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The Sodium-Driven Flagellar Motor Controls Exopolysaccharide Expression in Vibrio cholerae. Crystal M. Lauriano, 2004.Vibrio cholerae causes the life-threatening diarrheal disease cholera . This organism persists in aquatic environments in areas of endemicity, and it is believed that the ability of the bacteria to form biofilms in the environment contributes to their persistence . Expression of an exopolysaccharide (EPS), encoded by two vps gene clusters, is essential for biofilm formation and causes a rugose colonial phenotype . We previously reported that the lack of a flagellum induces V . cholerae EPS expression . To uncover the signaling pathway that links the lack of a flagellum to EPS expression, we introduced into a rugose flaA strain second-site mutations that would cause reversion back to the smooth phenotype . Interestingly, mutation of the genes encoding the sodium-driven motor (mot) in a nonflagellated strain reduces EPS expression, biofilm formation, and vps gene transcription, as does the addition of phenamil, which specifically inhibits the sodium-driven motor . Mutation of vpsR, which encodes a response regulator, also reduces EPS expression, biofilm formation, and vps gene transcription in nonflagellated cells . Complementation of a vpsR strain with a constitutive vpsR allele likely to mimic the phosphorylated state (D59E) restores EPS expression and biofilm formation, while complementation with an allele predicted to remain unphosphorylated (D59A) does not . Our results demonstrate the involvement of the sodium-driven motor and suggest the involvement of phospho-VpsR in the signaling cascade that induces EPS expression . A nonflagellated strain expressing EPS is defective for intestinal colonization in the suckling mouse model of cholera and expresses reduced amounts of cholera toxin and toxin-coregulated pili in vitro . Wild-type levels of virulence factor expression and colonization could be restored by a second mutation within the vps gene cluster that eliminated EPS biosynthesis . These results demonstrate a complex relationship between the flagellum-dependent EPS signaling cascade and virulence . In Vitro Effects of Albendazole Sulfoxide and Praziquantel against Taenia solium and Taenia crassiceps Cysts. Francisca Palomares, 2004.We investigated the minimum exposure times of prazicuantel (PZQ) and albendazole sulfoxide (ABZSO) required for their activities against Taenia cysts in vitro as well as the 50 and 99% effective concentrations . The results showed that although the effects of both drugs are time and concentration dependent, ABZSO acts much slower and is less potent than PZQ . The Competitiveness of Pseudomonas chlororaphis Carrying pJP4 Is Reduced in the Arabidopsis thaliana Rhizosphere. Heike Schmidt-Eisenlohr, 2003.The effect of the large catabolic IncP plasmid pJP4 on the competitiveness of Pseudomonas chlororaphis SPR044 and on its derivatives SPR244 (GacS deficient), SPR344 (phenazine-1-carboxamide overproducer), and SPR644 (phenazine-1-carboxamide deficient) in the Arabidopsis thaliana rhizosphere was assessed . Solitary rhizosphere colonization by the wild type, SPR244, and SPR644 was not affected by the plasmid . The size of the population of SPR344 carrying pJP4, however, was significantly reduced compared to the size of the population of the plasmid-free derivative . The abiotic stress caused by phenazine-1-carboxamide overproduction probably resulted in a selective disadvantage for cells carrying pJP4 . Next, the effect of biotic stress caused by coinoculation of other bacteria was analyzed . Cells carrying pJP4 had a selective disadvantage compared to plasmid-free cells in the presence of the efficient colonizer Pseudomonas fluorescens WCS417r . This effect was not observed after coinoculation with a variety of other bacteria, and it was independent of quorum sensing and phenazine-1-carboxamide production . Thus, the presence of large catabolic plasmids imposes a detectable metabolic burden in the presence of biotic stress . Plasmid transfer in the A . thaliana rhizosphere from P . chlororaphis and its derivatives to Ralstonia eutropha was determined by using culture-dependent and culture-independent techniques . With the cultivation-independent technique we detected a significantly higher portion of exconjugants, but pJP4 transfer was independent of the quorum-sensing system and of phenazine-1-carboxamide production .
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