Climate change adaptation in Wales: much ado about nothing?

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An investigation of horizontal transfer of feed introduced DNA to the aerobic microbiota of the gastrointestinal tract of rats

Background: Horizontal gene transfer through natural transformation of members of the microbiota of the lower gastrointestinal tract (GIT) of mammals has not yet been described. Insufficient DNA sequence similarity for homologous recombination to occur has been identified as the major barrier to interspecies transfer of chromosomal DNA in bacteria. In this study we determined if regions of high DNA similarity between the genomes of the indigenous bacteria in the GIT of rats and feed introduced DNA could lead to homologous recombination and acquisition of antibiotic resistance genes. Results: Plasmid DNA with two resistance genes (nptII and aadA) and regions of high DNA similarity to 16S rRNA and 23S rRNA genes present in a broad range of bacterial species present in the GIT, where constructed and added to standard rat feed. Six rats, with a normal microbiota, were fed DNA containing pellets daily over four days before sampling of the microbiota from the different GI compartments (stomach, small intestine, cecum and colon). In addition, two rats were included as negative controls. Antibiotic resistant colonies growing on selective media were screened for recombination with feed introduced DNA by PCR targeting unique sites in the putatively recombined regions. Conclusions: The analyses showed that extensive ingestion of DNA (100 \ub5g plasmid) per day did not lead to increased proportions of kanamycin resistant bacteria, nor did it produce detectable transformants among the aerobic microbiota examined for 6 rats (detection limit <1 transformant per 1.1 x 108 cultured bacteria). The key methodological challenges to HGT detection in animal feedings trials are identified and discussed

Dynamic X-ray imaging of the penetration of boron carbide

The U.S. Army Research Laboratory has adapted two l-MeV x-ray pulsers to obtain multiple dynamic, real time x-rays of the impact of 7.62-mm APM2 armor-piercing projectiles on a boron carbide ceramic. The goal was to conduct a high fidelity diagnostic analysis of the impact during the initial transient period and document the penetrator/target interaction. Three conditions of the projectile were tested : the full metal jacket projectile ; the steel core and lead tip only ; and just the steel core. These different conditions allow the observation of the tip breakup mechanism and determination of the average penetration velocity, the time for initiation of rigid body penetration into the ceramic/backing and the ballistic contributions of the projectile components