Mode of action of lactocin 705, a two-component bacteriocin from Lactobacillus casei CRL705

Lactocin 705 is a bacteriocin whose activity depends on the complementary action of two peptides (705alpha and 705beta) of 33-amino-acid residues each and is produced by Lactobacillus casei CRL705. Biologically active, synthetic lactocin 705 was used to study the mode of action on sensitive cells of Lactobacillus plantarum CRL691. The addition of 90 nmol l(-1) of lactocin 705 to cells of L. plantarum dissipated both, the membrane potential (DeltaPsi) and the pH gradient (DeltapH). Energized membrane, obtained after the addition of glucose, were more susceptible to lactocin 705 action leading to the immediate release of intracellular K(+) and inorganic phosphate. When the role of various ions on sensitive cells were analyzed, only Ca(2+) ion exhibited a protective effect against lactocin 705. These data suggest that the presence of a proton motive force (PMF) promotes the interaction of the bacteriocin with the cytoplasmic membrane of energized cells, leading to pore formation which allows for the efflux of ions, thereby ensuring efficient killing of target bacteria.     

Lightpath arrangement in survivable rings to minimize the switchingcost

This paper studies the design of low-cost survivable wavelength-division-multiplexing (WDM) networks. To achieve survivability, lightpaths are arranged as a set of rings. Arrangement in rings is also necessary to support SONET/SDH protection schemes such as 4FBLSR above the optical layer. This is expected to be the most common architecture in regional (metro) networks. We assume that we are given a set of lightpaths in an arbitrary network topology and aim at finding a partition of the lightpaths to rings adding a minimum number of lightpaths to the original set. The cost measure that we consider (number of lightpaths) reflects the switching cost of the entire network. In the case of a SONET/SDH higher layer, the number of lightpaths is equal to the number of add-drop multiplexers (ADMs) (since two subsequent lightpaths in a ring can share an ADM at the common node). We prove some negative results on the tractability and approximability of the problem and provide an approximation algorithm with a worst case approximation ratio of 8/5. We study some special cases in which the performance of the algorithm is improved. A similar problem was introduced, motivated, and studied by Liu, Li, Wan and Frieder (see Proc. INFOCOM 2000, p.1020-1025, 2000) Gerstel, Lin and Sasaki, (see Proc. IEEE INFOCOM '98, p. 94-101, 1998)(where it was termed minimum ADM problem). However, these two works focused on a ring topology while we generalize the problem to an arbitrary network topology