Showing papers by "University of Konstanz published in 1988"

The capacity of hydrogenotrophic anaerobic bacteria to compete for traces of hydrogen depends on the redox potential of the terminal electron acceptor

Abstract: The effect of different electron acceptors on substrate degradation was studied in pure and mixed cultures of various hydrogenotrophic homoacetogenic, methanogenic, sulfate-reducing, fumarate-reducing and nitrate-ammonifying bacteria. Two different species of these bacteria which during organic substrate degradation produce and consume hydrogen, were cocultured on a substrate which was utilized only by one of them. Hydrogen, which was excreted as intermediate by the first strain (and reoxidized in pure culture), could, depending on the hydrogen acceptor present, also be used by the second organism, resulting in interspecies hydrogen transfer. The efficiency of H2 transfer was similar when methanol, lactate or fructose were used as organic substrate, although the free energy changes of fermentative H2 formation of these substrates are considerably different. In coculture experiments nitrate or fumarate>sulfate> CO2/CH4>sulfur or CO2/acetate were the preferred electron acceptors, and an increasing percentage of H2 was transferred to that bacterium which was able to utilize the preferred electron acceptor. In pure culture the threshold values for hydrogen oxidation decreased in the same order from ≤1,100 ppm for homoacetogenic bacteria to about 0.03 ppm for nitrate or fumarate reducing bacteria. The determined H2-threshold values as well as the percentage of H2 transfer in cocultures were related to the Gibbs free energy change of the respective hydrogen oxidizing reaction.

Self-Enforcing Wage Contracts

Abstract: We examine long-term wage contracts between a risk-neutral firm and a risk-averse worker when both can costlessly renege and buy or sell labour at a random spot market wage. A self-enforcing contract is one in which neither party ever has an incentive to renege. In the optimum self-enforcing contract, wages are sticky: they are less variable than spot market wages and positively serially correlated. They are updated by a simple rule: around each spot wage is a time invariant interval, and the contract wage changes each period by the smallest amount necessary to bring it into the current interval.

Magnetic order and fluctuations in superconducting UPt3.

Abstract: Neutron diffraction shows that superconducting ${\mathrm{UPt}}_{3}$ can be an antiferromagnet with an ordered moment of (0.02\ifmmode\pm\else\textpm\fi{}0.01)${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$ and a N\'eel temperature (${\mathrm{T}}_{\mathrm{N}}$) of 5 K. The squared order parameter is linear function of temperature from ${\mathrm{T}}_{\mathrm{N}}$ to the superconducting transition temperature, ${\mathrm{T}}_{\mathrm{c}}$=0.5 K, below which it ceases to evolve. Inelastic neutron scattering demonstrates that the fluctuating moments are strongly correlated; the characteristic energy for fluctuations with wave vectors close to the ordering wave vector is 0.2 meV\ensuremath{\approxeq}4${\mathrm{kT}}_{\mathrm{c}}$..AE

Camptothecin, a specific inhibitor of type I DNA topoisomerase, induces DNA breakage at replication forks.

Abstract: The structure of replicating simian virus 40 minichromosomes, extracted from camptothecin-treated infected cells, was investigated by biochemical and electron microscopic methods. The authors found that camptothecin frequently induced breaks at replication forks close to the replicative growth points. Replication branches were disrupted at about equal frequencies at the leading and the lagging strand sides of the fork. Since camptothecin is known to be a specific inhibitor of type I DNA topoisomerase, the authors suggest that this enzyme is acting very near the replication forks. This conclusion was supported by experiments with aphidicolin, a drug that blocks replicative fork movement, but did not prevent the camptothecin-induced breakage of replication forks. The drug teniposide, and inhibitor of type II DNA topoisomerase, had only minor effects on the structure of these replicative intermediates.

Concept learning by pigeons: Matching-to-sample with trial-unique video picture stimuli

Abstract: Pigeons were trained to match-to-sample with several new methodologies: a large number of stimuli, computer-drawn color picture stimuli, responses monitored by a computer touch screen, stimuli presented horizontally from the floor, and grain reinforcement delivered onto the picture stimuli. Following acquisition, matching-to-sample concept learning was assessed by transfer to novel stimuli on the first exposure to pairs of novel stimuli. One group (trial-unique), trained with 152 different pictures presented once daily, showed excellent transfer (80% correct). Transfer and baseline performances were equivalent, indicating that the matching-to-sample concept had been learned. A second group (2-stimulus), trained with only two different pictures, showed no evidence of transfer. These results are discussed in terms of the effect of numbers of exemplars on previous failures to find concept learning in pigeons, and the implications of the positive finding from this experiment on abstract concept learning and evolutionary cognitive development.

Sporomusa termitida sp. nov., an H2/CO2-utilizing acetogen isolated from termites

Abstract: H2-oxidizing CO2-reducing acetogenic bacteria were isolated from gut contents of Nasutitermes nigriceps termites. Isolates were strictly anaerobic, Gram negative, endospore-forming, straight to slightly curved rods (0.5–0.8×2–8 μm) that were motile by means of lateral flagella. Cells were oxidase negative, but catalase positive and possessed a b-type cytochrome(s) associated with the cell membrane. Cells grew anaerobically with H2+CO2 as energy source and catalyzed a total synthesis of acetate from this gas mixture. H2 uptake by a representative isolate (strain JSN-2) displayed a Km=6 μM and Vmax=380 nmol x min-1 x mg protein-1. Other substrates used as energy sources for growth and acetogenesis included CO, methanol, betaine, trimethoxybenzoate, and various other organic acids. Succinate was also fermented, but propionate was formed from this substrate instead of acetate. Of a variety of sugars and sugar alcohols tested, only mannitol supported growth. Cells grew optimally at 30° C and pH 7.2 and required yeast extract or a source of amino acids (e.g. Casamino acids) for good growth. During initial enrichment and isolation, cells appeared sensitive to various reducing agents commonly employed in media for anaerobes. The DNA base composition of strain JSN-2 was 48.6 mol% G+C. On the bases of cell morphology, substrate utilization spectrum, and DNA base composition, strain JSN-2 is here-with proposed as the type strain of the new species Sporomusa termitida.

The Organization of Mechanosensory Neuropiles in Locust Thoracic Ganglia

Abstract: This paper describes the neuropilar areas of the thoracic ganglia of locusts ( Locusta migratoria ) in which projections from mechanoreceptors terminate. Reference transverse, sagittal and parasagittal sections through a meso- and metathoracic ganglion illustrate the relation of these neuropiles to known structures such as longitudinal tracts and commissures. The ventral association centres (VAC), divided into anterior (aVAC), medial (mVAC), ventralmost (vVAC) and lateral (IVAC) parts, receive terminals from tactile hairs (H; aVAC, vVAC and IVAC) and chordotonal organs (CO; mVAC). Newly defined neuropilar areas are the lateral association centres (LAC) which are divided into an anterior (aLAC) and posterior part (pLAC). These receive projections from hair plates (HP), campaniform sensilla (CS), multipolar sensory cells (MS), strand receptors (SR) and chordotonal organs (CO). In contrast to the VACs they also contain fibres of motorneurons.

Maternal care in house mice (Mus musculus): II. The energy cost of lactation as a function of litter size

Abstract: In mammals, lactation performance may influence future reproduction of a mother and her young. We measured the quantity and quality of milk produced by female house mice (Mus musculus) during a period of 28 days after birth of a litter. We aimed to analyse how females cope with the energy demands of different sized litters as a tradeoff between current and future reproduction. Litter sizes examined were small (six young), intermediate (7.3 0–7), and large (12 young). Females met the energy demand of a growing litter both by increasing the amount of milk given to the young and by improving the quality (through an increase in total solid and fat concentrations) to a peak during days 9–16. At the onset of weaning (day 17), milk production decreased and young shifted to solid food. The main energy source in the milk of house mice was fat, which provided more than 80% of the energy to the suckling young. Average lipid concentrations were 20%, and peak values of 33% were reached during days 13–16. Protein concentrations were 6–8% and carbohydrate (lactose) concentrations 3–4%. With larger litters, females increased both the amount of milk and the absolute amount of major nutrients (lipids, proteins, lactose). However, regulation was imperfect. When litter size was doubled from six to 12, amount of milk produced rose by 44%, and energy content only rose by 30%. The reduction in milk supply for individual young in larger litters was reflected in slower growth and lower weaning weight. The efficiency of conversion of milk energy into biomass of young was highest for intermediate litters (51%; for small litters, 43%; for large ones, 36%). During days 5–16, a single pup in an intermediate litter needed less energy for metabolism and growth than pups in the other litter sizes examined. Although individual young of small litters have a relatively high weaning weight-which might improve their future reproduction-females gain higher reproductive success by dividing the energy available per litter between the largest number of young they can raise to a weaning weight of on average 9 g. For the time-lifen reproductive success of a female house mouse-at least for the strain used in this study-an intermediate litter size of seven seems to be best because of a favourable ratio of energy cost of lactation to number and size of young produced.

Eubacterium acidaminophilum sp. nov., a versatile amino acid-degrading anaerobe producing or utilizing H2 or formate: description and enzymatic studies

Abstract: An obligately anaerobic, rod-shaped bacterium was isolated on alanine in co-culture with H2-scavenging Desulfovibrio and obtained in pure culture with glycine as sole fermentation substrate. The isolated strain, al-2, was motile by a polar to subpolar flagellum and stained Gram-positive. The guanine plus cytosine content of the DNA was 44.0 mol%. Strain al-2 grew in defined, reduced glycine media supplemented with biotin. The pure culture fermented 4 mol glycine to 3 mol acetate, 4 mol ammonia and 2 mol CO2. Under optimum conditions (34°C, pH 7.3), the doubling time on glycine was 60 min and the molar growth yield 7.6 g cell dry mass. Serine was fermented to acetate, ethanol, CO2, H2 and ammonia. In addition, betaine, sarcosine or creatine served as substrates for growth and acetate production if H2, formate or e.g. valine were added as H-donors. In pure culture on alanine under N2, strain al-2 grew very poorly and produced H2 up to a partial pressure of 3.6 kPa (0.035 atm). Desulfovibrio species, Methanospirillum hungatei and Acetobacterium woodii served as H2-scavengers that allowed good syntrophic growth on alanine. The co-cultures also grew on aspartate, leucine, valine or malate. Alanine and aspartate were stoichiometrically degraded to acetate and ammonia, whereas the reducing equivalents were recovered as H2S, CH4 or newly synthetized acetate, respectively. Growth of strain al-2 in co-culture with the hydrogenase-negative, formate-utilizing Desulfovibrio baarsii indicated that a syntrophy was also possible by interspecies formate transfer. Growth on glycine, or on betaine, sarcosine or creatine (plus H-donors) depended strictly on the addition of selenite (≥0.1 μM); selenite was not required for fermentation of serine, or for degradation of alanine, aspartate or valine by the co-cultures. Cell-free extracts of glycine-grown cells contained active glycine reductase, glycine decarboxylase and reversible methyl viologen-dependent formate dehydrogenase in addition to the other enzymes necessary for an oxidation to CO2. In all reactions NADP was the preferred H-carrier. Both formate and glycine could be synthesized from bicarbonate. Serine-grown cells did not contain serine hydroxymethyl transferase but serine dehydratase and other enzymes commonly involved in pyruvate metabolism to acetate, CO2 and H2. The enzymes involved in glycine metabolism were repressed during growth on serine. By its morphology and physiology, strain al-2 did not resemble described amino acid-degrading species. Therefore, the new isolate is proposed as type strain of a new species, Eubacterium acidaminophilum.

Ion channels activated by osmotic and mechanical stress in membranes of opossum kidney cells.

Abstract: For patch-clamp measurements cultured kidney (OK) cells were exposed to osmotic and mechanical stress. Superfusion of a cell in whole cell configuration with hypotonic media (190 mOsm) evokes strong depolarization, which is reversible by returning to the isotonic bath medium. In the cell-attached configuration the exposure to hypotonic media evokes up to six ion channels of homogeneous single-channel properties in the membrane patch. Subsequently, the channels became activated after a time lag of a few seconds. At an applied membrane potential of 0 mV, the corresponding membrane current is directed inward and shows a transient behavior in the time range of minutes. In the same membrane patch these ion channels can be activated by application of negative hydrostatic pressure. The channel has a single-channel conductance of about 22 pS and is permeable to Na+ and K+ as well as to C1-. It is suggested that volume regulation involves mechanoreceptor-operated ion channels.

A New UV-A/B Protecting Pigment in the Terrestrial Cyanobacterium Nostoc commune.

Abstract: A new ultraviolet (UV)-A/B absorbing pigment with maxima at 312 and 330 nanometers from the cosmopolitan terrestrial cyanobacterium Nostoc commune is described. The pigment is found in high amounts (up to 10% of dry weight) in colonies grown under solar UV radiation but only in low concentrations in laboratory cultures illuminated by artificial light without UV. Its experimental induction by UV as well as its capacity to efficiently protect Nostoc against UV radiation is reported.

Chitinases and β-1,3-Glucanases in the Apoplastic Compartment of Oat Leaves (Avena sativa L.)

Abstract: To isolate chitinases and β-1,3-glucanases from the intercellular space of oats (Avena sativa L.), primary leaves were infiltrated with buffer and subjected to gentle centrifugation to obtain intercellular washing fluid (IWF). Approximately 5% of the chitinase and 10% of the β-1,3-glucanase activity of the whole leaf were released. Only small amounts (0.01-0.03%) of the intracellular marker malate-dehydrogenase were released into the IWF during infiltration. Activities of chitinase and β-1,3-glucanase in the IWF and in the leaf extract were compared by different chromatographic methods. On Sephadex G-75, chitinase appeared as a single peak (Mr 29.8 kD) both in IWF and homogenate. β-1,3-Glucanase, however, showed two peaks in the IWF (Mr 52 and 31.3 kD), whereas the elution pattern of the homogenate showed only one major peak at 22 kD. Chromatofocusing indicated that the IWF contained four chitinases and five β-1,3-glucanases. The elution pattern of the homogenate and IWF were similar with regard to the elution pH, but the peak intensities were distinctly different. Our results demonstrate that extracellular β-1,3-glucanases are different from those located intracellularly. Extracellular and intracellular chitinases do not differ in molecular properties, except for one isozyme which seems to be confined to the extracellular space. We suggest that both enzymes might play a special role in pathogenesis during fungal infection.

Fibre types, calcium-sequestering proteins and metabolic enzymes in denervated and chronically stimulated muscles of the rat.

Abstract: 1. Fibre types, Ca2+-sequestering proteins (parvalbumin, sarcoplasmic reticulum Ca2+-ATPase), enzyme activities of energy metabolism, and lactate dehydrogenase isozymes were studied in extensor digitorum longus (EDL) and soleus muscles of adult rats after denervation and direct stimulation for 45-61 days. The stimulation resembled the firing patterns of normal motor units (Hennig & Lomo, 1985) in either soleus (20 Hz, high amount) or EDL (150 Hz, low and high amount). 2. Low- and high-amount 150 Hz stimulation maintained essentially normal properties in the denervated EDL and induced many EDL-like properties in the denervated soleus, e.g. pronounced increases in Ca2+-ATPase and parvalbumin contents, a rise in the glycolytic enzyme activities, as well as a reversal of the lactate dehydrogenase H/M subunit ratio. The 150 Hz high-amount stimulation was not as efficient as the 150 Hz low amount in maintaining the fast properties of denervated EDL with the exception of the enzymes of aerobic oxidative metabolism. High-amount 20 Hz stimulation maintained essentially normal properties in the soleus but induced only moderate slow muscle characteristics in the EDL. 3. The maintenance of essentially normal properties by 'native' and the changes induced by 'foreign' stimulus patterns in the absence of the nerve indicate that evoked muscle activity plays a major role in controlling the phenotypic expression of muscle properties. However, the different responses of the denervated fast- and slow-twitch muscles to identical stimulus patterns further suggest that rat EDL and soleus muscles contain intrinsically different muscle fibres.

Species-specific effects of chronic nerve stimulation upon tibialis anterior muscle in mouse, rat, guinea pig, and rabbit.

Abstract: Tibialis anterior (TA) muscle of mouse, rat, guinea pig, and rabbit was indirectly stimulated for 10 h/day at 10 Hz up to 28 days. Changes in the activity levels of hexokinase (HK), phosphofructokinase (PFK) glyceraldehydephosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH), creatine kinase (CK), citrate synthase (CS), malate dehydrogenase (MDH), 3-hydroxyacyl-CoA dehydrogenase (HADH), and β-hydroxybutyrate dehydrogenase (HBDH) were compared. Although the direction of changes in the enzyme activity pattern was in accordance with previous findings on rabbit TA, the magnitude of the responses varied markedly between themammals under study. Mouse TA was almost unaffected. A major effect of chronic stimulation in rat, guinea pig and rabbit was an increase in enzyme activities of aerobic-oxidative metabolism. According to intrinsic differences of the muscles under study, the increases varied among the species and appeared to be inversely related to the basal levels of these enzymes in the unstimulated muscles. Conversely, glycolytic enzyme activities (PFK, GAPDH, LDH) markedly decreased in rat, guinea pig, and rabbit, and were only slightly reduced in mouse. Changes in HK and HBDH activities displayed the largest variations in the induced change between species. These results indicate species-specific patterns of metabolic adaptation to increased contractile activity.

Methane and hydrogen in seawater (Atlantic Ocean)

Abstract: Measurements of dissolved methane and hydrogen from the Atlantic Ocean, between 50°N and 35°S, showed the surface water to be supersaturated, while the deep ocean water was in equilibrium or slightly undersaturated with respect to atmospheric CH4 and H2. Dissolved H2 was highest in surface water and decreased within the upper 100 m of the water column, whereas dissolved CH4 remained high within the entire euphotic water layer. There is evience for a diurnal variation of dissolved H2, with higher amplitudes at the water surface compared to 20m depth. Dissolved CH4 at 4 m depth also was measured using a continuously working equilibration technique which procided information on short-term fluctuations. The dissolved CH4 showed no diurnal variations and was independent of wind speed. Highest CH4 concentrations were observed in areas with high nutrient input, e.g. in the upwelling areas off West Africa, and correlated well with the observed chorophyll a concentrations. Based on an average CH4 saturation factor of about 1.1, the total source strength for atmospheric CH4 is calculated to about 1.5 Tg y−1.

Association of DNA topoisomerase I and RNA polymerase I: a possible role for topoisomerase I in ribosomal gene transcription

Abstract: RNA polymerase I preparations purified from a rat hepatoma contained DNA topoisomerase activity. The DNA topoisomerase associated with the polymerase had an Mr of 110000, required Mg2+ but not ATP, and was recognized by anti-topoisomerase I antibodies. When added to RNA polymerase I preparations containing topoisomerase activity, anti-topoisomerase I antibodies were able to inhibit the DNA relaxing activity of the preparation as well as RNA synthesis in vitro. RNA polymerase II prepared by analogous procedures did not contain topoisomerase activity and was not recognized by the antibodies. The topoisomerase I: polymerase I complex was reversibly dissociated by column chromatography on Sephacryl S200 in the presence of 0.25 M (NH4)2SO4. Topoisomeras I was immunolocalized in the transcriptionally active ribosomal gene complex containing RNA polymerase I in situ. These data indicate that topoisomerase I and RNA polymerase I are tightly complexed both in vivo and in vitro, and suggest a role for DNA topoisomerase I in the transcription of ribosomal genes.