摘要:

The thermophilic fungusHumicola griseavar.thermoideaproduced β-glucosidase activity when grown in a solid-state culture on wheat bran as carbon source. A β-glucosidase was purified to apparent homogeneity by ultrafiltration, gel filtration chromatography on Sephacryl S-100, and ion-exchange chromatography on S-Sepharose, as judged by sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS–PAGE) on a 12.5% (w/v) slab gel. The enzyme had a molecular mass of 82 and 156 kDa, as estimated by SDS–PAGE and gel filtration on a high performance liquid chromatographic column, respectively, suggesting that the native enzyme may consist of two identical subunits. The purified enzyme was thermostable at 60 °C for 1 h with a half-life of 15 min at 65 °C, and displayed optimum activity at 60 °C and a pH range of 4.0–4.5. TheKmandVmaxvalues forp-nitrophenyl β-D-glucopyranoside were determined to be 0.316 mM and 0.459 IU∙mL−1, respectively.D-Glucose,D-gluconic acid lactone, Hg2+, Cu2+, and Mn2+inhibited β-glucosidase activity. The enzyme activity was competitively inhibited byD-glucose (Ki = 0.6 mM). The purified enzyme was very active against cellobiose andp-nitrophenyl β-D-glucopyranoside.Key words:Humicola, β-glucosidase, purification, characterizatio

ISSN:0008-4166    

DOI:10.1139/m96-001

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Inhibition by glucosamine of the utilization of hexoses bySaccharomyces cerevisiaeis induced by growing the cells in media with galactose as carbon source. The intensity of inhibition parallels the induction of the galactose pathway. These findings contrast with the fact that glucosamine is a substrate of the constitutive glucose but not of the inducible galactose transport and phosphorylation systems. The inhibition by glucosamine is pH dependent; the extent seems to be related with the phosphorylation of the hexosamine, as shown by its greater effect with substrates or with conditions that less interfere with the phosphorylation of the inhibitor. Inhibition is not a consequence of ATP depletion of the cell. Intracellular accumulated glucosamine derivatives impair the transport of glucose and mannose in yeast cells grown in galactose-supplemented media but not those grown with glucose or ethanol supplements (i.e., under conditions in which the utilization of these sugars is inhibited). However, impairment of the transport is not enough to explain the characteristics of the observed inhibition. The changes induced by growing the yeast in galactose that render the cells sensitive to glucosamine are under the control of thegal80andgal4genes.Key words: yeast, glycolysis inhibition, glucosamine,Saccharomyces cerevisiae.

ISSN:0008-4166    

DOI:10.1139/m96-002

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Escherichia coli2418 strain is resistant to β-lactam antibiotics (ampicillin, carbenicillin, and cephalothin), streptomycin, tetracycline, kanamycin, and chloramphenicol. This strain contains at least two conjugative plasmids (R2418 and R2418S) encoding resistance to β-lactam antibiotics and resistance to both β-lactam antibiotics and streptomycin, respectively. Restriction endonuclease mapping of plasmid DNAs indicates that the plasmid R2418S has evolved from R2418 DNA by the insertion of 2.5-kb DNA betweenBamHI andPvuII sites, and deletion of 0.5-kb DNA within theEcoRI–EcoRV region. The 2.5-kb DNA insert is responsible for streptomycin resistance. This evolution is also associated with a reduction in the efficiency of conjugal transfer for the plasmid R2418S. The conjugal transfer of streptomycin resistance occurs only through the coresidence of the conjugative plasmid R2418 or R2418S in the donor cell. In accordance with the hypothesis that the Smrdeterminant is due to a putative transposon, plasmid-free transconjugants resistant to streptomycin only were isolated. Southern blot analysis ofHindIII chromosomal digests extracted from these transconjugants shows that the Smrdeterminant is inserted into different sites in chromosomal DNA.Key words:Escherichia coli, antibiotic resistance, conjugation, transformation, plasmid, transposon, restriction map.

ISSN:0008-4166    

DOI:10.1139/m96-003

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Serratia marcescensN28b produces bacteriocin 28b, active againstEscherichia coli. Bacteriocin sensitivity tests performed on a collection ofE.colienvelope mutants, and isolation and characterization ofE.colibacteriocin-28b-insensitive mutants, showed that the core lipopolysaccharide, outer membrane proteins OmpA and OmpF, and TolQ, TolA, and TolB proteins are involved in bacteriocin 28b lethal activity. These mutants were assayed for bacteriocin 28b sensitivity under normal and bypass conditions, and their bacteriocin-binding ability was determined. The results obtained suggest that the core lipopolysaccaride and outer membrane proteins OmpA and OmpF are involved in bacteriocin 28b binding. Furthermore, bacteriocin 28b translocation requires proteins TolA, TolB, and TolQ.Key words: bacteriocin, receptors, translocation,Serratia marcescens.

ISSN:0008-4166    

DOI:10.1139/m96-004

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Analysis of cellular fatty acid profiles was used to distinguish among introduced pathogen- suppressive strains and indigenous strains ofStreptomycesspp. isolated from soil of field plots established to test the efficacy ofStreptomycesstrains PonSSII and PonR in the biological control of potato scab. Reference libraries of fatty acid profiles were developed for a collection of known pathogenic strains and the introduced suppressive strains. Population densities of pathogen-related, suppressive, and saprophyticStreptomycesstrains were determined from the relationship of field isolates to mean library profiles using cluster analysis and the unweighted pair-group method using arithmetic averages. Community diversity was similarly determined.Streptomycesstrains PonSSII and PonR were distinguished from each other and from the pathogen group (which clustered together) based on fatty acid profiles. The introduced, suppressive strains successfully colonized the soil and represented 2–19% of the isolates sampled over 2 years. The introduction of the suppressive strains inhibited the population of strains related to the pathogen library at each sample date; the pathogen population was substantially lower in soil from treatments where the suppressive strains were introduced compared with the nonamended control. At harvest, the pathogen-related population was suppressed 85–93 and 36–44% in 1991 and 1992, respectively, in treatments with the suppressive strains compared with the nonamended control. Diversity of the community was not affected by the introduced strains, and diversity and equitability indices were similar among treatments at any sample time. The inhibition of the pathogen-related population was correlated with a reduction of scab symptoms observed in the field plots into which the suppressive strains were introduced. Implications of a fundamental shift in the pathogen-related population in response to the introduction of the suppressive strains for long-term biological control of potato scab are encouraging.Key words:Streptomyces, fatty acid analysis, biological control, community ecology.

ISSN:0008-4166    

DOI:10.1139/m96-005

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Calculations are made of the thermodynamic changes accompanying the growth ofPseudomonas saccharophilaautotrophically on hydrogen and heterotrophically on acetic acid, pyruvic acid, lactic acid, glucose, and sucrose, for the purpose of determining the extent to which the energetics of autotrophic and heterotrophic growth are related. Growth with respect to each substrate is divided into equations representing the processes of anabolism and catabolism, the sum of which is an equation representing metabolism. Using appropriate values for the thermodynamic properties of the substances represented by the terms in the equations, it becomes possible to calculate the changes in free energy, enthalpy, and entropy accompanying these processes. The results suggest, but do not rigorously prove, that the quantity of available electrons conserved within the substance of the cells is linearly related to those potentially available from the electron donors, whether these latter are organic or inorganic. The efficiency of electron conservation can be used to calculate the changes in free energy, enthalpy, and entropy accompanying metabolism.Key words: bacterial growth thermodynamics, electron conservation.

ISSN:0008-4166    

DOI:10.1139/m96-006

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The prokaryotic transposon Tn3requires the transposase protein, as well as thecis-acting terminal inverted repeats (IRs), for transposition. The first step in the transposition process requires transposase binding to the IRs, as well as target site selection for element insertion. The primary aim of this study is to define the relationship between the structure of Tru3transposase and its DNA binding functions. We have defined, by UV cross-linking, two broad regions of transposase that interact with DNA: a 70-kDa N-terminal domain and a 30-kDa C-terminal domain. The 70-kDa N-terminal domain encompasses the IR sequence-specific binding domain, as well as a nonspecific DNA binding domain that has been previously described. We have also defined, by UV cross-linking, a region in the nonspecific DNA binding domain centered at amino acids 376 and 381 that is in contact with DNA. We have used site-directed mutagenesis of amino acids 376 and 381 to help delineate the function of this region of the transposase protein. Mutations in this region reduce transposition frequency to 30–40% of the wild type. These mutations reduce nonspecific DNA binding three- to four-fold but do not appear to affect specific binding to the IR. Transposition immunity is unaffected by mutations in the nonspecific DNA binding domain. This suggests that this region may be involved in target site selection.Key words: transposon, Tn3, DNA–protein cross-linking, UV cross-linking, transposase.

ISSN:0008-4166    

DOI:10.1139/m96-007

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The bactericidal properties of peracetic acid (PAA) were tested usingEscherichia coliH10407, in sterilized artificial seawater, sewage effluent water, and distilled water microcosms. No LT enterotoxin synthesis was detected by GM1 enzyme-linked immunosorbent assay of the water supernatants, but a specific fragment of theeltBgene was always amplified by polymerase chain reaction for 21 days after PAA treatment. The resuscitation capacity of starved cells was assayed in rich medium and their inability to overcome the effects of PAA stress was observed, despite the emergence of viable but nonculturable cells in microcosms 24 or 48 h after treatment. Moreover, no obvious differences in response were obtained, concerning enterotoxigenesis, between bacteria subjected to osmotic and (or) nutrient starvation-induced stress with or without PAA treatment.Key words: peracetic acid, disinfection, enterotoxigenicEscherichia coli.

ISSN:0008-4166    

DOI:10.1139/m96-008

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Sphingomonas paucimobilisBPSI-3 was previously isolated from a mixed microbial consortium growing on biphenyl as the sole source of carbon and energy. Transformation of 4 -chlorobiphenyl (4CBP) was demonstrated by this strain, although little or no growth was observed. In minimal salts medium supplemented with 4CBP or bromobiphenyl and dextrose, yellow coloured product(s) were rapidly formed. Gas chromatography – mass spectrometry (GC–MS) revealed single ring N-heterocyclic compounds that were identified as halopicolinic acids. We believe this to be the first report of such compounds being formed via biological transformation of halobiphenyls. A mechanism is proposed for their formation.Key words: halobiphenyl degradation, halopicolinic acid,Sphingomonas paucimobilisBPSI-3, bioremediation.

ISSN:0008-4166    

DOI:10.1139/m96-009

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Sixty samples of commercial North American legume inoculants manufactured for sale in 1994 using nonsterile peat as carrier were tested forRhizobium(orBradyrhizobium) content and nonRhizobiumbiological contaminant load. Products of three major producers of such inoculants for sale in Canada were examined. ViableRhizobiumcontent varied from 5.6 × 105to 8.1 × 109 cells/g, while the contaminant load varied from 1.8 × 108to 5.5 × 1010 cfu/g. Most of the inoculants contained more nonrhizobial organisms than they did rhizobia. Identifications were made of the most numerous nonrhizobial bacteria occurring in 100 samples of inoculants collected in 1993 and 1994. The most commonly identified contaminant wasXanthomonas maltophilia.Pseudomonas aeruginosa,Klebsiella pneumoniae, andEnterobacter cloacaewere also found at high levels in some products. Contaminant organisms capable of inhibiting rhizobial growth in plate culture were found in the products of all three manufacturers.Key words:Rhizobium, contaminant, inoculant.

ISSN:0008-4166    

DOI:10.1139/m96-010

出版商:NRC Research Press    

年代:1996

数据来源: NRC