Showing papers by "Edgardo Moreno published in 1997"

In search of a bacterial species definition.

Abstract: The bacterial species concept was examined within the framework of plant and animal associated alpha-2 proteobacteria, taking into consideration the phylogenetic, taxonomic and biological approaches as well as the microbiologists' perception. The virtue of the phylogenetic approach is that it gives an evolutionary perspective of the bacterial lineage; however the methods used possess low resolution for defining species located at the terminal branches of the phylogenetic trees. The merit of the taxonomic approach is that species are defined on the basis of multiple characteristics allowing high resolution at the terminal branches of dendograms; its disadvantage is the inaccuracy in the earlier nodes. On an individual level, the qualitative biological characteristics used for the definition of species frequently reveal shortcomings because many of these properties are the result of coevolution, parallel evolution or the horizontal transfer of genes. Nevertheless, when considered together with the phylogenetic and taxonomic approaches, important uncertainties are discovered: these must be weighed if a practical definition of bacterial species is conceived. The microbiologists' perception is the criterion expressed by a group of sponsors who, based on scientific and practical grounds, propose a new bacterial species. The success of this new proposal is measured by its widespread acceptance and its permanence. A difficult problem concerned with defining bacterial species is how to distinguish if they are independent evolutionary units or if they are reticulate evolutionary units. In the first case the inherence is vertically transmitted as a result of binary fission and clonal expansion. This may be the case of some animal cell associated bacteria in which recombination appears to be precluded or exceptional. In the second case adaptive changes occurring within an individual can be horizontally transferred to many or all group members. This seems to be the condition of many intestinal and plant associated bacteria. Genetic drift and speciation in clonal bacteria will depend almost exclusively on mutation and internal genetic rearrangement processes, whereas speciation in reticulate bacteria will depend not only on these processes but in their genetic interactions with other bacterial strains. This uncertainty, which corresponds to the evolutionary process, is at the same time one of the key factors in defining a bacterial species.

When intracellular pathogens invade the frontiers of cell biology and immunology.

Abstract: Cellular microbiology has recently been described as a new discipline emerging at the interface between cell biology and microbiology (Cossart et al., 1996). Many microbial pathogens can enter eukaryotic cells and live intracellularly either inside vacuoles or in the cytoplasm. The different steps during the invasion process are on the way of being dissected at the molecular level revealing new insights in basic cellular functions. Indeed, bacterial pathogenesis can help us to better understand the dynamics of cell cytoskeleton, intracellular membrane traffic and signal transduction events. The recent advancements in the field of microbial pathogenesis are creating a new cross-talk between cell biologists, microbiologists and immunologists. In this review, the different strategies used by several pathogens are presented and the mechanisms elaborated by host cells from the immune system to eliminate the parasites discussed.