Showing papers by "Aarhus University published in 1983"

Microelectrode studies of the photosynthesis and O2, H2S, and pH profiles of a microbial mat1

Abstract: The profiles of O,, H,S, and pH within a microbial mat of the hypcrsaline pond Solar Lake, Sinai, were measured by 2-208pm-thick microelectrodes during diurnal and artificial light cycles. The oxygen concentration in the photic layer varied from a maximum of 1,400 PM during the day to 0 during the night. The pH in the same layer varied between 9.6 in the early afternoon and 7.7 in the early morning. Sulfide was not present in the photic zone during the day, but built up to about 50 /IM during the night. The diffusion gradients of sulfide and oxygen were very steep and the two compounds coexisted in a layer only 0.25 mm thick during the day. Diffusion flux calculations showed that the average turnover time of sulfide within this layer was 21 s. The rapid turnover indicated that the oxidation of sulfide must be biologically mediated. Oxygenic photosynthesis was measured by a new oxygen microprofile method which accurately determines the vertical distribution of photosynthetic activity. There was no difference in the efficiency of photosynthesis between morning and afternoon. The photosynthetic efficiency of the whole mat was about fourfold higher at low light intensities, ~120 PEinst. m-z.s-1, than at high light intensities, 120-1,600 pEinst*m-“es-‘. Anoxygenic photosynthesis within the mat was not quantitatively important.

Walking on potential energy surfaces

Abstract: Developpement d'un algorithme pour la marche automatisee sur une surface, en combinant l'approximation quadratique locale a la surface d'energie potentielle et une mise a l'echelle d'une coordonnee active

Partial primary structure of bovine plasma fibronectin: three types of internal homology.

Abstract: Approximately one-half of the amino acid sequence (911 amino acid residues out of 1,880 expected) for bovine plasma fibronectin (cold-insoluble globulin) has been determined. Three types of internal homology were identified, showing that a number of partial gene duplications (multiplications) have occurred during the evolution of this protein. Digestion of fibronectin with plasmin results in major fragments with molecular masses of 29, 170, 23, and 6 kilodaltons (kDal). The NH2-terminal 29-kDal fragment consists of 259 residues ordered as five mutually homologous domains (type I homology) with two disulfide bonds in each domain. The 170-kDal fragment shows two to three bands after NaDodSO4 gel electrophoresis, indicating heterogeneity. This fragment contains the gelatin binding site and the strong heparin binding site present in fibronectin. Digestion of the 170-kDal fragment with chymotrypsin liberates a 45-kDal fragment that also binds to gelatin. This fragment contains at least one domain of type I homology and two domains of type II homology. Further digestion of the 170-kDal fragment with chymotrypsin results in the formation of a 30-kDal fragment that retains the heparin binding activity. This fragment contains sequences constituting type III homology. The 23-kDal fragment consists of 178 residues having three domains of type I homology. The 6-kDal fragment consists of two identical peptides of 26 residues, and these two peptides are linked to each other by two disulfide bonds that form the interchain bridges. Another one of the peptides for which the sequence was determined links the COOH-terminus of the 29-kDal fragment to the NH2-terminus of the 170-kDal fragment. This and the fact that the COOH-terminal residue of the 6-kDal fragment is a glutamic acid residue order the four plasmin-digestion fragments as 29-, 170-, 23-, and 6-kDal in the intact fibronectin molecule.

Photosynthesis and structure of benthic microbial mats: Microelectrode and SEM studies of four cyanobacterial communities1

Abstract: The microzonation of photosynthetic organisms in four cyanobacterial mats of Solar Lake, Sinai, was studied by light and scanning electron microscopy. The zonation was compared to the distribution of photosynthesis and of O/sub 2/, H/sub 2/S, and pH. Microelectrodes were used to measure the chemical gradients as well as the photosynthetic rates by a newly developed technique which allows a spatial resolution of 100 ..mu..m. Two-dimensional maps of oxygen and photosynthesis distribution at the mat surface demonstrated a strong heterogeneity with rapid oxygen production within dense diatom tufts of 0.2-0.5-mm diameter overgrowing the cyanobacteria. Gas bubbles within the mat served as dynamic reservoirs for oxygen during light-dark cycles and buffered against extreme diurnal variations between oxygen and sulfide.

Nitrogen cycling in different types of sediments from Danish waters1

Abstract: Variations in sediment N:C ratios were correlated with water depth and season. 15NH,+ was used to measure the rates of NH,+ production (d) and incorporation into bacterial cells (i) in sediments from different stations, at different seasons. The validity of the rates d and i was indicated by the predicted correlation of cl:i ratios with N:C ratios of the sediment, and the predicted N:C ratio at which net NH4+ uptake occurred. There was also a correlation between rate cl and product (total NH,+). In the O-2-cm stratum correlations were also established between d, exchangeable NH4+ pool, ratio exchangeable NH?+ : porewater NH4+, flux of NH,+ from sediment, and flux of NH4+ into exchangeable pool. The NO:,- flux from sediment was correlated with nitrification rate and with season. Benthic infauna increased the flux of NHI’ from the sediment by 50%. The rates of transfer of nitrogen (NO,-, NH?+, N,) from sediment to water were 44-66% of the net rates of organic nitrogen mineralization (d - i). Flux of NO,- + NII,+ from the sediment could supply 30-82% of the nitrogen requirement of the planktonic primary producers.

Colorless Sulfur Bacteria, Beggiatoa spp. and Thiovulum spp., in O(2) and H(2)S Microgradients.

Abstract: The interactions between colorless sulfur bacteria and the chemical microgradients at the oxygen-sulfide interface were studied in Beggiatoa mats from marine sediments and in Thiovulum veils developing above the sediments. The gradients of O2, H2S, and pH were measured by microelectrodes at depth increments of 50 μm. An unstirred boundary layer in the water surrounding the mats and veils prevented microturbulent or convective mixing of O2 and H2S. The two substrates reached the bacteria only by molecular diffusion through the boundary layer. The bacteria lived as microaerophiles or anaerobes even under stirred, oxic water. Oxygen and sulfide zones overlapped by 50 μm in the bacterial layers. Both compounds had concentrations in the range of 0 to 10 μmol liter−1 and residence times of 0.1 to 0.6 s in the overlapping zone. The sulfide oxidation was purely biological. Diffusion calculations showed that formation of mats on solid substrates or of veils in the water represented optimal strategies for the bacteria to achieve a stable microenvironment, a high substrate supply, and an efficient competition with chemical sulfide oxidation. The continuous gliding movement of Beggiatoa cells in mats or the flickering motion of Thiovulum cells in veils were important for the availability of both O2 and H2S for the individual bacteria.

Respiration rates in heterotrophic, free-living protozoa.

Abstract: Published estimates of protozoan respiratory rates are reviewed with the object of clarifying their value in ecological studies. The data show a surprisingly large variance when similarly sized cells or individual species are compared. This is attributed to the range of physiological states in the cells concerned. The concept of basal metabolism has little meaning in protozoa. During balanced growth, energy metabolism is nearly linearly proportional to the growth rate constant; at the initiation of starvation, metabolic rate rapidly declines. Motility requires an insignificant fraction of the energy budget of protozoans. For growing cells, metabolic rate is approximately proportional to weight0.75 and the data fall nearly exactly on a curve extrapolated from that describing the respiration rates of poikilotherm metazoans as a function of body weight. It is conceivable that protozoan species exist with lower maximum potential growth and metabolic rates than those predicted from cell volume and the equations derived from the available data. However, the lack of information concerning the state of the cells studied prevents verification of this idea. Laboratory measurements of protozoan respiratory rates have no predictive value for protozoa in nature other than delimiting a potential range. For small protozoans, this range may, on an individual basis, represent a factor of 50.

Lesion‐induced mossy fibers to the molecular layer of the rat fascia dentata: Identification of postsynaptic granule cells by the Golgi‐EM technique

Abstract: The axons of the dentate granule cells, the hippocampal mossy fibers, sprout "backward" into the dentate molecular layer when this is heavily denervated. Using the combined Golgi-electron microscopy (EM) technique we now demonstrate that these aberrant supragranular mossy fibers at least in part terminate on granule cell dendrites. Sprouting of mossy fibers into the dentate molecular layer was induced in adult rats by simultaneous surgical removal of the commissural and entorhinal afferents to the fascia dentata. After at least 7 weeks survival, the presence of mossy fiber terminals in the inner part of the dentate molecular layer was demonstrated by light microscopy. In the electron microscope the mossy fiber terminals were identified by their unique structural characteristics, namely, the unusually large size of the terminals, the dense packing of clear synaptic vesicles with a few dense core vesicles intermingled, the presence of asymmetric synaptic contacts with spines and desmosome-like contacts with dendritic shafts, and the continuity with a thin unmyelinated preterminal axon. Golgi-stained granule cells were first identified in the light microscope, and then, after deimpregnation, the same cells were examined in the electron microscope. In ultrathin, serial sections lesion-induced mossy fiber terminals were found in synaptic contact with spines on proximal dendritic segments of such identified Golgi-impregnated granule cells. From this we conclude that the aberrant, supragranular mossy fibers can innervate dendrites of the parent cell group, the dentate granule cells. The results, moreover, provide an example of reactive synaptogenesis where both the sprouted afferents and its postsynaptic element have been identified.

Vesicular‐arbuscular mycorrhiza in field‐grown crops

Abstract: SUMMARY Development of infection by vesicular-arbuscular mycorrhiza (VAM) was studied in some field-grown crops. An infection plateau was reached within the first month after seedling emergence of spring barley, oats and peas. During the rest of the growth period the proportion of root length infected by VAM remained at about 50% in the cereals and 75% in the peas. In the spring, infection levels were low in winter wheat, winter rye and winter barley, and development of infection was slower in them than in the spring-sown crops. VAM infection was also studied in relation to soil depth and root density. The proportion of root length infected decreased markedly below 40 cm soil depth. Root density varied greatly between crops, whereas the absolute length of infected roots was similar in all crops. This indicates that susceptibility to infection was independent of host species. The results are discussed in relation to final phosphorus uptake and dry-matter production, and it is proposed that a relatively low soil-phosphorus availability was counterbalanced, to some extent, by a well-developed VAM infection.

Natural History of Epileptic Seizures

Abstract: Summary: Since 1963 a continuous registration of patients with epileptic seizures has been carried out in Greater Aarhus, Denmark. This registration has been attempted by means of medical records dating back to 1940. On the basis of the established prevalence and the calculated cumulated incidence, we have tried to describe the natural history of the different types of epilepsy. The prevalence of all types of epileptic seizures (including febrile convulsions) has been found to be 2,441/100,000, whereas for patients with the diagnosis of epilepsy the rate is 1,274/100,000. The study describes the natural history of the different types of epilepsy. In addition, the risk-increasing effect of a febrile convulsive seizure on the development of epilepsy is analyzed. RESUMEN Desde 1.963 se ha llevado a cabo un registro continuo de enfermos con ataques epilepticos en la ciudad danesa de Greater Aarhus. Este registro se ha basado en protocolos medicos fechados desde 1.940. Basan-dose en la prevalencia establecida y la calculable incidencia acumulativa se ha intentado describir la historia natural de los diversos tipos de epilepsyia. La prevalencia de todos los tipos de epilepsyia, incluyendo ataques febriles, ha sido de 2.441/100.000 mientras que. considerando los pacientes con diagnostico de epilepsyia la crifra fue de 1.274/100.000. Este estudio describe la historia natural de los diversos tipos de epilepsyia. Ademas analiza el riesgo de que las convulsiones febriles incrementen el desarrollo de epilepsyia. ZUSAMMENFASSUNG Seit 1963 werden alle Patienten mit epileptischen Anfallen im Bezirk Gros-Aarhus, einer danischen Stadt, registriert. Diese Registrierung geschieht mit Hilfe von Krankengeschichten bis zuruck zum Jahre 1940. Auf der Grundlage der bekannten Pravalenz und der kalkulierten und kumulierten Inzidenzwurde versucht, den naturlichen Verlauf verschiedener Epilepsietypen zu beschreiben. Die Pravalenz aller Typen epileptischer Anfalle (einschlieslich von Fieberkrampfen) betragt 2.441/100.000. Die entsprechende Ziffer fur Patienten mit der Diagnose Epilepsie betragt 1.274/100.00. Die Untersuchung beschreibt die naturlichen Verlaufe vershiedener Epilepsietypen. Darub-erhinaus wird die Risikozunahme hinsichtlich der Entwicklung einer Epilepsie durch Fieberkrampfe analysiert.

House-Dust Mites and Absolute Indoor Humidity

Abstract: The concentration of house-dust mites (Dermatophagoides spp.) was investigated for four seasons in three locations in each of 50 Danish apartments. Simultaneously the absolute humidity was recorded and the previously known correlation between mite counts and indoor humidity was confirmed. It appeared, however, that apartments which had a low absolute indoor humidity in the winter period (due to low household load of water vapour) did not contain noticeable concentrations of house-dust mites in the summer and autumn despite the fact that the indoor absolute humidity in these apartments could be high enough to allow for a high peak-population of mites. Because of this it is suggested that in a temperate climate avoidance measures against house-dust mites should be supplemented at least by a drying out period in the winter, when this process is convenient to perform because of the low outdoor absolute humidity.

Renal enlargement: comparative autoradiographic studies of 3H-thymidine uptake in diabetic and uninephrectomized rats.

Abstract: Incorporation of 3H-thymidine into renal cortical tissue has been studied by light microscopic autoradiography in streptozotocin-diabetic rats, uninephrectomized rats, uninephrectomized diabetic rats, insulin-treated diabetic rats and control rats. The percentage of labelled cortical nuclei (the labelling index) was determined separately in glomeruli, proximal tubules and distal tubules after 2, 4 and 6 days on autoradiographs from 1 μm thick plastic embedded sections. The incorporation of thymidine in glomerular nuclei was consistantly low (< 1%) and no differences were found between the control and experimental groups. In both proximal and distal tubules an increase in thymidine incorporation was seen on day 2 followed by a decline on days 4 and 6. The maximal labelling on day 2 in proximal tubules was 9.1% in the uninephrectomized diabetic group, 3.7% in the diabetic group and 1.4% in the uninephrectomized group. In distal tubules the corresponding values were 5.2, 3.5 and 1.1%. The increase in kidney weight after 6 days was 83, 62 and 37%, respectively. Estimates of the net increase in the number of cortical tubular cells in the different experimental groups showed that the kidney enlargement followed different patterns with respect to the extent of cellular hyperplasia and hypertrophy. The kidney growth in uninephrectomized diabetic rats was dominated by tubular cellular hyperplasia, in the diabetic group hyperplasia and hypertrophy participated to approximately the same extent, whereas cellular hypertrophy was most pronounced in the uninephrectomized animals. Nuclear labelling in the insulin-treated diabetic rats was not different from that of control rats and consequently a hyperplastic effect of streptozotocin can be ruled out.

Fiber types in the striated urethral and anal sphincters

Abstract: Seven normal human striated urethral and anal sphincters obtained by autopsy were examined using histochemical techniques. In both the urethral sphincter and the subcutaneous (s.c.) and superficial part of the anal sphincter a characteristic pattern with two populations of muscle fibers, abundant connective tissue, and numerous intramuscular nerves are seen. No spindles are observed. The muscle fibers, particularly the predominant type 1 fibers are very small (about 15 μm in diameter). The fiber characteristics of the sphincters indicate that these muscles have a capacity to produce sustained contractions and to react in stress conditions with fast increase in tension.

Particle sizes and their distributions estimated from line- and point-sampled intercepts. Including graphical unfolding

Abstract: SUMMARY Information about particle size is currently obtained almost exclusively by the use of stereological methods which lead to estimates of the number distribution of linear particle size. The main point of this presentation is to stress the freedom to choose more appropriate parameters for size among a host of options, including particle surface area and volume. Moreover, particle size information may often be considered advantageously in terms of particle distributions based on structural characteristics rather than number distributions. Some of these other distribution types are correctly represented in samples of intercept lengths obtained by line- and point-sampling, respectively. The known and quite simple theory of sampling intercepts is summarized and developed further in several different directions, including a derivation of the distribution of intercept length in ellipsoids, graphical unfolding procedures, and mean size estimators. The potential of the approach is illustrated—but not exhausted—by the existence of a general mean size estimator based on minimal assumptions regarding particle shape.

Occurrence and nature of bacterial IgA proteases.

Abstract: Secretory immunoglobulin A (sIgA) is the principal mediator of specific immunity on human mucosal surfaces. Although the exact mechanisms are partly unclear, it is generally accepted that sIgA antibodies maintain the integrity of the mucous membranes by reducing their colonization by microorganisms, by neutralizing toxins and viruses, and by preventing the penetration of microbial and other antigens and allergens through the surfaces.' IgA in serum appears to play an important role in the regulation of inflammatory responses particularly in submucosal tissues.' Recent studies in rodents have suggested, furthermore, that serum IgA is involved in the disposal of antigens from the circulation.' For sIgA to successfully protect mucosal surfaces it must resist proteolytic attack from digestive and microbial enzymes that occur in these environments. Changes in the structure of IgA induced by bacteria was first demonstrated in vitro by Miiller in 1971.3 He reported that strains of Neisseria meningitidis and N. gonorrhoeae possess proteolytic activity that invariably induce selective changes in the electrophoretic mobility of human IgA. Although the exact nature of these changes were not identified, Milller suggested that bacterium-induced alterations of IgA is a possible factor in the pathogenesis of infections caused by N. meningitidis and N. gonorrhoeae. Strains of a number of other bacterial species, including Pseudomonas aeruginosa, Bacteroides melaninogenicus, and Proteus vulgaris, were shown to have a strong proteolytic activity capable of causing progressive degradation of IgA. In addition, several human-pathogenic organisms induced changes in the electrophoretic mobility of IgA and various other human serum glycoproteins by attacking their carbohydrate moieties. The existence of a bacterial proteolytic enzyme with the capacity to induce specific cleavage of IgA in the hinge region, yielding intact Fab, and Fc, fragments was first reported by Metha and coworkers in 1973.4 The enzyme was demonstrated in human feces of six normal subjects examined. The intestinal bacterium responsible for this cleavage has never been identified. Subsequent studies by Plaut, Genco, and Tomasi revealed that a similar enzymatic activity is present in human saliva, and that an organism indigenous to the oral cavity, Streptococcus sanguis, produces an enzyme with this characteristic activity.'

Possible causes of temporal fluctuations in primary production of the microphytobenthos in the Danish Wadden Sea

Abstract: Short-term changes of the benthic primary production on a tidal sandflat were investigated during low tide and correlated with fluctuations in environmental parameters (light, temperature, salinity and pH) and the possible causal relations were tested in laboratory experiments There was an almost linear relationship between temperature and photosynthetic rate up to the optimum temperature (20°C in May and 30°C in September) Maximum photosyn-thesis occurred at salinities between 15 and 30‰ S and decreased to 37% at a salinity of 50‰ S Increase in temperature (187° to 226°C in May, 82° to 183°C in September) correlated with photosynthesis during the first h of the low tide period (in May and September), whereas increased salinity (30 to 50‰ S in May and 30 to 48‰ S in September) and possibly also high pH values (up to pH 93) correlated negatively with photosynthetic rate during the last part of the period

Preventive measures in mite asthma. A controlled trial.

Abstract: To evaluate the effect of preventive measures 46 patients, all allergic to house-dust mites (Dermatophagoides spp.), were randomly allocated to a study and a control group. According to the patients' subjective recordings of symptom score and use of medicine, compared with the control group, the study group had improved. There was, however, no improvement when comparing the objective recordings of morning and evening peak flow and use of medicine, and it is concluded that the preventive measures in this programme are not very effective for patients allergic to house-dust mites. The reduction in indoor humidity in the study group was limited and, as a high indoor humidity is the cause of huge populations of house-dust mites in homes, it is emphasized that future programmes of preventive measures should focus more on damp problems, particularly those related to bad housing construction.

Localization of exogenous silver in brain and spinal cord of silver exposed rats

Abstract: Exogenous silver in brain and spinal cord sections from rats treated with Protargol, silver lactate or silver nitrate was visualized by physical development. The silver penetrated the blood-brain barrier and accumulated in neurones and glia. The distribution of silver in the CNS was heterogenous. Even with low doses and short survival periods, silver was found to accumulate in large motoneurones in the brain stem and spinal cord and neurones in the cerebellar nuclei. Silver was only found in di- and telencephalic structures after extensive exposure.