegetations (SEVs). Single clinical bloodstream isolates of
Candida albicans
,
Candida glabrata
,
Candida parapsilosis
, and
Candida tropicalis
were used. All four isolates were susceptible to 5FC, while
C. glabrata
was resistant to Vor and
C. tropicalis
had a paradoxical resistance phenotype to Mica. The SEVs were prepared with an initial inoculum of 1 × 10
6
CFU/g of SEV and added to a PDM, which utilized yeast nitrogen broth-2% glucose and incubation at 35°C and simulated antifungal pharmacokinetic profiles. Fungal densities in the SEVs were determined in quadruplicate over 72 h. Scanning electron microscopy (SEM) was used to evaluate treatment and control SEVs. Vor was the least active single agent against all
Candida
spp. except for
C. parapsilosis
, where it was comparable to Mica. In contrast, 5FC was the most active against all
Candida
spp. except for
C. tropicalis
, where it was comparable to Mica. The combination of 5FC plus Vor was superior to either agent alone against
C. parapsilosis
. The combination of Vor plus Mica was inferior to the use of Mica alone against
C. tropicalis
. The triple combination of 5FC plus Vor plus Mica was no better than single or dual agents against any of the
Candida
spp. The ultrastructural features of infected SEVs were unique for each
Candida
sp., with
C. parapsilosis
in particular manifesting friable biofilm clusters. In general, 5FC and Mica were superior in their rates and extents of fungal burden reduction compared to Vor against
Candida
-infected SEVs. Evaluation of 5FC and Mica in animal models of
Candida
endocarditis is warranted.
Impact of Mycophenolic Acid on the Functionality of Human Polymorphonuclear Neutrophils and Dendritic Cells during Interaction withAspergillus fumigatus
Authors: Mezger Markus , Wozniok Iwona , Blockhaus Christian , Kurzai Oliver , Hebart Holger , Einsele Hermann , Loeffler Juergen
Published: April 2008

Mycophenolic acid (MPA) is used clinically to prevent graft rejection but may increase the risk of fungal infection. We observed that MPA enhanced theAspergillus fumigatus-induced oxidative burst of polymorphonuclear neutrophils, but without a corresponding increase in fungal killing. Furthermore, MPA inhibited the proinflammatory cytokine response and maturation of dendritic cells.
CCL28 Is Increased in Human
Helicobacter pylori
-Induced Gastritis and Mediates Recruitment of Gastric Immunoglobulin A-Secreting Cells
Authors: Hansson Malin , Hermansson Michael , Svensson Helena , Elfvin Anders , Hansson Lars-Erik , Johnsson Erik , Sjöling Åsa , Quiding-Järbrink Marianne
Published: April 2008

Human
Helicobacter pylori
infection gives rise to an active chronic gastritis and is a major risk factor for the development of duodenal ulcer disease and gastric adenocarcinoma. The infection is accompanied by a large accumulation of immunoglobulin A (IgA)-secreting cells in the gastric mucosa, and following mucosal immunization only
H. pylori
-infected volunteers mounted a B-cell response in the gastric mucosa. To identify the signals for recruitment of gastric IgA-secreting cells, we investigated the gastric production of CCL28 (mucosa-associated epithelial chemokine) and CCL25 (thymus-expressed chemokine) in
H. pylori
-infected and uninfected individuals and the potential of gastric B-cell populations to migrate toward these chemokines. Gastric tissue from
H. pylori
-infected individuals contained significantly more CCL28 protein and mRNA than that from uninfected individuals, while CCL25 levels remained unchanged. Chemokine-induced migration of gastric lamina propria lymphocytes isolated from patients undergoing gastric resection was then assessed using the Transwell system. IgA-secreting cells and IgA
+
memory B cells from
H. pylori
-infected tissues migrated toward CCL28 but not CCL25, while the corresponding cells from uninfected patients did not. Furthermore, IgG-secreting cells from
H. pylori
-infected patients did not migrate to CCL28 but instead to CXCL12 (SDF-1α). However, chemokine receptor expression did not correlate to the migratory pattern of the different B-cell populations. These studies are the first to show increased CCL28 production during gastrointestinal infection in humans and provide an explanation for the large influx of IgA-secreting cells to the gastric mucosa in
H. pylori
-infected individuals.
Expression of
Staphylococcus epidermidis
SdrG Increases following Exposure to an In Vivo Environment
Authors: Sellman Bret R. , Timofeyeva Yekaterina , Nanra Jasdeep , Scott Adrienne , Fulginiti James P. , Matsuka Yury V. , Baker Steve M.
Published: April 2008

SdrG is a surface-associated fibrinogen binding protein present in most strains of
Staphylococcus epidermidis
. Surface expression of SdrG was not detected by flow cytometry or immunofluorescence microscopy on
S. epidermidis
0-47 grown in nutrient broth or in the presence of human serum.
sdrG
transcript levels increased 1 hour following a shift from growth in nutrient broth to growth in the bloodstream of a mouse and resulted in a concomitant increase in protein levels as detected by immunofluorescence microscopy. The environmental signal(s) resulting in the increase in expression is elusive, as growth under conditions known to mimic in vivo conditions (elevated CO
2
, iron limitation, human serum, and citrated human blood) did not affect expression of SdrG. Immunizing mice with either the N1N2N3 (amino acids 50 to 597) or N2N3 (amino acids 273 to 597) subdomain of the N-terminal A domain of recombinant SdrG (rSdrG) elicited a robust antibody response; however, only mice vaccinated with rSdrG
N23
exhibited a significant reduction in 0-47 recovered after experimental infection. Since SdrG is expressed early during infection in response to specific host environmental cues present in the bloodstream and since antibodies to it are effective in reducing bacteremia, SdrG possesses attributes of a vaccine component effective against the pathogenic form of the ubiquitous human commensal
S. epidermidis
.
Immunogenicity and Protective Efficacy of Recombinant
Campylobacter jejuni
Flagellum-Secreted Proteins in Mice
Authors: Baqar Shahida , Applebee Lisa A. , Gilliland Theron C. , Lee Lanfong H. , Porter Chad K. , Guerry Patricia
Published: April 2008

Immunogenicity and protective efficacy of three
Campylobacter jejuni
flagellum-secreted proteins, FlaC, FspA1, and FspA2, were compared by use of a mouse model. Mice were immunized intranasally with each protein with or without LTR192G as the adjuvant and challenged intranasally with
C. jejuni
81-176 or CG8486. All three proteins were immunogenic, although FspA1 induced the highest levels of serum immunoglobulin G (IgG) and fecal IgA. Although immunogenic, FlaC provided only 18% protection against disease from
C. jejuni
81-176. Immunization with FspA1 resulted in 57.8% protection without adjuvant or 63.8% protection with adjuvant against homologous challenge with 81-176. Alternatively, immunization with FspA2 provided 38.4% (without adjuvant) or 47.2% (with adjuvant) protection against disease from homologous challenge with CG8486. In contrast to FspA2, FspA1 provided some heterologous protection against
C. jejuni
CG8486 when delivered with (31.2%) or without (44.8%) LTR192G. These results suggest that FspA1 may be a good subunit vaccine candidate against
C. jejuni
disease.
Role of Aromatic Amino Acids in Receptor Binding Activity and Subunit Assembly of the Cytolethal Distending Toxin of
Aggregatibacter actinomycetemcomitans
Authors: Cao Linsen , Bandelac Georges , Volgina Alla , Korostoff Jonathan , DiRienzo Joseph M.
Published: April 2008

The periodontal pathogen
Aggregatibacter actinomycetemcomitans
produces a cytolethal distending toxin (Cdt) that inhibits the proliferation of oral epithelial cells. Structural models suggest that the CdtA and CdtC subunits of the Cdt heterotrimer form two putative lectin domains with a central groove. A region of CdtA rich in heterocyclic amino acids (aromatic patch) appears to play an important role in receptor recognition. In this study site-specific mutagenesis was used to assess the contributions of aromatic amino acids (tyrosine and phenylalanine) to receptor binding and CdtA-CdtC assembly. Predominant surface-exposed aromatic residues that are adjacent to the aromatic patch region in CdtA or are near the groove located at the junction of CdtA and CdtC were studied. Separately replacing residues Y105, Y140, Y188, and Y189 with alanine in CdtA resulted in differential effects on binding related to residue position within the aromatic region. The data indicate that an extensive receptor binding domain extends from the groove across the entire face of CdtA that is oriented 180° from the CdtB subunit. Replacement of residue Y105 in CdtA and residues Y61 and F141 in CdtC, which are located in or at the periphery of the groove, inhibited toxin assembly. Taken together, these results, along with the lack of an aromatic amino acid-rich region in CdtC similar to that in CdtA, suggest that binding of the heterotoxin to its cell surface receptor is mediated predominantly by the CdtA subunit. These findings are important for developing strategies designed to block the activity of this prominent virulence factor.
Late Endocytic Multivesicular Bodies Intersect the Chlamydial Inclusion in the Absence of CD63
Authors: Beatty Wandy L.
Published: April 2008

Chlamydiae are obligate intracellular bacterial pathogens that replicate solely within a membrane-bound vacuole termed an inclusion. Within the confines of the inclusion, the replicating bacteria acquire amino acids, nucleotides, and other precursors from the host cell. Trafficking from CD63-positive multivesicular bodies to the inclusion was previously identified as a novel interaction that provided essential precursors for the maintenance of a productive intracellular infection. The present study analyzes the direct delivery of resident protein and lipid constituents of multivesicular bodies to the intracellular chlamydiae. The manipulation of this trafficking pathway with an inhibitor of multivesicular body transport and the delivery of exogenous antibodies altered protein and cholesterol acquisition and delayed the maturation of the chlamydial inclusion. Although inhibitor studies and ultrastructural analyses confirmed a novel interaction between CD63-positive multivesicular bodies and the intracellular chlamydiae, neutralization with small interfering RNAs and anti-CD63 Fab fragments revealed that CD63 itself was not required for this association. These studies confirm CD63 as a constituent in multivesicular body-to-inclusion transport; however, other requisite components of these host cell compartments must control the delivery of key nutrients that are essential to intracellular bacterial development.
Impact of Mating Type, Serotype, and Ploidy on the Virulence of
Cryptococcus neoformans
Authors: Lin Xiaorong , Nielsen Kirsten , Patel Sweta , Heitman Joseph
Published: April 2008

Hybridization with polyploidization is a significant biological force driving evolution. The effect of combining two distinct genomes in one organism on the virulence potential of pathogenic fungi is not clear.
Cryptococcus neoformans
, the most common cause of fungal infection of the central nervous system, has a bipolar mating system with
a
and α mating types and occurs as A (haploid), D (haploid), and AD hybrid (mostly diploid) serotypes. Diploid AD hybrids are derived either from
a
-α mating or from unisexual mating between haploid cells. The precise contributions of increased ploidy, the effect of hybridization between serotypes A and D, and the combination of mating types to the virulence potential of AD hybrids have remained elusive. By using in vitro and in vivo characterization of laboratory-constructed isogenic diploids and AD hybrids with all possible mating type combinations in defined genetic backgrounds, we found that higher ploidy has a minor negative effect on virulence in a murine inhalation model of cryptococcosis. The presence of both mating types
a
and α in AD hybrids did not affect the virulence potential, irrespective of the serotype origin. Interestingly, AD hybrids with only one mating type behaved differently, with the virulence of αADα strains similar to that of other hybrids, while
a
AD
a
hybrids displayed significantly lower virulence due to negative epistatic interactions between the A
a
and D
a
alleles of the mating type locus. This study provides insights into the impact of ploidy, mating type, and serotype on virulence and the impact of hybridization on the fitness and virulence of a eukaryotic microbial pathogen.
Deficiency of Indoleamine 2,3-Dioxygenase Enhances Commensal-Induced Antibody Responses and Protects against
Citrobacter rodentium
-Induced Colitis
Authors: Harrington Lynne , Srikanth Chittur V. , Antony Reuben , Rhee Sue J. , Mellor Andrew L. , Shi Hai Ning , Cherayil Bobby J.
Published: April 2008

Indoleamine 2,3-dioxygenase (IDO) is a negative regulator of lymphocyte responses that is expressed predominantly in macrophages and dendritic cells. We detected it at high levels in the small intestine and mesenteric lymph node of young adult mice, suggesting a role in intestinal immunity. Consistent with this idea, we found that IDO-deficient mice had elevated baseline levels of immunoglobulin A (IgA) and IgG in the serum and increased IgA in intestinal secretions. These abnormalities were corrected by a course of broad-spectrum oral antibiotics started at weaning, indicating that they were dependent on the intestinal microbiota. Kynurenine and picolinic acid, two IDO-generated metabolites of tryptophan, were able to inhibit lipopolysaccharide-induced antibody production by splenocytes in vitro, and kynurenine also induced B-cell apoptosis, findings that provide an explanation for the elevated Ig levels in animals lacking IDO. The intestinal secretions of IDO-deficient mice had elevated levels of IgA antibodies that cross-reacted with the gram-negative enteric bacterial pathogen
Citrobacter rodentium
. In keeping with the functional importance of this natural secretory IgA, the mutant animals were more resistant to intestinal colonization by
Citrobacter
, developed lower levels of serum
Citrobacter
-specific IgM and IgG antibodies following oral infection, and had significantly attenuated
Citrobacter
-induced colitis. Our observations point to an important role for IDO in the regulation of immunity to the gut commensal microbiota that has a significant impact on the response to intestinal pathogens.
Serendipitous Discovery of an Immunoglobulin-Binding Autotransporter in
Bordetella
Species
Authors: Williams Corinne L. , Haines Robert , Cotter Peggy A.
Published: April 2008

We describe the serendipitous discovery of BatB, a classical-type
Bordetella
autotransporter (AT) protein with an ∼180-kDa passenger domain that remains noncovalently associated with the outer membrane. Like genes encoding all characterized protein virulence factors in
Bordetella
species,
batB
transcription is positively regulated by the master virulence regulatory system BvgAS. BatB is predicted to share similarity with immunoglobulin A (IgA) proteases, and we showed that BatB binds Ig in vitro. In vivo, a
Bordetella bronchiseptica
Δ
batB
mutant was unable to overcome innate immune defenses and was cleared from the lower respiratory tracts of mice more rapidly than wild-type
B. bronchiseptica
. This defect was abrogated in SCID mice, suggesting that BatB functions to resist clearance during the first week postinoculation in a manner dependent on B- and T-cell-mediated activities. Taken together with the previous demonstration that polymorphonuclear neutrophils (PMN) are critical for the control of
B. bronchiseptica
in mice, our data support the hypothesis that BatB prevents nonspecific antibodies from facilitating PMN-mediated clearance during the first few days postinoculation. Neither of the strictly human-adapted
Bordetella
subspecies produces a fully functional BatB protein; nucleotide differences within the putative promoter region prevent
batB
transcription in
Bordetella pertussis
, and although expressed, the
batB
gene of human-derived
Bordetella parapertussis
(
B. parapertussis
hu
) contains a large in-frame deletion relative to
batB
of
B. bronchiseptica
. Taken together, our data suggest that BatB played an important role in the evolution of virulence and host specificity among the mammalian-adapted bordetellae.
Incorporation ofMycobacterium tuberculosisLipoarabinomannan into Macrophage Membrane Rafts Is a Prerequisite for the Phagosomal Maturation Block
Authors: Welin Amanda , Winberg Martin E. , Abdalla Hana , Särndahl Eva , Rasmusson Birgitta , Stendahl Olle , Lerm Maria
Published: April 2008

Lipoarabinomannan (LAM) is one of the key virulence factors forMycobacterium tuberculosis, the etiological agent of tuberculosis. During uptake of mycobacteria, LAM interacts with the cell membrane of the host macrophage and can be detected throughout the cell upon infection. LAM can inhibit phagosomal maturation as well as induce a proinflammatory response in bystander cells. The aim of this study was to investigate how LAM exerts its action on human macrophages. We show that LAM is incorporated into membrane rafts of the macrophage cell membrane via its glycosylphosphatidylinositol anchor and that incorporation of mannose-capped LAM fromM. tuberculosisresults in reduced phagosomal maturation. This is dependent on successful insertion of the glycosylphosphatidylinositol anchor. LAM does not, however, induce the phagosomal maturation block through activation of p38 mitogen-activated protein kinase, contradicting some previous suggestions.
Type IV Pili inFrancisella tularensis: Roles ofpilFandpilTin Fiber Assembly, Host Cell Adherence, and Virulence
Authors: Chakraborty Subhra , Monfett Michael , Maier Tamara M. , Benach Jorge L. , Frank Dara W. , Thanassi David G.
Published: April 2008

Francisella tularensis, a highly virulent facultative intracellular bacterium, is the causative agent of tularemia. Genome sequencing of allF. tularensissubspecies revealed the presence of genes that could encode type IV pili (Tfp). The live vaccine strain (LVS) expresses surface fibers resembling Tfp, but it was not established whether these fibers were indeed Tfp encoded by thepilgenes. We show here that deletion of thepilFputative Tfp assembly ATPase in the LVS resulted in a complete loss of surface fibers. Disruption of thepilTputative disassembly ATPase also caused a complete loss of pili, indicating thatpilTfunctions differently inF. tularensisthan in model Tfp systems such as those found inPseudomonas aeruginosaandNeisseriaspp. The LVSpilFandpilTmutants were attenuated for virulence in a mouse model of tularemia by the intradermal route. Furthermore, although absence of pili had no effect on the ability of the LVS to replicate intracellularly, thepilFandpilTmutants were defective for adherence to macrophages, pneumocytes, and hepatocytes. This work confirms that the surface fibers expressed by the LVS are encoded by thepilgenes and provides evidence that theFrancisellapili contribute to host cell adhesion and virulence.
Comparison of the Contributions of Heat-Labile Enterotoxin and Heat-Stable Enterotoxin b to the Virulence of EnterotoxigenicEscherichia coliin F4ac Receptor-Positive Young Pigs
Authors: Erume Joseph , Berberov Emil M. , Kachman Stephen D. , Scott Michael A. , Zhou You , Francis David H. , Moxley Rodney A.
Published: April 2008

In swine, the most common and severe enterotoxigenicEscherichia coli(ETEC) infections are caused by strains that express K88 (F4)+fimbriae, heat-labile enterotoxin (LT), heat-stable enterotoxin b (STb), and enteroaggregativeE. coliheat-stable toxin 1. Previous studies based on a design that involved enterotoxin genes cloned into a nontoxigenic fimbriated strain have suggested that LT but not STb plays an important role in dehydrating diarrheal disease in piglets <1 week old and also enhances bacterial colonization of the intestine. In the present study, we compared these two toxins in terms of importance for piglets >1 week old with a study design that involved construction of isogenic single- and double-deletion mutants and inoculation of 9-day-old F4ac receptor-positive gnotobiotic piglets. Based on the postinoculation percent weight change per h and serum bicarbonate concentrations, the virulence of the STb−mutant (ΔestB) did not significantly differ from that of the parent. However, deletion of the LT genes (ΔeltAB) in the STb−mutant resulted in a complete abrogation of weight loss, dehydration, and metabolic acidosis in inoculated pigs, and LT complementation restored the virulence of this strain. These results support the hypothesis that LT is a more significant contributor than STb to the virulence of F4+ETEC infections in young F4ac receptor-positive pigs less than 2 weeks old. However, in contrast to previous studies with gnotobiotic piglets, there was no evidence that the expression of LT enhanced the ability of the F4+ETEC strain to colonize the small intestine.
Why a Great Lakes Fishery Commission and Why a Sea Lamprey International Symposium
Authors: Fetterolf Jr. Carlos M.
Published: April 2008

Efforts to establish international fishery commissions and/or effective, complementary regulations and management programs for Great Lakes fisheries failed repeatedly from 1893 to 1952. By 1946 the sea lamprey (Petromyzon marinus), a parasitic predator native to the Atlantic Ocean, was established in the upper Great Lakes and recognized as an impending international catastrophe for the fisheries. This threat provided an added incentive to recast and complete earlier negotiations, and the Convention on Great Lakes Fisheries was entered into force in 1955. The Convention established the Great Lakes Fishery Commission to develop and coordinate fishery research programs, to advise governments on measures to improve the fisheries, and to develop measures and implement programs to control sea lamprey. Sea lamprey populations are currently at levels in all of the Great Lakes to allow acceptable survival and growth of desirable fish species. The commercial and recreational fisheries have revived to the point that their 1979 total economic impact is estimated at $1.16 billion. In 23 yr of operation the Commission has spent $54.5 million for sea lamprey control and research and feels a strong obligation to continue seeking more efficient and cost-effective management techniques. To produce a synthesis of opinion and recommendations for consideration in its future plans the Commission sponsored the Sea Lamprey International Symposium.Key words: sea lamprey, Great Lakes, Great Lakes Fishery Commission, Sea Lamprey International Symposium, international agreements, international organizations
Description and Key to Metamorphosed Specimens and Ammocoetes of Petromyzonidae Found in the Great Lakes Region
Authors: Vladykov Vadim D. , Kott Edward
Published: April 2008

At present five species of Petromyzonidae are found in the Great Lakes region. Of these, three are parasitic: Petromyzon marinus, Ichthyomyzon unicuspis, and I. castaneus; two are nonparasitic: I. fossor and Lethenteron lamottenii. It is quite possible that a nonparasitic sixth species, Lampetra aepyptera, could be found in the Lake Erie basin.Key words: lampreys, Great Lakes, keys, P. marinus, abnormality, L. lamottenii, gigantism
Comments on the Classification and Nomenclature of Lampreys — An Alternative View
Authors: Bailey Reeve M.
Published: April 2008

Current classifications of lampreys as reflected in this symposium are incongruent and unnecessarily split. It is suggested that modern lampreys be classified in one family, three subfamilies, and six genera. Most species are in a single genus Lampetra consisting of six subgenera. Intraspecific variation in dentition is greater than recognized previously. Reasons are given for use of the stem Petromyzont- for suprageneric names based on Petromyzon.Key words: taxonomy, terminology, morphology, lampreys
Spawning Behavior and Fecundity of Lampreys from the Upper Three Great Lakes
Authors: Manion Patrick J. , Hanson Lee H.
Published: April 2008

Five species of lampreys are found in the upper three Great Lakes. All species require certain physical factors for successful spawning such as suitable bottom substrates, water velocities, and temperatures. Nest construction (usually started by males) and spawning behavior are similar although some differences exist. In sea lamprey an average spawning act lasts about 2–5 s and is repeated every 4–5 min; generally nesting is monogamous with little polyandrous nesting (1.2–5.0%); average egg production is about 60 000 eggs. An estimated 86% of the eggs of sea lamprey are not deposited in the nests; however, the fertilization and survival of eggs deposited in the nest is high and may approach 90%.Key words: Petromyzon marinus, Ichthyomyzon unicuspis, I. castaneus, I. fossor, Lampetra lamottei, spawning requirement, nest construction, fecundity, nest productivity, water temperature
Morphology and Physiology of Lamprey Metamorphosis
Authors: Youson J. H.
Published: April 2008

Metamorphosis is highly synchronized in both landlocked and anadromous sea lampreys, Petromyzon marinus, and can be divided into seven clearly defined stages. Although there may be some subtle internal changes several months before the beginning of external metamorphosis, most internal and external changes are initiated simultaneously in early July in P. marinus. The time and degree to which various external anatomical features take place does not differ to any large degree in landlocked and anadromous sea lampreys. Observations on P. marinus and other lamprey species shows that variations in the time of completion of transformation or development of organs reflect the immediate needs of the animal. For example, transformation of the liver and development of the kidneys occur very early (stage 4) whereas organs and tissues involved in osmoregulation, feeding, and digestion do not reach their definitive adult condition until later stages. All organ systems seem to undergo some morphological transformation during metamorphosis. After the beginning of metamorphosis lipid is utilized as the primary source of energy during the nontrophic period which may last up to 10 mo. Physiological modifications accompanying the initiation of metamorphosis include changes in rate of oxygen consumption, in serum osmolarity and thyroxine levels, in the biochemistry of the blood, and in aspects of intermediary metabolism. There is no definitive information as to the factor(s) which control the metamorphic process in lampreys.Key words: lampreys, metamorphosis, morphology, physiology
Respiration of Lampreys
Authors: Lewis S. V.
Published: April 2008

In lampreys, though the gross morphology of the branchial chamber and the method of ventilating the gills are radically different from that found in gnathostomes, the total gill area of larval (1462–2717 mm2∙g−1) and adult (1402–2337 mm2∙g−1) lampreys, the ultrastructure of the gills, and the thickness of the water–blood barrier are similar to active teleosts. The standard rates of oxygen consumption of ammocoetes are low, values for medium-sized Ichthyomyzon hubbsi ranging from 18.1 μL∙g−1∙h−1 at 3.5 °C to 90.1 μL∙g−1∙h−1 at 22.5 °C. The consumption rates increase during metamorphosis rising in Lampetra fluviatilis held at 10 °C from 29.3 to 60.4 μL∙g−1∙h−1, and at the same time a circadian rhythm of consumption develops; maximum rates occur in the dark. Adult lampreys have consumption rates ranging from 66.1 μL∙g−1∙h−1 in L. fluviatilis to 36.9 μL∙g−1∙h−1 in Petromyzon marinus, and Q10's in the temperature range 5–15 °C are from 1.6 to 4.83. Sexually mature males of L. planeri and L. fluviatilis have higher metabolic rates than the females. The active oxygen consumption of P. marinus at 332.5 μL∙g−1∙h−1 is within the range reported for teleosts. Resting ventilation rates are higher in adults than ammocoetes and reach maximum values in sexually mature spawning males. Hypoxia results in an increase in the ventilation and heart rates.Key words: lampreys, respiration; gills, morphology; oxygen consumption, sexual maturity, ventilation rates
Osmoregulation in Juvenile and Adult Lampreys
Authors: Beamish F. W. H.
Published: April 2008

Nonparasitic lampreys are well adapted for a freshwater existence but are less tolerant of salt water than representatives of the parasitic species. Anadromous feeding juvenile sea lampreys, Petromyzon marinus, are able to control serum osmotic and ionic concentrations in all salinities between 0 and 34‰. Juveniles of the anadromous European river lamprey, Lampetra fluviatilis, are slightly less tolerant of salinity change. The transition of P. marinus to a landlocked existence has resulted in a reduction in the capacity for marine osmoregulation. Tolerance to salt water among landlocked P. marinus is related directly to size emphasizing the advantage afforded through a reduction of surface area relative to body volume. Changes in serum osmolality are primarily the result of corresponding shifts in sodium and chloride ions. Changes in chloride are not accompanied by an equivalent shift in sodium suggesting that the relationship between the two ions is not passive. Regulation of sodium by landlocked P. marinus is not precise as that exhibited by the anadromous form particularly in the higher salinities. Nontrophic upstream migrant lampreys display a reduction in their marine osmoregulatory mechanisms and a restoration of the freshwater osmoregulatory apparatus. Freshwater osmotic and ionic regulation deteriorates in spent adult lampreys.Key words: blood, ionic regulation, osmotic regulation, parasitic and nonparasitic lampreys, salinity, life cycle
Biology and Physiology of Feeding in Adult Lampreys
Authors: Farmer G. J.
Published: April 2008

Although landlocked sea lampreys (Petromyzon marinus) attack all but a few of the smallest teleosts in the Great Lakes, the large cold-water species have received the most predation. Information on the feeding habits of anadromous lampreys is limited, but they probably are not specific in their choice of hosts. Species differences exist in the relative proportions of blood and muscle tissue which are consumed. The landlocked sea lamprey primarily feeds on the blood of host fishes at rates of 3–30% of its wet body weight∙d−1 (10 °C). The estimated gross conversion efficiency for this species feeding ad libitum at 10 °C is 39%. This relatively high efficiency is partly attributable to the nature of their blood diet which results in small fecal energy losses of about 3.4% of intake energy. Maximum growth rates occur at 20 °C for sea lampreys of 10–30 g initial weight and at 15 °C for lampreys of 30–90 g. At all experimental temperatures (5–20 °C), growth rates decline with increases in lamprey weight. Increases in sea lamprey weight and in water temperature up to 20 °C cause the rate of host mortality to rise suggesting that, under natural conditions, mortality is seasonal. Landlocked sea lampreys show a preference for specific areas on their hosts, select larger hosts more frequently, and are not attracted to hosts that have lampreys feeding on them. Such strategies serve to maximize food intake and prolong host survival while ensuring food material of constant energy content.Key words: adult lampreys, feeding, hosts, growth rate, temperature, host mortality, behavior
Physiology of Adult Lampreys, with Special Regard to Natural Starvation, Reproduction, and Death after Spawning
Authors: Larsen Lis Olesen
Published: April 2008

In this review I have attempted to define (1) how the genetic program responsible for migration, sexual maturation, and death after spawning is implemented via the endocrine system, and (2) to what extent environmental factors influence the implementation of the genetic program. The time of upstream migration and the body size at migration may vary enormously (e.g. in Lampetra fluviatilis). Whether the differences reflect different genetic backgrounds in different populations or different environmental conditions in previous stages is unknown. Migration is correlated with lack of food intake, loss of marine osmoregulatory capacity, and atrophy of the intestine. The possible endocrine control of this phase is not clear. Development of secondary sex characters, final maturation of the gonads, spermiation, and ovulation seem to depend on a gonadotropic factor secreted by the pro- and meso-adenohypophysis, but gonadotropin is not as important as in higher vertebrates. Increases in day length or in temperature do not appear to be important clues for initiating sexual maturation; rather this may depend on a metabolic signal related to starvation. The period of natural starvation, from upstream migration until death after spawning, involves atrophy or degeneration in most organs and tissues at the same time as the gonads are developing. With the exception of the intestine and the size of the liver in males, degeneration is generally slow during upstream migration. Upon sexual maturation, the changes are rapid. Energy expenditure and gonadal growth are based on mobilization of lipid and protein, mainly from the body wall. The mobilization of lipid and of protein runs in parallel, both being slow before and rapid during sexual maturation. The possible role of gonadotropin, sex hormones, and insulin in the metabolism of the starving lamprey is discussed. Other hormones seem of little importance. Little is known about the role of the autonomic nervous system in the catabolic processes. Death after spawning can be delayed considerably by hypophysectomy and seems to depend on gonadotropin in females and on some pituitary factor different from gonadotropin in males. Treatment with estradiol surprisingly prolongs life. In all cases of prolonged life induced experimentally, the rate of reduction in body length is slow, probably reflecting a reduced intensity of starvation.Key words: physiology, starvation, reproduction, death, metabolism, migration
Sea Lamprey (Petromyzon marinus) in the Lower Great Lakes
Authors: Pearce W. A. , Braem R. A. , Dustin S. M. , Tibbles J. J.
Published: April 2008

Sea lamprey (Petromyzon marinus) are established in each of the several discrete areas in the St. Lawrence River system between Lake Huron and the Moses–Saunders Power Dam (160 km below Lake Ontario) except for the Niagara River between Niagara Falls and Lake Ontario. However, chemical lampricide treatments are being used to control these populations only in Lake Ontario. Experimental introductions of trout and salmon in Lake Ontario between 1968 and 1971 were not successful. Survival was limited and the number of sea lamprey attack marks on the fish that did mature was very high. After the first round of lampricide treatments of most sea lamprey producing tributaries in 1972, survival of fish improved and lamprey attacks declined. Studies are being completed to determine the desirability of including Oneida Lake in the treatment schedule to prevent recruitment of sea lampreys from this area to Lake Ontario and to improve the fish populations of Oneida Lake. Treatment of Lake Champlain also is being studied by management agencies concerned with its fisheries. Lake St. Clair and Lake Erie and connecting waters, the Finger Lakes, and the St. Lawrence River below Lake Ontario do not appear to have sea lampreys in the numbers necessary to cause unacceptable levels of predation on fish populations and are not being considered for inclusion in the Great Lakes Fishery Commission control program at this time.Key words: sea lamprey, predation, abundance, history, Erie, Ontario, Oneida, Finger Lakes, Champlain
Effects of Temperature on Metamorphosis and the Age and Length at Metamorphosis in Sea Lamprey (Petromyzon marinus) in the Great Lakes
Authors: Purvis H. A.
Published: April 2008

Sea lamprey (Petromyzon marinus) ammocoetes of known age were confined in three locations to determine the effects of temperature on the incidence of metamorphosis. Sixty ammocoetes were held in each of Lake Superior, the Big Garlic River, and in an aquarium at room temperature for each of 4 yr. The highest incidence of metamorphosis (75–100%) occurred at 20–21 °C (aquarium), an intermediate rate (46–76%) at 14–16 °C (Big Garlic River), and the lowest (5–10%) at 7–11 °C (Lake Superior). Density appeared to be the dominant factor in regulating the length of larval and transformed sea lampreys. Mean lengths of larval and transformed sea lampreys increased markedly after stream treatments with selective lampricides. Prediction of lengths at which metamorphosis occurs in re-established populations of sea lampreys is uncertain because of variability in growth rates. Initial metamorphosis in a year-class is dependent on growth rates of ammocoetes. Because of wide variation in growth rates, metamorphosis may begin at age III among fast-growing populations and not until age VII among slow-growing populations.Key words: Petromyzon marinus, sea lamprey; metamorphosis, age, length, Great Lakes
Ecological Impacts of Lampricide Treatments on Sea Lamprey (Petromyzon marinus) Ammocoetes and Metamorphosed Individuals
Authors: Torblaa R. L. , Westman R. W.
Published: April 2008

Sea lamprey (Petromyzon marinus) ammocoetes are found in fewer locations now than before lampricide treatments began. Posttreatment reinfestation does not always occur in those tributaries previously infested. Abundance of ammocoetes and transformed individuals has declined in most watersheds with a few exceptions where density-dependent factors may have been influential. Increased growth was related to reduced density. Sex compositions of larval and metamorphosing populations were highly variable during initial lampricide treatments. Females predominated in some streams, males in others. Streams once dominated by males now favor females in residual and reestablished populations of larvae. The shift to femaleness in the larval populations has precipitated a similar shift in adult sea lamprey populations of the upper Great Lakes.Key words: sea lamprey, ammocoetes, transformed, distribution, abundance, growth, sex composition