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Evidence for Targeting of Yop Effectors by the Chromosomally Encoded Ysa Type III Secretion System of Yersinia enterocolitica. Briana M. Young, 2002.Yersinia enterocolitica O:8 has two contact-dependent type III secretion systems (TTSSs) . The Ysa TTSS is encoded by a set of genes located on the chromosome and exports Ysp proteins . The Ysc TTSS and the Yop effector proteins it exports are encoded by genes located on plasmid pYVe8081 . In this study, secretion of YspG, YspH, and YspJ by the Ysa TTSS was shown to require pYVe8081 . Furthermore, mutations that blocked the function of the Ysc TTSS did not affect YspG, YspH, and YspJ production . This indicated that YspG, YspH, and YspJ are encoded by genes located on pYVe8081 and that they may correspond to Yops . A comparison of Ysps with Yop effectors secreted by Y . enterocolitica indicated that YspG, YspH, and YspJ have apparent molecular masses similar to those of YopN, YopP, and YopE, respectively . Immunoblot analysis demonstrated that antibodies directed against YopN, YopP, and YopE recognized YspG, YspH, and YspJ . Furthermore, mutations in yopN, yopP, and yopE specifically blocked YopN, YopP, and YopE secretion by the Ysc TTSS and YspG, YspH, and YspJ secretion by the Ysa TTSS . These results indicate YspG, YspH, and YspJ are actually YopN, YopP, and YopE . Additional analysis demonstrated that YopP and YspH secretion was restored to yopP mutants by complementation in trans with a wild-type copy of the yopP gene . Examination of Y . enterocolitica-infected J774A.1 macrophages revealed that both the Ysc and Ysa TTSSs contribute to YopP-dependent suppression of tumor necrosis factor alpha production . This indicates that both the Ysa and Ysc TTSSs are capable of targeting YopP and that they influence Y . enterocolitica interactions with macrophages . Taken together, these results suggest that the Ysa and Ysc TTSSs contribute to Y . enterocolitica virulence by exporting both unique and common subsets of effectors . Three-Dimensional Structure of the Neisseria meningitidis Secretin PilQ Determined from Negative-Stain Transmission Electron Microscopy. Richard F. Collins, 2003.The PilQ secretin from the pathogenic bacterium Neisseria meningitidis is an integral outer membrane protein complex which plays a crucial role in the biogenesis of type IV pili . We present here the first three-dimensional structure of this type of secretin at 2.5-nm resolution, obtained by single-particle averaging methods applied to the purified protein complex visualized in a negative stain . In projection, the PilQ complex is circular, with a donut-like appearance . When viewed from the side it has a rounded, conical profile . The complex was demonstrated to have 12-fold rotational symmetry, and this property was used to improve the quality of the density map by symmetry averaging . The dominant feature of the structure is a cavity, 10 nm deep, within the center of the molecule . The cavity is funnel-shaped in cross section, measures 6.5 nm in diameter at the top of the complex, and tapers to a closed point, effectively blocking formation of a continuous pore through the PilQ complex . These results suggest that the complex would have to undergo a conformational change in order to accommodate an assembled pilus fiber of diameter 6.5 nm running through the outer membrane . Exopolysaccharide and Kestose Production by Lactobacillus sanfranciscensis LTH2590. Maher Korakli, 2003.The effect was investigated of sucrose concentration on sucrose metabolism and on the formation of exopolysaccharide (EPS) by Lactobacillus sanfranciscensis LTH2590 in pH-controlled fermentations with sucrose concentrations ranging from 20 to 160 g liter-1 . The EPS production increased and the relative sucrose hydrolysis activity decreased by increasing the sucrose concentration in the medium . The carbon recovery decreased from 95% at a sucrose concentration of 30 g liter-1 to 58% at a sucrose concentration of 160 g liter-1 because of the production of an unknown metabolite by L . sanfranciscensis . This metabolite was characterized as a fructo-oligosaccharide . The oligosaccharide produced by L . sanfranciscensis was purified and characterized as a trisaccharide with a glucose/fructose ratio of 1:2 . The comparison of the retention time of this oligosaccharide and that of pure oligosaccharide standards using two different chromatography methods revealed that the oligosaccharide produced by L . sanfranciscensis LTH2590 is 1-kestose . Kestose production increased concomitantly with the initial sucrose concentration in the medium .
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