摘要:

The ways in which plant growth promoting rhizobacteria facilitate the growth of plants are considered and discussed. Both indirect and direct mechanisms of plant growth promotion are dealt with. The possibility of improving plant growth promoting rhizobacteria by specific genetic manipulation is critically examined.Key words: plant growth promoting rhizobacteria, PGPR, bacterial fertilizer, soil bacteria.

ISSN:0008-4166    

DOI:10.1139/m95-015

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The field population dynamics ofBacillus thuringiensisvar.kurstakiDMU67R isolated from cabbage leaves was investigated. Two experimental cabbage plots were spray inoculated with a suspension of sporulated bacteria containing 6.5 × 107colony-forming units (cfu)/mL DMU67R or with a sterile medium control. To study transport between phyllosphere and soil, plastic covering was used during spraying to ensure that DMU67R was applied only on leaves (8.5 × 106cfu/g) or on soil (1.2 × 104cfu/g). Numbers of DMU67R declined five log units during the first 4 weeks after spraying of leaves; the initial half-life (1st week) was 16 h. In topsoil, however, a long-term persistency was demonstrated with a half-life exceeding 100 days. Dispersal by rain splash from topsoil to lower leaves of cabbage was demonstrated. After 1 year, analysis of the top 15 cm of soil showed that 77% of DMU67R remained in the 0- to 2-cm topsoil layer. When DMU67R was applied on leaves, larvae ofPieris brassicaewere killed within 7 days after spraying. Germination of DMU67R was demonstrated in deadP.brassicaelarvae but not in any leaf or soil sample. Pitfall sampling demonstrated dispersal of DMU67R by means of carabid beetles (up to 135 m) and other surface-active insects carrying 102–103 cfu/g wet mass.Key words:Bacillus thuringiensis,Pieris brassicae, cabbage, soil, dispersal, population dynamics.

ISSN:0008-4166    

DOI:10.1139/m95-016

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

In this study, the potential of differentPseudomonasstrains to utilize heterologous siderophores was compared with their competitiveness in the rhizosphere of radish. This issue was investigated in interactions betweenPseudomonas putidaWCS358 andPseudomonas fluoresceinsWCS374 and in interactions between strain WCS358 and eight indigenousPseudomonasstrains capable of utilizing pseudobactin 358. During four successive plant growth cycles of radish, strain WCS358 significantly reduced rhizosphere population densities of the wild-type strain WCS374 by up to 30 times, whereas derivative strain WCS374(pMR), harboring the siderophore receptor PupA for ferric pseudobactin 358, maintained its population density. Studies involving interactions between strain WCS358 and eight different indigenousPseudomonasstrains demonstrated that despite the ability of these indigenous isolates to utilize pseudobactin 358, their rhizosphere population densities were significantly reduced by strain WCS358 by up to 20 times. Moreover, rhizosphere colonization by WCS358 was not affected by any of these indigenous strains, even though siderophore-mediated growth inhibition of WCS358 by a majority of these strains was demonstrated in a plate bioassay. In conclusion, it can be stated that siderophore-mediated competition for iron is a major determinant in interactions between WCS358 and WCS374 in the rhizosphere. Moreover, our findings support the common assumption that cloning of siderophore receptor genes from onePseudomonasstrain into another can confer a competitive advantage in interactions in the rhizosphere. Interactions between WCS358 and the selected indigenous rhizosphere isolates, however, indicate that other traits also contribute to the rhizosphere competence of fluorescentPseudomonasspp.Key words: siderophore, siderophore receptors, root colonization, fluorescentPseudomonas.

ISSN:0008-4166    

DOI:10.1139/m95-017

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Secretions from exocrine metapleural glands ofMyrmecia gulosa(Australian bull ant) exhibit broad-spectrum antimicrobial activity. Treatment of the yeastCandida albicanswith metapleural secretion resulted in the rapid and total leakage of K+ions from cells within 10 min. Ultrastructural analysis of the bacteriaBacillus cereus,Escherichia coli, andPseudomonas aeruginosa, and cells and protoplasts ofCandida albicansdemonstrated gross damage of the cell membrane and aggregation of the cytoplasmic matrix of treated cells. Degradation of membrane-bound organelles was also observed inCandida albicans. The antimicrobially active components of metapleural secretions were nonpolar and interacted with the phospholipid bilayer, causing damage to the structural integrity of liposomes and the release of carboxyfluorescein. The data suggest that the antimicrobial agents in metapleural secretion act primarily by disrupting the structure and function of the phospholipid bilayer of the cytoplasmic membrane.Key words: ant metapleural secretion, antimicrobial,Candida albicans, cytoplasmic membrane.

ISSN:0008-4166    

DOI:10.1139/m95-018

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The effects of vitamin B12availability on the physiology of the cyanobacteriumSynechococcussp. strain PCC 7002 were examined in a continuous culture chemostat system. The availability of vitamin B12within the system was demonstrated to control the cell density and cellular chlorophyll levels under nutrient-limiting conditions. Electron micrographs of vitamin B12replete and vitamin B12deficient cyanobacteria indicated that a reduction in vitamin B12availability induced a loss of thylakoid integrity within the system. Polyacrylamide gel electrophoresis demonstrated that the expression of outer membrane proteins of 95, 70, and 34 kDa was enhanced during vitamin B12limited growth. Cellular quotients were determined to be a minimum of 256 molecules of vitamin B12/cell to sustain a growth rate of 0.6/day. A comparison with eukaryotic plankton demonstrated that the vitamin B12requirements of cyanobacteria may be more similar to those of chloroplasts than to those of the entire group of eukaryotic algae.Key words: chemostats, cellular quotients, cyanobacterial physiology,Synechococcus, vitamin B12.

ISSN:0008-4166    

DOI:10.1139/m95-019

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

We describe a method for isolating and determining differences in gene expression between related bacterial strains. The method is based upon differences in mRNA expression. To demonstrate this procedure, cDNA generated from total RNA ofListeria monocytogenesserotype 1/2a was hybridized to total RNA from a Tn916mutant of serogroup 1/2a (M3) that was deficient in the production of listeriolysin O, the product of thehlygene. The single-stranded cDNA fragments remaining after hybridization represent the difference in expressed genes between the two strains. These subtraction products were used as hybridization probes to identify the correspondinghlygene in a Southern hybridization.Key words: subtractive hybridization,Listeria monocytogenes, hemolysin, gene expression, isogenic.

ISSN:0008-4166    

DOI:10.1139/m95-020

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The development of a culture medium in which the growth rate was limited by initial phosphate concentration permitted spiramycin production during the growth phase. The influence of the growth rate on spiramycin production in this medium was studied. Addition of glycerol before spiramycin production increased the growth rate by 100% and spiramycin production began at a low rate. Spiramycin production yield was decreased by 50%. Addition of fatty acids such as hexanoate before spiramycin production increased the global yield of spiramycin by 47% and a high level of acetate excretion was observed just before spiramycin production. The development of a biphasic growth medium increased the spiramycin global yield. In this biphasic growth medium, in the first phase there was fast growth during which no acetate was excreted and no spiramycin was detected. During a second phase of slow growth, acetate excretion preceded spiramycin production and the spiramycin biosynthetic rate was maintained at a high level.Key words:Streptomyces ambofaciens, spiramycin, electrophoresis, nitrogen source, regulation.

ISSN:0008-4166    

DOI:10.1139/m95-021

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The verotoxigenicEscherichia colistrain H.I.8 (originally O128:B12, now not typeable) contained a ColB+M plasmid and two morphologically identical temperate bacteriophages (HI8A and HI8B). Both phages were O128ab specific, using the lipopolysaccharide O side chains of susceptible clinical isolates as receptors. SDS polyacrylamide gel electrophoresis with silver staining of O128ab lipopolysaccharide revealed four distinct types of ladder with different interband spacings. No specificity was found between ladder type and sensitivity to either phage. One of the numerous large plasmids present in O128ab isolates was found to modify the structure of the lipopolysaccharide O side chains to provide phage receptors.Key words: bacteriophage, plasmid, lipopolysaccharide, O antigen.

ISSN:0008-4166    

DOI:10.1139/m95-022

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Though bacteria of the radiation-resistant genusDeinococcushave a high resistance to the lethal and mutagenic effects of many DNA-damaging agents, the mechanisms involved in the response of these bacteria to oxidative stress are poorly understood. To investigate antioxidant enzyme responses inDeinococcusspp., the catalase activity produced by these bacteria was measured and the sensitivity of these bacteria to hydrogen peroxide was tested.Deinococcusspp. had higher levels of catalase and were more resistant to hydrogen peroxide thanEscherichia coliK12. The high levels of catalase produced byDeinococcus radioduranswere, in part, regulated by growth phase. Cultures ofD.radiodurans, when pretreated with sublethal levels of hydrogen peroxide, became relatively resistant to the lethal effects of hydrogen peroxide and exhibited higher levels of catalase than untreated control cultures. These pretreated cells were also resistant to lethality mediated by ultraviolet light and γ-rays. These results suggest thatDeinococcusspp. possess inducible defense mechanism(s) against the deleterious effects of oxidants and ionizing and ultraviolet radiation.Key words: catalase, oxidative stress, radiation resistance,Deinococcusspp.

ISSN:0008-4166    

DOI:10.1139/m95-023

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Some of the factors that influence the biosynthesis of theCandida molischianaβ-glucosidase were investigated. The yeast produced maximal enzyme activity when grown at 28 °C in a carbohydrate-containing complex medium (YM) in which the initial pH was adjusted to 6.0. The enzyme appeared to be produced constitutively, as activity was detected when either ethanol, glycerol, xylose, glucitol, mannitol, maltose, trehalose, cellobiose, cellodextrins, or soluble starch was used as the carbohydrate source. The presence of either glucose, mannose, or fructose (> 25 g/L) repressed β-glucosidase expression; however,C.molischianadid produce β-glucosidase when the initial glucose concentration was <25 g/L. When the yeast was grown in YM medium containing glucose plus cellobiose, diauxic utilization of the carbon sources was observed, and β-glucosidase activity was not detected until the glucose was depleted from the medium.Key words: β-glucosidase, glucose repression, fermentation, yeast.

ISSN:0008-4166    

DOI:10.1139/m95-024

出版商:NRC Research Press    

年代:1995

数据来源: NRC