摘要:

Root colonization by introduced bacteria is an important step in the interaction of beneficial bacteria with the host plant. Investigators attempting to measure root colonization by bacteria must face several issues. A clear concept or definition of root colonization should be stated in each research summary, as several different definitions have been proposed. We consider true root colonists to be those bacteria that colonize roots in competitive conditions, i.e., natural field soils. Different methods of processing root samples are required if one is measuring external root colonization alone, internal colonization alone, or both. Given that most beneficial bacterial strains currently under investigation as root colonists are members of taxa naturally found in soils, a marking system is required to differentiate the introduced strain from members of the indigenous rhizosphere community. Spontaneous antibiotic resistance, immunological approaches, and foreign DNA sequences are among the marking systems that have been used and each has some possible advantages and disadvantages. More research is needed in the development and comparison of marking systems. The design of experiments to measure root colonization should take into account several statistical issues. One must decide what constitutes the sample unit for each replication of a given treatment, e.g., whole root systems or root segments. Consideration should also be given to how best to express the estimated population of root colonists (e.g., cfu/g fresh or dry weight root, cfu/cm root, or cfu/surface area root). Statistical analysis by standard analysis of variance tests should be used whenever possible to separate treatment means of colonization levels; however, one must determine that the underlying assumptions of these tests are correct for each experiment. Finally, in quantification of populations on roots, one will almost certainly encounter replications with no bacteria, i.e., zeros. There are several options for how to calculate treatment means when one or more replications is a zero, and the implications of these options are discussed.Key words: bioluminescence, genetic markers, plant growth-promoting rhizobacteria, rhizosphere bacteria, root, colonization.

ISSN:0008-4166    

DOI:10.1139/m92-202

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A prototrophic strain ofSaccharomyces cerevisiaeCSIR Y190MATa xyl−, resistant to high levels of ethanol, was hybridized with xylose-fermenting, auxotrophic mutants ofCandida shehataeandPichia stipitisthrough polyethylene glycol-induced protoplast fusion in an attempt to produce ethanol-tolerant, xylose-fermenting hybrids. Mononucleate fusants were obtained, but these dissociated into a mixture of parental-type segregants. PurifiedCandida- andPichia-resembling segregants failed to acquire improved ethanol tolerance but expressed other novel properties ofS.cerevisiae, suggesting that karyogamy was impaired after internuclear gene transfer.Key words:Pichia,Candida,Saccharomycesprotoplast fusion.

ISSN:0008-4166    

DOI:10.1139/m92-203

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Azospirillum brasilenseandAzospirillum lipoferumshowed optimum acetylene-reducing activity at 25 and 30 °C, respectively, although both the bacteria grew optimally at 35 °C.Azospirillum halopraeferensdisplayed optimum growth and acetylene-reducing activity at 40–41 °C. Our experiments indicated that expression ofnifgenes was generally more sensitive to temperature than was nitrogenase activity. The NifA-dependent activation of a heterologousnifH–lacZ fusion was used to assess the impact of temperature on native NifA activity ofA.brasilenseandA.lipoferum. Maximum NifA activity was observed at 25 °C inA.brasilenseand at 30 °C inA.lipoferum.Key words: temperature, nitrogen fixation,nifH–lacZ fusion, NifA activity,Azospirillum.

ISSN:0008-4166    

DOI:10.1139/m92-204

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A survey of yeasts capable of growing onL(+)-tartaric acid as the sole source of carbon and energy showed that this organic acid is assimilated by a significant number of species of basidiomycetous affinity and is seldom utilized by ascomycetous yeasts. This conclusion was further supported by the fact that among approximately 100 isolates from various natural substrates, using selective media withL(+)-tartaric acid, only one strain of ascomycetous affinity was obtained. In a more comprehensive survey 442 yeast strains belonging to 138 species, mostly of basidiomycetous affinity, were also screened for the assimilation of different aldaric acids:D(−)-tartaric acid,meso-tartaric acid,L(−)-malic acid,D(+)-glucaric acid (saccharic acid), and galactaric acid (mucic acid).L(+)-Tartrate was the most frequently utilized tartaric acid isomer (55% of the total number of strains of basidiomycetous affinity belonging to either the Tremellales/Filobasidiales or the Ustilaginales) when compared with theD(−) andmesoforms, which were assimilated by 12 and 18% of the total number of strains, respectively (mainly of tremellaceous species). Saccharic acid was utilized by about 75% of the total number of species of Tremellales affinity and by less than 20% of the ustilaginaceous species. Assimilation of mucic acid occurred in more than 50% of the tremellaceous species and only in 5% of the species related to the Ustilaginales. These tests, not used in standard yeast identification sets, appear to contribute to distinguishing taxa at or above the species level.Key words: assimilation, tartaric acid, aldaric acids, yeasts, taxonomy.

ISSN:0008-4166    

DOI:10.1139/m92-205

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A study was made of the effects of potassium sorbate on growth, morphology, and heat sensitivity of an osmotolerant yeast,Zygosaccharomyces rouxii, grown in media (water activity (aw) 0.93) supplemented with glucose and sucrose. Growth patterns ofZ.rouxiiin YM broth supplemented with glucose (YMBG) and sucrose (YMBS) were similar, although increased potassium sorbate concentration in both media resulted in decreased growth rates. Growth in YMBS containing potassium sorbate was not as prolific as that in YMBG containing potassium sorbate. Inhibition of growth was indicated by decreased absorbance (at 600 nm) of cells grown in YMBS and in YMBG and YMBS supplemented with potassium sorbate at 600 or 1000 μg/mL. Slight decreases in cell size and alteration of cellular morphology were associated with increased potassium sorbate concentration. Plasmolysis increased as potassium sorbate concentration was elevated in YMBS but not in YMBG. Tolerance ofZ.rouxiito potassium sorbate was enhanced by previous adaptation of cells in media with elevated potassium sorbate concentrations. Heat resistance of cells unadapted to potassium sorbate showed little or no increase regardless of culture age, but increased substantially in cells grown in media containing potassium sorbate, particularly YMBS.Key words:Zygosaccharomyces rouxii, potassium sorbate, glucose, sucrose, heat resistance.

ISSN:0008-4166    

DOI:10.1139/m92-206

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The structure and functionality of the ribosomal subunits of the substrate and the aerial mycelium ofStreptomyces antibioticuswere compared. Using SDS-PAGE and HPLC, several differences between the ribosomal protein pattern from both stages of development were observed, including a clear decrease in the L7/L12 content of the aerial mycelium. The activity of the aerial mycelia ribosomes was also decreased when compared with that of the substrate mycelium. This effect was more pronounced in the 50S subunit. These results suggest that during cell differentiation inStreptomycesimportant changes occur at the ribosomal level, particularly in the transition from the substrate to the aerial mycelium.Key words: ribosomes,Streptomyces, differentiation.

ISSN:0008-4166    

DOI:10.1139/m92-207

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Inoculation of soybean withBradyrhizobium japonicumis often unsuccessful owing to the failure of inoculum strains to nodulate soybeans (Glycine max(L.) Merr.) in the presence of indigenous strains of rhizobia in soil. Previous studies have shown that it is possible to reduce nodulation with indigenous strains of rhizobia by amending the soil with a bacteriophage specific for the indigenous strain. The objective of the current study was to determine whether the coating of seed with phage affected nodule occupancy and soybean growth. A phage specific forB.japonicumUSDA 469 and a symbiotically superior strain of rhizobium (B.japonicumUSDA 110) were coated together onto soybean seed and planted into both greenhouse and field soil previously inoculated withB.japonicumUSDA 469. The phage coated onto seed reduced nodulation byB.japonicumUSDA 469 to 48% occupancy, compared with 64% for the untreated control value. Nodulation by the superior inoculum strain was increased from 48 to 82% occupancy by coating seed with the homologous phage andB.japonicumUSDA 110. The rate of nitrogenase activity (on a per plant basis) was increased by coating seed with the phage andB.japonicumUSDA 110. No other plant or symbiotic parameters were affected by phage coating of seed. These results indicate that the nodulation of soybeans can be significantly affected by the coating of seed with phage specific for undesirable strains of rhizobia in soil and the concurrent coating of seed with desirable strains of rhizobia.Key words: competition, rhizobiophage, rhizobia, soybeans.

ISSN:0008-4166    

DOI:10.1139/m92-208

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A field trial was conducted near Kelowna, British Columbia, to determine the effect of biological treatments alone and in combination with formalin fumigation in apple replant disease soil. The response was measured by the increase in cross-sectional trunk area, total shoot growth, and fruit yield of McIntosh apple trees on M.26 rootstock. The postplanting drench application of strain EBW-4 ofBacillus subtilisalone was consistently effective in increasing cross-sectional trunk area for 5 years, total shoot growth for 4 years, and fruit yield for 3 years. The biological agent EBW-4 ofB.subtilisin combination with formalin fumigation was also effective in promoting total shoot growth and cross-sectional trunk area. The application of formalin fumigation alone was effective in increasing shoot growth for 2 years and cross-sectional trunk area for 1 year only. This treatment did not increase fruit yield for 3 years. The consistent performance of strain EBW-4 ofB.subtilisduring 1986–1991 indicates that this bacterium has the potential for biological control of replant disease under orchard conditions in the Okanagan Valley of British Columbia.Key words:Enterobacter aerogenes, replant problem, growth promoting bacteria, plant growth promoting rhizobacteria.

ISSN:0008-4166    

DOI:10.1139/m92-209

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A strain ofGliocladium virens(GL-21 = G-20) formulated in alginate prill was grown for 3 days in a commercial soilless potting medium. Chloroform extractions were separated by thin-layer chromatography and individual bands from G-20 cultures in soilless medium were identified by standards, mass spectrometry, and nuclear magnetic resonance as (i) a mixture of fatty acids, (ii) viridin, (iii) gliotoxin, (iv) dimethylgliotoxin, (v) viridiol, and (vi) a mixture of phenolics including ferulic acid. None of these compounds was detected in the medium not amended with prills of isolate G-20 ofG.virens. Other isolates ofG.virens, including G-3 and G-9, produced gliovirin and did not produce gliotoxin. Of all the metabolites produced by G-20 in soilless medium, only gliotoxin strongly inhibited germination of sporangia and growth ofPythium ultimum(growth prevention at 1.0 μg/mL), growth ofRhizoctonia solanimycelium (0.5 μg/mL), or germination of sclerotia and growth ofSclerotium rolfsii(50 μg/mL). Viridin was more inhibitory to growth ofR.solani(1.0 μg/mL, minimum inhibitory concentration) than toP.ultimum(25 μg/mL) orS.rolfsii(50 μg/mL). Growth ofG.virensisolate G-20 was inhibited by 25 μg/mL of viridin but not by 100 μg/mL gliotoxin. In contrast, growth of isolate G-3 was inhibited by 50 μg/mL gliotoxin but not by 100 μg/mL of viridin. Dimethylgliotoxin, fatty acids, and phenolics were not inhibitory to any of the fungi tested. These results suggest that gliotoxin is the major antibiotic metabolite inhibitory toPythiumandRhizoctoniaof this formulated strain ofG.virens. This information will be useful for monitoring metabolite production byG.virens, determining optimum gliotoxin productionin situ, and improving strain performance for biocontrol of plant pathogens.Key words: antibiotic, biological control, antagonist.

ISSN:0008-4166    

DOI:10.1139/m92-210

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The synthesis of proteins in the psychrotrophic bacteriumBacillus psychrophilusin response to both cold shock and continuous growth at low temperatures was examined. Cold shocks of 20 to 0, 5, or 10 °C resulted in the induction of nine, seven, and five cold shock proteins, respectively, as determined by 2-dimensional gel electrophoresis and computing scanning laser densitometry. Two cold shock proteins, with molecular masses of 61 and 34 kDa, which were induced inB.psychrophilusby cold shocks of 20 to 0 or 5 °C, were not induced in a cold-sensitive mutant ofB.psychrophilus. Analysis of protein profiles ofB.psychrophilusduring continuous growth at 0, 5, or 10 °C revealed the synthesis of 11, 10, and 4 cold acclimation proteins, respectively. Some of these cold acclimation proteins were similar to cold shock proteins. In addition, the relative synthesis of both cold shock proteins and cold acclimation proteins increased with decreasing temperature. Thus, both types of proteins increased both in number and relative synthesis in response to cold shock and continuous growth at low temperature.Key words: cold shock proteins, cold acclimation proteins, psychrotrophic bacterium.

ISSN:0008-4166    

DOI:10.1139/m92-211

出版商:NRC Research Press    

年代:1992

数据来源: NRC