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

A heat and mass transfer study of carbon paste baking

Ramming paste is a particular type of carbon paste which is used as lining for electric smelting furnaces and Hall-Héroult cells for the production of aluminium. The purpose of this lining is to form an impenetrable barrier, keeping the liquid within the furnace. If the lining has cracks or holes, then liquid can escape, which can lead to safety risks and financial losses, so the integrity of the lining is of great importance. In the present study, we develop a first principles mathematical model for the heat and mass transfer processes occurring during the baking of carbon paste. We then obtain numerical simulations using this model and compare the simulation results to experimental data, demonstrating that the model solutions do indeed describe and predict realistic behaviors of the carbon paste baking process. The simulations indicate a strong pressure buildup during the evaporation of water from fresh paste during the baking process, which is likely to lead to cracking of the paste as it hardens. Furthermore, we are able to show that more gradual heating during the baking process can lower the maximal pressures predicted by the model, which in turn may reduce the prevalence of cracks within the hardened paste

A heat and mass transfer study of carbon paste baking

Ramming paste is a particular type of carbon paste which is used as lining for electric smelting furnaces and Hall-Héroult cells for the production of aluminium. The purpose of this lining is to form an impenetrable barrier, keeping the liquid within the furnace. If the lining has cracks or holes, then liquid can escape, which can lead to safety risks and financial losses, so the integrity of the lining is of great importance. In the present study, we develop a first principles mathematical model for the heat and mass transfer processes occurring during the baking of carbon paste. We then obtain numerical simulations using this model and compare the simulation results to experimental data, demonstrating that the model solutions do indeed describe and predict realistic behaviors of the carbon paste baking process. The simulations indicate a strong pressure buildup during the evaporation of water from fresh paste during the baking process, which is likely to lead to cracking of the paste as it hardens. Furthermore, we are able to show that more gradual heating during the baking process can lower the maximal pressures predicted by the model, which in turn may reduce the prevalence of cracks within the hardened paste