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ZntB Is a Novel Zn2+ Transporter in Salmonella enterica Serovar Typhimurium. Ashley J. Worlock, 2002.A Zn2+ transport system encoded by the zntB locus of Salmonella enterica serovar Typhimurium has been identified . The protein encoded by this locus is homologous to the CorA family of Mg2+ transport proteins and is widely distributed among the eubacteria . Mutations at zntB confer an increased sensitivity to the cytotoxic effects of Zn2+ and Cd2+, a phenotype that suggests that the encoded protein mediates the efflux of both cations . A direct analysis of transport activity identified a capacity for Zn2+ efflux . These data identify ZntB as a zinc efflux pathway in the enteric bacteria and assign a new function to the CorA family of cation transporters . NolX of Sinorhizobium fredii USDA257, a Type III-Secreted Protein Involved in Host Range Determination, Is Localized in the Infection Threads of Cowpea (Vigna unguiculata [L.] Walp) and Soybean (Glycine max [L.] Merr.) Nodules. Hari B. Krishnan, 2002.Sinorhizobium fredii USDA257 forms nitrogen-fixing nodules on soybean (Glycine max [L.] Merr.) in a cultivar-specific manner . This strain forms nodules on primitive soybean cultivars but fails to nodulate agronomically improved North American cultivars . Soybean cultivar specificity is regulated by the nolXWBTUV locus, which encodes part of a type III secretion system (TTSS) . NolX, a soybean cultivar specificity protein, is secreted by TTSS and shows homology to HrpF of the plant pathogen Xanthomonas campestris pv . vesicatoria . It is not known whether NolX functions at the bacterium-plant interface or acts inside the host cell . Antibodies raised against S . fredii USDA257 NolX were used in immunocytochemical studies to investigate the subcellular localization of this protein . Immunostaining of paraffin-embedded sections of developing soybean and cowpea (Vigna unguiculata [L.] Walp) nodules revealed localization of NolX in the infection threads . Protein A-gold immunocytochemical localization studies utilizing affinity-purified NolX antibodies revealed specific deposition of gold particles in the fibrillar material inside infection threads . Similar immunogold localization studies failed to detect NolX in thin sections of mature soybean and cowpea nodules . The results from this study indicate that NolX is expressed in planta only during the early stages of nodule development . Detachment of Actinobacillus actinomycetemcomitans Biofilm Cells by an Endogenous ß-Hexosaminidase Activity. Jeffrey B. Kaplan, 2003.When cultured in broth, fresh clinical isolates of the gram-negative periodontal pathogen Actinobacillus actinomycetemcomitans form tenaciously adherent biofilm colonies on surfaces such as plastic and glass . These biofilm colonies release adherent cells into the medium, and the released cells can attach to the surface of the culture vessel and form new colonies, enabling the biofilm to spread . We mutagenized A . actinomycetemcomitans clinical strain CU1000 with transposon IS903  kan and isolated a transposon insertion mutant that formed biofilm colonies which were tightly adherent to surfaces but which lacked the ability to release cells into the medium and disperse . The transposon insertion in the mutant strain mapped to a gene, designated dspB, that was predicted to encode a secreted protein homologous to the catalytic domain of the family 20 glycosyl hydrolases . A plasmid carrying a wild-type dspB gene restored the ability of biofilm colonies of the mutant strain to disperse . We expressed A . actinomycetemcomitans DspB protein engineered to contain a hexahistidine metal-binding site at its C terminus in Escherichia coli and purified the protein by using Ni affinity chromatography . Substrate specificity studies performed with monosaccharides labeled with 4-nitrophenyl groups showed that DspB hydrolyzed the 1 4 glycosidic bond of ß-substituted N-acetylglucosamine, which is consistent with the known functions of other family 20 glycosyl hydrolases . When added to culture medium, purified DspB protein, but not heat-inactivated DspB, restored the ability of the mutant strain to release cells and disperse . DspB protein also caused the detachment of cells from preformed biofilm colonies of strain CU1000 grown attached to plastic and the disaggregation of highly autoaggregated clumps of CU1000 cells in solution . We concluded that dspB encodes a soluble ß-N-acetylglucosaminidase that causes detachment and dispersion of A . actinomycetemcomitans biofilm cells .
Adhesion, Invasion, and Translocation Characteristics of Listeria monocytogenes Serotypes in Caco-2 Cell and Mouse Models. Ziad W. Jaradat, 2003.Adhesion is a crucial first step in Listeria monocytogenes pathogenesis . In this study, we examined how the adhesion properties of serotypes correlate with their invasion efficiencies in a cell culture model (Caco-2) and in a mouse model . Adhesion characteristics of all 13 serotypes of L . monocytogenes (25 strains) were analyzed, which yielded three distinct groups (P < 0.05) with high-, medium-, and low-level-adhesion profiles . The efficiency of these strains in invading the Caco-2 cell line was analyzed, which produced two groups; however, the overall correlation (R2) was only 0.1236 . In the mouse bioassay, all selected strains, irrespective of their adhesion profiles, translocated to the liver and the spleen with almost equal frequencies that did not show any clear relationship with adhesion profiles . However, the serotypes with increased adhesion showed a slightly increased translocation to the brain (R2 = 0.3371) . Collectively, these results indicate that an in vitro adhesion profile might not be an accurate assessment of a strain's ability to invade a cultured cell line or organs or tissues in a mouse model .
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