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The Escherichia coli tppB (ydgR) Gene Represents a New Class of OmpR-Regulated Genes. Ee-Been Goh, 2004.The EnvZ/OmpR two-component regulatory system plays a critical role in the Escherichia coli stress response . In this study, we examined the expression of a new OmpR-regulated gene, ydgR . Our results indicate that ydgR is equivalent to the Salmonella enterica serovar Typhimurium tppB gene and represents a new class of OmpR-regulated genes . Plasmid-Mediated Carbapenem-Hydrolyzing Enzyme KPC-2 in an Enterobacter sp.. Ashfaque Hossain, 2004.A strain of an Enterobacter sp . with reduced susceptibility to imipenem, which produced a plasmid-mediated class A carbapenem-hydrolyzing enzyme, KPC-2 ß-lactamase, was isolated from a patient with sepsis at a Boston hospital . This is the first report of the production of a plasmid-encoded KPC-2 ß-lactamase by an Enterobacter sp . Expression of an Exogenous 1-Aminocyclopropane-1-Carboxylate Deaminase Gene in Sinorhizobium meliloti Increases Its Ability To Nodulate Alfalfa. Wenbo Ma, 2004.1-Aminocyclopropane-1-carboxylate (ACC) deaminase has been found in various plant growth-promoting rhizobacteria, including rhizobia . This enzyme degrades ACC, the immediate precursor of ethylene, and thus decreases the biosynthesis of ethylene in higher plants . The ACC deaminase of Rhizobium leguminosarum bv . viciae 128C53K was previously reported to be able to enhance nodulation of peas . The ACC deaminase structural gene (acdS) and its upstream regulatory gene, a leucine-responsive regulatory protein (LRP)-like gene (lrpL), from R . leguminosarum bv . viciae 128C53K were introduced into Sinorhizobium meliloti, which does not produce this enzyme, in two different ways: through a plasmid vector and by in situ transposon replacement . The resulting ACC deaminase-producing S . meliloti strains showed 35 to 40% greater efficiency in nodulating Medicago sativa (alfalfa), likely by reducing ethylene production in the host plants . Furthermore, the ACC deaminase-producing S . meliloti strain was more competitive in nodulation than the wild-type strain . We postulate that the increased competitiveness might be related to utilization of ACC as a nutrient within the infection threads .
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