bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymorphic Mutation Frequencies of Clinical and Environmental
Stenotrophomonas maltophilia
Populations
Authors: Turrientes María Carmen , Baquero María Rosario , Sánchez María Blanca , Valdezate Sylvia , Escudero Esther , Berg Gabrielle , Cantón Rafael , Baquero Fernando , Galán Juan Carlos , Martínez José Luis 
Published: January 2010

ABSTRACT

Mutation frequencies were studied in 174
Stenotrophomonas maltophilia
isolates from clinical and nonclinical environments by detecting spontaneous rifampin-resistant mutants in otherwise-susceptible populations. The distribution of mutation frequencies followed a pattern similar to that found for other bacterial species, with a modal value of 1 × 10
−8
. Nevertheless, the proportion of isolates showing mutation frequencies below the modal value (hypomutators) was significantly higher for
S. maltophilia
than those so far reported in other organisms. Low mutation frequencies were particularly frequent among environmental
S. maltophilia
strains (58.3%), whereas strong mutators were found only among isolates with a clinical origin. These results indicate that clinical environments might select bacterial populations with high mutation frequencies, likely by second-order selection processes. In several of the strong-mutator isolates, functional-complementation assays with a wild-type allele of the
mutS
gene demonstrated that the mutator phenotype was due to the impairment of MutS activity.
In silico
analysis of the amino acid changes present in the MutS proteins of these hypermutator strains in comparison with the normomutator isolates suggests that the cause of the defect in MutS might be a H683P amino acid change.
Characterization of Wet-Heat Inactivation of Single Spores of
Bacillus
Species by Dual-Trap Raman Spectroscopy and Elastic Light Scattering
Authors: Zhang Pengfei , Kong Lingbo , Setlow Peter , Li Yong-qing 
Published: January 2010

ABSTRACT

Dual-trap laser tweezers Raman spectroscopy (LTRS) and elastic light scattering (ELS) were used to investigate dynamic processes during high-temperature treatment of individual spores of
Bacillus cereus
,
Bacillus megaterium
, and
Bacillus subtilis
in water. Major conclusions from these studies included the following. (i) After spores of all three species were added to water at 80 to 90°C, the level of the 1:1 complex of Ca
2+
and dipicolinic acid (CaDPA; ∼25% of the dry weight of the spore core) in individual spores remained relatively constant during a highly variable lag time (
T
lag
), and then CaDPA was released within 1 to 2 min. (ii) The
T
lag
values prior to rapid CaDPA release and thus the times for wet-heat killing of individual spores of all three species were very heterogeneous. (iii) The heterogeneity in kinetics of wet-heat killing of individual spores was not due to differences in the microscopic physical environments during heat treatment. (iv) During the wet-heat treatment of spores of all three species, spore protein denaturation largely but not completely accompanied rapid CaDPA release, as some changes in protein structure preceded rapid CaDPA release. (v) Changes in the ELS from individual spores of all three species were strongly correlated with the release of CaDPA. The ELS intensities of
B. cereus
and
B. megaterium
spores decreased gradually and reached minima at
T
1
when ∼80% of spore CaDPA was released, then increased rapidly until
T
2
when full CaDPA release was complete, and then remained nearly constant. The ELS intensity of
B. subtilis
spores showed similar features, although the intensity changed minimally, if at all, prior to
T
1
. (vi) Carotenoids in
B. megaterium
spores' inner membranes exhibited two changes during heat treatment. First, the carotenoid's two Raman bands at 1,155 and 1,516 cm
−1
decreased rapidly to a low value and to zero, respectively, well before
T
lag
, and then the residual 1,155-cm
−1
band disappeared, in parallel with the rapid CaDPA release beginning at
T
lag
.
Membrane Topology of Outer Membrane Protein AlgE, Which Is Required for Alginate Production in
Pseudomonas aeruginosa
Authors: Hay Iain D. , Rehman Zahid U. , Rehm Bernd H. A. 
Published: January 2010

ABSTRACT

The ubiquitous opportunistic human pathogen
Pseudomonas aeruginosa
secretes a viscous extracellular polysaccharide, called alginate, as a virulence factor during chronic infection of patients with cystic fibrosis. In the present study, it was demonstrated that the outer membrane protein AlgE is required for the production of alginate in
P. aeruginosa
. An isogenic marker-free
algE
deletion mutant was constructed. This strain was incapable of producing alginate but did secrete alginate degradation products, indicating that polymerization occurs but that the alginate chain is subsequently degraded during transit through the periplasm. Alginate production was restored by introducing the
algE
gene. The membrane topology of the outer membrane protein AlgE was assessed by site-specific insertions of FLAG epitopes into predicted extracellular loop regions.
Wide Dispersal and Possible Multiple Origins of Low-Copy-Number Plasmids inRickettsiaSpecies Associated with Blood-Feeding Arthropods
Authors: Baldridge Gerald D. , Burkhardt Nicole Y. , Labruna Marcelo B. , Pacheco Richard C. , Paddock Christopher D. , Williamson Philip C. , Billingsley Peggy M. , Felsheim Roderick F. , Kurtti Timothy J. , Munderloh Ulrike G. 
Published: January 2010

ABSTRACTPlasmids are mobile genetic elements of bacteria that can impart important adaptive traits, such as increased virulence or antibiotic resistance. We report the existence of plasmids inRickettsia(Rickettsiales;Rickettsiaceae) species, includingRickettsia akari, “CandidatusRickettsia amblyommii,”R. bellii,R. rhipicephali, and REIS, the rickettsial endosymbiont ofIxodes scapularis. All of the rickettsiae were isolated from humans or North and South American ticks.R. parkeriisolates from both continents did not possess plasmids. We have now demonstrated plasmids in nearly allRickettsiaspecies that we have surveyed from three continents, which represent three of the four major proposed phylogenetic groups associated with blood-feeding arthropods. Gel-based evidence consistent with the existence of multiple plasmids in some species was confirmed by cloning plasmids with very different sequences from each of two “Ca. Rickettsia amblyommii” isolates. Phylogenetic analysis of rickettsial ParA plasmid partitioning proteins indicated multipleparAgene origins and plasmid incompatibility groups, consistent with possible multiple plasmid origins. Phylogenetic analysis of potentially host-adaptive rickettsial small heat shock proteins showed thathsp2genes were plasmid specific and thathsp1genes, found only on plasmids of “Ca. Rickettsia amblyommii,”R. felis,R. monacensis, andR. peacockii, were probably acquired independently of thehsp2genes. Plasmid copy numbers in sevenRickettsiaspecies ranged from 2.4 to 9.2 per chromosomal equivalent, as determined by real-time quantitative PCR. Plasmids may be of significance in rickettsial evolution and epidemiology by conferring genetic plasticity and host-adaptive traits via horizontal gene transfer that counteracts the reductive genome evolution typical of obligate intracellular bacteria.
Streptomyces coelicolor
A3(2) CYP102 Protein, a Novel Fatty Acid Hydroxylase Encoded as a Heme Domain without an N-Terminal Redox Partner
Authors: Lamb David C. , Lei Li , Zhao Bin , Yuan Hang , Jackson Colin J. , Warrilow Andrew G. S. , Skaug Tove , Dyson Paul J. , Dawson Eric S. , Kelly Steven L. , Hachey David L. , Waterman Michael R. 
Published: January 2010

ABSTRACT

The gene from
Streptomyces coelicolor
A3(2) encoding CYP102B1, a recently discovered CYP102 subfamily which exists solely as a single P450 heme domain, has been cloned, expressed in
Escherichia coli
, purified, characterized, and compared to its fusion protein family members. Purified reconstitution metabolism experiments with spinach ferredoxin, ferredoxin reductase, and NADPH revealed differences in the regio- and stereoselective metabolism of arachidonic acid compared to that of CYP102A1, exclusively producing 11,12-epoxyeicosa-5,8,14-trienoic acid in addition to the shared metabolites 18-hydroxy arachidonic acid and 14,15-epoxyeicosa-5,8,11-trienoic acid. Consequently, in order to elucidate the physiological function of
CYP102B1
, transposon mutagenesis was used to generate an
S. coelicolor
A3(2) strain lacking CYP102B1 activity and the phenotype was assessed.
Effect of Starvation on the Endocytic Pathway in Dictyostelium Cells
Authors: Smith Ewan W. , Lima Wanessa C. , Charette Steve J. , Cosson Pierre 
Published: January 2010

ABSTRACT

Dictyostelium discoideum
amoebae have been used extensively to study the structure and dynamics of the endocytic pathway. Here, we show that while the general structure of the endocytic pathway is maintained in starved cells, its dynamics rapidly slow down. In addition, analysis of
apm3
and
lvsB
mutants reveals that the functional organization of the endocytic pathway is profoundly modified upon starvation. Indeed, in these mutant cells, some of the defects observed in rich medium persist in starved cells, notably an abnormally slow transfer of endocytosed material between endocytic compartments. Other parameters, such as endocytosis of the fluid phase or the rate of fusion of postlysosomes to the cell surface, vary dramatically upon starvation. Studying the endocytic pathway in starved cells can provide a different perspective, allowing the primary (invariant) defects resulting from specific mutations to be distinguished from their secondary (conditional) consequences.
Comparative Transcriptome Analysis Reveals Novel Roles of the Ras and Cyclic AMP Signaling Pathways in Environmental Stress Response and Antifungal Drug Sensitivity in Cryptococcus neoformans
Authors: Maeng Shinae , Ko Young-Joon , Kim Gyu-Bum , Jung Kwang-Woo , Floyd Anna , Heitman Joseph , Bahn Yong-Sun 
Published: January 2010

ABSTRACT

The cyclic AMP (cAMP) pathway plays a central role in the growth, differentiation, and virulence of pathogenic fungi, including
Cryptococcus neoformans
. Three upstream signaling regulators of adenylyl cyclase (Cac1), Ras, Aca1, and Gpa1, have been demonstrated to control the cAMP pathway in
C. neoformans
, but their functional relationship remains elusive. We performed a genome-wide transcriptome analysis with a DNA microarray using the
ras1
Δ,
gpa1
Δ,
cac1
Δ,
aca1
Δ, and
pka1
Δ
pka2
Δ mutants. The
aca1
Δ,
gpa1
Δ,
cac1
Δ, and
pka1
Δ
pka2
Δ mutants displayed similar transcriptome patterns, whereas the
ras1
Δ mutant exhibited transcriptome patterns distinct from those of the wild type and the cAMP mutants. Interestingly, a number of environmental stress response genes are modulated differentially in the
ras1
Δ and cAMP mutants. In fact, the Ras signaling pathway was found to be involved in osmotic and genotoxic stress responses and the maintenance of cell wall integrity via the Cdc24-dependent signaling pathway. Notably, the Ras and cAMP mutants exhibited hypersensitivity to a polyene drug, amphotericin B, without showing effects on ergosterol biosynthesis, which suggested a novel method of antifungal combination therapy. Among the cAMP-dependent gene products that we characterized, two small heat shock proteins, Hsp12 and Hsp122, were found to be involved in the polyene antifungal drug susceptibility of
C. neoformans
.
The Transposon impala Is Activated by Low Temperatures: Use of a Controlled Transposition System To Identify Genes Critical for Viability of Aspergillus fumigatus
Authors: Carr Paul D. , Tuckwell Danny , Hey Peter M. , Simon Laurence , d'Enfert Christophe , Birch Mike , Oliver Jason D. , Bromley Michael J. 
Published: January 2010

ABSTRACT

Genes that are essential for viability represent potential targets for the development of anti-infective agents. However, relatively few have been determined in the filamentous fungal pathogen
Aspergillus fumigatus
. A novel solution employing parasexual genetics coupled with transposon mutagenesis using the
Fusarium oxysporum
transposon
impala
had previously enabled the identification of 20 essential genes from
A. fumigatus
; however, further use of this system required a better understanding of the mode of action of the transposon itself. Examination of a range of conditions indicated that
impala
is activated by prolonged exposure to low temperatures. This newly identified property was then harnessed to identify 96 loci that are critical for viability in
A. fumigatus
, including genes required for RNA metabolism, organelle organization, protein transport, ribosome biogenesis, and transcription, as well as a number of noncoding RNAs. A number of these genes represent potential targets for much-needed novel antifungal drugs.
Role of Transcription Factor CaNdt80p in Cell Separation, Hyphal Growth, and Virulence in Candida albicans
Authors: Sellam Adnane , Askew Christopher , Epp Elias , Tebbji Faiza , Mullick Alaka , Whiteway Malcolm , Nantel André 
Published: January 2010

ABSTRACT

The NDT80/PhoG transcription factor family includes ScNdt80p, a key modulator of the progression of meiotic division in
Saccharomyces cerevisiae
. In
Candida albicans
, a member of this family, CaNdt80p, modulates azole sensitivity by controlling the expression of ergosterol biosynthesis genes. We previously demonstrated that CaNdt80p promoter targets, in addition to
ERG
genes, were significantly enriched in genes related to hyphal growth. Here, we report that CaNdt80p is indeed required for hyphal growth in response to different filament-inducing cues and for the proper expression of genes characterizing the filamentous transcriptional program. These include noteworthy genes encoding cell wall components, such as
HWP1
,
ECE1
,
RBT4
, and
ALS3
. We also show that CaNdt80p is essential for the completion of cell separation through the direct transcriptional regulation of genes encoding the chitinase Cht3p and the cell wall glucosidase Sun41p. Consistent with their hyphal defect,
ndt80
mutants are avirulent in a mouse model of systemic candidiasis. Interestingly, based on functional-domain organization, CaNdt80p seems to be a unique regulator characterizing fungi from the CTG clade within the subphylum Saccharomycotina. Therefore, this study revealed a new role of the novel member of the fungal NDT80 transcription factor family as a regulator of cell separation, hyphal growth, and virulence.
The Aspergillus fumigatus P-Type Golgi Apparatus Ca
2+
/Mn
2+
ATPase PmrA Is Involved in Cation Homeostasis and Cell Wall Integrity but Is Not Essential for Pathogenesis
Authors: Pinchai Nadthanan , Juvvadi Praveen Rao , Fortwendel Jarrod R. , Perfect B. Zachary , Rogg Luise E. , Asfaw Yohannes G. , Steinbach William J. 
Published: January 2010

ABSTRACT

The
Aspergillus fumigatus
Δ
pmrA
(Golgi apparatus Ca
2+
/Mn
2+
P-type ATPase) strain has osmotically suppressible basal growth defects and cationic tolerance associated with increased expression of calcineurin pathway genes. Despite increased β-glucan and chitin content, it is hypersensitive to cell wall inhibitors but remains virulent, suggesting a role for PmrA in cation homeostasis and cell wall integrity.
Activation of ExoU Phospholipase Activity Requires Specific C-Terminal Regions
Authors: Schmalzer Katherine M. , Benson Marc A. , Frank Dara W. 
Published: January 2010

ABSTRACT

Pseudomonas aeruginosa
is a Gram-negative opportunistic pathogen that utilizes a type III secretion system to subvert host innate immunity. Of the 4 known effector proteins injected into eukaryotic cells, ExoS and ExoU are cytotoxic. The cytotoxic phenotype of ExoU depends on the enzymatic activity of the patatin-like phospholipase A
2
domain localized to the N-terminal half of the protein. Amino acid residues located within the C-terminal region of ExoU are postulated to be required for trafficking or localization to the plasma membrane of eukaryotic cells. This report describes the characterization of a transposon-based linker insertion library in ExoU. Utilizing an unbiased screening approach and sensitive methods for measuring enzymatic activity, we identified regions of ExoU that are critical for activation of the phospholipase activity by the only known cofactor, SOD1. Insertions at D572 and L618 reduced the rate of substrate cleavage. Enzymatic activity could be restored to almost parental levels when SOD1 concentrations were increased, suggesting that the linker insertion disrupted the interaction between ExoU and SOD1. An enzyme-linked immunosorbent assay (ELISA)-based binding test was developed to measure ExoU-SOD1 binding. These experiments suggest that ExoU activation by SOD1 is hampered by linker insertion. ExoU derivatives harboring minimal phospholipase activity retained biological activity in tissue culture assays. These proteins affected primarily cellular architecture in a manner similar to that of ExoT. Our studies suggest that conformational changes in ExoU are facilitated by SOD1. Importantly, the level of phospholipase activity influences the biological outcome of ExoU intoxication.
Precise Excision of IS
5
from the Intergenic Region between the
fucPIK
and the
fucAO
Operons and Mutational Control of
fucPIK
Operon Expression in
Escherichia coli
Authors: Zhang Zhongge , Yen Ming Ren , Saier Milton H. 
Published: January 2010

ABSTRACT

Excision of transposable genetic elements from host DNA occurs at low frequencies and is usually imprecise. A common insertion sequence element in
Escherichia coli
, IS
5
, has been shown to provide various benefits to its host by inserting into specific sites. Precise excision of this element had not previously been demonstrated. Using a unique system, the fucose (
fuc
) regulon, in which IS
5
insertion and excision result in two distinct selectable phenotypes, we have demonstrated that IS
5
can precisely excise from its insertion site, restoring the wild-type phenotype. In addition to precise excision, several “suppressor” insertion, deletion, and point mutations restore the wild-type Fuc
+
phenotype to various degrees without IS
5
excision. The possible bases for these observations are discussed.
Pyruvate Carboxylase Plays a Crucial Role in Carbon Metabolism of Extra- and Intracellularly ReplicatingListeria monocytogenes
Authors: Schär Jennifer , Stoll Regina , Schauer Kristina , Loeffler Daniela I. M. , Eylert Eva , Joseph Biju , Eisenreich Wolfgang , Fuchs Thilo M. , Goebel Werner 
Published: January 2010

ABSTRACTThe human pathogenL. monocytogenesis a facultatively intracellular bacterium that survives and replicates in the cytosol of many mammalian cells. The listerial metabolism, especially under intracellular conditions, is still poorly understood. Recent studies analyzed the carbon metabolism ofL. monocytogenesby the13C isotopologue perturbation method in a defined minimal medium containing [U-13C6]glucose. It was shown that these bacteria produce oxaloacetate mainly by carboxylation of pyruvate due to an incomplete tricarboxylic acid cycle. Here, we report that apycAinsertion mutant defective in pyruvate carboxylase (PYC) still grows, albeit at a reduced rate, in brain heart infusion (BHI) medium but is unable to multiply in a defined minimal medium with glucose or glycerol as a carbon source. Aspartate and glutamate of thepycAmutant, in contrast to the wild-type strain, remain unlabeled when [U-13C6]glucose is added to BHI, indicating that the PYC-catalyzed carboxylation of pyruvate is the predominant reaction leading to oxaloacetate inL. monocytogenes. ThepycAmutant is also unable to replicate in mammalian cells and exhibits high virulence attenuation in the mouse sepsis model.
Thermosensing Function of theEscherichia coliRedox Sensor Aer
Authors: Nishiyama So-ichiro , Ohno Shinji , Ohta Noriko , Inoue Yuichi , Fukuoka Hajime , Ishijima Akihiko , Kawagishi Ikuro 
Published: January 2010

ABSTRACTEscherichia colichemoreceptors can sense changes in temperature for thermotaxis. Here we found that the aerotaxis transducer Aer, a homolog of chemoreceptors lacking a periplasmic domain, mediates thermoresponses. We propose that thermosensing by the chemoreceptors is a general attribute of their highly conserved cytoplasmic domain (or their less conserved transmembrane domain).
Pseudomonas aeruginosaIncreases Formation of Multidrug-Tolerant Persister Cells in Response to Quorum-Sensing Signaling Molecules
Authors: Möker Nina , Dean Charles R. , Tao Jianshi 
Published: January 2010

ABSTRACTBacterial persister cells constitute a small portion of a culture which is tolerant to killing by lethal doses of bactericidal antibiotics. These phenotypic variants are formed in numerous bacterial species, including those with clinical relevance like the opportunistic pathogenPseudomonas aeruginosa. Although persisters are believed to contribute to difficulties in the treatment of many infectious diseases, the underlying mechanisms affecting persister formation are not well understood. Here we show that even thoughP. aeruginosacultures have a significantly smaller fraction of multidrug-tolerant persister cells than cultures ofEscherichia coliorStaphylococcus aureus, they can increase persister numbers in response to quorum-sensing-related signaling molecules. The phenazine pyocyanin (and the closely related molecule paraquat) and the acyl-homoserine lactone 3-OC12-HSL significantly increased the persister numbers in logarithmicP. aeruginosaPAO1 or PA14 cultures but not inE. coliorS. aureuscultures.
The Zur-Regulated ZinT Protein Is an Auxiliary Component of the High-Affinity ZnuABC Zinc Transporter That Facilitates Metal Recruitment during Severe Zinc Shortage
Authors: Petrarca Patrizia , Ammendola Serena , Pasquali Paolo , Battistoni Andrea 
Published: January 2010

ABSTRACT

The pathways ensuring the efficient uptake of zinc are crucial for the ability of bacteria to multiply in the infected host. To better understand bacterial responses to zinc deficiency, we have investigated the role of the periplasmic protein ZinT in
Salmonella enterica
serovar Typhimurium. We have found that
zinT
expression is regulated by Zur and parallels that of ZnuA, the periplasmic component of the zinc transporter ZnuABC. Despite the fact that ZinT contributes to
Salmonella
growth in media containing little zinc, disruption of
zinT
does not significantly affect virulence in mice. The role of ZinT became clear using strains expressing a mutated form of ZnuA lacking a characteristic histidine-rich domain. In fact,
Salmonella
strains producing this modified form of ZnuA exhibited a ZinT-dependent capability to import zinc either
in vitro
or in infected mice, suggesting that ZinT and the histidine-rich region of ZnuA have redundant function. The hypothesis that ZinT and ZnuA cooperate in the process of zinc recruitment is supported by the observation that they form a stable binary complex
in vitro
. Although the presence of ZinT is not strictly required to ensure the functionality of the ZnuABC transporter, our data suggest that ZinT facilitates metal acquisition during severe zinc shortage.