Die Rolle der Fimbrien bei der eigenartigen Sternbildung von Agrobacterium luteum

Zusammenfassung Die bemerkenswerte Sternbildung von Agrobacterium luteum Stamm A61 (Moll et al., 1967; Ahrens, 1968) ist auf polare Fimbrien zurückzuführen, die um die Sternaggregate ausgebreitet sind. Es wird angenommen, daß sich Schwärmzellen an den Fimbrien verfangen und durch Kontraktion rasch zum Stern gezogen werden. Nach elektronenoptischen Präparaten sind die Fimbrien bis zu 10,5 lang und können die beobachtete Sternbildung gut erklären. Agrobacterium luteum Stamm B14 besitzt ebenfalls lange polare Fimbrien. Beide Stämme tragen peritriche Geißeln, deren Struktur sich deutlich von den dünnen und unregelmäßigen Fimbrien unterscheidet.

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The function of fimbriae in the peculiar star formation of Agrobacterium luteum

Summary The remarkable way of star formation in Agrobacterium luteum strain A61 (Moll et al., 1967; Ahrens, 1968) was found to be due to polar fimbriae which are spread around the star-shaped aggregates. It is assumed that swarmers adhere to the fimbriae and, by contraction, are swiftly pulled towards the star. As seen in electron microscopic preparations, the fimbriae are up to 10,5 long and may well explain the star formation observed. Agrobacterium luteum strain B 14 also possesses long polar fimbriae. Both strains have peritrichous flagella, the structure of which being clearly distinct from the delicate and irregular fimbriae.

     

Inhibition of Swarming of Proteus by Sodium Tetradecyl Sulfate, β-Phenethyl Alcohol,and p-Nitrophenylglycerine

The effects of sodium tetradecyl sulfate (STS), β-phenethyl alcohol (PEA), and p-nitrophenylglycerol (PNPG) on motility, swarming, flagellation, and growth of Proteus were examined. Growth-inhibitory concentrations (GIC) and swarming-inhibitory concentrations (SIC) were determined. A characterization of the swarming-inhibitory efficacy of these compounds was based on their GIC/SIC ratio and their concentration inhibition curves. Using the homologous series of sodium alkyl sulfates as a standard reference, we showed that PNPG was more effective than STS, which was the most effective of the homologous series. PEA was less effective than sodium decyl sulfate but more effective than sodium octyl sulfate. Motility tests in liquid medium and electron microscope investigations indicated that the modes of action of the three compounds, all of which effectively inhibit the swarming of Proteus, are different. Whereas STS and PEA inhibit swarming by inhibition of motility, PNPG seems to act on the swarming mechanism sensu strictori, without impairment of motility. STS immobilizes by inhibition of flagellum formation or by some lytic action on the flagella already synthesized. PEA acts by impairing flagellar function, but leaves the flagella morphologically intact.     

Detection of Petunia Asteroid Mosaic, Carnation Ringspot and Tobacco Necrosis Viruses in Ditches and Drainage Canals in a Grapevine-Growing Area in West Germany

A number of virus isolates were obtained from ditches and drainage canals in the Palatinate grapevine-growing area (‘Rheinpfalz’) in West Germany. By means of the immunoelectron microscopical decoration and the agar gel double diffusion tests these isolates were identified as petunia asteroid mosaic virus, carnation ringspot virus and tobacco necrosis virus strain D, respectively.     

High affinity insulin binding and insulin receptor-effector coupling: modulation by Ca2+.

Insulin binding and insulin stimulated amino acid and glucose uptake were determined in cultured HTC hepatoma cells in the presence of Ca2+ and ruthenium red (RR) in order to further characterise the putative calcium binding site on the receptor. These ions increased insulin receptor high affinity binding and the sensitivity of these responses to insulin. The insulin concentration required to half-maximally stimulate amino acid uptake decreased significantly from 26.9 +/- 5.8 ng/ml to 6.0 +/- 1.3 ng/ml in the presence of 10 mM Ca2+ and to 1.3 +/- 0.5 ng/ml in the presence of RR. The effect of Ca2+ and RR was more pronounced on insulin stimulated glucose uptake. These agents also increased receptor-effector coupling, reducing the percentage of occupied receptors required for maximal insulin stimulation of amino acid uptake from 10.8% in control cells to 3.4 and 1.4% in the presence of Ca2+ and RR respectively. The receptor occupancy required to produce maximal insulin responses on glucose uptake decreased from 20% (control) to 3.8% (Ca2+ and RR). We hypothesize that since Ca2+ and RR have similar effects, that occupation of Ca2+ binding sites on the receptor produces a conformational change in the insulin receptor which increases insulin receptor affinity, insulin sensitivity and acts on an early post-receptor event responsible for coupling binding to insulin action.     

Adaptive surface antigen variation in Mycoplasma bovis to the host immune response

Abstract The variability of predominant Mycoplasma bovis surface antigens in the presence of specific immune pressure was analyzed in an in vitro assay to determine if M. bovis could escape immune destruction. We have shown that serum antibodies from immunized or experimentally infected calves and monoclonal antibodies which specifically react with previously characterized or as yet undefined major M. bovis membrane surface proteins cause repression of expression or shortening of the target protein, or induce switching to expression of an antigenically distinct variant protein. We have further demonstrated that removal of the inducing antibody results in reversion to the original phenotype. These results suggest that the level of expression and the length of M. bovis surface antigens in the host is modulated by cognate antibodies. According to the surface antigenic variation systems, random selection of preexisting variants resistant to antibody-mediated inhibition or direct regulation of gene expression may be means by which this organism evades host immune defences.     

Interaction between fatty-acid and starch synthesis in isolated amyloplasts from cauliflower floral buds

The interaction of fatty-acid synthesis with starch synthesis has been studied in intact amyloplasts isolated from floral buds of cauliflower (Brassica oleracea L.). These amyloplasts perform acetate-dependent fatty acid synthesis at maximum rates only at high external ATP concentrations. Neither pyruvate nor malate inhibit acetate-dependent fatty-acid synthesis. In contrast, acetate is inhibitory to the low pyruvate-dependent fatty acid synthesis. These observations indicate that neither pyruvate nor malate are used as natural precursors of fatty-acid synthesis. In contrast to fatty-acid synthesis, the rate of glucose-6-phosphate-dependent starch synthesis is already saturated in the presence of much lower ATP concentrations. Rising rates of starch synthesis influence negatively the process of acetate-dependent fatty acid synthesis. This inhibition appears to occur under both limiting and saturating concentrations of external ATP, indicating that the rate of ATP uptake is limiting when both biochemical pathways are active. The rate of starch synthesis is modulated specifically by the concentration of 3-phosphoglycerate in the incubation medium. This observation leads to the conclusion that the activity of ADP-glucose pyrophosphorylase is of primary importance for the control of both, starch and fatty-acid synthesis. Using the modified approach of Kacser and Burns (1973; Symp. Soc. Exp. Biol.27, 65–104) we have quantified the contribution of the rate of starch synthesis to the control of the metabolic flux through fatty-acid synthesis.Abbreviations ADPGlc-PPase ADPglucose pyrophosphorylase - Glc6P glucose-6-phosphate - PGA 3-phosphoglyceric acid     

Information about previous phosphate fluctuations is stored via an adaptive response of the high-affinity phosphate uptake system of the cyanobacterium Anacystis nidulans

The high-affinity uptake system of phosphatelimited cyanobacterium Anacystis nidulans [Synechococcus leopoliensis (Raciborski) Komarek] is characterized by a threshold value below which uptake cannot occur. Here it is shown that, if phosphate-limited cyanobacteria are challenged with a short pulse of high phosphate concentration that appreciably exceeds this threshold value, the uptake system undergoes an adaptive response, leading to the attainment of new kinetic properties and a new threshold value. These new properties are maintained for several hours after the pulse. A notable characteristic of this new state is a wide linear dependence of the uptake rate on the external phosphate potential that is a function of the driving force of the uptake process. According to theoretical arguments it is shown that this “linear operation mode” can be explained by the simultaneous operation of several uptake systems with different, staggered threshold values and kinetic properties. Moreover, the new linear uptake properties, in turn, reflect the prehistory of phosphate supply experienced by the population. The consequences of this result with regard to environmental fluctuations of the phosphate concentration in lakes are discussed.     

INFLUENCE OF FLUCTUATING PHOSPHATE SUPPLY ON THE REGULATION OF PHOSPHATE UPTAKE BY THE BLUE-GREEN ALGA ANACYSTZS NIDULANS1

The blue-green alga Anacystis nidulans Drouet (Synechococcus leopoliensis Raciborski) cultivated under phosphate-limited conditions adopts a threshold value in the nanomolar range below which uptake ceases. In this study, we investigated the influence of phosphate pulses on the regulation of uptake behavior during reestablishment of the threshold value. Short-term pulses had only a slight effect on uptake kinetics and, hence, on the threshold value, even if the population had been exposed several times to elevated concentrations above the steady-state level in the growth medium. The threshold value was also practically insensitive to the amount of phosphate stored during these short-term fluctuations. Long-term phosphate pulses resulted in a transition to a metastable state that was characterized by a severalfold higher threshold value. This transition, apparently an adaptation to the transiently elevated phosphate concentrations, was further studied by following the influx of ³²P-phosphate at constant external concentrations and was shown to be complete after a period of 10–20 min. After adaptation to pulses, the uptake behavior followed a linear flow-force relation over a wide range of external concentrations. This behavior was explained by the simultaneous operation of at least two uptake systems with different, but coordinated kinetic parameters. This linear flow-force relation facilitated a direct determination of the threshold value from uptake measurements. For applicability in the field the force-flow relation can be a diagnostic tool to assay for fluctuating phosphate and to establish threshold values below the normal measurable range .