To infect a susceptible host, the gastrointestinal pathogen Yersinia enterocolitica must survive passage through the acid environment of the stomach. In this study, we showed that Y. enterocolitica serotype O8 survives buffered acidic conditions as low as pH 1.5 for long periods of time provided urea is available. Acid tolerance required an unusual cytoplasmically located urease that was activated 780-fold by low-pH conditions. Acid tolerance of Helicobacter species has also been attributed to urease activity, but in that case urease was not specifically activated by low-pH conditions. A ure mutant strain of Y. enterocolitica was constructed which was hypersensitive to acidic conditions when urea was available and, unlike the parental strain, was unable to grow when urea was the sole nitrogen source. Examination of other urease-producing gram-negative bacteria indicated that Morganella morganii survives in acidic conditions but Escherichia coli 1021, Klebsiella pneumoniae, Proteus mirabilis, Providencia stuartii, and Pseudomonas aeruginosa do not. Consistent with these results, biochemical evidence demonstrated that Y. enterocolitica and M. morganii ureases were activated in vitro by low pH with an unusually low activity optimum of pH 5.5. In whole cells activation occurred as medium values decreased below pH 3.0 for Y. enterocolitica and pH 5.5 for M. morganii, suggesting that in vivo activation occurs as a result of cytoplasmic acidification. DNA sequence analysis of portions of the M. morganii ure locus showed that the predicted primary structure of the enzyme structural subunits is most similar to those of Y. enterocolitica urease. One region of similarity between these two ureases located near the active site is distinct from most other ureases but is present in the urease of Lactobacillus fermentum. This region of similarity may be responsible for the unique properties of the Y. enterocolitica and M. morganii ureases since the L. fermentum urease also has been shown to have a low pH optimum for activity.

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Decision makers often need to take into account multiple conflicting objectives when selecting a solution for their problem. This can result in a potentially large number of candidate solutions to be considered. Visualizing a Pareto Frontier, the optimal set of solutions to a multi-objective problem, is considered a difficult task when the problem at hand spans more than three objective functions. We introduce a novel visual-interactive approach to facilitate coping with multi-objective problems. We propose a characterization of the Pareto Frontier data and the tasks decision makers face as they reach their decisions. Following a comprehensive analysis of the design alternatives, we show how a semantically-enhanced Self-Organizing Map, can be utilized to meet the identified tasks. We argue that our newly proposed design provides both consistent orientation of the 2D mapping as well as an appropriate visual representation of individual solutions. We then demonstrate its applicability with two real-world multi-objective case studies. We conclude with a preliminary empirical evaluation and a qualitative usefulness assessment.

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Before requirements analysis takes place in a business context, business analysis is usually performed. Important concerns emerge during this analysis that need to be captured and communicated to requirements engineers. In this paper, we take the position that tagging is a promising approach for identifying and organizing these concerns. The fact that tags can be attached freely to entities, often with multiple tags attached to the same entity and the same tag attached to multiple entities, leads to multi-dimensional structures that are suitable for representing crosscutting concerns and exploring their relationships. The resulting tag structures can be hardened into classifications that capture and communicate important concerns.