Prophage-mediated modulation of interaction of Streptococcus thermophilus J34 with human intestinal epithelial cells and its competition against human pathogens.

The human intestinal microbiota plays an important role in human health. While adhesion to gastrointestinal mucosa is a prerequisite for colonisation, inhibition of adhesion is a property which may prevent or reduce infections by food borne pathogens. Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus represent the two lactic bacteria constituting the yoghurt culture. These starter cultures have been claimed to be probiotic. In our study we compared two S. thermophilus strains (i.e. lysogenic strain J34 and corresponding non-lysogenic [prophage-cured] strain J34-6), with respect to (1) their in vitro adhesion properties to HT29 cells and (2) their cell surface hydrophobicities. Effects of the two strains on inhibition of adhesion of the pathogens Listeria monocytogenes Scott A, Staphylococcus aureus 6732 and Salmonella enteritidis S489 were studied in vitro with HT29 cell cultures. Lysogenic strain J34 was shown to be considerably more effective than the non-lysogenic derivative strain J34-6.

Acridizinium salts as a novel class of DNA-binding and site-selective DNA-photodamaging chromophores.

It was demonstrated that the interaction of the aminoacridizinium salts 2a-2d with DNA depends on the substitution pattern of the chromophore. Spectrophotometric and fluorometric titrations of the acridizinium salts 2a-2d with natural and synthetic polynucleotides reveal that the degree of interaction of the acridizinium salts 2a-2d with the nucleic acid differs significantly. The binding mode of the dyes with DNA was evaluated by circular dichroism and linear dichroism spectroscopy and compared with the parent system 2c. Whereas the 9-aminoacridizinium (2a) mainly intercalates into DNA, the salts 2b-c show a higher degree of association to the DNA backbone. The intercalated aminoacridizinium 2a caused few strand breaks upon UVA exposure, whereas the salts 2b-2d exhibit relatively efficient DNA-damaging properties. All acridizinium salts showed a sequence-selective strand cleavage for guanine-rich DNA regions.

Studies on single-strand scissions to cell-free plasmid DNA by the dopaminergic neurotoxin 'TaClo' (1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline).

The DNA-damaging effect of the potent dopaminergic neurotoxin 'TaClo' (1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline) is reported. After irradiation (300 nm, 350 nm) of cell-free pBR322 DNA in the presence of TaClo, single-strand breaks were observed by gel electrophoresis. It seems likely that TaClo undergoes a light-induced formation of reactive species (probably radicals). In comparison with TaClo, the bromo derivative exhibits an increased toxic action while the fluoro derivative shows a weaker effect towards DNA. In the presence of Cu(II) at 37 degrees C in the dark, DNA strand scissions were found to occur, too. The formation of Cu(I), as detected by UV-absorption at 480 nm using the Cu(I) complexing ligand BCS, hints at the formation of a reactive species by a Cu(II)/Cu(I) mediated redox cycle. Until now, the chemical nature of this reactive species has not been elucidated.

New dyes based on amino-substituted acridizinium salts--synthesis and exceptional photochemical properties

The novel amino-substituted acridizinium salts 5a and 5b represent a new class of cyanine dyes which exhibit intense color along with efficient fluorescence properties. These dyes show moderate solvatochromism in their absorption and emission spectra. The absorption and emission shifts of the two chromophores display a reasonable correlation with solvent parameters such as donor and acceptor number. It was found that the dyes 5a and 5b interact with DNA, with quenching of the band intensies accompanied with a red shift of the absorption and emission bands. Moreover, irradiation of salts 5a and 5b in the presence of DNA results in DNA damage. Solution photolysis of acridizinium salt 5a gave the head-to-tail dimers as the major products (>95%), whereas the acridizinium salt 5b afforded the anti-head-to-tail dimer along with both head-to-head isomers. The latter are thermally labile and rapidly revert to the monomer.

Nonequilibrium ion transport through pores. The influence of barrier structures on current fluctuations, transient phenomena and admittance.

In this paper is presented an investigation of the influence of the internal structure of pores in membranes on a) the time dependent macroscopic relaxation current after a voltage jump, b) the macroscopic frequency dependent admittance and c) the microscopic current fluctuations around stationary (nonequilibrium) states. All these quantities are determined by the time dependent transport equations, which are calculated with the use of the eigenvectors and eigenvalues of the matrix of coefficients, occurring in the transport equations. Numerical calculations for channels with up to 31 barriers are presented. The treatment of the fluctuations is done with the use of a general approach to nonequilibrium transport noise recently developed by one of the authors. It is shown that the influence of the internal barrier structure as, e.g., the height of central or decentral barriers in the pores is of great complexity. Nevertheless we hope that the calculations lead to a better understanding especially of the microscopic nonequilibrium transport fluctuations in complex systems.