摘要:

The phytohormone indole-3-acetic acid is involved in several types of microorganism-plant interactions. In the most widely studied pathway, tryptophan-2-monooxygenase converts tryptophan to the intermediate indole-3-acetamide, and indole-3-acetamide hydrolase catalyzes the conversion of indole-3-acetamide to indole-3-acetic acid. The genetic determinants for these enzymatic conversions areiaaMandiaaH, respectively. This pathway has been observed in many pathogenic and symbiotic soil bacteria. The associative soil bacteria of the genusAzospirillumare known to promote plant growth, probably via the secretion of phytohormones, including indole-3-acetic acid. The following evidence is presented for the existence of the above-described indole-3-acetic acid pathway inAzospirillum brasilenseSp7: the high toxicity of α-methyltryptophan as compared with that of 5-methyltryptophan; indole-3-acetic acid formationin vivofrom indole-3-acetamide; the existence of two tryptophan-induced proteins, one of which has a molecular weight similar to that of tryptophan-2-monooxygenase; tryptophan-2-monooxygenase activity observed on nondenaturing gel; the existence of a protein with high tryptophan-2-monooxygenase activity with a molecular weight similar to that of one of the tryptophan-induced proteins on a two-dimensional gel; and the partial homology between theiaaMgene, which encodes tryptophan-2-monooxygenase inPseudomonas savastanoi, andA.brasilenseSp7 total DNA.Key words:Azospirillum brasilenseSp7, indole-3-acetic acid, tryptophan, indole-3-acetamide.

ISSN:0008-4166    

DOI:10.1139/m93-011

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Renodulation and nitrogen fixation potential of indigenous and exotic isolates ofRhizobiumwere studied in a field experiment withAcacia niloticafrom July 1990 to June 1991. The inoculum isolates belonged to different serotypes and did not show cross-reaction with the native population ofRhizobium. Nitrogenase activity of root nodules observed at 4-month intervals covering three seasons snowed a decline during winter months, which corresponded with the senescence of the nodules. Maximal renodulation as checked by serotyping and antibiotic resistance pattern was observed with isolate AB 3 followed by AD 4 and USDA 3325. The highest nitrogenase activity was exhibited in plants inoculated with AD 4 at 12 months. Plants inoculated withRhizobiumisolate USDA 3325 showed the highest increase in dry-matter yield at 12 months. Except for AB 3, dual inoculation withRhizobiumisolates andGlomus fasciculatumdid not enhance dry matter production as compared with uninoculated controls or single inoculation of eitherRhizobiumisolate orG.fasciculatum.Key words:Rhizobium,Acacia nilotica, nitrogenase activity, renodulation.

ISSN:0008-4166    

DOI:10.1139/m93-012

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

In experiments designed to Tn5 mutagenize the indigenous plasmid pBRC60 ofAlcaligenessp. BR60, kanamycin-resistant mutants were isolated that were cured of this plasmid and that exhibited recombination of the plasmid-located chlorobenzoate catabolic transposon Tn5271 into the chromosome. These events were independent of the location of Tn5 insertions into the genome of strain BR60. The chromosomal recombinants carried at least two novel copies of IS1071, the class II insertion sequence flanking Tn5271, compared with the parent strain. Recombination of Tn5271 into the chromosome ofAlcaligenessp. BR60 was also detected following mating in of pBRC60-incompatible (IncP1) plasmids, R68 and pGS65. Chromosomal copies of Tn5271 could be mobilized betweenAlcaligenesstrains via plasmids pBRC40 or R68. Conjugation of the incompatible plasmid pGS65 intoAlcaligenesstrains in the absence of selection for 3-chlorobenzoate catabolism resulted in the recovery of 85% of transconjugants in which the entire pBRC60 plasmid had integrated into the chromosome. These transconjugants exhibited complex rearrangements in chromosomal IS1071 copies. A model of recombinational equilibrium involving homologous recombination between plasmid and chromosomal copies of IS1071 is presented. The results are discussed in terms of the IS1071 (class II) transposition mechanism and the observed products of IS 1071-mediated recombination in natural recipients of pBRC60 in aquatic environments.Key words: transposon, 3-chlorobenzoate catabolism, rearrangement.

ISSN:0008-4166    

DOI:10.1139/m93-013

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Seasonal changes in bacterial colonization of the epithelial tissue were examined in the rumen of high-arctic Svalbard reindeer. Samples of tissue were collected from eight sites in the rumen of reindeer during summer and winter and bacterial colonization was examined using scanning and transmission electron microscopy. At two of these sites, colonization by adherent bacteria was estimated to cover approximately 30% of the ruminal epithelium in specimens collected from reindeer during summer. Bacteria at these sites resembledRuminococcussp. and were surrounded by large amounts of glycocalyx. In winter specimens, less than 10% of the epithelial surface was covered by adherent bacteria. Those bacteria that did colonize the epithelial surface were smaller and had virtually no glycocalyx on their surface. Bacteria attached to plant cell wall material in summer samples of reindeer ingesta contained large intracellular glycogen deposits, whereas feed particle-associated bacteria in ingesta collected in winter contained no intracellular glycogen. These data demonstrate that the ruminal bacterial population responds to seasonal changes in feed intake and quality. It is yet to be determined if these bacterial changes enhance the ability of Svalbard reindeer to survive in the hostile environment of the high Arctic.Key words: ruminal bacteria, attachment, epithelium, reindeer.

ISSN:0008-4166    

DOI:10.1139/m93-014

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The outer membrane proteins (OMPs) of several strains ofSerratia marcescenshave been studied by sodium dodecyl sulphate – urea – polyacrylamide gel electrophoresis. Four major OMPs, named Omp1, Omp2, Omp3, and OmpA (42, 40, 39, and 37 kDa, respectively), have been visualized. The relative proportions of Omp2 and Omp3 depend on cultural conditions (temperature of incubation, osmolarity, and nutrient availability).Key words:Serratia marcescens, outer membrane proteins, porin.

ISSN:0008-4166    

DOI:10.1139/m93-015

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Studies of the molecular biology of human papillomavirus type 16 have been limited by the lack of a tissue culture system that is fully permissive for virus replication; as a result, high-titre stocks of infectious virus are not readily available. Therefore, studies of viral gene expression have relied on analysis of transformed or tumour cell lines harbouring latent or integrated viral genomes, or on the behaviour of transfected reporter gene constructs. To provide a method of efficiently delivering papillomavirus information into the nuclei of mammalian cells, we constructed a herpes simplex virus type 1 recombinant bearing the entire human papillomavirus type 16 genome. The resulting recombinant was capable of lytic replication and induced the accumulation of papillomavirus mRNAs initiated from the p97 early promoter during infection of Vero cells. This and other herpes simplex – papillomavirus recombinants should facilitate molecular analysis of the life cycle of human papillomavirus type 16.Key words: herpes simplex virus, vectors, human papillomavirus, transcription.

ISSN:0008-4166    

DOI:10.1139/m93-016

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Cercospora kikuchiiis a fungal pathogen of soybean that produces a photosensitizing and phytotoxic polyketide, cercosporin, in culture andin planta. We have studied the influence of growth stage, light, and growth medium on cercosporin accumulation in a wild-type isolate and three mutant strains with altered toxin phenotypes. After an initial logarithmic growth phase, the wild-type isolate accumulated high levels of cercosporin on either complete medium or potato dextrose broth, but only when cultured in the light. Dark-grown cultures of the wild-type and light-grown cultures of two uv-induced mutant derivatives accumulated 100-fold lower cercosporin levels. A third mutant strain accumulated wild-type cercosporin levels, but only when cultured in the light in potato dextrose broth. Two-dimensional gel electrophoresis of both extracted proteins andin vitrotranslation products from wild-type cultures revealed the presence of polypeptides and poly A + RNAs whose accumulation was positively regulated by light. Comparison of translated polypeptide patterns from wild-type and mutant cultures also demonstrated differential accumulation of translatable poly A + RNAs in cercosporin-producing and nonproducing cultures.Key words: nonspecific toxin, photo induction,in vitrotranslation.

ISSN:0008-4166    

DOI:10.1139/m93-017

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A cell-associated β-glucosidase was purified 152-fold to homogeneity from the ectomycorrhizal fungusPisolithus tinctoriusstrain SMF. The apparent molecular weight of the native protein, as determined by size exclusion chromatography, was approximately 450 000. A single band with a molecular weight of 150 000 was obtained after polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). Thus, the native enzyme may consist of three monomers. The pI of the enzyme was determined to be 3.8 by isoelectric focusing. The enzyme had an optimal pH of 4.0 and an optimal temperature for activity of 65 °C. It showed a high substrate specificity toward aryl-β-glucosides, such asp-nitrophenyl β-D-glucopyranoside (PNPG), and β-1,6 glucosidic linkages. Cellobiose was hydrolyzed at about two-thirds the rate of PNPG. TheKmfor hydrolysis of PNPG was 0.87 mM. Strong inhibitors of the enzyme were aluminum, copper, ethylenediaminetetraacetic acid (EDTA), deoxynojirimycin, gluconic acid, and SDS. Calcium, manganese, andp-hydroxymercuribenzoic acid reduced the activity to a lesser extent. Potassium, mercury, cobalt, dithiothreitol, and glucosamine had no effect on activity. Enzyme activity was slightly increased to 112% in the presence of 1% glycerol. The enzyme was more stable under acidic conditions than under alkaline conditions.Key words:Pisolithus, ectomycorrhizal, β-glucosidase, purification.

ISSN:0008-4166    

DOI:10.1139/m93-018

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A particulate enzyme preparation fromCryptococcus neoformanstransferred the mannosyl residue from GDP-mannose:o an acceptor consisting of a commercial preparation of methyl 3-O-α-mannopyranosyl-α-mannopyranoside (confining 10% 2-O-α-mannopyranosyl-α-mannopyranoside). The configuration of the new bond was alpha by its susceptibility to α-mannosidase; the amount of product was dependent on the concentration of enzyme, of GDP-mannose, and of acceptor. The optimal temperature and pH were 37 °C and 7.0, respectively. Manganous ion was required for activity and acetyl coenzyme A was stimulatory. Studies suggested that dolichyl phosphate intermediates were not involved in this mannose transfer. The fact that none of the several acapsular mutants tested were deficient in this mannosyltransferase suggested that this enzyme was not involved in synthesis of backbone mannan linkages in capsular polysaccharide. NMR analysis of the methylmannotriose product showed only α(1 → 2) linkages between sugar moieties. This mannosyltransferase evidently extends α(1 → 2) mannan by adding another α(1 → 2)-linked mannosyl residue. Its activity is appropriate for a role in synthesis of "high mannose" oligosaccharide moieties of glycoproteins.Key words: virulence, capsular polysaccharide, acapsular mutants, dolichol pathway, oligomannans.

ISSN:0008-4166    

DOI:10.1139/m93-019

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

An endo-β-1,4-xylanase gene was cloned fromNeocallimastix patriciarum27 in the bacteriophage vector λgtWESλB and was subcloned into the plasmid vectors pUC18 and pUC19 in which xylanase activity was expressed in both orientations. The xylanase was located in the periplasmic space of the host,Escherichia coliHB101. The pH and temperature optima for periplasmic xylanase activity were 6.2 and 40 °C, respectively, and theKmfor oat spelt xylan hydrolysis was 0.89 mg∙mL−1. It also exhibited hydrolytic activity on carboxymethyl cellulose that was equivalent to 28% of the activity exhibited by the enzyme on xylan. It bound to crystalline cellulose, but lacked hydrolytic activity on amorphous cellulose. SDS-PAGE followed by zymogram analysis showed active bands of 68, 58, and 51 kDa. Isoelectric focusing in gels combined with zymogram analysis showed one band of xylanase activity with a pI of 3.6.Key words:Neocallimastix patriciarum, xylanase, gen

ISSN:0008-4166    

DOI:10.1139/m93-020

出版商:NRC Research Press    

年代:1993

数据来源: NRC