A genome-wide strategy for the identification of essential genes in Staphylococcus aureus.

To address the need for new approaches to antibiotic drug development, we have identified a large number of essential genes for the bacterial pathogen, Staphylococcus aureus, using a rapid shotgun antisense RNA method. Staphylococcus aureus chromosomal DNA fragments were cloned into a xylose-inducible expression plasmid and transformed into S. aureus.

Mycotoxicological control on raw material and tablets of cascara sagrada (Rhamnus purshiana).

Among phytotherapic medicines, tablets of cascara sagrada (Rhamnus purshiana) dried bark, usually used as laxative, are commercially widespread in our market. Taking into account natural origin and/or inappropriate procedures that may allow the occurrence of toxinogenic Aspergillus flavus group, a study on susceptibility to aflatoxin contamination and natural aflatoxin incidence was performed by TLC and HPLC methods. This survey allows one to conclude that bark of Cascara Sagrada is a good substrate for the growth of A.

Thermal control of metabolic cold defence in pigeons columba livia.

Metabolic rate (MR) and various body temperatures were recorded in pigeons Columba livia during gradual lowering of the ambient temperature (Ta) and during cold exposure (-10 degrees C) for an entire circadian cycle. The aim was to study how changes in MR accorded with the observed body temperature displacements and our knowledge of regional cold sensitivity. When Ta was lowered from 28 to -10 degrees C, the threefold increase in MR was accompanied by a significant increase in deep-body and spinal cord temperatures.

A computational fluid dynamic study of hawkmoth hovering.

A computational fluid dynamic (CFD) modelling approach is used to study the unsteady aerodynamics of the flapping wing of a hovering hawkmoth. We use the geometry of a Manduca sexta-based robotic wing to define the shape of a three-dimensional 'virtual' wing model and 'hover' this wing, mimicking accurately the three-dimensional movements of the wing of a hovering hawkmoth. Our CFD analysis has established an overall understanding of the viscous and unsteady flow around the flapping wing and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing.

Electrophysiological and endocrinological evidence that F-series prostaglandins function as priming pheromones in mature male Atlantic salmon (Salmo salar parr.

Previous work has demonstrated that the urine from mature female salmonids contains a priming pheromone that significantly enhances the reproductive physiology of receiving males. The chemical identity of the pheromone(s) has not yet been identified. The present study investigated the possibility that F-type prostaglandins (PGFs) may have a pheromonal role in Atlantic salmon by measuring the olfactory sensitivity of male salmon to PGFs, the effect of waterborne PGFs on male reproductive physiology and the PGF content of mature female urine.

Analysis of switching phenomena in a dense medium of two-level atoms.

The switching characteristics of a dense medium of two-level atoms is studied analytically. Switching depends on the ratio of the Rabi frequency to the strength of the near-dipole-dipole interaction. When this ratio is nearly one, an exact solution is obtained.