A Tale of Two Oxidation States: Bacterial Colonization of Arsenic-Rich Environments

Microbial biotransformations have a major impact on contamination by toxic elements, which threatens public health in developing and industrial countries. Finding a means of preserving natural environments—including ground and surface waters—from arsenic constitutes a major challenge facing modern society. Although this metalloid is ubiquitous on Earth, thus far no bacterium thriving in arsenic-contaminated environments has been fully characterized. In-depth exploration of the genome of the β-proteobacterium Herminiimonas arsenicoxydans with regard to physiology, genetics, and proteomics, revealed that it possesses heretofore unsuspected mechanisms for coping with arsenic. Aside from multiple biochemical processes such as arsenic oxidation, reduction, and efflux, H. arsenicoxydans also exhibits positive chemotaxis and motility towards arsenic and metalloid scavenging by exopolysaccharides. These observations demonstrate the existence of a novel strategy to efficiently colonize arsenic-rich environments, which extends beyond oxidoreduction reactions. Such a microbial mechanism of detoxification, which is possibly exploitable for bioremediation applications of contaminated sites, may have played a crucial role in the occupation of ancient ecological niches on earth

A study of dynamic thermal expansion using a laser-generated ultrasound one-dimensional model

International audienceThe laser-ultrasound 1D model is used to describe phenomenologically the behavior of a non-conductive infinite plate subjected to different types of temperature raises: uniform (in z) and instantaneous (in t), uniform and non-instantaneous, non-uniform (exponential) and instantaneous. We show that this simple model can be used to understand the basics of dynamic thermal expansion

Phase optimization for quantitative analysis using phase Fourier transform photoacoustic spectroscopy

International audienceThe phase of the photoacoustic signal is of prime importance for obtaining accurate optical absorption coefficients using the photoa-coustic technique. Variations in the spectrometer or the photoacoustic cell parameters between the measurement of the sample spectrum and the carbon black reference spectrum are the main source of phase shifts. We reconsider a simple model that provides an accurate description of the photoacoustic effect—including photoacoustic saturation—for thermally thick, homogeneous samples. The model includes absorption from a thin layer at the sample surface. We propose a method for optimizing the photoacoustic phase for this model. The method is based on the internal calibration at the onset of the photoacoustic saturation, and on a simple analysis of the shape of the calculated surface absorption spectrum. Optimization is illustrated with a simulated spectrum and an experimental spectrum of ethylene-propylene-rubber

A two-dimensional model for sensitivity studies on laser-generated ultrasound

International audienceA two-dimensional simulation model is presented that, within certain limitative assumptions, calculates the displacements generated by the absorption of a laser pulse in the thermoelastic regime. This model solves the Christoffel equations in an axisymmetrical configuration (the laser excitation is supposed to have a gaussian surface profile) over an infinite plate of finite thickness presenting a cylindrical orthotropy. The resolution of these Christoffel equations is made in the Laplace and Hankel spaces. After the validation of this model by the confrontation of its predictions to experimental data, we present two applications of it concerning the related temporal convolutions occurring to produce the longitudinal precursor