Tuberculosis vaccine strain _Mycobacterium bovis_ BCG Russia is a natural _recA_ mutant

The current tuberculosis vaccine is a live vaccine derived from _Mycobacterium bovis_ and attenuated by serial _in vitro_ passaging. All vaccine substrains in use stem from one source, strain Bacille Calmette-Guérin. However, they differ in regions of genomic deletions, antigen expression levels, immunogenicity, and protective efficacy. As a RecA phenotype increases genetic stability and may contribute restricting the ongoing evolution of the various BCG substrains, we aimed to inactivate _recA_ by allelic replacement in BCG vaccine strains representing different phylogenetic lineages (Pasteur, Frappier, Denmark, Russia). Homologous gene replacement was successful in three out of four strains. However, only illegitimate recombination was observed in BCG substrain Russia. Sequence analyses of _recA_ revealed that a single nucleotide insertion in the 5' part of _recA_ led to a translational frameshift with an early stop codon making BCG Russia a natural _recA_ mutant. At the protein level BCG Russia failed to express RecA. According to phylogenetic analyses BCG Russia is an ancient vaccine strain most closely related to the parental _M. bovis_. Our data suggest that _recA_ inactivation in BCG Russia occurred early and is in part responsible for its high degree of genomic stability, resulting in a substrain that has less genetic alterations than other vaccine substrains with respect to _M. bovis_ AF2122/97 wild type

Origin and stratigraphy of Holocene sediments, Souris and Des Lacs glacial-lake spillways, north-central North Dakota

In the past few years, a new interpretation of the formation of the Souris and Des Lacs glacial-lake spillways has been proposed. Now, based on geomorphological evidence, it is concluded that the Souris and Des Lacs Valleys were formed by massive glacial-lake outburst floods at the end of the late Wisconsinan deglaciation. Five phases of drainage have been recognized with the first forming the Des Lacs Valley and the other four associated with drainage in the Souris Valley from different proglacial lakes in Canada. The last of these floods down the Souris Valley was the most erosive. This study is concerned with Holocene sediments that have filled the Souris and Des Lacs Valleys in Ward and Renville Counties. Most of the discussion is focused on the Souris Valley. Twelve cross sections were constructed from data gathered in the field, from the U.S. Army Corps of Engineers, and the North Dakota State Water Commission. These data include: texture, structure, fossils, and amount of organic material. Study of these data allows reconstruction of the depositional environment of the Holocene sediments and of the history of the valleys. While the Souris Valley was being eroded during the last glacial-lake outburst, a headward-migrating knickpoint developed in the Souris Valley. This was caused by downcutting of the valley bottom while the flood was discharging into Glacial Lake Souris. After the flood subsided, an aggrading, meandering Souris River occupied the valley. Initially, the sides of both the Souris and Des Lacs Valleys were steep, and slumping occurred. Numerous intermittent streams entered the valleys from the sides and deposited coarse material close to the valley walls. The centers of the valleys contain silt with sand and clay lenses typical of fluvial systems dominated by meandering streams. The center of the Souris Valley, between its confluence with the Des Lacs River and the position of the Soo Line R.R. to the north, is characterized by a coffipletely different stratigraphic sequence that includes a central clay plug. Differences in the types of organic materials and fossil assemblages in this section suggest a swampy to shallow-pond environment. This pond may have been dammed by an alluvial fan deposited by the higher-gradient Des Lacs River. Three organic horizons were recognized and are interpretee to represent cool, moist, climatic conditions that enabled vegetation to stabilize the steep valley sides. The lower horizon has been correlated with the Aggie Brown Member of the Oahe Formation of early Holocene ase by C-14 dating. The other two horizons are not dated but may be correlative with the late Holocene Riverdale Member of the Oahe Formation. A warm and drier climate during the raiddle Holocene was characterized by greater slope erosion and more deposition in the valleys

Slabs of stabilized jellium: Quantum-size and self-compression effects

We examine thin films of two simple metals (aluminum and lithium) in the stabilized jellium model, a modification of the regular jellium model in which a constant potential is added inside the metal to stabilize the system for a given background density. We investigate quantum-size effects on the surface energy and the work function. For a given film thickness we also evaluate the density yielding energy stability, which is found to be slightly higher than the equilibrium density of the bulk system and to approach this value in the limit of thick slabs. A comparison of our self-consistent calculations with the predictions of the liquid-drop model shows the validity of this model.Comment: 7 pages, 6 figures, to appear in Phys. Rev.

Innovations in Spacecraft Proximity & Navigation Lighting

New spacecraft bound for the Moon and Mars should be exploring lighting technologies that can reduce safety risks while increasing capability. The operational lighting environment for these new missions will not have the forgiving 90 minute orbit of the International Space Station. Advances in solid state lighting and optics design are yielding new form factors for lamps that have the potential to reduce operational risk for both humans and imaging systems that are impacted by high contrast lighting environments. This project evaluated light source form factors and control innovations for spacecraft exterior proximity and navigation lighting by building a demonstration test rig and testing the effectiveness of the light sources and their controls to increase visibility and usability