摘要:

Endophytic bacteria are ubiquitous in most plant species, residing latently or actively colonizing plant tissues locally as well as systemically. Several definitions have been proposed for endophytic bacteria; in this review endophytes will be defined as those bacteria that can be isolated from surface-disinfested plant tissue or extracted from within the plant, and that do not visibly harm the plant. While this definition does not include nonextractable endophytic bacteria, it is a practical definition based on experimental limitations and is inclusive of bacterial symbionts, as well as internal plant-colonizing nonpathogenic bacteria with no known beneficial or detrimental effects on colonized plants. Historically, endophytic bacteria have been thought to be weakly virulent plant pathogens but have recently been discovered to have several beneficial effects on host plants, such as plant growth promotion and increased resistance against plant pathogens and parasites. In general, endophytic bacteria originate from the epiphytic bacterial communities of the rhizosphere and phylloplane, as well as from endophyte-infested seeds or planting materials. Besides gaining entrance to plants through natural openings or wounds, endophytic bacteria appear to actively penetrate plant tissues using hydrolytic enzymes like cellulase and pectinase. Since these enzymes are also produced by pathogens, more knowledge on their regulation and expression is needed to distinguish endophytic bacteria from plant pathogens. In general, endophytic bacteria occur at lower population densities than pathogens, and at least some of them do not induce a hypersensitive response in the plant, indicating that they are not recognized by the plant as pathogens. Evolutionarily, endophytes appear to be intermediate between saprophytic bacteria and plant pathogens, but it can only be speculated as to whether they are saprophytes evolving toward pathogens, or are more highly evolved than plant pathogens and conserve protective shelter and nutrient supplies by not killing their host. Overall, the endophytic microfloral community is of dynamic structure and is influenced by biotic and abiotic factors, with the plant itself constituting one of the major influencing factors. Since endophytic bacteria rely on the nutritional supply offered by the plant, any parameter affecting the nutritional status of the plant could consequently affect the endophytic community. This review summarizes part of the work being done on endophytic bacteria, including their methodology, colonization, and establishment in the host plant, as well as their role in plant–microbe interactions. In addition, speculative conclusions are raised on some points to stimulate thought and research on endophytic bacteria.Key words: endophytic bacteria, methods, localization, diversity, biological control.

ISSN:0008-4166    

DOI:10.1139/m97-131

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Chocolate spot caused byBotrytis cinereaandBotrytis fabaeis a serious disease ofVicia fabaL. beans. Aggressive infection of that disease can result in severe yield losses (up to 100%). Genetic resistance to chocolate spot inV.fabaL. is weak. Chemical control of the disease gives only partial crop protection because of widespread fungicide resistance in both chocolate spot agents. Biological control with applications of bacteria antagonistic toBotrytismay provide a useful alternative to chemicals. Of 270Bacillusisolates tested, 54 (20%) were found to cause necrosis and (or) chlorosis when placed on leaves ofV.fabaL. Only 14 strains (6.5%) were able to prevent chocolate spot symptoms from developing in vivo and all of these antagonisedBotrytis cinereaandBotrytis fabaein vitro by antibiosis.Bacillus maceransBS 153 was selected for biocontrol experiments in both the greenhouse and field in which plants were sprayed with bacterial suspensions. Detached leaves were inoculated withBotrytisat intervals afterBacillus maceransBS 153 application. The beneficial effect of the biocontrol agent persisted much longer in greenhouse-grown plants. The estimated ED50was 1.3 times less in the greenhouse spray than in the field spray. From the high number of bacteria required and the rate of decline of introducedBacilluspopulation in field-grown plants, it was concluded that biocontrol of chocolate spot byBacillusis impractical unless improved formulations and spray application techniques are developed.Key words: chocolate spot,Bacillusisolates, biocontrol.

ISSN:0008-4166    

DOI:10.1139/m97-132

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The rates of CH4oxidation by strains of groups I and II methanotrophs in pure culture were studied at various O2concentrations from 0 to 63 % v/v. In the presence of nonlimiting dissolved CH4and inorganic nitrogen, O2concentrations from 0.45 to 20% v/v supported maximum rates of CH4oxidation. The critical dissolved O2concentration under our conditions was about 5.7 μM, below which O2was limiting for CH4oxidation. Concentrations of O2up to 63% v/v depressed the activity of CH4oxidation by ≥ 23%. We conclude that methanotrophs are not microaerophilic under the conditions of our experiments and that they have a high affinity for O2.Key words: CH4oxidation, O2response,Methylosinus trichosporium,Methylobacter luteus.

ISSN:0008-4166    

DOI:10.1139/m97-133

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A strain ofFusarium oxysporum, isolated from an industrial effluent containing a high cyanide concentration, detoxifies cyanide via formamide hydro-lyase (FHL). The importance of the coexistence of the alternative (cyanide insensitive) respiratory system and the synthesis of FHL was assessed. This enzyme, induced by cyanide, converts this compound to formamide and is partially responsible for the tolerance ofF.oxysporumto high cyanide concentration. The FHL induction for cyanide detoxification depends on the alternative respiratory system when the terminal oxidase of the electron transport chain is blocked by cyanide used during the induction process. The respiratory metabolism of aF.oxysporumstrain was studied. Whole cells exhibited a cyanide-sensitive respiration but developed a partially cyanide-resistant respiration under certain physiological conditions, namely, in the stationary phase of growth, in the presence of chloramphenicol in the growth medium, or upon aeration in the absence of nutrients (starvation conditions). Cycloheximide prevented the appearance of cyanide-insensitive respiration when the cells were aerated under starvation conditions. This fact suggested some form of induction involving de novo protein synthesis.Key words: cyanide tolerance, cyanide-resistant respiration, formamide hydro-lyase,Fusarium oxysporum.

ISSN:0008-4166    

DOI:10.1139/m97-134

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Leachate from a municipal landfill site was treated in a laboratory using fixed-film cultures under anaerobic conditions. Serum-bottle cultures were used for optimization of the growth parameters. The reduction of the chemical oxygen demand (COD) of the leachate was faster at 29 °C compared with lower temperatures. Gradual acclimation of the microbial population to temperatures as low as 4 °C considerably increased the rate of COD removal at these temperatures. Addition of supplements to the leachate was not needed and it was not necessary to adjust the pH (5.9) for optimal COD reduction. Continuously fed reactors were also used to treat the leachate. The maximum organic loading rate of the reactor at 22 °C to obtain 85% COD removal was 2.1 kg COD∙m−3∙day−1, which corresponded to an hydraulic retention time of 1.5 days. After treatment under these conditions, the toxicity (Microtox method) of the leachate was completely eliminated and the required quality standards were met for iron, oil and grease, and phenols. The fermentative microorganisms in the biofilm of the reactor were evaluated to 4.6 × 107cells∙cm−2and identified asStreptococcus gallinarum,Clostridium glycolicum,Clostridium bifermentansorsadallii,Citrobacter amalonaticus,Bacteroides capillosus, andEubacteriumsp.Key words: anaerobic treatment, landfill, leachate, growth parameters, fixed-film reactor, microbi

ISSN:0008-4166    

DOI:10.1139/m97-135

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Both living and fixed cells ofSchizosaccharomyces japonicusvar.versatilisshowed thread-like mitochondria when studied by phase-contrast and fluorescence microscopy. In the interphase cells, mitochondria extended from pole to pole and converged towards the growing tips. The mitochondrial threads did not disrupt but persisted during mitosis and, subsequently, their bundle was split between the two daughter cells by a concentrically growing septum. Mitochondria in the interphase cells were accompanied by cytoplasmic microtubules. These disappeared during mitosis and, instead, spindle microtubules were formed in the nucleus. The cytoplasmic microtubules reappeared after anaphase B, again in coaligment with mitochondria. Protoplasting as well as the action of microtubule inhibitors methyl-1-(butylcarbamoyl)-2-benzimidazolecarbamate (benomyl) and 2-methylbenzimidazole (MBC) resulted in rapid disintegration of microtubules and, suprisingly, also in disruption of mitochondria into small bodies. Removal of the inhibitors or a short regeneration of protoplasts allowed both the cytoplasmic microtubules and the thread-like mitochondria to reaggregate into the original pattern. Cytochalasin D treatment caused a complete disintegration of actin filaments, while the cytoplasmic microtubules and mitochondria remained intact. These findings of a transient close association of mitochondria and microtubules and their relative independence of the arrangement of actin filaments suggest that microtubules, but not actin cables, form supports for positioning or movement of mitochondria along the cylindrical cells. The persistence of mitochondria in the cell centre during mitosis may be accounted for by the fact that disrupted microtubules fail to provide support for mitochondrial movement towards the cell poles.Key words: microtubules, mitochondria, yeast, actin, microtubular drugs, cell cycle,Schizosaccharomyces japonicusvar.versatilis.

ISSN:0008-4166    

DOI:10.1139/m97-136

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The influence of altered plasma membrane fatty acid composition on cesium uptake and toxicity was investigated inSaccharomyces cerevisiae. Detailed kinetic studies revealed that both theVmaxandKmvalues for Cs+transport increased (by approximately twofold in the latter case) whenS.cerevisiaewas grown in medium supplemented with the polyunsaturated fatty acid linoleate. In addition, Cs+uptake by linoleate-enriched cells was considerably less sensitive to the competitive effects of other monovalent cations (K+, Rb+, and NH4+) than that by unsupplemented cells. Stimulation of Cs+uptake in the presence of certain K+and Rb+concentrations was only evident in linoleate-enrichedS.cerevisiae. At 100 mM CsCl, the initial rate of Cs+uptake was greater in linoleate-supplemented cells than in unsupplemented cells and this was reflected in a more rapid displacement of cellular K+. However, little difference in net Cs+accumulation between linoleate-supplemented and unsupplemented cells was evident during prolonged incubation in buffer or during growth. Thus, Cs+toxicity was similar in linoleate-supplemented and unsupplemented cells. The results were consistent with the Cs+(K+) transport mechanism adopting an altered conformational state in linoleate-enrichedS.cerevisiae.Key words: monovalent cation transport, plasma membrane fatty acid composition, lipid–protein interactions, metal–microbe interactions, cation competition.

ISSN:0008-4166    

DOI:10.1139/m97-137

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The phenotypic characterization of aSaccharomyces cerevisiaemutant unable to grow under agitated conditions is presented here. When this strain was incubated under aerobic conditions, it did not grow and the viability of the culture decreased. The loss in viability was prevented by the addition of antioxidants or chelating agents to the medium, indicating that this mutant was unable to withstand the oxidative stress generated by aerobic metabolism. This strain was complemented with plasmids from a yeast genomic library. The transformants that were obtained carried plasmids harbouring theTYR1gene, which codes for one of the enzymes involved in tyrosine biosynthesis. A monogenicS.cerevisiae tyr1mutant obtained from the Yeast Genetic Stock Center showed higher sensitivity to hydrogen peroxide than aTYR1strain. This sensitivity was reverted when this strain was complemented with theTYR1gene. Considering these results, we propose that tyrosine plays a role in the protection against oxidative stress.Key words: oxidative stress, amino acid biosynthesis, reactive oxygen intermediates, nitrogen metabolism.

ISSN:0008-4166    

DOI:10.1139/m97-138

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The wildRhizopusstrain spT3 extracted from tempeh of Bali, Indonesia (Institute of Microbial Resources, Taichung, Taiwan) had first been identified asRhizopus microsporesvar.oligosporusspT3. This strain is used to ferment soybeans, to detoxify them and improve their nutritional value. Analysis of fermented seeds showed that this strain strongly degrades numerous noxious antinutritional factors, which is unusual forR.microsporusvar.oligosporus. The activity of strain spT3 on carbohydrates, compared with that ofR.microsporusvar.oligosporusNRRL 2710 (= CBS 338.62 = ATCC 22959 = IMI 174457 = IFO 8631 = Scholer's M140), presented differences suggesting that strain spT3 was not aR.microsporusvar.oligosporus. As a matter of fact, strain spT3 hydrolyzed sucrose and raffinose, whereasR.microsporusvar.oligosporusNRRL 2710 did not. A taxonomic study including morphology, growth temperature, and mating showed that the strain spT3 was similar toR.microsporusvar.chinensisCBS 261.28 (= Scholer's M213).Key words:Rhizopus microsporusvar.oligosporus,Rhizopus microsporusvar.chinensis,Rhizopus microsporusvar.rhizopodiformis, mating, carbohydrate utilization, taxonomy, scanning electron microscopy.

ISSN:0008-4166    

DOI:10.1139/m97-139

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

An optimized method for cultivating aerobic spore-forming bacteria in drinking water is described. Such organisms offer the potential as an indicator of water treatment efficiency. The various parameters evaluated were recovery media, incubation, and pasteurization conditions. The optimal conditions consisted of pasteurization for 15 min at 75 °C, followed by membrane filtration and incubation for 24 h at 35 °C on a pad to which 1.4 mL trypticase soy broth had been added. Aerobic spore-forming bacteria were detected in large numbers (1.0 × 102− 3.2 × 103 CFU/100 mL) in raw waters and daily samples showed that in natural waters they remained stable over the test period (3 weeks).Key words: aerobic spores, method, indicator.

ISSN:0008-4166    

DOI:10.1139/m97-140

出版商:NRC Research Press    

年代:1997

数据来源: NRC