摘要:

Production of the phytohormone indole-3-acetic acid (IAA) is widespread among bacteria that inhabit the rhizosphere of plants. Several different IAA biosynthesis pathways are used by these bacteria, with a single bacterial strain sometimes containing more than one pathway. The level of expression of IAA depends on the biosynthesis pathway; the location of the genes involved, either on chromosomal or plasmid DNA, and their regulatory sequences; and the presence of enzymes that can convert active, free IAA into an inactive, conjugated form. The role of bacterial IAA in the stimulation of plant growth and phytopathogenesis is considered.Key words: auxin, indoleacetic acid, microbial, biosynthesis, pathways.

ISSN:0008-4166    

DOI:10.1139/m96-032

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Six nonfermentative Gram-negative bacilli were isolated from Manitoban soils after enrichment with diclofopmethyl. Microscopic examination and physiological and biochemical tests have identified the organisms asSphingomonas paucimobilis,Acinetobacter baumannii,Chryseomonas luteola,Pseudomonas aureofaciens,Pseudomonas cepacia, andPseudomonas fluorescens. Growth curve studies showed that each of the isolates was able to grow in minimal medium with diclofop-methyl as the sole source of carbon and energy. Chemical analysis confirmed that all of the added diclofop-methyl (1.5 μg ∙ mL−1) had been utilized after 31 h of incubation at 25 °CKey words: diclofop-methyl, biodegradation, herbicid

ISSN:0008-4166    

DOI:10.1139/m96-033

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Pure cultures ofChryseomonas luteolaandSphingomonas paucimobilisisolated from Manitoban soils were able to utilize diclofop-methyl (methyl-2-[4-(2,4-dichlorophenoxy)phenoxy]propanoate) as the sole source of carbon and energy. An actively growing culture ofC.luteolacompletely degraded 1.5 μg diclofop-methyl∙mL−1to diclofop acid and 4-(2,4-dichlorophenoxy)phenol within 71 h, as determined by gas chromatographic analysis. The accumulation of these metabolites in the growth medium resulted in the cessation of growth, indicating the organism's inability to degrade phenoxyphenol in the presence of diclofop acid.Sphingomonas paucimobilismineralized 1.5 μg diclofop-methyl∙mL−1to diclofop acid within 54 h. A biphasic growth pattern indicated that this organism was capable of degrading diclofop acid to 4-(2,4-dichlorophenoxy)phenol and 2,4-dichlorophenol and (or) phenol. Neither of the organisms was able to utilize 2,4 -dichlorophenol as the sole source of carbon and energy.Key words: diclofop-methyl, biodegradation, herbic

ISSN:0008-4166    

DOI:10.1139/m96-034

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The attachment ofBradyrhizobiumsp. (Lupinus) strain MSDJ718 to excised roots of white lupin was examined. Maximal attachment occurred at early to middle log phases of bacterial growth. This binding was pH dependent, with an optimal value reached at 6.6. Irrespective of the culture age, the attachment was strongly affected by the calcium concentration of the growth medium: a Ca2+limitation in the Bergersen medium led to optimal attachment of the bacteria. WhenL-fucose was added during the attachment assay, a significant inhibition was observed. The binding was stimulated when bacteria were cultivated with lupin root extracts, genistein and genistin (two lupin isoflavonoids), and some monosaccharides. In addition, with a spectrofluorimetric method using fluoresceinylated neoglycoproteins, it was shown that the increase of the attachment of bacteria to host cells was correlated to the increase of theL-fucoside binding capacity of the rhizobial cells. Taken together, the results obtained in the present study evidenced a possible role of theL-fucose specific bacterial lectin previously described in theRhizobium– lupin host cell recognition.Key words: rhizobia, lupin, attachment, bacterial lectin, root extracts.

ISSN:0008-4166    

DOI:10.1139/m96-035

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

An extracellular surface-active agent, PM-factor, was obtained by high-speed centrifugation from the culture broth ofPseudomonas marginalisPD-14B. PM-factor exhibited emulsifying activity on a broad spectrum of hydrocarbon liquids, including aromatics, aliphatics, crude oil, and creosote. The factor appeared as ball-shaped particles of varying diameter when examined by electron microscopy (0.16–1.4 μm). Gel filtration chromatography demonstrated a high molecular mass of the factor (> 106 Da). The ultraviolet absorption spectrum manifested a peak in the region 200 nm rather in the region 260–280 nm. Amino acid analysis showed a very low amount of aromatic amino acids residues in the protein moiety of PM-factor. The presence of 3-deoxy-D-mannooctulosonic acid, heptose, hexosamine, phosphorus, and 3-hydroxy fatty acid indicated that PM-factor contained lipopolysaccharide. The emulsifying activity of PM-factor was inhibited strongly by mercuric chloride and moderately by EDTA. Polymyxin B, Ca2+, and Mg2+markedly stimulated the factors emulsifying activity. Roles of the bioemulsifier in the functioning ofP.marginalisas a plant pathogen and in bioremediation are discussed.Key words: bioemulsifier,Pseudomonas marginalis, polycyclic aromatic hydrocarbons, plant pathogenesis, bioremediation.

ISSN:0008-4166    

DOI:10.1139/m96-036

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A most-probable-number (MPN) procedure was developed to separately enumerate aliphatic and aromatic hydrocarbon degrading bacteria, because most of the currently available methods are unable to distinguish between these two groups. Separate 96-well microtiter plates are used to estimate the sizes of these two populations. The alkane-degrader MPN method uses hexadecane as the selective growth substrate and positive wells are detected by reduction of iodonitrotetrazolium violet, which is added after incubation for 2 weeks at 20 °C. Polycyclic aromatic hydrocarbon degraders are grown on a mixture of phenanthrene, anthracene, fluorene, and dibenzothiophene in a second plate. Positive wells turn yellow to greenish-brown from accumulation of the partial oxidation products of the aromatic substrates and they can be scored after a 3-week incubation period. These MPN procedures are accurate and selective. For pure cultures, heterotrophic plate counts on a nonselective medium and the appropriate MPN procedure provide similar estimates of the population density. Bacteria that cannot grow on the selective substrates do not produce false positive responses even when the inoculum density is very high. Thus, this method, which is simple enough for use in the field, provides reliable estimates for the density and composition of hydrocarbon-degrading microbial populations.Key words: most probable number, polycyclic aromatic hydrocarbon, alkane, hydrocarbon, bacteria.

ISSN:0008-4166    

DOI:10.1139/m96-037

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The occurrence and metabolic capacities of sulfate-reducing bacteria (SRB) were studied in 23 water samples taken from producing wells at 14 different sites. Oil fields in France, the North Sea, and the Gulf of Guinea were selected and classified according to physicochemical parameters (salinity ranging from 0.3 to 120 g∙L−1and temperature between 29 and 85 °C). After the distribution of SRB within oil fields was studied, several strains of SRB were isolated and characterized metabolically. Twenty of the thirty-seven strains were not related to any known species. Most of the identified strains were members of the generaDesulfovibrioandDesulfotomaculumby molecular, morphological, and physiological properties.Key words: sulfate-reducing bacteria, oil-field ecology, metabolic identification, biodiversit

ISSN:0008-4166    

DOI:10.1139/m96-038

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A genomic library ofRuminococcus albus8 DNA was constructed inEscherichia coliusing bacteriophage λZapII. This library was screened for cellulase components and several Ostazin brilliant red/carboxymethyl cellulose positive clones were isolated. All of these clones contained a common 3.4-kb insert, which was recovered as a plasmid by helper phage excision. The carboxymethyl cellulase coding region was localized to a 1.4-kb region of DNA by nested deletions, and a clone containing the entirecelAgene was sequenced. Analysis of the sequence revealed a 1231-bp open reading frame, coding for a protein of 411 amino acids with a predicted molecular weight of 45 747. This protein, designated CelA, showed extensive homology with family 5 endoglucanases by both primary amino acid sequence alignment and hydrophobic cluster analysis. Cell-free extracts ofE.colicontaining thecelAclone demonstrated activity against carboxymethyl cellulose and acid swollen cellulose but not against any of thep-nitrophenol glycosides tested, indicating an endo-β-1,4-glucanase type of activity. In vitro transcription–translation experiments showed that three proteins of 48 000, 44 000, and 23 000 molecular weight were produced by clones containing thecelAgene. Northern analysis of RNA extracted fromR.albus8 grown on cellulose indicated acelAtranscript of approximately 2700 bases, whereas whenR.albus8 was grown on cellobiose,celAtranscripts of approximately 3000 and 600 bases were detected. Primer extension analysis of these RNAs revealed different transcription initiation sites for thecelAgene when cells were grown with cellulose or cellobiose as the carbon source. These two sites differed by 370 bases in distance. A model, based on transcription and sequence data, is proposed forcelAregulation.Key words:Ruminococcus albus, endoglucanase, transcription, hydrophobic cluster analysis.

ISSN:0008-4166    

DOI:10.1139/m96-039

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Early seedling root growth of the nonlegumes canola (Brassica campestriscv. Tobin,Brassica napuscv. Westar) and lettuce (Lactuca salivacv. Grand Rapids) was significantly promoted by inoculation of seeds with certain strains ofRhizobium leguminosarum, including nitrogen- and nonnitrogen-fixing derivatives under gnotobiotic conditions. The growfh-promotive effect appears to be direct, with possible involvement of the plant growth regulators indole-3-acetic acid and cytokinin. AuxotrophicRhizobiummutants requiring tryptophan or adenosine (precursors for indole-3-acetic acid and cytokinin synthesis, respectively) did not promote growth to the extent of the parent strain. The findings of this study demonstrate a new facet of theRhizobium–plant relationship and thatRhizobium leguminosarumcan be considered a plant growth-promoting rhizobacterium (PGPR).Key words:Rhizobium, plant growth-promoting rhizobacteria, PGPR, indole-3-acetic acid, cytokinin, roots, auxotrophic mutants.

ISSN:0008-4166    

DOI:10.1139/m96-040

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A gene encoding aStreptomyces lividanshomologue of the chymotrypsin-like serine protease (SAM-P20) ofStreptomyces albogriseoluswas isolated using theStreptomyces griseus prtB gene as a hybridization probe. Nucleotide sequence analysis of a representative clone uncovered the possible presence of a sequence of 900 nucleotides encoding 300 amino acids, including a putative "prepro" region of 115 amino acids. Alignment of the predicted amino acid sequence of this putative gene with other members of the family ofStreptomycesextracellular chymotrypsin-like proteases indicated a high degree of homology in all cases, especially with the SAM-P20 protease. This gene product has been identified as the second member of a potentially larger family of SAL (SAM-P20-like) proteases inS.lividans66.Keywords:Streptomyces, protease, chymotrypsin.

ISSN:0008-4166    

DOI:10.1139/m96-041

出版商:NRC Research Press    

年代:1996

数据来源: NRC