Relationships among the streptothricin resistance transposons Tn1825 and Tn1826 and the trimethoprim resistance transposon Tn7

The streptothricin resistance transposons Tn1825 and Tn1826 are closely related, based on physical and genetic characteristics, to the trimethoprim resistance transposon Tn7. These transposons may be considered to be members of a transposon family sharing in common the transposition functions and a basic streptomycin/spectinomycin resistance determinant but differing from one another with respect to particular additional resistance genes inserted to the left of the aadA gene.     

Fluorescence characteristics of cyanobacteria (blue-green algae)

The fluorescence characteristics of the cyanobacteria Synechocystisaquatilis Sauv., Microcystis firma (Breb. et Lenorm.) Schmidleand Synechococcus leopoliensis (Racib.) Kom. and the green algaScenedesmus quadricauda (Turp.) Breb. were examined. In thethree cyanobacteria, phycocyanin is the main accessory pigment.Phycoerythrin is not present in our investigated strains ofcyanobacteria. The highest excitation of the chlorophyll a (Chla) fluorescence of cyanobacteria resulted from light with wavelengthsof 620–630 nm. A definite ‘Kautsky’ effectis also evident at this wavelength. However, excitation withblue light (420–520 nm) produced only very slight fluorescence.The Kautsky effect is not evident at these wavelengths, evenat high photon flux densities. For Scenedesmus, fluorescencecharacteristics typical of green algae were found. The fluorescenceexcitation of cyanobacteria at 620 nm corresponds to a photosynthesispeak in the action spectrum measured in terms of O₂ production.The results underline the necessity of fluorescence measurementsat several wavelengths whenever mixed populations are involved.Such measurements also present possibilities for more accurateestimation of biomass and potential photosynthetic productionin mixed populations.     

A new cell wall structure in a symbiotic and a free-living strain of the blue-green alga genus Chroococcidiopsis (Pleurocapsales)

Freeze etching studies in a symbiotic and a freeliving strain of Chroococcidiopsis revealed a specific layer in the outer cell wall not described so far from Cyanophyta. The layer showed a complex organisation: The main unit are ribbons, 2–3 nm thick, striated at right angle to the longitudinal axis. They are interwoven to a patchwork-like leaflet. The ribbons are virtually composed of globular particles associated in parallel rows. The cytoplasmic membrane and the cell walls of the symbiotic and the free-living strain were compared.Abbreviations cm cytoplasmic membrane - CW 1,2,3 cell wall layer 1,2,3 - EF exoplasmic fracture face - PF protoplasmic fracture face     

Untersuchungen über die Insulinmikromelie am Hühnerembryo

Ohne ZusammenfassungDie Arbeit wurde auf Anregung von Herrn Prof. Dr. H.Wurmbach ausgeführt. Ich danke ihm für die freundliche Förderung der Arbeit, sowie Herrn Prof. Dr. A.Goebel, Pathol. Inst. d. Univ. Köln, für wertvolle Hinweise. Die Untersuchungen wurden von derDeutschen Forschungsgemeinschaft, Bad Godesberg, gefördert.     

The osmoprotectant proline betaine is a major substrate for the binding-protein-dependent transport system ProU of Escherichia coli K-12

The ProP and ProU transport systems of Escherichia coli mediate the uptake of several osmoprotectants including glycine betaine. Here we report that both ProP and ProU are involved in the transport of the potent osmoprotectant proline betaine. A set of isogenic E. coli strains carrying deletions in either the proP or proU loci was constructed. The growth properties of these mutants in high osmolarity minimal media containing 1 mM proline betaine demonstrated that the osmoprotective effect of this compound was dependent on either an intact ProP or ProU uptake system. Proline betaine competes with glycine betaine for binding to the proU-encoded periplasmic substrate binding protein (ProX) and we estimate a K_D of 5.2 μM for proline betaine binding. This value is similar to the binding constant of the ProX protein determined previously for the binding of glycine betaine (K_D of 1.4 μM). Our results thus demonstrate that the binding-protein-dependent ProU transport system of E. coli mediates the efficient uptake of the osmoprotectants glycine betaine and proline betaine.     

Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU

Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Fscherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K⁺ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K⁺-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K⁺-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K⁺ ions with compounds that are less d eleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.