The resistance of intra-amoebal grown legionella pneumophila

Survival studies were conducted on Legionella pneumophila cells that had been grown intracellulary in Acanthamoeba polyphaga and then exposed to polyhexamethylene biguanide (PHMB), benzisothiazolone (BIT), 5-chloro-N-methylisothiazolone (CMIT) and tetradecyltrimethyl ammonium bromide (TTAB). Susceptibilities were also determined for L.pneumophila grown under nutrient sufficient and iron-, nitrogen- and phosphate-depleted conditions, in a chemically defined medium. BIT was relatively ineffective against cells grown under iron-depletion; in contrast iron-depleted conditions increased the susceptibilities of cells to PHMB, TTAB and CMIT. Cells grown under phosphate-depletion showed a marked increase in sensitivity towards all the biocides. Conversely, the activities of all four biocides were greatly reduced against L.pneumophila grown in amoebae. To study the physiological basis for the increased resistance of intra-amoebal grown legionella, the surface properties of the cells were examined by studying outer membrane proteins (OMs), lipopolysaccharides and cellular fatty acids. Intra-amoebal grown legionella were found to differ in several respects compared to cells grown in vitro; they contained a novel 15-kDal OM protein and a monosaturated straight-chain fatty acid (18:19). These compounds were also found in abundant quantities in the host amoeba. Intra-amoebal grown legionella contained more LPS bands than did in vitro grown organisms and were less susceptible to protease K digestion. Cells grown under phosphate depletion were markedly sensitive to protease K digestion and contained lower levels of LPS. Immunoblot analysis of intra-amoebal grown legionella with anti-acanthamoebal serum revealed that both the surface of the bacteria and sarkosyl extracted OMs contained amoebal proteins. These findings suggest that the 15-kDal OM protein is likely to be of amoebal origin and binds tightly to the OM of the bacterium. It is proposed that disruption of amoebal membranes, as a result of intra-amoebal infection liberates macromolecules, including a 15-kDal polypeptide, a major constituent of the membrane, which associates closely with the surface of the legionellae. Thus L.pneumophila which have extraneous membrane material bound to their surface may respond differently to biocide inactivation, as these macromolecules may act as a penetration barrier to such agents. This phenomenon could contribute to the recalcitrance of legionellae in water systems.

Pollen and non-pollen palynomorphs counting data from Borsteler Moor (Germany)

In order to reconstruct regional vegetation changes and local conditions during the fen-bog transition in the Borsteler Moor (northwestern Germany), a sediment core covering the period between 7.1 and 4.5 cal kyrs BP was palynologically in vestigated. The pollen diagram demonstrates the dominance of oak forests and a gradual replacement of trees by raised bog vegetation with the wetter conditions in the Late Atlantic. At ~ 6 cal kyrs BP, the non-pollen palynomorphs (NPP) demonstrate the succession from mesotrophic conditions, clearly indicated by a number of fungal spore types, to oligotrophic conditions, indicated by Sphagnum spores, Bryophytomyces sphagni, and testate amoebae Amphitrema, Assulina and Arcella, etc. Four relatively dry phases during the transition from fen to bog are clearly indicated by the dominance of Calluna and associated fungi as well as by the increase of microcharcoal. Several new NPP types are described and known NPP types are identified. All NPP are discussed in the context of their palaeoecological indicator values.

Mathematical models for cellular aggregation: the chemotactic instability and clustering formation

In this thesis we present a mathematical formulation of the interaction between microorganisms such as bacteria or amoebae and chemicals, often produced by the organisms themselves. This interaction is called chemotaxis and leads to cellular aggregation. We derive some models to describe chemotaxis. The first is the pioneristic Keller-Segel parabolic-parabolic model and it is derived by two different frameworks: a macroscopic perspective and a microscopic perspective, in which we start with a stochastic differential equation and we perform a mean-field approximation. This parabolic model may be generalized by the introduction of a degenerate diffusion parameter, which depends on the density itself via a power law. Then we derive a model for chemotaxis based on Cattaneo's law of heat propagation with finite speed, which is a hyperbolic model. The last model proposed here is a hydrodynamic model, which takes into account the inertia of the system by a friction force. In the limit of strong friction, the model reduces to the parabolic model, whereas in the limit of weak friction, we recover a hyperbolic model. Finally, we analyze the instability condition, which is the condition that leads to aggregation, and we describe the different kinds of aggregates we may obtain: the parabolic models lead to clusters or peaks whereas the hyperbolic models lead to the formation of network patterns or filaments. Moreover, we discuss the analogy between bacterial colonies and self gravitating systems by comparing the chemotactic collapse and the gravitational collapse (Jeans instability).