Major differences between glutamate-fermenting species isolated from chemostat enrichments at different dilution rates

Abstract From chemostat enrichments conducted at dilution rates of 0.025, 0.12 and 0.25 h⁻¹ glutamate- and aspartate-fermenting bacteria were isolated. The dominant aspartate-fermenting strains in all these enrichments belonged to the genus Campylobacter , whereas 3 dissimilar types of glutamate-fermenting bacteria predominated at the different dilution rates. One of these strains was identified as Clostridium cochlearium . The remaining two were designated as strain DKglu16 (glutamate → acetate + propionate + ammonium + carbon dioxide) and DKglu21 (glutamate → acetate + formate + ammonium + carbon dioxide). Grown in continuous culture under glutamate limitation, strain DKglu16 (μ_max= 0.13 h⁻¹; K _s= 1.9 μM) outcompeted C. cochlearium (μ_max= 0.36 h⁻¹; K _s= 7 μM) at low dilution rates, but was outgrown at higher rates of dilution (0.044 h⁻¹). In glutamate-limited continuous culture the competitiveness of strain DKglu16 increased considerably when lactate was added to the feed in addition to glutamate.     

The structure of bovine liver rhodanese. II. The active site in the sulfur-substituted and the sulfur-free enzyme.

X-ray studies at 2.5 Å resolution show that the active site of bovine liver rhodanese is a depression between the two domains. In sulfur-substituted rhodanese the density of the essential Cys247 corresponds with that of a persulfide. Both sulfur atoms are interacting via hydrogen bonds with several peptide NH and side-chain OH groups. One side of the active site pocket contains mainly hydrophylic, the other side mainly hydrophobic residues. None of these hydrophylic or hydrophobic groups appears to interact strongly with the persulfide.Crystals of the sulfur-substituted enzyme were treated with cyanide, a sulfur acceptor. Subsequent difference Fourier studies show that the extra sulfur atom has been removed. Only minor conformational differences appear to exist between the two rhodanese species studied. These are a movement of the Sγ atom of Cys247 and some rearrangement of solvent molecules near the active site.The combination of these observations with the results of experiments performed by other investigators suggest a mechanism for sulfur transfer by rhodanese in which the thiol group of Cys247 is the essential nucleophile, whereas the positive charges on Arg186 and Lys249 act in various ways as “electrophilic assistants”. The transition state and the persulfide in the sulfur-substituted enzyme are stabilized by several hydrogen bonds.     

Subordinates explore but dominants profit: resource competition in high Arctic barnacle goose flocks

Social dominance plays an important role in assessing and obtaining access to patchy or scarce food sources in group-foraging herbivores. We investigated the foraging strategies of individuals with respect to their social position in the group in a flock of nonbreeding, moulting barnacle geese, Branta leucopsis, on high Arctic Spitsbergen. We first determined the dominance rank of individually marked birds. The dominance of an individual was best described by its age and its sex-specific body mass. Mating status explained the large variation in dominance among younger birds, as unpaired yearlings ranked lowest. In an artificially created, competitive situation, subordinate individuals occupied explorative front positions in the flock and were the first to find sites with experimentally enriched vegetation. Nevertheless, they were displaced quickly from these favourable sites by more dominant geese which were able to monopolize them. The enhanced sites were subsequently visited preferentially by individuals that succeeded in feeding there when the exclosures were first opened. Data on walking speed of foraging individuals and nearest-neighbour distances in the group suggest that subordinates try to compensate for a lower energy intake by exploring and by lengthening the foraging bout. Observations of our focal birds during the following breeding season revealed that females that returned to the study area were significantly more dominant in the previous year than those not seen in the area again. Copyright 2001 The Association for the Study of Animal Behaviour.     

Central assumptions of predator-prey models fail in a semi-natural experimental system

The relationship between the encounter rate of predators with prey and the density of this prey is fundamental to models of predator-prey interactions. The relationship determines, among other variables, the rate at which prey patches are depleted, and hence the impact of predator populations on their prey, and the optimal spatial distribution of foraging effort. Two central assumptions that are made in many models are that encounter rate is directly proportional to prey density and that it is independent of the proportion of prey already removed, other than via the decreased density. We show here, using captive great tits searching for winter moth caterpillars in their natural hiding positions, that neither of these assumptions hold. Encounter rate increased less than directly in proportion to prey density, and it depended not only on the current density of prey, but also on the proportion of prey already removed by previous foragers. Both of these effects are likely to have major consequences for the outcome of predator-prey interactions.     

A double test of the parasite manipulation hypothesis in a burrowing bivalve

The parasite manipulation hypothesis predicts that parasites should be selected to manipulate host behaviour to facilitate transmission to the next host. The bivalve Macoma balthica burrows less deep when parasitized by the trematode Parvatrema affinis. Shallow burrowing increases the likelihood of ingestion by birds, their final hosts, and therefore this has been interpreted as manipulation by the parasite. When unparasitized, M. balthica displays seasonal changes in burrowing depth, becoming less accessible to predators in winter. If shallow burrowing of parasitized individuals is due to direct manipulation by the parasite, the availability of parasitized individuals should be high throughout the year, or at least especially in the season when most birds are present and potential transmission rates are highest. We compared burrowing depths of parasitized and unparasitized individuals in a single population during seven consecutive years. Parasitized individuals showed reduced burrowing depths but, in contrast to the prediction, the effect of parasites on availability to predators was smallest, not largest, in the season with the highest bird numbers. The parasite P. affinis competes for energy with the host, and M. balthica with low energy stores are known to reduce depth of burrowing. When we included size-corrected somatic ash-free dry mass (as an estimate of the energy stores) in our statistical analysis, the effect of infection on burrowing depth disappeared. Thus the effect of infection on burrowing depth is likely to be an unavoidable, indirect effect of the channelling of energy towards the parasite, causing the starving individual to take greater risks in the acquisition of food. Since both the seasonal pattern and the magnitude of increased availability of parasitized individuals are inadequate, the increased exposure of parasitized M. balthica to the final host does not seem to represent an example of adaptive host manipulation by the parasite.     

Bronchoalveolar lavage fluid differential cell count. How many cells should be counted?

OBJECTIVE: To investigate the number of cells to be counted in cytocentrifuged bronchoalveolar lavage (BAL) fluid preparations in order to reach a reliable enumeration of each cell type. STUDY DESIGN: A total of 136 BAL fluid samples for patients with suspected pneumonia or interstitial lung disease were investigated. Differential cell counts were performed on May-Grünwald-Giemsa-stained cytocentrifuged preparations by 2 observers, each differentiating 500 cells. Reliability for the enumeration of each cell type was expressed as phi value, as calculated in generalizability theory. RESULTS: For polymorphonuclear neutrophils (PMNs), alveolar macrophages, lymphocytes and eosinophils, an acceptable phi value of > or = .95 was reached at a count of 300 cells by 1 observer. Mast cells reached a phi value of only .674 at a count of 500 cells by 1 observer, precluding a reliable count. At a count of 500 cells by 1 observer, squamous epithelial cells, bronchial epithelial cells and plasma cells displayed phi values of .868, .903 and .816, respectively. CONCLUSION: At a count of 300 cells, PMNs, alveolar macrophages, lymphocytes and eosinophils are reliably enumerated in cytocentrifuged BAL fluid samples.     

Satellite tracking of two Montagu’s Harriers (Circus pygargus): dual pathways during autumn migration

Autumn migration routes of two Dutch female Montagu’s Harriers (Circus pygargus) were documented for the first time using satellite telemetry. Both migrated to their African wintering area—one via the Straits of Gibraltar through the Mediterranean and the other via Italy/Tunisia. The rate of travel was comparable to values reported for larger raptor species.     

Interactions among oscillatory pathways in NF-kappa B signaling

Background  

Sustained stimulation with tumour necrosis factor alpha (TNF-alpha) induces substantial oscillations—observed at both the single cell and population levels—in the nuclear factor kappa B (NF-kappa B) system. Although the mechanism has not yet been elucidated fully, a core system has been identified consisting of a negative feedback loop involving NF-kappa B (RelA:p50 hetero-dimer) and its inhibitor I-kappa B-alpha. Many authors have suggested that this core oscillator should couple to other oscillatory pathways.     

Genetic architecture in a marine hybrid zone: comparing outlier detection and genomic clines analysis in the bivalve Macoma balthica

The role of natural selection in speciation has received increasing attention and support in recent years. Different types of approaches have been developed that can detect genomic regions influenced by selection. Here, we address the question whether two highly different methods--F(ST) outlier analysis and admixture analysis--detect largely the same set of non-neutral genomic elements or, instead, complementary sets. We study genetic architecture in a natural secondary contact zone where extensive admixture occurs. The marine bivalves Macoma balthica rubra and M. b. balthica descend from two independent trans-Arctic invasions of the north Atlantic and hybridize extensively where they meet, for example in the Kattegat-Danish Straits-Baltic Sea region. The Kattegat-Danish Straits region forms a steep salinity cline and is the only entrance to the recently (ca. 8000 years ago) established brackish water basin the Baltic Sea. Salinity along the contact zone drops from 30‰ (Skagerrak, M.b.rubra) to 3‰ (Baltic, M.b.balthica). Both outlier analysis and genomic clines analysis suggest that large parts of the genome are influenced by non-neutral effects. Contrasting samples from well outside the hybrid zone, outlier analysis detects 16 of 84 amplified fragment length polymorphism markers as significant F(ST) outliers. Genomic clines analysis detects 31 of 84 markers as non-neutral inside the hybrid zone. Remarkably, only three markers are detected by both methods. We conclude that the two methods together identify a suite of markers that are under the influence of non-neutral effects.