Skin microbiota is the main reservoir of Roseomonas mucosa, an emerging opportunistic pathogen so far assumed to be environmental.

Roseomonas spp. are increasingly involved in human infectious diseases. The environmental source for infection is generally admitted in published cases owing to the origin of most Roseomonas species and to their affiliation to the family Acetobacteraceae in Rhodospirillales, which mainly groups environmental bacteria. For a better delineation of Roseomonas habitat and infectious reservoir, we related phenotype, phylotype (16S rRNA gene), genomotype (pulsed-field gel electrophoresis) and origin of 33 strains isolated from humans, hospital environment and natural environment. Genetic and metagenomic databases were also surveyed. The population structure of the genus showed clades associated with humans, whereas others grouped environmental strains only. Roseomonas mucosa is the main human-associated species and the study supported the idea that opportunistic infections due to this species are related to the patient skin microbiota rather than to the environment. In contrast, some strains belonging to other species isolated from patients with cystic fibrosis were related to environmental clades, suggesting an exogenous source for patient colonization. Accurate knowledge about the reservoirs of opportunistic pathogens that have long been considered of environmental origin is still needed and would be helpful to improve infection control and epidemiological survey of emerging human pathogens.

Dynamics of a charged particle in a linearly polarized traveling electromagnetic wave.

The relativistic motion of a charged particle in a linearly polarized homogeneous electromagnetic wave is studied using the Hamiltonian formalism. First, a single particle in a linearly polarized traveling wave propagating in a nonmagnetized space is studied. It is shown that the charged particle can have a high average velocity along the propagation direction of the wave. The same result is derived considering an electromagnetic wave in a cold electron plasma. The case of a traveling wave propagating along a constant homogeneous magnetic field is then considered and shown to be nonintegrable. Using canonical transformations, it is shown that the equations of motion can be derived from an autonomous Hamiltonian and a formal solution is found for all the variables of the system. Considering that the wave propagates in vacuum and the particle is initially resonant and at rest, a set of equations is found coupling the energy of the particle and the phase of the wave. Then, the expression for the energy and the differential equation for the phase allow a solution in terms of quadratures. Finally, asymptotic solutions for the phase, the energy and consequently all of the variables are found.

Dynamics of a charged particle in a circularly polarized traveling electromagnetic wave

The relativistic motion of a charged particle in a transverse circularly or almost circularly polarized homogeneous electromagnetic wave is studied using the Hamiltonian formalism. First, the case of a circularly and almost circularly polarized traveling wave propagating in a nonmagnetized space is studied. In the case of an almost circularly polarized wave, it is shown that the charged particle has an average velocity along the propagation direction of the wave. The same result is derived considering a cold electron plasma. The case of a traveling wave propagating along a constant homogeneous magnetic field is then considered. Using canonical transformations, it is shown that the equations of motion can be derived from an autonomous Hamiltonian which has two degrees of freedom and a first integral. As a consequence, the system is completely integrable. An equation is found for the particle energy when it is initially resonant. This equation is solved exactly, and the asymptotic solution is obtained. The expression for the energy allows a solution for the system in terms of quadratures, and in consequence the asymptotic solution for all the variables. The case of an almost circularly polarized wave propagating along a constant homogeneous magnetic field is also studied. Finally, a magnetic field gradient is considered, and new acceleration mechanisms are found.