bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variation in Tolerance and Virulence in the Chestnut Blight Fungus-Hypovirus Interaction
Authors: Peever Tobin L. , Liu Yir-Chung , Cortesi Paolo , Milgroom Michael G. 
Published: July 2002

ABSTRACTChestnut blight, caused by the fungusCryphonectria parasitica, has been effectively controlled with double-stranded RNA hypoviruses in Europe for over 40 years. The marked reduction in the virulence ofC. parasiticaby hypoviruses is a phenomenon known as hypovirulence. This virus-fungus pathosystem has become a model system for the study of biological control of fungi with viruses. We studied variation in tolerance to hypoviruses in fungal hosts and variation in virulence among virus isolates from a local population in Italy. Tolerance is defined as the relative fitness of a fungal individual when infected with hypoviruses (compared to being uninfected); virulence is defined for each hypovirus as the reduction in fitness of fungal hosts relative to virus-free hosts. Six hypovirus-infected isolates ofC. parasiticawere sampled from the population, and each hypovirus was transferred into six hypovirus-free recipient isolates. The resulting 36 hypovirus-fungus combinations were used to estimate genetic variation in tolerance to hypoviruses, in hypovirus virulence, and in virus-fungus interactions. Four phenotypes were evaluated for each virus-fungus combination to estimate relative fitness: (i) sporulation, i.e., the number of asexual spores (conidia) produced; (ii) canker area on field-inoculated chestnut trees, (iii) vertical transmission of hypoviruses into conidia, and (iv) conidial germination. Two-way analysis of variance (ANOVA) revealed significant interactions (P< 0.001) between viruses and fungal isolates for sporulation and canker area but not for conidial germination or transmission. One-way ANOVA among hypoviruses (within each fungal isolate) and among fungal isolates (within each hypovirus) revealed significant genetic variation (P< 0.01) in hypovirus virulence and fungal tolerance within several fungal isolates, and hypoviruses, respectively. These interactions and the significant genetic variation in several fitness characters indicate the potential for future evolution of these characters. However, biological control is unlikely to break down due to evolution of tolerance to hypoviruses in the fungus because the magnitudes of tolerance and interactions were relatively small.
Ectomycorrhizal Specificity Patterns in a Mixed
Pinus contorta
and
Picea engelmannii
Forest in Yellowstone National Park
Authors: Cullings Kenneth W. , Vogler Detlev R. , Parker Virgil T. , Finley Sara Katherine 
Published: July 2002

ABSTRACT

We used molecular genetic methods to test two hypotheses, (i) that host plant specificity among ectomycorrhizal fungi would be common in a closed-canopy, mixed
Pinus contorta-Picea engelmannii
forest in Yellowstone National Park and (ii) that specificity would be more common in the early successional tree species,
P. contorta
, than in the invader,
P. engelmannii
. We identified 28 ectomycorrhizal fungal species collected from 27 soil cores. The proportion of
P. engelmannii
to
P. contorta
ectomycorrhizae was nearly equal (52 and 48%, respectively). Of the 28 fungal species, 18 composed greater than 95% of the fungal community. No species was associated exclusively with
P. contorta
, but four species, each found in only one core, and one species found in two cores were associated exclusively with
P. engelmannii
. These fungi composed less than 5% of the total ectomycorrhizae. Thus, neither hypothesis was supported, and hypothesized benefits of ectomycorrhizal specificity to both trees and fungi probably do not exist in this system.
Fatty Acid Competition as a Mechanism by Which
Enterobacter cloacae
Suppresses
Pythium ultimum
Sporangium Germination and Damping-Off
Authors: van Dijk Karin , Nelson Eric B. 
Published: July 2002

ABSTRACT

Interactions between plant-associated microorganisms play important roles in suppressing plant diseases and enhancing plant growth and development. While competition between plant-associated bacteria and plant pathogens has long been thought to be an important means of suppressing plant diseases microbiologically, unequivocal evidence supporting such a mechanism has been lacking. We present evidence here that competition for plant-derived unsaturated long-chain fatty acids between the biological control bacterium
Enterobacter cloacae
and the seed-rotting oomycete,
Pythium ultimum
, results in disease suppression. Since fatty acids from seeds and roots are required to elicit germination responses of
P. ultimum
, we generated mutants of
E. cloacae
to evaluate the role of
E. cloacae
fatty acid metabolism on the suppression of
Pythium
sporangium germination and subsequent plant infection. Two mutants of
E. cloacae
EcCT-501R3, Ec31 (
fadB
) and EcL1 (
fadL
), were reduced in β-oxidation and fatty acid uptake, respectively. Both strains failed to metabolize linoleic acid, to inactivate the germination-stimulating activity of cottonseed exudate and linoleic acid, and to suppress
Pythium
seed rot in cotton seedling bioassays. Subclones containing
fadBA
or
fadL
complemented each of these phenotypes in Ec31 and EcL1, respectively. These data provide strong evidence for a competitive exclusion mechanism for the biological control of
P. ultimum
-incited seed infections by
E. cloacae
where
E. cloacae
prevents the germination of
P. ultimum
sporangia by the efficient metabolism of fatty acid components of seed exudate and thus prevents seed infections.
Diacetyl and α-Acetolactate Overproduction by
Lactococcus lactis
subsp.
lactis
Biovar Diacetylactis Mutants That Are Deficient in α-Acetolactate Decarboxylase and Have a Low Lactate Dehydrogenase Activity
Authors: Monnet Christophe , Aymes Frédéric , Corrieu Georges 
Published: July 2002

ABSTRACT

Lactococcus lactis
subsp.
lactis
biovar diacetylactis strains are utilized in several industrial processes for producing the flavoring compound diacetyl or its precursor α-acetolactate. Using random mutagenesis with nitrosoguanidine, we selected mutants that were deficient in α-acetolactate decarboxylase and had low lactate dehydrogenase activity. The mutants produced large amounts of α-acetolactate in anaerobic milk cultures but not in aerobic cultures, except when the medium was supplemented with catalase, yeast extract, or hemoglobin.
Effect of Increased Yeast Alcohol Acetyltransferase Activity on Flavor Profiles of Wine and Distillates
Authors: Lilly M. , Lambrechts M. G. , Pretorius I. S. 
Published: July 2002

ABSTRACTThe distinctive flavor of wine, brandy, and other grape-derived alcoholic beverages is affected by many compounds, including esters produced during alcoholic fermentation. The characteristic fruity odors of the fermentation bouquet are primarily due to a mixture of hexyl acetate, ethyl caproate (apple-like aroma), iso-amyl acetate (banana-like aroma), ethyl caprylate (apple-like aroma), and 2-phenylethyl acetate (fruity, flowery flavor with a honey note). The objective of this study was to investigate the feasibility of improving the aroma of wine and distillates by overexpressing one of the endogenous yeast genes that controls acetate ester production during fermentation. The synthesis of acetate esters by the wine yeastSaccharomyces cerevisiaeduring fermentation is ascribed to at least three acetyltransferase activities, namely, alcohol acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT. To investigate the effect of increased AAT activity on the sensory quality of Chenin blanc wines and distillates from Colombar base wines, we have overexpressed the alcohol acetyltransferase gene (ATF1) ofS. cerevisiae. TheATF1gene, located on chromosome XV, was cloned from a widely used commercial wine yeast strain ofS. cerevisiae, VIN13, and placed under the control of the constitutive yeast phosphoglycerate kinase gene (PGK1) promoter and terminator. Chromoblot analysis confirmed the integration of the modified copy ofATF1into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression ofATF1at high levels in these yeast transformants. The levels of ethyl acetate, iso-amyl acetate, and 2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature, cultivar, and yeast strain used. The concentrations of ethyl caprate, ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect on the solvent or chemical aroma (associated with ethyl acetate and iso-amyl acetate) and the herbaceous and heads-associated aromas of the final distillate and the solvent or chemical and fruity or flowery characters of the Chenin blanc wines. This study establishes the concept that the overexpression of acetyltransferase genes such asATF1could profoundly affect the flavor profiles of wines and distillates deficient in aroma, thereby paving the way for the production of products maintaining a fruitier character for longer periods after bottling.
Quantitative Use of Fluorescent In Situ Hybridization To Examine Relationships between Mycolic Acid-Containing Actinomycetes and Foaming in Activated Sludge Plants
Authors: Davenport Russell J. , Curtis Thomas P. , Goodfellow Michael , Stainsby Fiona M. , Bingley Marc 
Published: July 2002

ABSTRACTThe formation of viscous foams on aeration basins and secondary clarifiers of activated sludge plants is a common and widespread problem. Foam formation is often attributed to the presence of mycolic acid-containing actinomycetes (mycolata). In order to examine the relationship between the number of mycolata and foam, we developed a group-specific probe targeting the 16S rRNA of the mycolata, a protocol to permeabilize mycolata, and a statistically robust quantification method. Statistical analyses showed that a lipase-based permeabilization method was quantitatively superior to previously described methods (P<< 0.05). When mixed liquor and foam samples were examined, most of the mycolata present were rods or cocci, although filamentous mycolata were also observed. A nested analysis of variance showed that virtually all of the measured variance occurred between fields of view and not between samples. On this basis we determined that as few as five fields of view could be used to give a statistically meaningful sample. Quantitative fluorescent in situ hybridization (FISH) was used to examine the relationship between foaming and the concentration of mycolata in a 20-m3completely mixed activated sludge plant. Foaming occurred when the number of mycolata exceeded a certain threshold value. Baffling of the plant affected foaming without affecting the number of mycolata. We tentatively estimated that the threshold foaming concentration of mycolata was about 2 × 106cells ml−1or 4 × 1012cells m−2. We concluded that quantitative use of FISH is feasible and that quantification is a prerequisite for rational investigation of foaming in activated sludge.
Contribution of
dps
to Acid Stress Tolerance and Oxidative Stress Tolerance in
Escherichia coli
O157:H7
Authors: Choi Sang Ho , Baumler David J. , Kaspar Charles W. 
Published: July 2002

ABSTRACT

An
Escherichia coli
O157:H7
dps
::
nptI
mutant (FRIK 47991) was generated, and its survival was compared to that of the parent in HCl (synthetic gastric fluid, pH 1.8) and hydrogen peroxide (15 mM) challenges. The survival of the mutant in log phase (5-h culture) was significantly impaired (4-log
10
-CFU/ml reduction) compared to that of the parent strain (ca. 1.0-log
10
-CFU/ml reduction) after a standard 3-h acid challenge. Early-stationary-phase cells (12-h culture) of the mutant decreased by ca. 4 log
10
CFU/ml while the parent strain decreased by approximately 2 log
10
CFU/ml. No significant differences in the survival of late-stationary-phase cells (24-h culture) between the parent strain and the mutant were observed, although numbers of the parent strain declined less in the initial 1 h of acid challenge. FRIK 47991 was more sensitive to hydrogen peroxide challenge than was the parent strain, although survival improved in stationary phase. Complementation of the mutant with a functional
dps
gene restored acid and hydrogen peroxide tolerance to levels equal to or greater than those exhibited by the parent strain. These results demonstrate that decreases in survival were from the absence of Dps or a protein regulated by Dps. The results from this study establish that Dps contributes to acid tolerance in
E. coli
O157:H7 and confirm the importance of Dps in oxidative stress protection.
Axial Differences in Community Structure of
Crenarchaeota
and
Euryarchaeota
in the Highly Compartmentalized Gut of the Soil-Feeding Termite
Cubitermes orthognathus
Authors: Friedrich Michael W. , Schmitt-Wagner Dirk , Lueders Tillmann , Brune Andreas 
Published: July 2002

ABSTRACT

Methanogenesis represents an important electron sink reaction in the hindgut of soil-feeding termites. This is the first comprehensive analysis of the archaeal community structure within the highly compartmentalized intestinal tract of a humivorous insect, combining clonal analysis and terminal restriction fragment (T-RF) length polymorphism (T-RFLP) fingerprinting of the archaeal communities in the different gut compartments of
Cubitermes orthognathus
. We found that the morphological and physicochemical heterogeneity of the gut is reflected in a large phylogenetic diversity and pronounced axial differences in the composition of the archaeal gut microbiota, notably among those clones or ribotypes that could be assigned to methanogenic taxa. Comparative analysis of the relative frequencies of different archaeal lineages among the small-subunit rRNA gene (SSU rDNA) clones and their corresponding T-RF indicated that the archaeal community in the anterior, extremely alkaline hindgut compartment (P1) consists mainly of members of the
Methanosarcinaceae
, whereas
Methanobacteriaceae
and
Methanomicrobiales
predominate in the subsequent, more posterior compartments (P3/4a and P4b). The relative abundance of
Thermoplasmales
increased towards the rectum (P5). SSU rDNA sequences representing
Crenarchaeota
, which have not yet been reported to occur in the intestinal tracts of arthropods, were detected in all gut sections. We discuss how the spatial distribution of methanogenic populations may be linked to axial heterogeneity in the physicochemical gut conditions and to functional adaptations to their respective ecological niches.
Vancomycin-ResistantEnterococcusspp. Isolated from Wastewater and Chicken Feces in the United States
Authors: Harwood Valerie J. , Brownell Miriam , Perusek William , Whitlock John E. 
Published: July 2002

ABSTRACTVancomycin-resistantEnterococcusspp. (VRE) were isolated from sewage and chicken feces but not from other animal fecal sources (dog, cow, and pig) or from surface waters tested. VRE from hospital wastewater were resistant to ≥20 μg of vancomycin/ml and possessed thevanAgene. VRE from residential wastewater and chicken feces were resistant to 3 to 5 μg of vancomycin/ml and possessed thevanCgene.
Determination of Oligopeptide Diversity within a Natural Population ofMicrocystisspp. (Cyanobacteria) by Typing Single Colonies by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry
Authors: Fastner Jutta , Erhard Marcel , von Döhren Hans 
Published: July 2002

ABSTRACTBesides the most prominent peptide toxin, microcystin, the cyanobacteriaMicrocystisspp. have been shown to produce a large variety of other bioactive oligopeptides. We investigated for the first time the oligopeptide diversity within a naturalMicrocystispopulation by analyzing single colonies directly with matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). The results demonstrate a high diversity of known cyanobacterial peptides such as microcystins, anabaenopeptins, microginins, aeruginosins, and cyanopeptolins, but also many unknown substances in theMicrocystiscolonies. Oligopeptide patterns were mostly related to specificMicrocystistaxa.Microcystis aeruginosa(Kütz.) Kütz. colonies contained mainly microcystins, occasionally accompanied by aeruginosins. In contrast, microcystins were not detected inMicrocystis ichthyoblabeKütz.; instead, colonies of this species contained anabaenopeptins and/or microginins or unknown peptides. Within a third group,Microcystis wesenbergii(Kom.) Kom. in Kondr., chiefly a cyanopeptolin and an unknown peptide were found. Similar patterns, however, were also found in colonies which could not be identified to species level. The significance of oligopeptides as a chemotaxonomic tool within the genusMicrocystisis discussed. It could be demonstrated that the typing of single colonies by MALDI-TOF MS may be a valuable tool for ecological studies of the genusMicrocystisas well as in early warning of toxic cyanobacterial blooms.
Deletion of the
GRE3
Aldose Reductase Gene and Its Influence on Xylose Metabolism in Recombinant Strains of
Saccharomyces cerevisiae
Expressing the
xylA
and
XKS1
Genes
Authors: Träff K. L. , Otero Cordero R. R. , van Zyl W. H. , Hahn-Hägerdal B. 
Published: July 2002

ABSTRACT

Saccharomyces cerevisiae
ferments hexoses efficiently but is unable to ferment xylose. When the bacterial enzyme xylose isomerase (XI) from
Thermus thermophilus
was produced in
S
.
cerevisiae,
xylose utilization and ethanol formation were demonstrated. In addition, xylitol and acetate were formed. An unspecific aldose reductase (AR) capable of reducing xylose to xylitol has been identified in
S
.
cerevisiae
. The
GRE3
gene, encoding the AR enzyme, was deleted in
S
.
cerevisiae
CEN.PK2-1C, yielding YUSM1009a. XI from
T
.
thermophilus
was produced, and endogenous xylulokinase from
S
.
cerevisiae
was overproduced in
S
.
cerevisiae
CEN.PK2-1C and YUSM1009a. In recombinant strains from which the
GRE3
gene was deleted, xylitol formation decreased twofold. Deletion of the
GRE3
gene combined with expression of the
xylA
gene from
T
.
thermophilus
on a replicative plasmid generated recombinant xylose utilizing
S
.
cerevisiae
strain TMB3102, which produced ethanol from xylose with a yield of 0.28 mmol of C from ethanol/mmol of C from xylose. None of the recombinant strains grew on xylose.
Habitat Association in Two Genetic Groups of the Insect-Pathogenic FungusMetarhizium anisopliae: Uncovering Cryptic Species?
Authors: Bidochka Michael J. , Kamp Andrena M. , Lavender T. Michael , Dekoning Jason , De Croos J. N. Amritha 
Published: July 2002

ABSTRACTStrains of insect-pathogenic fungi with high virulence toward certain pest insects have great potential for commercial biological control applications. Identifying such strains has been a central theme in using fungi for biological control. This theme is supported by a persistent paradigm in insect pathology which suggests that the host insect is the predominant influence on the population genetics of insect-pathogenic fungi. In this study, a population genetics analysis of the insect-pathogenic fungusMetarhizium anisopliaefrom forested and agricultural habitats in Ontario, Canada, showed a nonrandom association of alleles between two distinct, reproductively isolated groups (index of multilocus association = 1.2). Analyses of the mitochondrial DNA showed no differences between the groups. The two groups were associated with different habitat types, and associations with insect hosts were not found. The group from forested areas showed an ability for cold-active growth (i.e., 8°C), while the group from the agricultural area showed an ability for growth at high temperatures (i.e., 37°C) and resilience to UV exposure. These results represent a significant paradigm shift; habitat selection, not host insect selection, drives the population structure of these insect-pathogenic deuteromycetous fungi. With each group we observed recombining population structures as well as clonally reproducing lineages. We discuss whether these groups may represent cryptic species. Worldwide,M. anisopliaemay be an assembly of cryptic species, each adapted to certain environmental conditions. The association of fungal genotypes with habitat but not with host insects has implications on the criteria for utility of this, and perhaps other, fungal biocontrol agents.
Comparison ofnifHGene Pools in Soils and Soil Microenvironments with Contrasting Properties
Authors: Poly Franck , Ranjard Lionel , Nazaret Sylvie , Gourbière François , Monrozier Lucile Jocteur 
Published: July 2002

ABSTRACTThe similarities and differences in the structures of thenifHgene pools of six different soils (Montrond, LCSA-p, Vernon, Dombes, LCSA-c, and Thysse Kaymor) and five soil fractions extracted from LCSA-c were studied. Bacterial DNA was directly extracted from the soils, and a region of thenifHgene was amplified by PCR and analyzed by restriction. Soils were selected on the basis of differences in soil management, plant cover, and major physicochemical properties. Microenvironments differed on the basis of the sizes of the constituent particles and the organic carbon and clay contents. Restriction profiles were subjected to principal-component analysis. We showed that the composition of the diazotrophic communities varied both on a large scale (among soils) and on a microscale (among microenvironments in LCSA-c soil). Soil management seemed to be the major parameter influencing differences in thenifHgene pool structure among soils by controlling inorganic nitrogen content and its variation. However, physicochemical parameters (texture and total C and N contents) were found to correlate with differences amongnifHgene pools on a microscale. We hypothesize that the observednifHgenetic structures resulted from the adaptation to fluctuating conditions (cultivated soil, forest soil, coarse fractions) or constant conditions (permanent pasture soil, fine fractions). We attempted to identify a specific band within the profile of the clay fraction by cloning and sequencing it and comparing it with the gene databases. Unexpectedly, thenifHsequences of the dominant bacteria were most similar to sequences of unidentified marine eubacteria.