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Bacterial Communities Associated with Flowering Plants of the Ni Hyperaccumulator Thlaspi goesingense. Rughia Idris, 2004.Thlaspi goesingense is able to hyperaccumulate extremely high concentrations of Ni when grown in ultramafic soils . Recently it has been shown that rhizosphere bacteria may increase the heavy metal concentrations in hyperaccumulator plants significantly, whereas the role of endophytes has not been investigated yet . In this study the rhizosphere and shoot-associated (endophytic) bacteria colonizing T . goesingense were characterized in detail by using both cultivation and cultivation-independent techniques . Bacteria were identified by 16S rRNA sequence analysis, and isolates were further characterized regarding characteristics that may be relevant for a beneficial plant-microbe interaction—Ni tolerance, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore production . In the rhizosphere a high percentage of bacteria belonging to the Holophaga/Acidobacterium division and  -Proteobacteria were found . In addition, high-G+C gram-positive bacteria, Verrucomicrobia, and microbes of the Cytophaga/Flexibacter/Bacteroides division colonized the rhizosphere . The community structure of shoot-associated bacteria was highly different . The majority of clones affiliated with the Proteobacteria, but also bacteria belonging to the Cytophaga/Flexibacter/Bacteroides division, the Holophaga/Acidobacterium division, and the low-G+C gram-positive bacteria, were frequently found . A high number of highly related Sphingomonas 16S rRNA gene sequences were detected, which were also obtained by the cultivation of endophytes . Rhizosphere isolates belonged mainly to the genera Methylobacterium, Rhodococcus, and Okibacterium, whereas the majority of endophytes showed high levels of similarity to Methylobacterium mesophilicum . Additionally, Sphingomonas spp . were abundant . Isolates were resistant to Ni concentrations between 5 and 12 mM; however, endophytes generally tolerated higher Ni levels than rhizosphere bacteria . Almost all bacteria were able to produce siderophores . Various strains, particularly endophytes, were able to grow on ACC as the sole nitrogen source .
The DevT Protein Stimulates Synthesis of FruA, a Signal Transduction Protein Required for Fruiting Body Morphogenesis in Myxococcus xanthus. Anders Boysen, 2002.Fruiting body formation in Myxococcus xanthus involves three morphologic stages—rippling, aggregation, and sporulation—all of which are induced by the cell surface-associated C-signal . We analyzed the function of the DevT protein, a novel component in the C-signal response pathway . A mutant carrying an in-frame deletion in the devT gene displays delayed aggregation and a cell autonomous sporulation defect, whereas it remains rippling proficient . To further define the function of DevT, the methylation pattern of FrzCD, a cytoplasmic methyl-accepting chemotaxis protein homologue, was examined in the  devT mutant, and we found that DevT is required for methylation of FrzCD during development . Specifically, DevT was found to be required for the C-signal-dependent methylation of FrzCD . The
devT mutant produced wild-type levels of C-signal . However, accumulation of the FruA response regulator protein, which is essential for the execution of the C-signal-dependent responses, was reduced in the
devT mutant . The DevT protein was found to stimulate the developmentally activated transcription of the fruA gene . Epistasis analyses indicate that DevT acts independently of the A- and E-signals to stimulate fruA transcription . These findings suggest that the developmental defects of the
devT mutant are associated with a lack of FruA to ensure a proper response to the C-signal during the aggregation and sporulation stages of development .
A Rhizobium leguminosarum AcpXL Mutant Produces Lipopolysaccharide Lacking 27-Hydroxyoctacosanoic Acid. Vinata Vedam, 2003.The structure of the lipid A from Rhizobium etli and Rhizobium leguminosarum lipopolysaccharides (LPSs) lacks phosphate and contains a galacturonosyl residue at its 4' position, an acylated 2-aminogluconate in place of the proximal glucosamine, and a very long chain  -1 hydroxy fatty acid, 27-hydroxyoctacosanoic acid (27OHC28:0) . The 27OHC28:0 moiety is common in lipid A's among members of the Rhizobiaceae and also among a number of the facultative intracellular pathogens that form chronic infections, e.g., Brucella abortus, Bartonella henselae, and Legionella pneumophila . In this paper, a mutant of R . leguminosarum was created by placing a kanamycin resistance cassette within acpXL, the gene which encodes the acyl carrier protein for 27OHC28:0 . The result was an LPS containing a tetraacylated lipid A lacking 27OHC28:0 . A small amount of the mutant lipid A may contain an added palmitic acid residue . The mutant is sensitive to changes in osmolarity and an increase in acidity, growth conditions that likely occur in the nodule microenvironment . In spite of the probably hostile microenvironment of the nodule, the acpXL mutant is still able to form nitrogen-fixing root nodules even though the appearance and development of nodules are delayed . Therefore, it is possible that the acpXL mutant has a host-inducible mechanism which enables it to adapt to these physiological changes .
Design and Application of a New Cryptic-Plasmid-Based Shuttle Vector for Magnetospirillum magneticum. Yoshiko Okamura, 2003.A 3.7-kb cryptic plasmid designated pMGT was found in Magnetospirillum magneticum MGT-1 . It was characterized and used for the development of an improved expression system in strain AMB-1 through the construction of a shuttle vector, pUMG . An electroporation method for magnetic bacteria that uses the cryptic plasmid was also developed .
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