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Volume 143,
Issue 12,
1997
Volume 143, Issue 12, 1997
- Physiology And Growth
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Acetate acts as a protonophore and differentially affects bead movement and cell migration of the gliding bacterium Cytophaga johnsonae (Flavobacterium johnsoniae)
More LessCells of Cytophaga johnsonae (now Flavobacterium johnsoniae) are able to translocate on solid surfaces but are unable to swim in liquid media. Organelles that may be involved in this gliding motility have not been detected, and the mechanism(s) responsible remains unknown. The movement of latex beads attached to the cell surface is considered by some to be a manifestation of the gliding machinery. In this study, acetate (in nutrient-level quantity, 45 mom) was found to inhibit bead movement on cell surfaces, whilst formation and movement of groups of cells (rafts) and typical colony spread were not affected; generation time (in liquid culture) was only slightly increased. Since acetate is a weak acid and is recognized as a protonophore, various electron-transport-associated features were assessed in an effort to understand the differential effects of acetate on bead movement and cell motility. Selected protonophores and electron transport inhibitors were tested to compare their effects on cell translocation and metabolic activities with those of acetate. Although O2 consumption was not significantly affected in the presence of acetate and the protonmotive force decreased only minimally, ATP levels were markedly decreased. Arsenate and cyanide were also shown to inhibit bead movement but did not inhibit either movement of rafts of cells or colony spreading. Cyanide lowered O2 consumption, while arsenate did not; both compounds effected substantial decreases in cellular ATP content, but little or no decrease in protonmotive force. The inhibitory effects of these compounds on bead movement over cell surfaces contrasted with the continued ability of cells to form rafts, to glide and to form spreading colonies and led to the conclusion that bead movement is not a complete correlate of the gliding machinery of C. johnsonae. In addition, it seems likely that bead movement is more affected by the level of cellular ATP than it is by the protonmotive force, which has been assumed to provide the energy (derived from the transmembrane gradients) for the gliding machinery.
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Cytochemical studies of cell viability and gene expression in Bacillus subtilis macrofibres
More LessThe viability of cells and the expression of a reporter gene in Bacillus subtilis macrofibres have been examined using cytochemical approaches. Previous studies have shown that macrofibres grow at an exponential rate in fluid environments and undergo complex dynamic motions as they elongate but the behaviour of individual cells in them has never been examined. A fluorescence staining procedure that distinguishes living cells from dead cells was used in the experiments described to examine cells in both left- and right-handed macrofibres. Very few dead cells were found in individual fibres. Their locations appeared to be random, suggesting that neither the extreme shape deformation imposed upon cells in the loop ends of fibres, nor the entrapment of cells in the interior of a fibre compromise viability. In related experiments, initial studies of reporter gene expression during fibre morphogenesis were conducted using a strain previously studied as conventional colonies. Spatial and temporal differences in the appearance of the blue cleavage product of X-Gal were found, suggesting that differential gene expression may arise in macrofibres in contrast to the results found in colonies. Two conclusions may be drawn from the findings: (i) virtually all cells in macrofibres are viable and (ii) all the cells in macrofibres do not always behave in an identical manner.
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Influence of Na+ and anions on the dimorphic transition of Candida albicans
More LessThe effect of Na+ (CI- or gluconate salt) on growth and dimorphic potential of the pathogenic yeast Candida albicans has been examined. Profiles of germ tube formation as a function of salt addition, pH and temperature indicated Na+ inhibition of germ tube outgrowth at high ambient pH (pH 8.0) which was exacerbated by replacement of CI- with gluconate (as an impermeant analogue). At acidic pH (pH 5.5) and permissive temperature (37 °), gluconate alone promoted the dimorphic transition. Rates of glucose-induced medium acidification and plasma membrane H+-ATPase activity have been measured to assess whether salt treatments could retard the cytoplasmic alkalinization known to precede germ tube formation. The precise site of Na+ action remains unclear but the anion effects may be interpreted in terms of anion-exchanger and channel activity acting to modulate cytosolic pH.
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Effect of carbon substrate and aeration on nitrate reduction and expression of the periplasmic and membrane-bound nitrate reductases in carbon-limited continuous cultures of Paracoccus denitrificans Pd1222
More LessThe expression and in situ activity of the membrane-bound and periplasmic nitrate reductases have been assayed in Paracoccus denitrificans Pd1222 grown under a range of aeration regimes in malate-limited or butyrate-limited chemostat cultures. In butyrate-limited cultures the expression of periplasmic nitrate reductase and the rate of in situ nitrate reduction were high at all oxygen concentrations measured between 0% and 100% air saturation. By contrast, in malate-limited cultures expression of the periplasmic nitrate reductase was low at 80-100% air saturation but increased to a maximum between 20% and 50% air saturation. Aerobic nitrate reduction was much higher in butyrate-limited than in malate-limited cultures, demonstrating a significant role for this process during butyrate metabolism. The rate of nitrate respiration increased in both the malate- and butyrate-limited cultures as aerobic metabolism switched completely to anaerobic metabolism. Expression of the membrane-bound nitrate reductase could be detected in butyrate-limited chemostat cultures maintained at an oxygen level of 100% air saturation. No membrane-bound nitrate reductase was detectable under similar conditions in malate-limited cultures but expression was detected at oxygen concentrations of 50% air saturation and below. Taken together, the results show that the nature of the carbon substrate and oxygen concentration can both influence expression of the periplasmic and membrane-bound nitrate reductases. The conditions under which expression of the periplasmic nitrate reductase and aerobic nitrate respiration are maximal can be rationalized in terms of a role for the periplasmic nitrate reductase in dissipating excess reductant generated during oxidative metabolism of reduced carbon substrates.
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- Plant-Microbe Interactions
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Biological control of Pythium ultimum by Stenotrophomonas maltophilia W81 is mediated by an extracellular proteolytic activity
More LessStenotrophomonas maltophilia strain W81, isolated from the rhizosphere of field-grown sugar beet, produced the extracellular enzymes chitinase and protease and inhibited the growth of the phytopathogenic fungus Pythium ultimum in vitro. The role of these lytic enzymes in the interaction between W81 and P. ultimum was investigated using Tn5 insertion mutants of W81 incapable of producing extracellular protease (W81M1), extracellular chitinase (W81M2) or the two enzymes (W81A1). Lytic enzyme activity was restored in W81A1 following introduction of a 15 kb cosmid-borne fragment of W81 genomic DNA. Incubation of P. ultimum in the presence of commercial purified protease or cell-free supernatants from cultures of wild-type W81, the chitinase-negative mutant W81M2 or the complemented derivative W81A1 (pCU800) resulted in hyphal lysis and loss of subsequent fungal growth ability once re-inoculated onto fresh plates. In contrast, commercial purified chitinase or cell-free supernatants from cultures of the protease-negative mutant WS1M1 or the chitinase- and protease-negative mutant W81A1 had no effect on integrity of the essentially chitin-free Pythium mycelium, and did not prevent subsequent growth of the fungus. In soil microcosms containing soil naturally infested by Pythium spp., strains W81, W81M2 and W81A1(pCU800) reduced the ability of Pythium spp. to colonize the seeds of sugar beet and improved plant emergence compared with the untreated control, whereas W81A1 and W21M1 failed to protect sugar beet from damping-off. Wild-type W81 and its mutant derivatives colonized the rhizosphere of sugar beet to similar extents, it was concluded that the ability of S. maltophilia W81 to protect sugar beet from Pythium -mediated damping-off was due to the production of an extracellular protease.
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Functional redundancy of genes for sulphate activation enzymes in Rhizobium sp. BR816
The broad-host-range, heat-tolerant Rhizobium strain BR816 produces sulphated Nod metabolites. Two ORFs highly homologous to the Sinorhizobium meliloti nodPQ genes were isolated and sequenced. It was found that Rhizobium sp. BR816 contained two copies of these genes; one copy was localized on the symbiotic plasmid, the other on the megaplasmid. Both nodP genes were interrupted by insertion of antibiotic resistance cassettes, thus constructing a double nodP1P2 mutant strain. However, no detectable differences in Nod factor TILC profile from this mutant were observed as compared to the wild-type strain. Additionally, plant inoculation experiments did not reveal differences between the mutant strain and the wild-type. It is proposed that a third, functionally homologous locus complements mutations in the Nod factor sulphation genes. Southern blot analysis suggested that this locus contains genes necessary for the sulphation of amino acids.
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- Genome Analysis
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Physical map of the Bacillus subtilis 166 genome: evidence for the inversion of an approximately 1900 kb continuous DNA segment, the translocation of an approximately 100 kb segment and the duplication of a 5 kb segment
More LessAn I-Ceul-Notl-Sfil endonuclease map of the Bacillus subtilis 166 genome was constructed. It was almost identical to that of B. subtilis 168 except for the inversion of an approximately 1900 kb DNA segment, the translocation of an approximately 100 kb segment and the duplication of a 5 kb segment. Continuity of the inverted segment was investigated by direct measurement of the distances between the two genomic loci where I-Scel recognition sites were created in the 168 and the 166 genomes. Size difference of the I-Scel fragments between the two strains fully demonstrated the inversion of an approximately 1900 kb long continuous DNA segment and the location of the two inversion junctions in the genome. The 100 kb DNA segment including the lysogenic SP prophage was translocated close to one of the inversion junctions and was probably associated with the duplication of a 5 kb segment These rearrangements are consistent with those indicated by genetic analyses
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