摘要:

Fluoride is widely used as a highly effective anticaries agent. Although it is felt that its anticaries action is related mainly to effects on mineral phases of teeth and on the process of remineralization, fluoride also has important effects on the bacteria of dental plaque, which are responsible for the acidification of plaque that results in demineralization. The results of recent studies have shown that fluoride can affect bacterial metabolism through a set of actions with fundamentally different mechanisms. It can act directly as an enzyme inhibitor, for example for the glycolytic enzyme enolase, which is inhibited in a quasi-irreversible manner. Direct action seems also to occur in inhibition of heme-based peroxidases with binding of fluoride to heme. The flavin-based peroxidases of many oral bacteria are insensitive to fluoride. Another mode of action involves formation of metal–fluoride complexes, most commonly AlF4−. These complexes are responsible for fluoride inhibition of proton-translocating F-ATPases and are thought to act by mimicking phosphate to form complexes with ADP at reaction centers of the enzymes. However, the actions of fluoride that are most pertinent to reducing the cariogenicity of dental plaque are those related to its weak-acid character. Fluoride acts to enhance membrane permeabilities to protons and compromises the functioning of F-ATPases in exporting protons, thereby inducing cytoplasmic acidification and acid inhibition of glycolytic enzymes. Basically, fluoride acts to reduce the acid tolerance of the bacteria. It is most effective at acid pH values. In the acidic conditions of cariogenic plaque, fluoride at levels as low as 0.1 mM can cause complete arrest of glycolysis by intact cells ofStreptococcus mutans. Overall, the anticaries actions of fluoride appear to be complex, involving effects both on bacteria and on mineral phases. The antibacterial actions of fluoride appear themselves to be complex but to be dominated by weak-acid effects.Key words: fluoride, oral bacteria, dental caries, glycolysis.

ISSN:0008-4166    

DOI:10.1139/m95-133

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Thetet(O) tetracycline resistance gene, originally cloned fromCampylobacter jejuni, mediates resistance by ribosomal protection. Using partially purified Tet(O) protein of 68 000 Da whose identity was verified by ribosomal protection assays, amino terminal sequencing, and immunoblotting using an antibody raised against the deduced 15 amino acids at the carboxyl terminus of the Tet(O) protein, the Tet(O) protein was found to bind to [α-32P]GTP and [3H]GDP using a filter binding assay. [γ-32P]GTP hydrolysis by Tet(O) was also demonstrated and was found to be time dependent with more than 50% of the hydrolysis activity occurring within the first 5 min. The GTPase activity of Tet(O) appears to be ribosome dependent, suggesting that ribosomes act as an effector similar to other G proteins involved in signal transduction.Key words: ribosomes, tetracycline resistance, GTPase, protein synthesis.

ISSN:0008-4166    

DOI:10.1139/m95-134

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The fungal metabolite brefeldin A (BFA) is known for its ability to block the secretory process in eukaryotic cells by interfering in the endoplasmic reticulum (ER) to Golgi membrane traffic, causing the disassembly of Golgi apparatus and redistribution of Golgi enzymes into the ER. In sensitive yeasts, underglycosylated forms of secretory proteins accumulate in the cytoplasm in the presence of BFA. We investigated whether the incomplete glycosylation of mannoproteins could be due to repression of the synthesis of Golgi-located terminal mannosyltransferases and whether the underglycosylated mannoproteins can be incorporated into the cell walls inCandida albicans. However, we found that the microsomal membranes isolated from the yeast cells grown in the presence of 14 μg∙mL−1of BFA had on average three times higher overall specific activity of mannan synthase than membranes from control cells. The increase in specific activity of mannan synthase was mainly due to accumulation of Golgi-specific mannosyltransferases responsible for elongation of theO-glycosidically linked mannooligosaccharides and for the synthesis of theN-glycosidically linked mannan outer chain. As a consequence, the mannans synthesized in vitro from GDP-[U-14C]mannose by the membranes from cells grown in the presence of BFA had longerO-glycosidically linked oligosaccharides and longer side-chains in theN-glycosidically linked polymannose part of the molecule than mannans synthesized by membranes from the control cells. Contrary to results obtained in vitro, the structural features of cell wall mannans isolated from intact BFA-grown and from control cells were almost indistinguishable.Key words: brefeldin A, Golgi apparatus, mannoproteins, mannosyltransferase,Candida albican

ISSN:0008-4166    

DOI:10.1139/m95-135

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The effect of glucose on superoxide dismutase (SOD) activity produced inHumicola lutea110 was determined. The relatively high glucose concentration in the medium did not repress SOD levels in the cells. Glycerol, a nonfermentable carbon source, caused a slight stimulation of SOD synthesis. Furthermore, the specific rates of enzyme production in the medium with different glucose concentration showed an insignificant difference. Cyclic AMP had no effect on SOD levels. The shift in metabolism as glucose was depleted resulted in an increase in the rate of synthesis of both isocitric dehydrogenase and SOD. Pentachlorophenol and paraquat, which cause the production of superoxide radicals, caused an increase in SOD activity. These results led us to conclude that it is superoxide ion rather than glucose that is controlling SOD levels.Key words:Humicola lutea, fungi, superoxide dismutase, intracellular enzyme, glucose effect.

ISSN:0008-4166    

DOI:10.1139/m95-136

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Many microbes reduce the nitro substituents of 2,4,6-trinitrotoluene (TNT), producing aminodinitrotoluenes (ADNTs). These compounds are recalcitrant to further breakdown and are acutely toxic. In a search for organisms capable of metabolizing ADNTs, a bacterial strain was isolated for the ability to use 2-aminobenzoate (anthranilate) as sole C-source. This isolate,Pseudomonas aeruginosaMA01, metabolized TNT by first reducing one nitro group to form either 2-amino-4,6-dinitrotoluene (2ADNT) or 4-amino-2,6-dinitrotoluene (4ADNT). However, strain MA01 was distinct from other TNT-reducing organisms in that it transformed these compounds into highly polar metabolites through an O2-dependent process. Strain MA01 was able to cometabolize TNT, 2ADNT, and 4ADNT in the presence of a variety of carbon and energy sources. During aerobic cometabolism with succinate, 45% of uniformly ring-labeled [14C]TNT was transformed to highly polar compounds. Aerobic cometabolism of purified [14C]2ADNT and [14C]4ADNT with succinate as C-source produced similar amounts of these polar metabolites. During O2-limited cometabolism with succinate as C-source and nitrate as electron acceptor, less than 8% of the [14C]TNT was transformed to polar metabolites. Purified 2,6-diamino-4-nitrotoluene was not metabolized, and while 2,4-diamino-6-nitrotoluene was acetylated, the product (N-acetyl-2,4-diamino-6-nitrotoluene) was not further metabolized. Therefore, strain MA01 metabolized TNT by oxidation of the ADNTs and not by reduction the remaining nitro groups on the ADNTs.Key words: 2,4,6-trinitrotoluene, aminodinitrotoluene,Pseudomonas aeruginosa, cometabolism.

ISSN:0008-4166    

DOI:10.1139/m95-137

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The low nodule occupancy achieved by superior nitrogen-fixing inoculant strains is a problem in the production of many traditional legume species, includingPhaseolus vulgaris. Cultivars that select for inoculant strains, rather than nodulate with ineffective indigenous rhizobia, offer one approach to the resolution of this problem. In this study we identify a bean cultivar, RAB39, that nodulates preferentially withRhizobium tropici, including the inoculant-quality strain UMR1899. This preference in nodulation was not affected by temperature or pH, though strain preference by a second, alkaline-producingRhizobium etlistrain did vary markedly with temperature. When RAB39 was inoculated with 1:1 mixtures of UMR1899 and seven serologically distinct strains ofRhizobium etli, more than 75% of the nodules formed by each strain pair contained UMR1899. A number of studies have reported close correlations between the percent nodule occupancy and speed of nodulation, measured using the root-tip-marking procedure. Exceptions to this correlation were evident in the present study, suggesting that host preference in nodulation was not related to differences in the parameters normally used to estimate speed of nodulation. The preference of RAB39 forR.tropici, a speciesof Rhizobiumthat occurs at low frequency in most bean soils, and especially for the inoculant-quality strain UMR1899, provides a tool to overcome the lack of response to inoculation in common bean.Key words: competition, nodulation efficiency, strain preference, common bean.

ISSN:0008-4166    

DOI:10.1139/m95-138

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Nitrogen fixation and colonization by associative cyanobacteria in the aerial roots (pneumatophores) of black mangrove trees was evaluated in situ at Balandra lagoon, Baja California Sur, Mexico, for 18 consecutive months. Year-round vertical zonation of cyanobacterial colonization was determined along the pneumatophores. The bottom part close to the sediment was colonized mainly by nonheterocystous, filamentous cyanobacteria resemblingLyngbyasp. andOscillatoriasp. The central zone was colonized mainly by filaments resemblingMicrocoleussp. and the upper part was colonized by coccoidal cyanobacteria within defined colonies resemblingAphanothecesp. mixed with undefined filamentous cyanobacteria. Two of the cyanobacteria (Microcoleussp. andAnabaenasp.) isolated from the pneumatophore were diazotrophs. Massive biofilm production along the pneumatophores was evident throughout the observation period. The surrounding sediment was seasonally dominated by heterocystousAnabaenasp. Glass and dead-wood surfaces incubated for 18 months in the pneumatophore vicinity showed no zonation in the colonization pattern, although they were heavily colonized. In situ N2fixation showed seasonal and diurnal fluctuations. N2fixation was low during winter, increased in early summer, and reached its peak in midsummer. N2fixation in the summer showed diurnal peaks: one in the morning until midday and the second in the late afternoon. N2fixation was at its lowest levels near midnight. Light and water temperature are probably primary environmental factors governing N2fixation on the pneumatophores.Key words:Avicennia germinans, black mangrove, diazotrophic cyanobacteria, nitrogen fixation, pneumatophore.

ISSN:0008-4166    

DOI:10.1139/m95-139

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

An isolate of the filamentous cyanobacteriumMicrocoleussp. was obtained from black mangrove aerial root (pneumatophore) and inoculated onto young mangrove seedlings to evaluate N2-fixation and root-colonization capacities of the bacterium under in vitro conditions in closed-system experiments. N2fixation (acetylene reduction) gradually increased with time and reached its peak 5 days after inoculation. Later, it decreased sharply. The level of N2fixation in the presence of the plant was significantly higher than the amount of nitrogen fixed by a similar quantity of cyanobacteria on a N-free growth medium. The main feature of this root colonization was the gradual production of a biofilm in which the cyanobacterial filaments were embedded. Visible biofilm production increased with time until it completely covered the entire root system of the plant. The in-and-out movement of cyanobacterial filaments from the biofilm probably allows colonization of uncolonized portions of the root several days after the initial inoculation. This is, to the best of our knowledge, the first report of the artificial inoculation of cyanobacteria on marine mangroves.Key words:Avicennia germinans, beneficial bacteria, biofilm, black mangrove, diazotrophic cyanobacteria,Microcoleussp., nitrogen fixation, plant growth-promoting bacteria, root colonization.

ISSN:0008-4166    

DOI:10.1139/m95-140

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Strain ATCC 51466, a motile peanutRhizobiumsp., showed patterns of utilization of diverse carbon sources characteristic of fast growers. Bacteria had periplasmic neutral glucans with molecular weight close to 3000. When the extracellular concentration of NaCl was raised to 400 mM, the lag phase of the culture was prolonged about threefold and the generation time was increased almost twice. The changes in growth behavior of salt-stressed bacteria were accompanied by the full suppression of periplasmic oligoglucans and the accumulation of cellular trehalose. Almost identical changes in cell-associated oligoglucans were observed after exposing peanutRhizobiumsp. strain ATCC 10317 to hypersalinity. When the osmotic pressure of the medium was augmented by the addition of either 200 mM mannitol or 16% (w/v) polyethylene glycol, cells of strain ATCC 51466 contained decreased levels of oligoglucans and accumulated trehalose. On the other hand, the content of cellular trehalose increased throughout logarithmic and stationary phases of growth of strain ATCC 51466 in a medium supplemented with 400 mM NaCl. When bacterial cultures were shifted from hypersaline to basal media, oligoglucans were the only oligosaccharides detected. The addition of 10 mM proline to bacteria grown under hypersalinity led to a 50% decrease in the level of trehalose and to the accumulation of oligoglucans. The addition of 10 mM glycine betaine to bacteria grown under hypersalinity also produced accumulation of oligoglucans, but the level of trehalose did not decrease. The results presented here are consistent with a role for trehalose as a compatible solute in peanutRhizobiumATCC 51466, and they suggest that exogenously added proline may act as a compatible solute in preference to trehalose.Key words: periplasmic glucans, trehalose, peanutRhizobium, osmotic stress.

ISSN:0008-4166    

DOI:10.1139/m95-141

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Borreliaspecies are microaerophilic spirochetes, i.e., they are unable to grow in the presence of atomospheric oxygen (21%) or under anaerobic conditions. Compounds that have been shown to quench toxic products of oxygen (i.e., superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen) were added toBorreliagrowth media (Kelly's medium). Among the compounds tested were catalase, superoxide dismutase, peroxidase, dithiothreitol (DTT), formate, fumarate, dimethyl sulfoxide (DMSO), manganese, activated charcoal (Norit A), mannitol, and a combination of ferric chloride and potassium (meta)bisulfite (iron-bisulfite). Of these, the compounds that were the most effective in enhancing the growth of the species ofBorreliatested were iron-bisulfite, DTT, and DMSO. DTT possesses the ability to break down hydrogen peroxide, and iron-bisulfite has been reported to have superoxide dismutase-like activity in artificial media. Iron-bisulfite, DMSO, sodium formate, DTT, and combinations of these compounds have been incorporated into solid and biphasic Kelley's medium to determine their effect on microaerobic and aerobic growth on plates and in biphasic medium. Iron-bisulfite was the most effective compound tested under these conditions.Key words:Borrelia, bisulfite, spirochetes, microaerobe.

ISSN:0008-4166    

DOI:10.1139/m95-142

出版商:NRC Research Press    

年代:1995

数据来源: NRC