bluuebunny/crossref_metadata_2025 huggingface dataset:
Crenarchaeota
and Their Role in the Nitrogen Cycle in a Subsurface Radioactive Thermal Spring in the Austrian Central Alps
Authors: Weidler Gerhard W. , Gerbl Friedrich W. , Stan-Lotter Helga
Published: August 2008

Previous results from a 16S rRNA gene library analysis showed high diversity within the prokaryotic community of a subterranean radioactive thermal spring, the “Franz-Josef-Quelle” (FJQ) in Bad Gastein, Austria, as well as evidence for ammonia oxidation by crenarchaeota. This study reports further characterization of the community by denaturing gradient gel electrophoresis (DGGE) analysis, fluorescence in situ hybridization (FISH), and semiquantitative nitrification measurements. DGGE bands from three types of samples (filtered water, biofilms on glass slides, and naturally grown biofilms), including samples collected at two distinct times (January 2005 and July 2006), were analyzed. The archaeal community consisted mainly of
Crenarchaeota
of the soil-subsurface-freshwater group (group 1.1b) and showed a higher diversity than in the previous 16S rRNA gene library analysis, as was also found for crenarchaeal
amoA
genes. No bacterial
amoA
genes were detected. FISH analysis of biofilms indicated the presence of archaeal cells with an abundance of 5.3% (±4.5%) in the total 4′,6-diamidino-2-phenylindole (DAPI)-stained community. Microcosm experiments of several weeks in duration showed a decline of ammonium that correlated with an increase of nitrite, the presence of crenarchaeal
amoA
genes, and the absence of bacterial
amoA
genes. The data suggested that only ammonia-oxidizing archaea (AOA) perform the first step of nitrification in this 45°C environment. The crenarchaeal
amoA
gene sequences grouped within a novel cluster of
amoA
sequences from the database, originating from geothermally influenced environments, for which we propose the designation “thermal spring” cluster and which may be older than most AOA from soils on earth.
Identification of Lacto-N-Biose I Phosphorylase fromVibrio vulnificusCMCP6
Authors: Nakajima Masahiro , Kitaoka Motomitsu
Published: August 2008

A β-1,3-galactosyl-N-acetylhexosamine phosphorylase (GalGlyNAcP) homolog gene was cloned fromVibrio vulnificusCMCP6. In synthetic reactions, the recombinant enzyme acted only with GlcNAc and GalNAc as acceptors in the presence of α-d-galactose-1-phosphate as a donor to form lacto-N-biose I (LNB) (Galβ1 → 3GlcNAc) and galacto-N-biose (GNB) (Galβ1 → 3GalNAc), respectively. GlcNAc was a much better acceptor than GalNAc. The enzyme also phosphorolysed LNB faster than it phosphorolysed GNB, and thekcat/Kmfor LNB was approximately 60 times higher than thekcat/Kmfor GNB. This result indicated that the enzyme was remarkably different from GalGlyNAcP fromBifidobacterium longum, which has similar activities with LNB and GNB, and GalGlyNAcP fromClostridium perfringens, which is a GNB-specific enzyme. The enzyme is the first LNB-specific enzyme that has been found and was designated lacto-N-biose I phosphorylase. The discovery of an LNB-specific GalGlyNAcP resulted in recategorization of bifidobacterial GalGlyNAcPs as galacto-N-biose/lacto-N-biose I phosphorylases.
C-Terminal Signals Regulate Targeting of Glycosylphosphatidylinositol-Anchored Proteins to the Cell Wall or Plasma Membrane in
Candida albicans
Authors: Mao Yuxin , Zhang Zimei , Gast Charles , Wong Brian
Published: August 2008

Fungal glycosylphosphatidylinositol (GPI)-anchored proteins localize to the plasma membrane (PM), cell wall (CW), or both. To study signals that regulate PM versus CW targeting in
Candida albicans
, we (i) fused the N and/or C termini of the GPI CW protein Hwp1p and the GPI PM protein Ecm331p to green fluorescent protein (GFP) and (ii) expressed and localized the resulting fusions. Forty-seven amino acids from the C terminus of Hwp1p were sufficient to target GFP to the CW, and 66 amino acids from the C terminus of Ecm331p were sufficient to target GFP to the PM. Truncation and mutagenesis studies showed that G390 was the ω cleavage site in Ecm331p. Domain exchange and mutagenesis studies showed that (i) the 5 amino acids immediately N-terminal to the ω sites (the ω − 5 to ω − 1 amino acids) played key roles in targeting to the PM or CW; (ii) KK and FE residues at positions ω − 1 and ω − 2, respectively, targeted to the PM and CW; and (iii) a loss of I at position ω − 5 increased PM retention. Small fluorescent reporters can be used to study the peptide signals that regulate PM versus CW targeting of GPI proteins and may be useful for identifying proteins that interact with key targeting signals.
Assembly of the
Trypanosoma brucei
60S Ribosomal Subunit Nuclear Export Complex Requires Trypanosome-Specific Proteins P34 and P37
Authors: Prohaska Kimberly , Williams Noreen
Published: August 2008

We previously identified two
Trypanosoma brucei
RNA binding proteins, P34 and P37, and determined that they are essential for proper ribosomal assembly in this organism. Loss of these proteins via RNA interference is lethal and causes a decrease in both 5S rRNA levels and formation of 80S ribosomes, concomitant with a decrease in total cellular protein synthesis. These data suggest that these proteins are involved at some point in the ribosomal biogenesis pathway. In the current study, we have performed subcellular fractionation in conjunction with immune capture experiments specific for 60S ribosomal proteins and accessory factors in order to determine when and where P34 and P37 are involved in the ribosomal biogenesis pathway. These studies demonstrate that P34 and P37 associate with the 60S ribosomal subunit at the stage of the nucleolar 90S particle and remain associated subsequent to nuclear export. In addition, P34 and P37 associate with conserved 60S ribosomal subunit nuclear export factors exportin 1 and Nmd3, suggesting that they are components of the 60S ribosomal subunit nuclear export complex in
T. brucei
. Most significantly, the pre-60S complex does not associate with exportin 1 or Nmd3 in the absence of P34 and P37. These results demonstrate that, although
T. brucei
60S ribosomal subunits utilize a nuclear export complex similar to that described for other organisms, trypanosome-specific factors are essential to the process.
Transitions in Sexuality: Recapitulation of an Ancestral Tri- and Tetrapolar Mating System in
Cryptococcus neoformans
Authors: Hsueh Yen-Ping , Fraser James A. , Heitman Joseph
Published: August 2008

Sex is orchestrated by the mating-type locus (
MAT
) in fungi and by sex chromosomes in plants and animals. In fungi, two patterns of sexuality occur: bipolar with a single, typically biallelic sex determinant that promotes inbreeding, and tetrapolar with two unlinked, often multiallelic sex determinants that restrict inbreeding. Multiallelism in either bipolar or tetrapolar mating systems promotes outcrossing.
Cryptococcus neoformans
is a pathogenic bipolar yeast with two unusually large
MAT
alleles (
a/
α) spanning >100 kb, ∼100-fold larger than many other fungal
MAT
loci. Based on comparative genomic analysis, this unusual
MAT
locus is hypothesized to have evolved from an ancestral tetrapolar system. In this model, the unlinked homeodomain (HD) transcription factor and pheromone/receptor tetrapolar loci acquired additional sex-related genes and then fused via chromosomal translocation, forming an intermediate transitional mating system (which we term tripolar), which then underwent recombination and gene conversion to fashion the extant bipolar
MAT
alleles. To experimentally validate this model,
C. neoformans
was engineered to have a tetrapolar mating system by relocating the
MAT SXI1
α and
SXI2
a
HD genes to an unlinked genomic locale. Genetic and molecular analyses revealed that this modified organism could complete a tetrapolar sexual cycle. Analysis of progeny generated from bipolar, tripolar, and tetrapolar crosses provides direct experimental evidence that the tripolar state confers decreased fertility and therefore may represent an unstable evolutionary intermediate. These findings illustrate how transitions between outcrossing and inbreeding preference occur by involving sex determinant linkage and collapse from multiallelic to biallelic sex determination, providing insights into both fungal sex evolution and early steps in sex chromosome evolution.
Functional Studies of Multiple Thioredoxins from
Mycobacterium tuberculosis
Authors: Akif Mohd , Khare Garima , Tyagi Anil K. , Mande Shekhar C. , Sardesai Abhijit A.
Published: August 2008

Cytoplasmic protein reduction via generalized thiol/disulfide exchange reactions and maintenance of cellular redox homeostasis is mediated by the thioredoxin superfamily of proteins. Here, we describe the characterization of the thioredoxin system from
Mycobacterium tuberculosis
, whose genome bears the potential to encode three putative thioredoxins from the open reading frames designated

trxA
Mtb

,

trxB
Mtb

, and

trxC
Mtb

. We show that all three thioredoxins, overproduced in
Escherichia coli
, are able to reduce insulin, a model substrate, in the presence of dithiothreitol. However, we observe that thioredoxin reductase is not capable of reducing TrxA

Mtb

in an NADPH-dependent manner, indicating that only TrxB

Mtb

and TrxC

Mtb

are the biologically active disulfide reductases. The absence of detectable mRNA transcripts of

trxA
Mtb

observed when
M. tuberculosis
strain H37Rv was cultivated under different growth conditions suggests that

trxA
Mtb

expression may be cryptic. The measured redox potentials of TrxB

Mtb

and TrxC

Mtb

(−262 ± 2 mV and −269 ± 2 mV, respectively) render these proteins somewhat more oxidizing than
E. coli
thioredoxin 1 (TrxA). In
E. coli
strains lacking components of cytoplasmic protein reduction pathways, heterologous expression of the mycobacterial thioredoxins was able to effectively substitute for their function.
In Vivo Inactivation of the Mycobacterial Integral Membrane Stearoyl Coenzyme A Desaturase DesA3 by a C-Terminus-Specific Degradation Process
Authors: Chang Yong , Wesenberg Gary E. , Bingman Craig A. , Fox Brian G.
Published: August 2008

DesA3 (Rv3229c) from
Mycobacterium tuberculosis
is a membrane-bound stearoyl coenzyme A Δ
9
desaturase that reacts with the oxidoreductase Rv3230c to produce oleic acid. This work provides evidence for a mechanism used by mycobacteria to regulate this essential enzyme activity. DesA3 expressed as a fusion with either a C-terminal His
6
or c-myc tag had consistently higher activity and stability than native DesA3 having the native C-terminal sequence of LAA, which apparently serves as a binding determinant for a mycobacterial protease/degradation system directed at DesA3. Fusion of only the last 12 residues of native DesA3 to the C terminus of green fluorescent protein (GFP) was sufficient to make GFP unstable. Furthermore, the comparable C-terminal sequence from the
Mycobacterium smegmatis
DesA3 homolog Msmeg_1886 also conferred instability to the GFP fusion. Systematic examination revealed that residues with charged side chains, large nonpolar side chains, or no side chain at the last two positions were most important for stabilizing the construct, while lesser effects were observed at the third-from-last position. Using these rules, a combinational substitution of the last three residues of DesA3 showed that either DKD or LEA gave the best enhancement of stability for the modified GFP in
M. smegmatis
. Moreover, upon mutagenesis of LAA at the C terminus in native DesA3 to either of these tripeptides, the modified enzyme had enhanced catalytic activity and stability. Since many proteases are conserved within bacterial families, it is reasonable that
M. tuberculosis
will use a similar C-terminal degradation system to posttranslationally regulate the activity of DesA3 and other proteins. Application of these rules to the
M. tuberculosis
genome revealed that ∼10% the proteins encoded by essential genes may be susceptible to C-terminal proteolysis. Among these, an annotation is known for less than half, underscoring a general lack of understanding of proteins that have only temporal existence in a cell.
The Transcriptional Factors MurR and Catabolite Activator Protein Regulate
N
-Acetylmuramic Acid Catabolism in
Escherichia coli
Authors: Jaeger Tina , Mayer Christoph
Published: August 2008

The MurNAc etherase MurQ of
Escherichia coli
is essential for the catabolism of the bacterial cell wall sugar
N
-acetylmuramic acid (MurNAc) obtained either from the environment or from the endogenous cell wall (i.e., recycling). High-level expression of
murQ
is required for growth on MurNAc as the sole source of carbon and energy, whereas constitutive low-level expression of
murQ
is sufficient for the recycling of peptidoglycan fragments continuously released from the cell wall during growth of the bacteria. Here we characterize for the first time the expression of
murQ
and its regulation by MurR, a member of the poorly characterized RpiR/AlsR family of transcriptional regulators. Deleting
murR
abolished the extensive lag phase observed for
E. coli
grown on MurNAc and enhanced
murQ
transcription some 20-fold. MurR forms a stable multimer (most likely a tetramer) and binds to two adjacent inverted repeats within an operator region. In this way MurR represses transcription from the
murQ
promoter and also interferes with its own transcription. MurNAc-6-phosphate, the substrate of MurQ, was identified as a specific inducer that weakens binding of MurR to the operator. Moreover,
murQ
transcription depends on the activation by cyclic AMP (cAMP)-catabolite activator protein (CAP) bound to a class I site upstream of the
murQ
promoter.
murR
and
murQ
are divergently orientated and expressed from nonoverlapping face-to-face (convergent) promoters, yielding transcripts that are complementary at their 5′ ends. As a consequence of this unusual promoter arrangement, cAMP-CAP also affects
murR
transcription, presumably by acting as a roadblock for RNA polymerase.
Chemotaxis as an Emergent Property of a Swarm
Authors: Taylor Rion G. , Welch Roy D.
Published: August 2008

We have characterized and quantified a form of bacterial chemotaxis that manifests only as an emergent property by measuring symmetry breaking in a swarm of
Myxococcus xanthus
exposed to a two-dimensional nutrient gradient from within an agar substrate.
M. xanthus
chemotaxis requires cell-cell contact and coordinated motility, as individual motile cells exhibit only nonvectorial movement in the presence of a nutrient gradient. Genes that specifically affect
M. xanthus
chemotaxis include at least 10 of the 53 that express enhancer binding proteins of the NtrC-like class, an indication that this behavior is controlled through transcription, most likely by a complex signal transduction network.
The
Anabaena
sp. Strain PCC 7120 Gene all2874 Encodes a Diguanylate Cyclase and Is Required for Normal Heterocyst Development under High-Light Growth Conditions
Authors: Neunuebel M. Ramona , Golden James W.
Published: August 2008

The genome of the heterocyst-forming cyanobacterium
Anabaena
sp. strain PCC 7120 harbors 14 genes containing a GGDEF diguanylate cyclase domain. We found that inactivation of one of these genes, all2874, caused abnormal heterocyst development. The all2874 mutant showed a pronounced reduction in heterocyst frequency during diazotrophic growth and reduced vegetative cell size compared to the wild type. The severity of the mutant phenotype varied with light intensity; at high light intensity, the mutant phenotype was accentuated, whereas at low light intensity the phenotype was similar to wild type. Under high-light growth conditions, the initial heterocyst frequency and pattern for the all2874 mutant were normal, but within 4 days following nitrogen step-down, many intervals between heterocysts increased to as many as 200 vegetative cells, whereas in the wild type the intervals were less than 25 vegetative cells. Filaments containing these unusually long vegetative cell intervals between heterocysts also contained intervals of normal length. An all2874 mutant strain carrying a P

patS

-
gfp
transcriptional reporter fusion failed to show normal upregulation of the reporter, which indicates that the decrease in heterocyst frequency is due to an early block in differentiation before induction of the
patS
gene, which in the wild type takes place 8 h after nitrogen step-down. Genetic epistasis experiments suggest that All2874 acts upstream of the master regulator HetR in differentiating cells. We also showed that purified All2874 functions as a diguanylate cyclase in vitro. We hypothesize that All2874 is required for the normal regulation of heterocyst frequency under high-light growth conditions.
σ32-Mediated Negative Regulation ofSalmonellaPathogenicity Island 1 Expression
Authors: Matsui Mari , Takaya Akiko , Yamamoto Tomoko
Published: August 2008

Salmonellapathogenicity island 1 (SPI1) enables infecting salmonellae to invade the intestinal epithelium and induce a proinflammatory response and macrophage cell death. SPI1 expression is controlled by a complex cascade with several transcriptional regulators within the island and global regulators outside it. Previously, we reported that DnaK-depleted salmonellae could neither invade epithelial cells nor secrete SPI1-encoded proteins, suggesting that DnaK is involved in the expression of SPI1. Here, we found that DnaK is involved in SPI1 expression through inhibition of σ32protein, which directs the transcription of a group of genes in response to various global stresses. Overproduction of σ32resulted in decreased levels of the SPI1-specific transcriptional regulators HilD and HilA. Further analysis demonstrated that the σ32-mediated system negatively regulates HilD and HilA at the posttranslational and transcriptional levels, respectively. The executioner of this negative regulation was shown to be a σ32-induced protein ATP-dependent Lon protease, which specifically degrades HilD. Since HilD can activatehilAtranscription, is at the top of the hierarchical SPI1 regulatory loop, and has a dominant role, the posttranslational control of HilD by Lon is critically important for precise expression of SPI1. Consequently, we suggest that SPI1 expression is controlled by the feedback regulatory loop in which σ32induces Lon to control turnover of HilD, and DnaK, which inhibits σ32function, leading to the modulation oflonexpression. This regulation in response to a specific combination of environmental signals would ensure that SPI1 expression is restricted to a few specific locations in the host.
Characterization of Spores of
Bacillus subtilis
That Lack Most Coat Layers
Authors: Ghosh Sonali , Setlow Barbara , Wahome Paul G. , Cowan Ann E. , Plomp Marco , Malkin Alexander J. , Setlow Peter
Published: August 2008

Spores of
Bacillus subtilis
have a thick outer layer of relatively insoluble protein called the coat, which protects spores against a number of treatments and may also play roles in spore germination. However, elucidation of precise roles of the coat in spore properties has been hampered by the inability to prepare spores lacking all or most coat material. In this work, we show that spores of a strain with mutations in both the
cotE
and
gerE
genes, which encode proteins involved in coat assembly and expression of genes encoding coat proteins, respectively, lack most extractable coat protein as seen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, as well as the great majority of the coat as seen by atomic force microscopy. However, the
cotE gerE
spores did retain a thin layer of insoluble coat material that was most easily seen by microscopy following digestion of these spores with lysozyme. These severely coat-deficient spores germinated relatively normally with nutrients and even better with dodecylamine but not with a 1:1 chelate of Ca
2+
and dipicolinic acid. These spores were also quite resistant to wet heat, to mechanical disruption, and to treatment with detergents at an elevated temperature and pH but were exquisitely sensitive to killing by sodium hypochlorite. These results provide new insight into the role of the coat layer in spore properties.
Stabilization of the Pertussis Toxin Secretion Apparatus by the C Terminus of PtlD
Authors: Verma Anita , Cheung Anissa M. , Burns Drusilla L.
Published: August 2008

Pertussis toxin (PT) is secreted fromBordetella pertussisby a type IV secretion system, known as the Ptl transporter, that comprises nine different proteins, PtlA to PtlI. In this study, we found that PtlD is required for the stability of three Ptl proteins, PtlE, PtlF, and PtlH. A region limited to the C-terminal 72 amino acids of PtlD (amino acids 392 to 463) was sufficient for maintaining the stability of PtlE, PtlF, and PtlH, although this region was not sufficient to support secretion of the toxin. Further analysis demonstrated that a stretch of 10 amino acids at the C-terminal end of PtlD (amino acids 425 to 434) contributes to transporter stability.
Injury risks associated with tackling in rugby union
Authors: Fuller Colin W , Ashton Tony , Brooks John H M , Cancea Rebecca J , Hall John , Kemp Simon P T
Published: August 2008

Objective

To examine factors associated with tackles in rugby union and to assess their impact on the risk of injury.

Design

Two-season (2003/2004 and 2005/2006) prospective cohort design with video analysis.

Setting

13 English Premiership clubs.

Participants

645 players.

Main outcome measure

RR (95% CI) calculated by comparing the frequency of occurrence of risk factors in a cohort of players injured during tackles with their frequency of occurrence in tackles in general play.

Risk factors

Playing position; player’s speed, impact force, head position, head/neck flexion and body region struck in the tackle; sequence, direction and type of tackle; and location and type of injury.

Results

High-speed going into the tackle, high impact force, collisions and contact with a player’s head/neck were identified as significant (p<0.01) risk factors for ball carriers (BCs) and tacklers. Midfield backs were significantly (p<0.01) more prone to injury when tackling than other players. Relatively few tacklers were penalised by referees for collision tackles (general play: 2.0%; injured players: 3.3%) and tackles above the line of the shoulder (general play: 5.9%; injured players: 16.7%).

Conclusions

Advice in national and international injury prevention programmes for reducing the risk of injury in tackles is strongly supported by the results obtained from this study. These programmes should be reviewed, however, to provide specific advice for each type of tackle. Stricter implementation of the Laws of Rugby relating to collisions and tackles above the line of the shoulder may reduce the number of head/neck injuries sustained by BCs.
Modelling the health benefits of smoking cessation in Japan
Authors: Avila-Tang E , Apelberg B J , Yamaguchi N , Katanoda K , Sobue T , Samet J M
Published: August 2008

Background:

In Japan, tobacco smoking is one of the main avoidable causes of disease and death. Although the benefits of smoking cessation for reducing disease risk and increasing longevity have been extensively documented, a relatively low proportion of Japanese smokers currently express a willingness to quit. This study attempted to quantify future reduction in the burden of smoking-attributable disease that could result from increases in smoking cessation.

Methods:

A simulation model was developed to project changes in mortality in Japan associated with increased quit attempts and use of nicotine replacement therapy (NRT) among smokers, incorporating data on smoking prevalence, cause-specific mortality rates, quitting behaviour and NRT use and effectiveness.

Results:

Approximately 46 000 lung cancer deaths and 56 000 cardiovascular disease deaths could be avoided over 20 years if the proportion of smokers making a quit attempt per year gradually increased to current US levels over 20 years. If each of these quit attempts were aided by NRT, the estimates of avoidable deaths would increase to 64 000 for lung cancer and 78 000 for cardiovascular disease. In this model, negligible deaths were avoided due to decreased smoking initiation over the 20-year simulation.

Conclusion:

Smoking cessation can have measurable short-term impacts on the smoking-related mortality burden in Japan. However, to achieve these gains, tobacco control policies should focus both on increasing smokers’ willingness to quit and providing the support and therapies to increase the likelihood that smoking cessation attempts will succeed.
Genetic Variation in Populations of Steelhead Trout (Salmo gairdneri) in British Columbia
Authors: Parkinson Eric A.
Published: August 2008

The geographic distributions of biochemical genetic variants at four loci in indigenous British Columbia steelhead (Salmo gairdneri) populations indicated that there was a large-scale subdivision of the species into three major groups. At intermediate geographic scales, gene frequencies were uniform over unexpectedly large areas, but at the smallest geographic scale, significant differentiation was observed between populations in adjacent streams. This pattern of variation supports the view that this species is subdivided into a large number of semi-isolated populations each having the potential to evolve adaptations to local environmental conditions.
Genetic Effect on the Dynamics of a Model of Pink (Oncorhynchus gorbuscha) and Chum (O. keta) Salmon
Authors: Smoker William W.
Published: August 2008

Different stock dynamics result from genetic and nongenetic mechanisms of determination of maturation age of chum salmon (Oncorhynchus keta) in a model of interacting pink (O. gorbuscha) and chum salmon stocks. When the model is disturbed from equilibrium by low survival in one pink salmon line, the genetic mechanism (high heritability of maturation age) leads to biennial cycles of numbers of even-aged chums and of numbers of pinks, similar to observed cycles. The nongenetic mechanism (zero heritability of maturation age) results in a new equlibrium at which neither stock cycles. When one pink salmon line is completely removed the genetic mechanism leads to biennial cycles of abundance of even-aged chums; the nongenetic mechanism does not lead to such cycles. These effects persist at intermediate values of heritability of maturation age and in spite of stochastic variability. The model is an adaptation of the Ricker curve to two interacting stocks, the recruitment for each depending on the density of both.
Particulate Allochthonous Inputs: Relationships with Stream Size in an Undisturbed Watershed
Authors: Conners M. Elizabeth , Naiman Robert J.
Published: August 2008

Four streams of a pristine boreal watershed in eastern Quebec were examined to assess the composition, seasonal pattern, and ash-free dry mass (AFDM) of particulate allochthonous input. Study sites on streams ranging from first to sixth order exhibited significant differences in the types and magnitude of litter input. Composition of litterfall varied according to vegetation and physical structure of the riparian zone. Although the forest in the watershed is dominated by conifers, deciduous leaves dominated annual budgets and seasonal input patterns. Annual litterfall per unit area of stream surface declined exponentially with increasing stream order (r2 = 0.98) from 307–534 g AFDM∙m−2∙yr−1 in a first-order stream to15–17 g AFDM∙m∙yr−1 in a sixth-order stream. Lateral inputs of 25–70 g AFDM∙m−1∙yr−1 were not related to stream size, but were strongly influenced by riparian structure and entrainment of organic matter during spring flooding. Total input per unit stream length increased logarithmically with increasing order (r2 = 0.87), approaching 1000 g AFDM∙m−1∙yr−1 in the fifth- and sixth-order streams. A watershed budget calculated from these results estimates a total input of 729 t∙yr−1 to streams of this 673-km2 watershed. When particulate allochthonous input is compared with primary production measurements in these streams, 81–95% of the organic carbon supplied to the first- and second-order streams is allochthonous, but 85–95% of the supply to the fifth- and sixth-order streams is autochthonous. While these trends agree with predictions of the synthetic continuum model, the importance of local effects in our results illustrates the need for a more mechanistic approch in allochthonous input research.
Intakes as Sampling Locations for Investigating Long-Term Trends in Zooplankton Populations
Authors: Evans Marlene S. , Flath Loren E.
Published: August 2008

We present data demonstrating the representativeness of a power plant intake as a sampling location for investigating long-term trends in zooplankton populations. The intake (Donald C. Cook Nuclear Plant) and the inshore region (southeastern Lake Michigan) were sampled within a matter of days on 54 occasions between April 1975 and November 1981. Intake population estimates were significantly correlated with inshore region population estimates for all 26 zooplankton taxa categories analyzed. Differences in abundances in intake and inshore region samples were not significant for most euplanktonic taxa. The plant apparently entrained water and microcrustaceans from the sediment–water interface. However, because vertically hauled plankton nets do not effectively sample the lower 1 m of the water column, intake sampling may provide a more accurate representation of nearshore region copepod and cladoceran community structure than traditionally employed methods for inshore region sampling.
Effect of an Intertidal Mudflat on Plankton of the Overlying Water Column
Authors: Carlson David J. , Townsend David W. , Hilyard Alan L. , Eaton Jonathan F.
Published: August 2008

The influence of a small tidal mudflat on the plankton of overlying waters was investigated by sampling flooding and ebbing waters. The mudflat depleted floodwaters of plankton during spring and summer. Removals of phytoplankton increased as the season progressed, indicating consumption as a function of activity of benthic filter feeders. Some zooplankton were removed from flooding waters in a similar seasonal pattern. We have demonstrated input of planktonic carbon to mudflats and indicated that mudflat organisms may consume significant portions of both primary and secondary planktonic production.
Diel onshore–offshore migrations in northern redbelly dace, Phoxinus eos (Cope), in relation to prey distribution in a small oligotrophic lake
Authors: Naud Marc , Magnan Pierre
Published: August 2008

Northern redbelly dace, Phoxinus eos (Cope), exhibit diel onshore–offshore migrations in a small oligotrophic Quebec lake. The fish swim in shoals in the littoral zone during the day, migrate to the pelagic zone at sunset, where the shoals break up into single fish, and then go back to the littoral zone at sunrise. Dace eat mainly two cladocerans, Daphnia and Holopedium. Zooplankton sampling indicated that Daphnia were significantly more abundant in the pelagic zone than in the littoral zone, and Holopedium were rarely found in the littoral zone. Dace showed a significant preference for a dense cover habitat over a sparse cover habitat in the littoral zone during the day. Our results support the hypothesis that dace migrate to the pelagic zone at sunset to increase their feeding efficiency on zooplankton. The foraging benefits of remaining in the offshore zone may be offset by increased risk of predation by brook charr, Salvelinus fontinalis (Mitchill), during the daylight hours, thus resulting in diel onshore–offshore migrations.
Size of digestive organs in breeding Brown-headed Cowbirds, Molothrus ater, relative to diet
Authors: Ankney C. Davison , Scott David M.
Published: August 2008

We weighed gizzards and livers and measured small intestines of male and female Brown-headed Cowbirds (Molothrus ater) collected before, during, and after the egg-laying season in southwestern Ontario in 1976. Previously published data about the diets of these birds were used to assess if their digestive organs changed in size in response to changes in diet quality (diets high in animal matter were considered high in quality). Gizzard weight decreased when the birds fed primarily on arthropods and increased when they fed primarily on seeds. Intestine length, particularly of females, was highest when the diet included the least amount of plant material. This result was unexpected, based on the limited data from other passerines. However, diets of females were lowest in plant material when they were laying eggs and we argue that the increased intestine length at that time reflects an increased rate of food consumption. Changes in liver weight were more equivocal but generally support the idea that rate of food consumption and nutrient demand can be more important than diet quality in determining changes in size of this organ. We conclude that attempts to assess changes in diet quality of wild passerines by looking at changes in size of their digestive organs should be done cautiously, particularly if baseline data are from captive birds.
Infection of post-teneral tsetse flies (Glossina morsitans morsitans and Glossina morsitans centralis) with Trypanosoma brucei brucei
Authors: Gooding R. H.
Published: August 2008

A significant proportion of post-teneral male Glossina morsitans morsitans Westwood and post-teneral male and female Glossina morsitans centralis Machado develop mature infections of Trypanosoma brucei brucei Plimmer and Bradford without being starved before feeding upon infected rabbits.
Culaeatrema inconstans gen.n., sp.n. (Digenea: Alloereadiidae) from the brook stickleback (Culaea inconstans) in Wisconsin and observations on parthenogenetic populations
Authors: Lasee Becky A. , Font William F. , Sutherland Daniel R.
Published: August 2008

Culaeatrema inconstans gen.n., sp.n. is described from the intestine of Culaea inconstans (Kirtland) collected in Wisconsin. Culaeatrema is a small, fusiform, nonspinous trematode resembling both allocreadiins and bunoderins. Culaeatrema is placed in the subfamily Bunoderinae because testes are oblique in position, uterus extends into the posterior region, and vitellaria do not extend beyond the anterior testis. Reproduction in two populations of the new species from Shell and Little Waumandee creeks appears to be parthenogenetic. Parthenogenetic worms exhibited larger phenotypic size, one or both testes lacking in 84% of the examined specimens, lack of spermatozoa, and reduced development of male reproductive structures. A discussion of parthenogenesis in parasitic helminths is included.
Hyperthermia and sporogony of Babesia microti in the tick Ixodes dammini: an ultrastructural study
Authors: Lewengrub S. , Rudzinska M. A. , Piesman J. , Spielman A. , Gubert E.
Published: August 2008

An ultrastructural study of Babesia microti sporozoites in fed and unfed heated nymphs of Ixodes dammini was performed to explain differences in the efficiency of sporozoite production. Three colonies of tick larvae, each deriving from eggs of a single female, were fed on hamsters infected with Babesia microti isolated from a human infection. They were kept at 19 °C in conditions of saturated humidity through the larval and nymphal stages. At the time of the experiment, the ages of nymphs from colonies 1, 2, and 3 were 2–2½, 4–4½, and 6½–7 months postmolt, respectively. Nymphs from all colonies were exposed to each of the following conditions: (i) no feeding at 19 °C for 4–7 days; (ii) feeding on an uninfected hamster for 62–64 h at room temperature; (iii) no feeding at 37 °C for 4–7 days. In unfed nymphs at 19 °C, Babesia remained in the sporoblast stage in all three colonies. In nymphs fed for 62–64 h, sporozoites developed in all three colonies. In unfed nymphs exposed for 4–7 days to a temperature of 37 °C, sporozoites formed only in the younger colonies (1 and 2). Only a part of some sporoblasts developed sporozoites and only a few sporozoites had all characteristic structures. Some of them lacked major specialized organelles and were apparently damaged or dead, particularly in colony 1. It appears from this study that colonies differ in their reaction to hyperthermia. In the oldest colony (6½–7 months postmolt), no sporozoites were formed after 4–7 days of exposure to 37 °C, indicating that sensitivity to hyperthermia is lost in older nymphs.
Fascioloides magna (Trematoda) and Taenia hydatigena (Cestoda) from white-tailed deer
Authors: Addison E. M. , Hoeve J. , Joachim D. G. , McLachlin D. J.
Published: August 2008

Livers of 164 white-tailed deer (Odocoileus virginianus) from the Peterborough Crown Game Preserve in central Ontario were examined for Fascioloides magna and Taenia hydatigena. Fascioloides magna was recovered from 2.6% of fawns and 68.3% of all older deer, and mean intensity of infection increased with age. Both prevalence and intensity of unencapsulated flukes were similar among all age-groups of deer 1 year of age and older. While the majority (96%) of encapsulated flukes were within capsules containing more than one fluke, aggregation of flukes is probably not required for either encapsulation or maturation. Infection with F. magna had no detectable effect on the condition of yearling or adult male deer, where condition was measured by depth of fat on the rump and sternum. Cysticerci of T. hydatigena were most prevalent among yearlings (70%) as compared with all other age-groups (29%). Mean intensity of infection with T. hydatigena tended to increase with age.
Sodium uptake from the gut of freshwater- and seawater-acclimated ducks and gulls
Authors: Hughes M. R. , Roberts J. R.
Published: August 2008

The first possible regulator of plasma sodium ([Na]pl) and chloride ([Cl]pl) concentrations is the gut epithelium. Its in vivo role in uptake of ingested salt in birds with salt glands has not been evaluated. In the present study the anterior gut 22Na uptake rate was measured in freshwater-acclimated ducks (Anas platyrhynchos) and gulls (Larus glaucescens) and was then measured in the same birds after acclimation to 2/3 seawater. The 22Na was given orally in 7–10 mL of 171 mM NaCl. In ducks, seawater acclimation increased [Na]pl and [Cl]pl but not Na space; in gulls seawater acclimation increased Na space, but not plasma ion concentration. The rate of gut 22Na uptake was the same in ducks and gulls and was not affected by seawater acclimation in either species. As determined from the 22Na distribution between erythrocytes and plasma 3 h after i.v. 22NaCl injection, duck erythrocytes sequestered more (9.3% ± 0.4%) of the load than did gull erythrocytes (6.9% ± 0.3%) (P < 0.001). Although gulls are better hyperosmotic regulators than ducks, there was no difference between the two species in the entry of sodium into the extracellular fluid volume from the gut. Immediately after oral gut loading with dilute saline, freshwater-acclimated gull [Cl]pl, increased more (2P < 0.001) than could be accounted for by equilibration of the administered Cl within the extracellular fluid volume. After gut loading, the increase in [Cl]pl, of freshwater-acclimated ducks was less rapid and could be accounted for by extracellular distribution of the oral Cl load. In seawater-acclimated gulls, [Cl]pl decreased following gut loading, but was unchanged in seawater-acclimated ducks.
Review of Sarcotretes Jungersen, 1911 (Copepoda: Pennellidae) from midwater and demersal fishes in the north Atlantic Ocean
Authors: Hogans W. E.
Published: August 2008

The genus Sarcotretes, parasitic copepods from midwater and demersal fishes in the Atlantic Ocean, is reviewed. The taxonomic status of the six nominal species is discussed. Two species, S. scopeli, from midwater fishes, and S. eristaliformis, from demersal fishes, are tentatively considered valid members of the genus. The remaining species (S. inflexus, S. lobatus, S. gempyli, and S. nodicornis) are probable synonyms of the type species, S. scopeli. A detailed description of S. scopeli from six midwater host species is presented.
Empirical analysis of the effect of temperature on marine harpacticoid copepod development time
Authors: Webb Donald G. , Parsons Timothy R.
Published: August 2008

Predictive equations to estimate development time from environmental temperature for marine harpacticoid copepods were developed from data extracted from the literature. Separate equations were constructed for egg, nauplius, copepodite, and total juvenile development, as well as for generation time. Power curves adequately described the data and each regression was significant (P < 0.001). Approximately 50% of the variance in each data set was explained by regression on temperature. Predictions of development time generally were precise, with the upper 95% confidence limit 39–65% greater than the prediction at low temperatures (4–5 °C), 7–13% greater at mean temperatures (17.6–19.3 °C), and 13–31% greater at high temperatures (28–40 °C). Application of these predictive equations will facilitate analysis of the population dynamics and production of marine harpacticoid copepods.
Predation on seabirds by sea otters
Authors: Riedman Marianne L. , Estes James A.
Published: August 2008

Although rarely reported in the past, predation by sea otters (Enhydra lutris) on seabirds has been observed more frequently in the last decade. A total of 23 incidents of definite or probable predation on seabirds have been observed in California (20) and in Alaska at Amchitka Island (3). In California, the most commonly eaten species were western grebes, although cormorants, gulls, common loons, and surf scoters were also consumed. All cases of seabird predation in California have occurred in the northern part of the sea otter's range in three locations: Point Lobos, Stillwater Cove, and the Monterey harbor area. When sex could be determined, most of the otters observed feeding on seabirds were adult males. At one site, it appeared that the same individual repeatedly captured birds. Predation on seabirds is indicative of the sea otter's ability to learn new and innovative foraging tactics, and is consistent with a high degree of individual variation in diet observed among sea otters in Monterey. Sea otters initially capture birds by diving and grabbing them from underwater while the bird rests on the surface, in a manner similar to that employed by coastal river otters to capture seabirds. When mink, freshwater-inhabiting otters, and sea otters are compared, a graded reduction in the tendency to eat birds appears to occur in the more aquatic mustelids, with the relative importance of birds in the diet being greatest in mink and least in sea otters.
Temporal changes in the pollinator fauna of tristylous Pontederia cordata, an aquatic plant
Authors: Wolfe Lorne M. , Barrett Spencer C. H.
Published: August 2008

Temporal changes in the composition of the pollinator fauna of the tristylous aquatic plant Pontederia cordata were documented during the flowering seasons of 1982 and 1983. A total of 18 species of insects, mainly bumblebees, and a single species of hummingbird were observed visiting flowers during the 2-month flowering period. The abundance of pollinators within each season varied greatly, with highest densities corresponding to peak flowering in both years. Although overall abundance was similar each year, the diversity of species was greater in 1983 because of the addition of short-tongued bumblebees and the longer residency periods of other species. It is suggested that low summer rainfall in 1983 decreased flowering levels in terrestrial plant communities of the region, resulting in several bee species shifting their feeding onto P. cordata. The study demonstrates that changes in the structure of a plant's pollinator fauna occur over time and that despite the possession of a specialized pollination mechanism, tristylous P. cordata is visited by a wide range of pollinator species.
Courtship and copulation in the terrestrial snail Helix aspersa
Authors: Adamo Shelley A. , Chase Ronald
Published: August 2008

Mating behaviour in Helix aspersa has three major components: introductory behaviour, dart shooting, and copulation. Introductory behaviour, which includes reciprocal tactile and oral contacts, lasts an average of 33.7 ± 23.3 (SD) min. Dart shooting, the pushing of a calcareous dart into the mating partner's body, occurs once for each snail per mating sequence. Snails that hit their partners during the first dart-shooting event copulated 14.5 ± 8.7 min after dart shooting, whereas snails that missed their partners took 40.5 ± 37.5 min to copulate. Dart shooting may facilitate mating by increasing behavioural synchrony. Copulation is reciprocal and has a duration of 421.8 ± 56.6 min. Spermatophores are transferred approximately 300 min after simultaneous intromission. There are significant differences in the mating behaviours of Helix aspersa and Helix pomatia.
Chromosome studies in pelagic opisthobranch molluscs
Authors: Thiriot-Quiévreux Catherine
Published: August 2008

Chromosome number and morphology were studied in nine species of pelagic opisthobranchs ("pteropods"). Among Thecosomata, seven species were investigated. Limacina inflata has a diploid chromosome number of 2n = 20 with metacentric and submetacentric chromosome pairs. Creseis acicula has 2n = 20 (five metacentric and five submetacentric pairs). Creseis virgula has 2n = 20 (seven metacentric, one submetacentric, one subtelocentric – submetacentric, and one submetacentric – subtelocentric pair). Clio pyramidata has 2n = 22 (five metacentric, one submetacentric, two submetacentric – subtelocentric, two subtelocentric, and one telocentric pair). Cavolinia inflexa has 2n = 24 (six metacentric, one submetacentric, two subtelocentric – submetacentric, one subtelocentric – telocentric, and two subtelocentric pairs). Peraclis reticulata has 2n = 24 (six metacentric and six submetacentric or subtelocentric pairs). Cymbulia peroni has 2n = 34 (six metacentric, three submetacentric, seven subtelocentric, and one telocentric pair). Among Gymnosomata, two species were investigated. Pneumodermopsis canephora has 2n = 32 (two metacentric, three submetacentric, four submetacentric – subtelocentric, one subtelocentric – submetacentric, five subtelocentric, and one telocentric – subtelocentric pair). Pneumoderma atlanticum has 2n = 32 (three metacentric, five submetacentric, four submetacentric – subtelocentric or subtelocentric – submetacentric, and four subtelocentric pairs). For three of the nine pteropod species, material was abundant enough to permit staining for the nucleolar organizer region. This region occurred on pair 9 in Creseis acicula, on pair 6 in Cavolinia inflexa and on pair 2 in Pneumodermopsis canephora. Results on number, morphology, and size of the chromosomes of each of the studied species are discussed. The present chromosomal evidence confirms the separation, sometimes seen as controversial, of the pelagic opisthobranchs into the orders Thecosomata and Gymnosomata. The Thecosomata constitute an isolated order among opisthobranchs by their striking chromosomal diversity. In contrast, the Gymnosomata show cytogenetic features that suggest an evolutionary trend with plesiomorphic characters, as in the Anaspidea and Sacoglossa.
THE GEODESIC RULE FOR HIGHER CODIMENSIONAL GLOBAL DEFECTS
Authors: CREACO ANTHONY J. , KALOGEROPOULOS NIKOS
Published: August 2008

We generalize the geodesic rule to the case of formation of higher codimensional global defects. Relying on energetic arguments, we argue that, for such defects, the geometric structures of interest are the totally geodesic submanifolds. On the other hand, stochastic arguments lead to a diffusion equation approach, from which the geodesic rule is deduced. It turns out that the most appropriate geometric structure that one should consider is the convex hull of the values of the order parameter on the causal volumes whose collision gives rise to the defect. We explain why these two approaches lead to similar results when calculating the density of global defects by using a theorem of Cheeger and Gromoll. We present a computation of the probability of formation of strings/vortices in the case of a system, such as nematic liquid crystals, whose vacuum is ℝP2.