Showing papers by "University of Konstanz published in 1991"

Identification of a central regulator of stationary‐phase gene expression in Escherichia coli

Abstract: During carbon-starvation-induced entry into stationary phase, Escherichia coli cells exhibit a variety of physiological and morphological changes that ensure survival during periods of prolonged starvation. Induction of 30-50 proteins of mostly unknown function has been shown under these conditions. In an attempt to identify C-starvation-regulated genes we isolated and characterized chromosomal C-starvation-induced csi::lacZ fusions using the lambda placMu system. One operon fusion (csi2::lacZ) has been studied in detail. csi2::lacZ was induced during transition from exponential to stationary phase and was negatively regulated by cAMP. It was mapped at 59 min on the E. coli chromosome and conferred a pleiotropic phenotype. As demonstrated by two-dimensional gel electrophoresis, cells carrying csi2::lacZ did not synthesize at least 16 proteins present in an isogenic csi2+ strain. Cells containing csi2::lacZ or csi2::Tn10 did not produce glycogen, did not develop thermotolerance and H2O2 resistance, and did not induce a stationary-phase-specific acidic phosphatase (AppA) as well as another csi fusion (csi5::lacZ). Moreover, they died off much more rapidly than wild-type cells during prolonged starvation. We conclude that csi2::lacZ defines a regulatory gene of central importanc e for stationary phase E. coli cells. These results and the cloning of the wild-type gene corresponding to csi2 demonstrated that the csi2 locus is allelic with the previously identified regulatory genes katF and appR. The katF sequence indicated that its gene product is a novel sigma factor supposed to regulate expression of catalase HPII and exonuclease III (Mulvey and Loewen, 1989). We suggest that this novel sigma subunit of RNA polymerase defined by csi2/katF/appR is a central early regulator of a large starvation/stationary phase regulon in E. coli and propose 'rpoS' ('sigma S') as appropriate designations.

Young’s double-slit experiment with atoms: a simple atom interferometer

Abstract: An atomic interferometer based on a Young's-type double-slit arrangement has been demonstrated. A supersonic beam of metastable helium atoms passes through a 2-\ensuremath{\mu}m-wide slit in a thin gold foil. This transversely coherent beam impinges on a second microfabricated transmission structure, consisting of two 1-\ensuremath{\mu}m-wide slits at a lateral distance of 8 \ensuremath{\mu}m. This double slit defines two possible paths on which the atoms can reach the detector slit. The good visibility of the observed fringes should make it possible to measure differential phase shifts in the interferometer of 1/3 rad in less than 10 min.

Transitive inference formation in pigeons.

Abstract: Pigeons were trained with 4 pairs of visual stimuli in a 5-term series―A+ B−, B+C, C+D→, and D+ E− (in which plus [+] denotes reward and minus [−] denotes nonreward)―before the unreinforced test pair B D was presented. All pigeons chose Item B, demonstrating inferential choice. A novel theory (value transfer theory), based on reinforcement mechanisms, is proposed. In experiment 2, the series was extended to 7 terms

Growth phase-regulated expression of bolA and morphology of stationary-phase Escherichia coli cells are controlled by the novel sigma factor sigma S.

Abstract: The novel sigma factor (sigma S) encoded by rpoS (katF) is required for induction of many growth phase-regulated genes and expression of a variety of stationary-phase phenotypes in Escherichia coli. Here we demonstrate that wild-type cells exhibit spherical morphology in stationary phase, whereas rpoS mutant cells remain rod shaped and are generally larger. Size reduction of E. coli cells along the growth curve is a continuous and at least biphasic process, the second phase of which is absent in rpoS-deficient cells and correlates with induction of the morphogene bolA in wild-type cells. Stationary-phase induction of bolA is dependent on sigma S. The "gearbox" a characteristic sequence motif present in the sigma S-dependent growth phase- and growth rate-regulated bolAp1 promoter, is not recognized by sigma S, since stationary-phase induction of the mcbA promoter, which also contains a gearbox, does not require sigma S, and other sigma S-controlled promoters do not contain gearboxes. However, good homology to the potential -35 and -10 consensus sequences for sigma S regulation is found in the bolAp1 promoter.

Trehalose synthesis genes are controlled by the putative sigma factor encoded by rpoS and are involved in stationary-phase thermotolerance in Escherichia coli.

Abstract: The rpoS (katF) gene of Escherichia coli encodes a putative sigma factor (sigma S) required for the expression of a variety of stationary phase-induced genes, for the development of stationary-phase stress resistance, and for long-term starvation survival (R. Lange and R. Hengge-Aronis, Mol. Microbiol. 5:49-59, 1991). Here we show that the genes otsA, otsB, treA, and osmB, previously known to be osmotically regulated, are also induced during transition into stationary phase in a sigma S-dependent manner. otsA and otsB, which encode trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase, respectively, are involved in sigma S-dependent stationary-phase thermotolerance. Neither sigma S nor trehalose, however, is required for the development of adaptive thermotolerance in growing cells, which might be controlled by sigma E.

Methane oxidation in the soil surface layer of a flooded rice field and the effect of ammonium

Abstract: The CH4 flux from intact soil cores of a flooded rice field in Italy was measured under aerobic and anaerobic incubation conditions. The difference between the anaerobic and aerobic CH4 fluxes was apparently due to CH4 oxidation in the oxic soil surface layer. This conclusion was supported by measurements of the vertical CH4 profile in the upper 2-cm layer, and of the V max of CH4 oxidation in slurried samples of the soil surface layer. About 80% of the CH4 was oxidized during its passage through the soil surface layer. CH4 oxidation was apparently limited by the concentration of CH4 and/or O2 in the active surface layer. The addition of ammonium to the water layer on top of the soil core reversibly increased the aerobic CH4 fluxes due to inhibition of CH4 oxidation in the soil surface layer.

A hierarchically constrained kinetic Ising model

Abstract: A concrete model for hierarchically constrained dynamics in the sense proposed by Palmer et al. (Phys. Rev. Lett.53, 958 (1984)) is presented. The model is a kinetic Ising chain with an asymmetric kinetic constraint, allowing a spin to flip only if its neighbour to the right is in the up spin state. The spin autocorrelation function is obtained by numerically exact calculation for finite chain length up toL=9 and by Monte Carlo simulation for effectively infinite chain length. The Kohlrausch-Williams-Watts formula is found to fit the results only with limited accuracy, and within limited time intervals. We also performed an analytical calculation using an effective-medium approximation. The approximation leads to a spurious blocking transition at a critical up spin concentrationc=0.5.

Use of prior knowledge in brain electromagnetic source analysis.

Abstract: Using multichannel measurements of EEG and/or MEG, macroscopic source activities can be estimated in the human brain using brain electric source analysis (BESA, Scherg 1990). If a discrete number of brain areas is active, functional brain images which depict the locations and orientations of equivalent dipole sources as well as the dynamics of the local macroscopic currents can be obtained from such data - in principle -without external knowledge. However, given a certain number of sources or ‘neural masses’ (Freeman 1975) which contribute to an event related response (ERP), it can be difficult to find the correct solution due to background noise in the data and distortions from the head model. Prior knowledge based on anatomy and physiology can be useful to constrain spatial or temporal parameters of the model and to define better cost functions for fitting locations and orientations. An analysis of the auditory evoked N100 complex and of the auditory mismatch negativity (MMN) is presented which illustrates the use of spatial constraints. Also, the use of a modified cost function is demonstrated which limits source currents in certain time intervals.

Non-Debye relaxation in structurally disordered ionic conductors: Effect of Coulomb interaction.

Abstract: We perform Monte Carlo simulations for diffusion of charged particles in structurally disorderd lattices. As a consequence of the Coulomb interaction, pronounced backward correlations occur which lead to power-law behavior of the relevant transport quantities at intermediate time and frequency scales. Both the exponents and the size of the dispersive regime depend on temperature. Our simulations suggest that the combined effect of disorder and Coulomb interaction provides a new mechanism for understanding non-Debye relaxation, which is experimentally known for a wide class of materials.

Evolution of the MIP family of integral membrane transport proteins.

Abstract: Six integral membrane proteins of bacterial, animal, and plant origin, which are believed to function in solute transport, share sequence identity and are grouped together as members of the MIP family. These include the Escherichia coli glycerol facilitator, the major intrinsic protein from bovine lens fibre junction membranes, a plant tonoplast membrane protein, a soybean protein from the peribacteroid membrane, and a Drosophila neurogenic protein. These proteins, each of which appears to consist of six transmembrane helical segments per subunit, apparently arose by internal duplication of a three-transmembrane segment. Phylogenetic 'trees' interrelating these proteins and segments are presented.

Uncovering Culture in Organizations

Abstract: There is a large interest in organization culture, yet only a few empirical studies address the topic. This fact may be due to the lack of appropriate research methods able to uncover such an elusi...

Comparative anatomy of pigment-dispersing hormone-immunoreactive neurons in the brain of orthopteroid insects

Abstract: In a comparative study, the anatomy of neurons immunoreactive with an antiserum against the crustacean β-pigment-dispersing hormone was investigated in the brain of several orthopteroid insects including locusts, crickets, a cockroach, and a phasmid. In all species studied, three groups of neurons with somata in the optic lobes show pigment-dispersing hormone-like immunoreactivity. Additionally, in most species, the tritocerebrum exhibits weak immunoreactive staining originating from ascending fibers, tritocerebral cells, or neurons in the inferior protocerebrum. Two of the three cell groups in the optic lobe have somata at the dorsal and ventral posterior edge of the lamina. These neurons have dense ramifications in the lamina with processes extending into the first optic chiasma and into distal layers of the medulla. Pigment-dispersing hormone-immunoreactive neurons of the third group have somata near the anterior proximal margin of the medulla. These neurons were reconstructed in Schistocerca gregaria, Locusta migratoria, Teleogryllus commodus, Periplaneta americana, and Extatosoma tiaratum. The neurons have wide and divergent arborizations in the medulla, in the lamina, and in several regions of the midbrain, including the superior and inferior lateral protocerebrum and areas between the pedunculi and α-lobes of the mushroom bodies. Species-specific differences were found in this third cell group with regard to the number of immunoreactive cells, midbrain arborizations, and contralateral projections, which are especially prominent in the cockroach and virtually absent in crickets. The unusual branching patterns and the special neurochemical phenotype suggest a particular physiological role of these neurons. Their possible function as circadian pacemakers is discussed.

Dipole modelling of eye activity and its application to the removal of eye artefacts from the EEG and MEG.

Abstract: The spatio-temporal dipole model approach has been used to identify the difference dipoles arising from changes in the ocular dipoles due to eye movements and blinks. Based on these results a method has been developed to remove eye artefacts from electrical or magnetic data. The method avoids distortions due to the head model by determining the spatial distribution of the signals from the eyes empirically. Using simultaneous modelling of the EEG or MEG activity with dipole sources distributed within the head together with the empirically determined spatial eye components, the eye activity can be estimated and removed from the EEG or MEG. This greatly reduces the distortion to the topography that is a concomitant of previous eye artefact correction methods. The advantages of the method are illustrated using simulated and real electrical data.

The spin-correlated radical pair as a reaction intermediate

Abstract: The concept of the spin-correlated radical pair has been used for some time in the interpretation of the results of magnetic polarization experiments in NMR and in ESR (CIDNP and CIDEP), and of the...

Imaging and focusing of atoms by a fresnel zone plate.

Abstract: Focusing of and imaging with atoms by means of a spherical Fresnel zone plate has been observed for the first time. An intense beam of metastable helium atoms with atomic de Broglie wavelength ${\ensuremath{\lambda}}_{\mathrm{dB}}$=0.5--2.5 \AA{} is passed through either a single or a double slip with dimensions in the 10-\ensuremath{\mu}m range. This transverse intensity distribution is imaged by a Fresnel zone plate, 210 \ensuremath{\mu}m in diameter and with an innermost zone diameter of 18.76 \ensuremath{\mu}m. For ${\ensuremath{\lambda}}_{\mathrm{dB}}$=1.96 \AA{} the focal length is 0.45 m. The imaging properties of the zone plate are presented and compared with numerical calculations.

The time course and frequency content of hydrodynamic events caused by moving fish, frogs, and crustaceans.

Abstract: In the present study the time course and spectral-amplitude distribution of hydrodynamic flow fields caused by moving fish, frogs, and crustaceans were investigated with the aid of laser-Doppler-anemometry. In the vicinity of a hovering fish sinusoidal water movements can be recorded whose velocity spectra peak below 10 Hz (Fig. 2). Single strokes during startle responses or during steady swimming of fish, frogs, and crustaceans cause short-lasting, low-frequency (<10 Hz), transient water movements (Fig. 3). Low-frequency transients also occur if a frog approaches and passes a velocity-sensitive hydrodynamic sensor. In contrast, transient water movements caused by a rapidly struggling or startled fish or water motions measured in the wake of a slowly swimming (≤47 cm/s) trout can be broadbanded, i.e., these water movements can contain frequency components up to at least 100 Hz (Figs. 4, 5A, 6). High-frequency hydrodynamic events can also be measured behind obstacles submerged in running water (Fig. 5C). The possible biological advantage of the ability to detect high-frequency hydroynamic events is discussed with respect to the natural occurrence of high frequencies and its potential role in orientation and predator-prey interactions of aquatic animals.

Seasonal succession of ciliates in lake constance

Abstract: We found a recurrent seasonal pattern in abundance and composition of planktonic ciliates in Lake Constance, FRG, over a three-year period. Abundance peaks occurred in early spring and summer/autumn, while ciliate numbers were low in late spring (clear-water phase) and winter. Prostomatida and Oligotrichida dominated in early spring. They responded immediately to the phytoplankton spring bloom, while Haptorida, Peritrichida, and large Scuticociliatida (Histiobalantium) were delayed by 1 to 2 weeks. The spring community broke down at the onset of the clear-water phase.Pelagohalteria viridis containing symbiontic algae appeared shortly after this event. A highly diverse community was recorded in summer/autumn. Peritrichida, small Oligotrichida, and large Scuticociliatida reached their maxima during this season. Small Scuticociliatida were rare throughout the year and contributed moderately to total ciliate numbers only during the cold season. The observed seasonal sequence of pelagic ciliates in Lake Constance is discussed in relation to simultaneously collected data on potential food organisms and grazers.

The nature of culture

Abstract: Niko Tinbergen laid great stress on the essential importance of cultural evolution for the understanding of human behaviour although he never, of course, made it a central subject of his research interests. In a short cautionary note about the future of humanity he wrote for example that ‘our unique position in the modern world is due to the consequences of our cultural evolution, which … has … progressively … superimposed (itself) on our still ongoing genetic evolution’ and that ‘we transfer …, from one generation to the next, not only our genetic heritage but also (our) accumulated non-genetically acquired … experience’ (Tinbergen, 1977, see also Tinbergen, 1976). Niko’s insights into the details of the processes of cultural evolution went much further than his writings reflect, however. A casual but memorable conversation between him and Konrad Lorenz in Stuttgart, Germany in 1959, at which I happened to be present, revealed that clearly. The role of song behaviour as a species-isolating mechanism in some sympatric birds had somehow cropped up. They were considering the selective forces that might have shaped the divergence of song patterns in such situations when Niko raised the important question: Selection of what? Surely not genes since the song of these birds was likely to be learned, not innate.

Characterization of a dense, purple sulfur bacterial layer in a meromictic salt lake

Abstract: In meromictic Mahoney Lake (British Columbia), purple sulfur bacteria formed a dense, IO-cm-thick layer at the primary chemocline. The dominant species (Amoebobucterpurpureus) reached a maximal cell concentration of 4 x lOa cells ml-l, 274/o of which were viable. A maximal concentration of 20,900 pg bacteriochlorophyll n liter’ was determinedthe highest concentration ever found in a natural body of water. Steep vertical gradients of conductivity, light, and sulfide concentration were detected across the bacterial layer, while the concentration of oxygen increased above it. Integrated primary production of the layer was 15 mg C m-2 h-l. Bacteriochlorophyllspecific assimilation rates reached maxima at the top of the layer. Anoxygenic photosynthesis was limited by reduced sulfur compounds at the top of the layer, whereas strong attenuation of irradiance resulted in light limitation for most of the cell population below. The sulfide flux from below the layer accounted for 63% of the sulfide oxidized during anoxygenic photosynthesis must have been produced within the layer. This calculation agrees well with sulfide production rates measured in situ (12.4 pm01 liter-’ h--l). In contrast to other lakes, considerable uptake of [14C]acetate by purple sulfur bacteria and comparatively high numbers of purple nonsulfur bacteria indicate an important role of dissolved organic matter and a short cycle of carbon and redox compounds in the dense purple microbial layer.

Metabolism of position-labelled glucose in anoxic methanogenic paddy soil and lake sediment

Abstract: Turnover times of radioactive glucose were shorter in paddy soil (4–16 min) than in Lake Constance sediment (18–62 min). In the paddy soil, 65–75% of the radioactive glucose was converted to soluble metabolites. In the sediment, only about 25% of the radioactive glucose was converted to soluble metabolites, the rest to particulate material. In anoxic paddy soil, the degradation pattern of position-labelled glucose was largely consistent with glucose degradation via the Embden-Meyerhof-Parnas (EMP) pathway followed by methanogenic acetate cleavage: CO2 mainly originated from C-3,4, whereas CH4 mainly originated from C-1 and C-6 of glucose. Acetate-carbon originated from C-1, C-2 and C-6 rather than from C-3,4 of glucose. In both paddy soil and Lake Constance sediment acetate and CO2 were the most important early metabolites of radioactive glucose. Other early products included propionate, ethanol/butyrate, succinate, and lactate, but accounted each for less than 1–8% of the glucose utilized. The labelling of propionate by [3,4-14C]glucose suggests that it was mainly produced from glucose or lactate rather than from ethanol. Isopropanol and caproate were also detectable in paddy soil, but were not produced from radioactive glucose. Chloroform inhibited methanogenesis, inhibited the further degradation of radioactive acetate and resulted in the accumulation of H2, however, did not inhibit glucose degradation. Since acetate was the main soluble fermentation product of glucose and was produced at a relatively high molar acetate: CO2 ratio (2.5:1), homoacetogenesis appeared to be the most important glucose fermentation pathway.

The activities of the Escherichia coli MalK protein in maltose transport, regulation, and inducer exclusion can be separated by mutations.

Abstract: The maltose regulon consists of several genes encoding proteins involved in the uptake and utilization of maltose and maltodextrins. Five proteins make up a periplasmic binding-protein-dependent active transport system. One of these proteins, MalK, contains an ATP-binding site and is thought to couple the hydrolysis of ATP to the accumulation of substrate. Beside its function in transport, MalK has two additional roles: (i) it negatively regulates mal regulon expression and (ii) it serves as the target for regulation of transport activity by enzyme IIIGlc of the phosphotransferase system. To determine whether the three functions of MalK are separable, we have isolated and characterized three classes of malK mutations. The first type (class I) exhibited constitutive mal gene expression but still allowed normal transport of maltose; the second type (class II) lacked the ability to transport maltose but retained the ability to repress the mal genes. Class I mutations were localized in the last third of the gene, at amino acids 267 (Trp to Gly) and 346 (Gly to Ser). Mutations of class II were found at the positions 137 (Gly to Ala), 140 (delta Gln Arg), and 158 (Asp to Asn). These mutations are near or within the region of MalK that exhibits extensive homology to the B site of an ATP-binding fold. In addition, site-directed mutagenesis was used to add or remove one amino acid in the A site of the ATP-binding fold. Plasmids carrying these mutations also behaved as class II mutants. The third class of malK mutations resulted in resistance to the enzyme IIIGlc-mediated inhibitory effects of alpha-methylglucoside. These mutations did not interfere with the regulatory function of MalK. One of these mutations (exchanging a serine at position 282 for leucine) is located in a short stretch of amino acids that exhibits homology to a sequence in the Escherichia coli Lac permease in which alpha-methylglucoside-resistant mutations have been found.

Quenched flow analysis of exocytosis in Paramecium cells: time course, changes in membrane structure, and calcium requirements revealed after rapid mixing and rapid freezing of intact cells.

Abstract: Synchronous exocytosis in Paramecium cells was analyzed on a subsecond time scale. For this purpose we developed a quenched flow device for rapid mixing and rapid freezing of cells without impairment (time resolution in the millisecond range, dead time approximately 30 ms). Cells frozen at defined times after stimulation with the noncytotoxic secretagogue aminoethyldextran were processed by freeze substitution for electron microscopic analysis. With ultrathin sections the time required for complete extrusion of secretory contents was determined to be less than 80 ms. Using freeze-fracture replicas the time required for resealing of the fused membranes was found to be less than 350 ms. During membrane fusion (visible 30 ms after stimulation) specific intramembranous particles in the cell membrane at the attachment sites of secretory organelles ("fusion rosette") disappear, possibly by dissociation of formerly oligomeric proteins. This hitherto unknown type of rapid change in membrane architecture may reflect molecular changes in protein-protein or protein-lipid interactions, presumably crucial for membrane fusion. By a modification of the quenched flow procedure extracellular [Ca++] during stimulation was adjusted to less than or equal to 3 x 10(-8) M, i.e., below intracellular [Ca++]. Only extrusion of the secretory contents, but not membrane fusion, was inhibited. Thus it was possible to separate both secretory events (membrane fusion from contents extrusion) and to discriminate their Ca++ requirements. We conclude that no Ca++ influx is necessary for induction of membrane fusion.

The processing of temporal intervals reflected by CNV-like brain potentials.

Abstract: The present study employed event-related potentials (ERPs) of the brain to improve the understanding of temporal processing. A reproduction paradigm was realized by presenting a visual stimulus (illuminated screen) for intervals of varying length. A few seconds after presentation of such standard intervals the visual stimulus was switched on again and subjects were asked to reproduce the duration of the standard interval by turning off the illumination after a corresponding interval had elapsed. The length of standard intervals varied randomly with each of the following lengths being presented 20 times: 1, 2, 3, 4, 6, and 8 s. Reproduction was accurate for standard intervals up to 3 s but deteriorated with increasing interval length. Brain potentials during reproduction intervals of 1–3 s differed from those recorded during the longer intervals. A CNV-like slow negative shift developed during the shorter reproduction intervals. Negativity was reduced or even absent, when subjects had to reproduce standard intervals of 4 s or longer. The ERP results suggest that intervals shorter than 3–4 s may evoke a processing mode that is qualitatively different from the one dominating when periods in the range of several seconds have to be processed.