High-energy acceleration phenomena in extreme-radiation-plasma interactions.

We simulate, using a particle-in-cell code, the chain of acceleration processes at work during the Compton-based interaction of a dilute electron-ion plasma with an extreme-intensity, incoherent γ-ray flux with a photon density several orders of magnitude above the particle density. The plasma electrons are initially accelerated in the radiative flux direction through Compton scattering. In turn, the charge-separation field from the induced current drives forward the plasma ions to near-relativistic speed and accelerates backwards the nonscattered electrons to energies easily exceeding those of the driving photons. The dynamics of those energized electrons is determined by the interplay of electrostatic acceleration, bulk plasma motion, inverse Compton scattering and deflections off the mobile magnetic fluctuations generated by a Weibel-type instability. The latter Fermi-like effect notably gives rise to a forward-directed suprathermal electron tail. We provide simple analytical descriptions for most of those phenomena and examine numerically their sensitivity to the parameters of the problem.

Barrier effect of Bifidobacterium longum on a pathogenic Escherichia coli strain by gut colonization in the germ-free rat.

The predominance of Bifidobacteria in normal breast-fed babies is well established. Even under unfavourable hygienic conditions of delivery and during the breast-feeding period Bifidobacteria develop and colonize the intestinal tract at high concentrations. In the present study we investigated the interaction between Bifidobacterium longum and a pathogenic E. coli strain in the germ-free rat. Sequential counts of the two bacterial strains allowed their proliferation to be followed. Electron microscopic as well as light microscopic examinations of selected intestinal mucosa segments revealed minor morphological changes. Bifidobacterium completely protected the rats against mortality from a consecutive infection with E. coli. Repeated inoculation of Bifidobacteria even decreased and kept down the initial E. coli population. Thus it appears that the germ-free rat is an appropriate model to study the development and interaction of both bacterial species and that the sequence of inoculation is most important.

Scanning and transmission electron microscopy of three strains of Bifidobacterium.

Scanning and transmission electron microscopy was applied for a morphological study of three strains of Bifidobacterium grown on solid or liquid media. The pronounced pleomorphism of the cultures previously observed by light microscopy was confirmed. A possible sequence of the morphological events during transformation from one to another pleomorphic form is proposed for B. bifidum and B. longum. Ultrastructural differences such as the formation of extensive mesosomal complexes in B. longum and characteristic plasmalemma particles only observed in the B. bifidum mutant are described and discussed.