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  • 1
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    German Medical Science GMS Publishing House; Düsseldorf
    In:  30. Jahrestagung der Retinologischen Gesellschaft; 20170623-20170624; Stuttgart; DOC17rg51 /20170622/
    Publication Date: 2017-06-22
    Keywords: ddc: 610
    Language: German
    Type: conferenceObject
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  • 2
    facet.materialart.
    facet.materialart.
    German Medical Science GMS Publishing House; Düsseldorf
    In:  30. Jahrestagung der Retinologischen Gesellschaft; 20170623-20170624; Stuttgart; DOC17rg49 /20170622/
    Publication Date: 2017-06-22
    Keywords: ddc: 610
    Language: German
    Type: conferenceObject
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  • 3
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Photobiological processes are relevant for microorganisms for energy generation, protection against excess and/or damaging radiation, and for signalling. In this review we give an overview of the knowledge on the functioning of photosensors in microorganisms, with special emphasis on the conformational changes that lead to signal generation and transduction. Light is absorbed by specific chromophores, which are tuned, by their proteinaceous environment, to function optimally. These chromophores belong to three classes: tetrapyrroles, polyenes and aromatics. The chemical structure of photosensing pigment/protein complexes has been resolved for many of the photobiological processes that have a characteristic sensitivity in the visible and infrared part of the spectrum of (solar) radiation. However, knowledge about the structure of photoreceptors responsible for several physiologically well-characterized photoresponses to UV- and blue light is still lacking. For a limited number of phototransduction processes, the details of light-induced signal transfer are beginning to be understood in atomic detail. This applies particularly to two photosensors involved in phototactic responses in bacteria: sensory rhodopsin I (SR-I) from Halobacterium salinarium and photoactive yellow protein (PYP) from Ectothiorhodospira halophila. The SR-I system is of special interest because the transducer accepting the signal from SR-I was recently identified as Htr-I, a homologue of the methyl-accepting chemotaxis proteins which have been characterized in Escherichia coli. PYP, on the other hand, may be the first photosensor to actually reveal all relevant details of the kinetics, thermodynamics, and molecular motion of light-induced signal generation, through an understanding of how the photo-isomerization of the chromophore forces the sensor protein into the signalling state. Here we compare these photosensors and discuss common themes in the initiation of photosensory signal transduction in microorganisms in terms of the molecular properties of photosensors and their signalling state.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The extracellular lipase from Acinetobacter calcoaceticus BD413 was purified to homogeneity, via hydrophobic-interaction fast performance liquid chromatography (FPLC), from cultures grown in mineral medium with hexadecane as the sole carbon source. The enzyme has an apparent molecular mass of 32 kDa on SDS-polyacrylamide gels and hydrolyses long acyl chain p-nitrophenol (pNP) esters, like pNP palmitate (pNPP), with optimal activity between pH 7.8 and 8.8. Additionally, the enzyme shows activity towards triglycerides such as olive oil and tributyrin and towards egg-yolk emulsions. The N-terminal amino acid sequence of the mature protein was determined, and via reverse genetics the structural lipase gene was cloned from a gene library of A. calcoaceticus DNA in Escherichia coli phage M13. Sequence analysis of a 2.1 kb chromosomal DNA fragment revealed one complete open reading frame, lipA, encoding a mature protein with a predicted molecular mass of 32.1 kDa. This protein shows high similarity to known lipases, especially Pseudomonas lipases, that are exported in a two-step secretion mechanism and require a lipase-specific chaperone. The identification of an export signai sequence at the N-terminus of the mature lipase suggests that the lipase of Acinetobacter is also exported via a two-step translocation mechanism. However, no chaperone-encoding gene was found downstream of lipA, unlike the situation in Pseudomonas. Analysis of an A. calcoaceticus mutant showing reduced lipase production revealed that a periplasmic disutphide oxidoreductase is involved in processing of the lipase. Via sequence alignments, based upon the crystal structure of the closely related Pseudomonas glumae lipase, a model has been made of the secondary-structure elements in AcLipA. The active site serine of AcLipA was changed to an alanine, via site-directed mutagenesis, resulting in production of an inactive extracellular lipase.
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  • 5
    ISSN: 1432-072X
    Keywords: Key words     DNA uptake ; Growth phase ; Dilution rate ; fis Promoter ; Stringent promoter ; Nutrient upshift ; Growth cessation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract       Acinetobacter calcoaceticus induced competence for natural transformation maximally after dilution of a stationary culture into fresh medium. Competence was gradually lost during prolonged exponential growth and after entrance into the stationary state. Growth cessation and nutrient upshift were involved in the induction of competence. The level of competence of a chemostat culture of A. calcoaceticus was dependent on the nature of the growth limitation. Under potassium limitation a transformation frequency of ± 1 × 10–4 was obtained. This frequency was independent of the specific growth rate. In phosphate-, nitrogen-, and carbon-limited chemostat cultures, in contrast, the transformation frequency depended on the specific growth rate; the transformation frequency equalled ± 10–4 at dilution rates close to μmax of 0.6 h–1 and decreased to ± 10–7 at a dilution rate of 0.1 h–1. We conclude that (1) DNA uptake for natural transformation in A. calcoaceticus does not serve a nutrient function and (2) competence induction is regulated via a promoter(s) that resembles the fis promoter from Escherichia coli.
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  • 6
    ISSN: 1432-072X
    Keywords: Potassium transport ; High-affinity transport system ; Kdp-ike potassium ATPase ; Expression ; Immunological cross-reactivity ; Internal pH regulation ; Photosynthetic bacteria (Rhodobacter sphaeroides, Rhodobacter capsulatus and Rhodospirillum rubrum)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cells of the purple non-sulphur bacterium Rhodobacter sphaeroides express a high-affinity K+ uptake system when grown in media with low K+ concentrations. Antibodies againts the catalytic KdpB protein or the whole KdpABC complex of Escherichia coli crossreact with a 70.0 kDa R. sphaeroides protein that was expressed only in cells grown in media with low K+ concentrations. In membranes derived from R. sphaeroides cells grown with low K+ concentrations (induced cells), a high ATPase activity could be detected when assayed in Tris-HCl pH 8.0 containing 1 mM MgSO4. This ATPase activity increased upon addition of 1 mM KCl from 166 to 289 μmol ATP hydrolysed x min-1 x g protein-1 (1.7-fold stimulation). The K+-stimulated ATPase activity was inhibited approximately 93% by 0.5 mM vanadate but hardly by N,N′-dicyclohexylcarbo-diimide (DCCD). These results indicate that the inducible K+-ATPase in R. sphaeroides resembles the Kdp K+-translocating ATPase of Escherichia coli. This Kdp-like transport system is also expressed in R. capsulatus and Rhodospirillum rubrum during growth in media with low K+ concentrations suggesting a wide distribution of this transport system among phototrophic bacteria.
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  • 7
    ISSN: 1432-072X
    Keywords: DNA uptake ; Growth phase ; Dilution rate fis Promoter ; Stringent promoter ; Nutrient upshift ; Growth cessation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Acinetobacter calcoaceticus induced competence for natural transformation maximally after dilution of a stationary culture into fresh medium. Competence was gradually lost during prolonged exponential growth and after entrance into the stationary state. Growth cessation and nutrient upshift were involved in the induction of competence. The level of competence of a chemostat culture of A. calcoaceticus was dependent on the nature of the growth limitation. Under potassium limitation a transformation frequency of ±1x10-4 was obtained. This frequency was independent of the specific growth rate. In phosphate-, nitrogen-, and carbon-limited chemostat cultures, in contrast, the transformation frequency depended on the specific growth rate; the transformation frequency equalled±10-4 at dilution rates close to µmax of 0.6h-1 and decreased to ±10-7 at a dilution rate of 0.1 h-1. We conclude that (1) DNA uptake for natural transformation in A. calcoaceticus does not serve a nutrient function and (2) competence induction is regulated via a promoter(s) that resembles the fis promoter from Escherichia coli.
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  • 8
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The stability of several pBR322-derived recombinant plasmids, carrying thethr operon fromEscherichia coli, was investigated in sulfur-limited chemostat cultures ofE. coli GT123. A marked increase in the segregational stability of one of these plasmids was observed. It is concluded that the increased stability was due to the spontaneous insertion of Tn1000 from the chromosome of the host into the plasmid.
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  • 9
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A transformation assay was used to assay the amount of DNA present in the extracellular medium of a growing culture of Acinetobacter calcoaceticus. It was observed that small amounts of DNA were liberated during the entire exponential growth phase in a batch culture. Release of DNA could be fully accounted for by lysis of cells. Lysis was quantified via simultaneous measurement of β-galactosidase activity of cells and supernatant, with a strain that contained a plasmid (pAPA100) with lacZ under control of a constitutive β-lactamase promoter. In conclusion, no evidence could be obtained indicating that Acinetobacter calcoaceticus actively excretes DNA, to be used for DNA exchange.
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  • 10
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
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