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A Movable Surface: Formation of Yersinia sp . Biofilms on Motile Caenorhabditis elegans. Li Tan, 2004.Bubonic plague is transmitted by fleas whose feeding is blocked by a mass of Yersinia pestis in the digestive tract . Y . pestis and the closely related Y . pseudotuberculosis also block the feeding of Caenorhabditis elegans by forming a biofilm on the nematode head . C . elegans mutants with severe motility defects acquire almost no biofilm, indicating that normal animals accumulate the biofilm matrix as they move through a Yersinia lawn . Using the lectin wheat germ agglutinin as a probe, we show that the matrix on C . elegans contains carbohydrate produced by Yersinia . The carbohydrate is present in bacterial lawns prior to addition of nematodes, indicating that biofilm formation does not involve signaling between the two organisms . Furthermore, biofilm accumulation depends on continuous C . elegans exposure to a lawn of Yersinia bacteria . Negative Cross-Communication among Wheat Rhizosphere Bacteria: Effect on Antibiotic Production by the Biological Control Bacterium Pseudomonas aureofaciens 30-84. J. E. Morello, 2004.Phenazine antibiotic production in the biological control bacterium Pseudomonas aureofaciens 30-84 is regulated in part via the PhzR/PhzI N-acyl homoserine lactone (AHL) system . Previous work showed that a subpopulation of the wheat rhizosphere community positively affected phenazine gene expression in strain 30-84 via AHL signals (E . A . Pierson, D . W . Wood, J . A . Cannon, F . M . Blachere, and L . S . Pierson III, Mol . Plant-Microbe Interact . 11:1078-1084, 1998) . In the present work, a second subpopulation, one that negatively affected phenazine gene expression, was identified from this rhizosphere community . Strain 30-84 grown in conditioned medium (CM) from several strains produced lower levels of phenazines (1.5- to 9.3-fold) than control when grown in CM from the strain 30-84I1/I2 . Growth of the phzB::lacZ reporter strain 30-84Z in this CM resulted in decreased lacZ expression (4.3- to 9.2-fold) compared to growth of the control strain in CM, indicating that inhibition of phzB occurred at the level of gene expression . Preliminary chemical and biological characterizations suggested that these signals, unlike other identified negative signals, were not extractable in ethyl acetate . Introduction of extra copies of phzR and phzI, but not phzI alone, in trans into strain 30-84Z reduced the negative effect on phzB::lacZ expression . The presence of negative-signal-producing strains in a mixture with strain 30-84 reduced strain 30-84's ability to inhibit the take-all disease pathogen in vitro . Together, the results from the previous work on the positive-signal subpopulation and the present work on the negative-signal subpopulation suggest that cross-communication among members of the rhizosphere community and strain 30-84 may control secondary metabolite production and pathogen inhibition . Chemiosmotic Energy Conservation with Na+ as the Coupling Ion during Hydrogen-Dependent Caffeate Reduction by Acetobacterium woodii. Frank Imkamp, 2002.Cell suspensions of Acetobacterium woodii prepared from cultures grown on fructose plus caffeate catalyzed caffeate reduction with electrons derived from molecular hydrogen . Hydrogen-dependent caffeate reduction was strictly Na+ dependent with a Km for Na+ of 0.38 mM; Li+ could substitute for Na+ . The sodium ionophore ETH2120, but not protonophores, stimulated hydrogen-dependent caffeate reduction by 280%, indicating that caffeate reduction is coupled to the buildup of a membrane potential generated by primary Na+ extrusion . Caffeate reduction was coupled to the synthesis of ATP, and again, ATP synthesis coupled to hydrogen-dependent caffeate reduction was strictly Na+ dependent and abolished by ETH2120, but not by protonophores, indicating the involvement of a transmembrane Na+ gradient in ATP synthesis . The ATPase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD) abolished ATP synthesis, and at the same time, hydrogen-dependent caffeate reduction was inhibited . This inhibition could be relieved by ETH2120 . These experiments are fully compatible with a chemiosmotic mechanism of ATP synthesis with Na+ as the coupling ion during hydrogen-dependent caffeate reduction by A . woodii .
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