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FNR-Mediated Oxygen-Responsive Regulation of the nrdDG Operon of Escherichia coli. T. Boston, 2003.Transcription of the nrdDG operon, which encodes the class III nucleotide reductase, which is only active under anaerobic conditions, was strongly induced after a shift to anaerobiosis . The induction was completely dependent on the transcriptional activator FNR and was independent of the ArcA-ArcB two-component response regulator system . The nrdD transcript start site was mapped to a position immediately downstream of two FNR binding sites . Transcription of the other two nucleotide reductase operons, nrdAB and nrdEF, did not respond to oxygen conditions in a wild-type background, but nrdAB expression was increased in the fnr mutant under anaerobic conditions . Role of the Cytoplasmic C Terminus of the FliF Motor Protein in Flagellar Assembly and Rotation. Björn Grünenfelder, 2003.Twenty-six FliF monomers assemble into the MS ring, a central motor component of the bacterial flagellum that anchors the structure in the inner membrane . Approximately 100 amino acids at the C terminus of FliF are exposed to the cytoplasm and, through the interaction with the FliG switch protein, a component of the flagellar C ring, are essential for the assembly of the motor . In this study, we have dissected the entire cytoplasmic C terminus of the Caulobacter crescentus FliF protein by high-resolution mutational analysis and studied the mutant forms with regard to the assembly, checkpoint control, and function of the flagellum . Only nine amino acids at the very C terminus of FliF are essential for flagellar assembly . Deletion or substitution of about 10 amino acids preceding the very C terminus of FliF resulted in assembly-competent but nonfunctional flagella, making these the first fliF mutations described so far with a Fla+ but Mot- phenotype . Removal of about 20 amino acids further upstream resulted in functional flagella, but cells carrying these mutations were not able to spread efficiently on semisolid agar plates . At least 61 amino acids located between the functionally relevant C terminus and the second membrane-spanning domain of FliF were not required for flagellar assembly and performance . A strict correlation was found between the ability of FliF mutant versions to assemble into a flagellum, flagellar class III gene expression, and a block in cell division . Motile suppressors could be isolated for nonmotile mutants but not for mutants lacking a flagellum . Several of these suppressor mutations were localized to the 5' region of the fliG gene . These results provide genetic support for a model in which only a short stretch of amino acids at the immediate C terminus of FliF is required for flagellar assembly through stable interaction with the FliG switch protein . Microbial Community Composition Affects Soil Fungistasis. Wietse de Boer, 2003.Most soils inhibit fungal germination and growth to a certain extent, a phenomenon known as soil fungistasis . Previous observations have implicated microorganisms as the causal agents of fungistasis, with their action mediated either by available carbon limitation (nutrient deprivation hypothesis) or production of antifungal compounds (antibiosis hypothesis) . To obtain evidence for either of these hypotheses, we measured soil respiration and microbial numbers (as indicators of nutrient stress) and bacterial community composition (as an indicator of potential differences in the composition of antifungal components) during the development of fungistasis . This was done for two fungistatic dune soils in which fungistasis was initially fully or partly relieved by partial sterilization treatment or nutrient addition . Fungistasis development was measured as restriction of the ability of the fungi Chaetomium globosum, Fusarium culmorum, Fusarium oxysporum, and Trichoderma harzianum to colonize soils . Fungistasis did not always reappear after soil treatments despite intense competition for carbon, suggesting that microbial community composition is important in the development of fungistasis . Both microbial community analysis and in vitro antagonism tests indicated that the presence of pseudomonads might be essential for the development of fungistasis . Overall, the results lend support to the antibiosis hypothesis . Characterization of Genes Involved in the Metabolism of  -Galactosides by Lactococcus raffinolactis.Isabelle Boucher, 2003.Lactococcus raffinolactis, unlike most lactococci, is able to ferment -galactosides, such as melibiose and raffinose . More than 12 kb of chromosomal DNA from L . raffinolactis ATCC 43920 was sequenced, including the
-galactosidase gene and genes involved in the Leloir pathway of galactose metabolism . These genes are organized into an operon containing aga (-galactosidase), galK (galactokinase), and galT (galactose 1-phosphate uridylyltransferase) . Northern blotting experiments revealed that this operon was induced by galactosides, such as lactose, melibiose, raffinose, and, to a lesser extent, galactose . Similarly,
-galactosidase activity was higher in lactose-, melibiose-, and raffinose-grown cells than in galactose-grown cells . No
-galactosidase activity was detected in glucose-grown cells . The expression of the aga-galKT operon was modulated by a regulator encoded by the upstream gene galR . The product of galR belongs to the LacI/GalR family of transcriptional regulators . In L . lactis, L . raffinolactis GalR acted as a repressor of aga and lowered the enzyme activity by more than 20-fold . We suggest that the expression of the aga operon in lactococci is negatively controlled by GalR and induced by a metabolite derived from the metabolism of galactosides .
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