共查询到20条相似文献,搜索用时 62 毫秒
1.
In order to determine the possible effect of nutrient limitations on the response of Corynebacterium glutamicum to a saline osmotic up-shock, the bacteria were grown in continuous cultures, at osmotic pressures of 0.4 osmol/kg and 1.2 osmol/kg,
under ammonia and potassium limitation. At the low osmolality of 0.4 osmol/kg, the glutamate and proline levels of 15 mg/g
and 5 mg/g dry weight respectively were lower than previously reported in glucose-limited continuous cultures (50 mg/g and
10 mg/g dry weight respectively). On the other hand, the internal trehalose pool was much higher at 40 mg/g dry weight. When
the medium osmolality was increased to 1.2 osmol/kg by NaCl addition, under ammonia limitation, the proline content rose from
5 mg/g to 20 mg/g dry weight and the trehalose content from 40 mg/g to 70 mg/g dry weight, whereas the intracellular pool
of glutamate remained essentially constant. An increase in the internal sodium content was also observed. Similar results
were found for the internal pool of glutamate, proline and trehalose when C. glutamicum was grown under potassium limitations at an osmolality of 1.2 osmol/kg. There were also higher levels of sodium ions, glutamine
and alanine. According to the present results, whereas proline was previously reported to be the dominantly accumulated osmoprotectant
in C. glutamicum grown under glucose limitations, under ammonia and potassium limitations trehalose represented the dominantly synthesized
metabolite.
Received: 19 December 1995/Received revision: 9 April 1996/Accepted: 15 April 1996 相似文献
2.
Use of an industrial effluent as a carbon source for denitrification of a high-strength wastewater 总被引:6,自引:0,他引:6
Denitrification of a high-strength synthetic wastewater (150 g NO-
3 l-1) was carried out using a wine distillery effluent as an example of an industrial carbon source (22.7 g chemical oxygen demand
l-1). Two configurations were tested: one consisted of an acidogenesis reactor followed by a denitrifying reactor and the other
was a single reactor directly fed with the raw effluents. In both cases, denitrification was achieved at a nitrate load of
9.54 g NO-
3 l-1 day-1 (2.19 g N as NO-
3 l-1 day-1) with good specific reduction rates: 32.6 mg and 35.2 mg N as NO
x
g volatile suspended solids h-1, calculated on a single day, for the two-step and the one-step process respectively. Dissimilatory nitrate reduction to ammonium
did not occur, even in the one-step process.
Received: 26 October 1995/Received revision: 15 February 1996/Accepted: 20 February 1996 相似文献
3.
J. Sánchez-Torres P. Pérez R. I. Santamaría 《Applied microbiology and biotechnology》1996,46(2):149-155
Several alkalophilic Bacillus spp. strains were selected for their capacity to produce alkaline cellulases. Culture supernatants of these strains showed
optimal cellulase activities between pH 8 and 9 and they were stable from pH 6 to pH 12. A cellulase gene (celB1) from the alkalophilic Bacillus sp. strain N186-1 was cloned in Escherichia coli using polymerase chain reaction techniques. The cloned gene was present in a 2.539-bp HindIII fragment and its nucleotide sequence was determined. The coding sequence showed an open-reading frame encoding 389 amino
acids. The amino acid sequence, deduced from the nucleotide sequence, permitted us to include it in family 5 (or A) of the
glycosyl hydrolases. The complete open-reading frame of celB1 was cloned in the plasmid pET-11d and expressed in E. coli BL21 (DE3), in which a protein of 39 kDa was obtained in the cytoplasm; however, no endoglucanase activity was detected.
A second construction in pET-12a allowed the production of a 39-kDa protein located in the periplasmic space of E. coli that had endoglucanase activity. The protein produced has optimal activity at pH 7 and 50°C and it retains more than 70%
of its activity after incubation for 1 h at pH 12.
Received: 27 December 1995/Received revision: 14 March 1996/Accepted: 25 March 1996 相似文献
4.
A. König C. Zaborosch A. Muscat K.-D. Vorlop F. Spener 《Applied microbiology and biotechnology》1996,45(6):844-850
Amperometric biosensors for naphthalene were developed using either immobilized Sphingomonas sp. B1 or Pseudomonas fluorescens WW4 cells. The microorganisms were immobilized within a polyurethane-based hydrogel, which was used for a microbial biosensor
for the first time. Both strains were shown to be equally suited for the quantification of naphthalene in aqueous solutions.
The biosensors were tested in a flow-through system and a stirred cell (batch method). In both systems a linear response down
to the detection limit was obtained. Measurements in the flow-through system gave sensitivities of up to 1.2 nA mg−1 l−1 and a linear range from 0.03 mg/l to 2.0 mg/l. The response time (t
95) was 2 min and the sample throughput six per hour; the repeatability was within ±5 %. With the batch method, sensitivities
of between 3 nA mg−1 l−1 and 5 nA mg−1l−1 and a linear range of 0.01–3.0 mg/l were obtained; the response time was between 3 min and 5 min. The sensors reached an
operational lifetime of up to 20 days. The sensitivity of both sensors for naphthalene was, in most cases, more than four
times higher than for various other substrates.
Received: 18 October 1995/Received revision: 22 December 1995/Accepted: 22 January 1996 相似文献
5.
M. T. Fernández-Espinar S. Vallés F. Piñaga J. A. Pérez-González D. Ramón 《Applied microbiology and biotechnology》1996,45(3):338-341
Using recombinant DNA techniques, an Aspergillus nidulans multicopy transformant for the gene xlnB coding for the minor X24 xylanase has been constructed. When grown on glucose as sole carbon source this transformant secretes 114 U of xylanase (mg
protein)-1. In this culture condition, X24 is the only xylanase secreted and the predominant protein in the culture filtrate. This strategy has been used to purify
the X24 enzyme to homogeneity. The purified xylanase showed a single band on sodium dodecyl sulphate/ polyacrylamide gel electrophoresis
with a molecular mass of 24 kDa and had an isoelectric point of approximately 3.5. The enzyme was a non-debranching endo-1,4-β-xylan
xylanohydrolase highly specific for xylans and showed optimal activity at pH 5.5 and 52°C. The X24 xylanase had a Michaelis constant, K
m, of 12.43 mg oat spelt xylan ml-1 and a V
max of 1639 μmol min-1 (mg protein)-1.
Received: 17 May 1995/Received last revision: 25 September 1995/Accepted: 29 September 1995 相似文献
6.
Purification and characterization of tubulin from ginkgo pollen 总被引:2,自引:0,他引:2
Tubulin was purified by a combination of acetone powder preparation, DEAE Sephadex A-50 chromatography, Sephacryl S-300 gel
filtration, and Mono Q anion exchange chromatography from the pollen of ginkgo (Ginkgo biloba L.), a typical gymnosperm. The average yield of tubulin is 2 mg per 100 g of pollen grain. The purified tubulin is electrophoretically
homogeneous. It seems to be composed of two subunits on SDS-PAGE and is resolved as two major spots on two-dimensional electrophoresis,
preliminarily indicating that there are no obvious tubulin isotypes in ginkgo pollen. The apparent molecular weights of the
two subunits are about 54 kDa and 52 kDa respectively, estimated from the SDS-PAGE. It was also demonstrated that tubulin
from ginkgo pollen is immunochemically related to animal brain tubulin, and the purified tubulin was polymerized to microtubular
aggregates in the presence of taxol and GTP in vitro.
Received: 13 April 1996 / Revision accepted: 24 March 1997 相似文献
7.
Trichoderma reesei endoglucanase I (EGI) was used as a reporter enzyme for screening mutagenized yeast strains for increased ability to produce
protein. Sixteen haploid Saccharomyces cerevisiae strains, transformed with a yeast multicopy vector pALK222, containing the EGI cDNA under the ADH1 promoter, produced EGI activity of 10-5–10-4 g/l. On the average 93% of the total activity was secreted into the culture medium. Two strains with opposite mating types
were mutagenized, and several mutants were isolated possessing up to 45-fold higher EGI activity. The best mutants were remutagenized
and a second-generation mutant, strain 2804, with an additional twofold increase in EGI activity was selected. The mutant
strain 2804 grew more slowly and reached a lower final cell density than the parental strain. In the selective minimal medium,
the 2804 strain produced 40 mg/l immunoreactive EGI protein, but only 2% was active enzyme. In the rich medium the secreted
EGI enzyme stayed active, but without selection pressure the EGI production ceased after 2 days of cultivation, when the strain
2804 had produced 10 mg/l of EGI. A sevenfold difference was found between the parental and the 2804 strain in their total
EGI production relative to cell density. The difference in favour of the mutant strain was also detected on the mRNA level.
The 2804 mutant was found to be more active than the parental strain also in the production of T. reesei cellulases, cellobiohydrolase I, and cellobiohydrolase II.
Received: 22 December 1995/Received revision: 26 February 1996/Accepted: 17 March 1996 相似文献
8.
The Ser-170 residue of a trypsin-like enzyme from Streptomyces fradiae (SFT), which is considered to be the active-site serine, was replaced with alanine by site-directed mutagenesis to improve
the affinity chromatography step for a Kazal-type trypsin inhibitor, pancreatic secretory trypsin inhibitor (PSTI). The resulting
mutant SFT, designated as [S170A]SFT, was expressed in Streptomyces lividans and purified to homogeneity. [S170A]SFT was catalytically inactive, but still had the ability to bind tightly to PSTI and
to soybean trypsin inhibitor with dissociation constants of 3.1×10-7 M and 1.9×10-8 M respectively. We further demonstrated that recombinant human PSTI secreted into Saccharomyces cerevisiae culture broth could be purified to homogeneity with a one-step [S170A]SFT-affinity column. The purified PSTI contained no
molecules intramolecularly cleaved by active trypsin, which are found when trypsin-affinity chromatography is used for the
purification. This eliminated the need for further separation of intact PSTI from intramolecularly cleaved PSTI by high-performance
liquid chromatography, thus simplifying and improving its purification process.
Received: 29 November 1995/Received revision: 24 January 1996/Accepted: 17 March 1996 相似文献
9.
Mapping genes controlling root morphology and root distribution in a doubled-haploid population of rice 总被引:31,自引:0,他引:31
R. Yadav B. Courtois N. Huang G. McLaren 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(5):619-632
A deep thick root system has been demonstrated to have a positive effect on yield of upland rice under water stress conditions.
Molecular-marker-aided selection could be helpful for the improvement of root morphological traits, which are otherwise difficult
to score. We studied a doubled-haploid population of 105 lines derived from an indica×japonica cross and mapped the genes controlling root morphology and distribution (root thickness, maximum root length, total root
weight, deep root weight, deep root weight per tiller, and deep root to shoot ratio). Most putative QTL activity was concentrated
in fairly compact regions on chromosomes 1, 2, 3, 6, 7, 8 and 9, but was widely spread on chromosome 5 and largely absent
on chromosomes 4, 10, 11 and 12. Between three and six QTLs were identified on different chromosomes for each trait. Individual
QTLs accounted for between 4 and 22% of the variation in the traits. Multiple QTL models accounted for between 14 and 49%.
The main QTLs were common between traits, showing that it should be possible to modify several aspects of root morphology
simultaneously. There was evidence of interaction between marker locations in determining QTL expression. Interacting locations
were mostly on different chromosomes and showed antagonistic effects with magnitudes large enough to mask QTL detection. The
comparison of QTL locations with another population showed that one to three common QTLs per trait were recovered, among which
the most significant was in one or other population. These results will allow the derivation of isogenic lines introgressed
with these common segments, separately in the indica and japonica backgrounds.
Received: 12 August 1996 / Accepted: 15 November 1996 相似文献
10.
The strain Penicillium purpurogenum P-26 was subjected to UV irradiation and N-methyl-N′-nitro-N-nitrosoguanidine treatment and mutants were isolated capable of synthesizing cellulase under the conditions of a high concentration
of glucose. Initially mutants resistant to catabolite repression by 2-deoxy-D-glucose were isolated on Walseth’s cellulose/agar plates containing 15–45 mM 2-deoxy-D-glucose. These mutants were again screened for resistance to catabolite repression by glycerol or glucose on Walseth’s cellulose/agar
plates containing 50 g/l glycerol or 50 g/l glucose respectively. Four mutants with different sizes of clearing zone on Walseth’s
cellulose/agar plates containing 50 g/l glucose were selected for flask culture. Among them, the mutant NTUV-45-4 showed better
carboxymethylcellulase activity in flask culture containing 1% Avicel plus 3% glucose than did the parental strain.
Received: 9 October 1995/Received revision: 27 November 1995/Accepted: 8 January 1996 相似文献
11.
The fungal solubilization of cell wall components of sugar-beet pulp, during solid-state fermentation of Thermoascus aurantiacus, is reported here. The extracellular fungal enzyme activities related to the substrate degradation were also studied. In
120 h, more than 60% of the main sugar-beet pulp polysaccharides, i.e. pectins, arabinose- and glucose-containing polysaccharides,
were rapidly brought into solution by the fungus. The slow accumulation of monosaccharides compared to the fast degradation
of the polysaccharides suggested that most of the released sugars were consumed by the fungus. The analysis of the enzymes
present in the water extracts of the solid-state cultures proved that the fungus was able to synthesize a complete enzymatic
system required for the hydrolysis of the main sugar-beet pulp polysaccharides. The highest enzyme activities measured were
β-glucosidase and α-L-arabinofuranosidase.
Received: 22 September 1995/Received revision: 15 January 1996/Accepted: 22 January 1996 相似文献
12.
Cell-linked and extracellular cholesterol oxidase activities from Rhodococcus erythropolis. Isolation and physiological characterization 总被引:1,自引:0,他引:1
M. Sojo R. Bru D. Lopez-Molina F. Garcia-Carmona J.-C. Argüelles 《Applied microbiology and biotechnology》1997,47(5):583-589
Rhodococcus erythropolis cells growing in a cholesterol-free glycerol-containing mineral medium displayed very low levels of a cell-wall-bound cholesterol
oxidase activity. Addition of cholesterol induced a marked increase in the synthesis of this enzyme, which reached a maximum
within 6 days and was subsequently followed by the appearance of extracellular cholesterol oxidase in the culture broth. Significant
levels of induction were only achieved when cholesterol emulsified with Tween 80. The presence of chloramphenicol at the time
of induction completely prevented the emergence of both enzymatic forms, suggesting the requirement of de novo protein synthesis.
Upon transfer of cholesterol-growing cultures to fresh medium lacking cholesterol, the extracellular cholesterol oxidase was
quickly erased, while the activity of the particulate enzyme decreased sharply. The electrophoretic pattern on native Western
blotting as well as on sodium dodecyl sulphate/polyacrylamide gels, together with kinetic data, strongly support the idea
that the particulate and extracellular cholesterol oxidases are two different forms of the same enzyme with an estimated molecular
mass of 55 kDa.
Received: 26 September 1996 / Received revision: 30 December 1996 / Accepted: 4 January 1997 相似文献
13.
K. M. J. Van Laere G. Beldman A. G. J. Voragen 《Applied microbiology and biotechnology》1997,47(3):231-235
An arabinofuranohydrolase (AXH-d3) was purified from a cell-free extract of Bifidobacterium adolescentis DSM 20083. The enzyme had a molecular mass of approximately 100 kDa as determined by gel filtration. It displayed maximum
activity at pH 6 and 30 °C. Using an arabinoxylan-derived oligosaccharide containing double-substituted xylopyranosyl residues
established that the enzyme specifically released terminal arabinofuranosyl residues linked to C-3 of double-substituted xylopyranosyl
residues. In addition, this arabinofuranohydrolase released arabinosyl groups from wheat flour arabinoxylan polymer but showed
no activity towards p-nitrophenyl α-l-arabinofuranoside or towards sugar-beet arabinan, soy arabinogalactan, arabino-oligosaccharides and arabinogalacto-oligosaccharides.
Received: 15 July 1996 / Received revision: 18 October 1996 / Accepted: 18 October 1996 相似文献
14.
Alcaligenes eutrophus was grown in batch cultures using either phenol as a sole substrate or mixtures of phenol and 4-chlorophenol. Phenol was
found to be the sole source for carbon and energy while 4-chlorophenol was utilized only as a cometabolite. Maximum growth
rates on phenol reached only 0.26 h-1, significantly below the growth rates reported earlier with Pseudomonas putida. The cometabolite was found to decrease biomass yield and increase lag time before logarithmic growth occurred. Both phenol
and 4-chlorophenol were found to inhibit the growth rate linearly with maximum concentrations of 1080 ppm and 69 ppm respectively,
beyond which no growth occurred. The best-fit parameters are incorporated into a simple, dynamic (i.e. time-varying) model
capable of predicting all the batch growth conditions presented here. It is shown that P. putida is capable of faster bioremediation when phenol is the sole carbon source or for mixed substrates with low concentrations
of the cometabolite, but for high concentrations of 4-chlorophenol, A. eutrophus becomes superior because of the long lag times that occur in the Pseudomonas species.
Received: 25 January 1996/Received revision: 13 March 1996/Accepted: 15 April 1996 相似文献
15.
A. M. Moilanen T. Lundell T. Vares A. Hatakka 《Applied microbiology and biotechnology》1996,45(6):792-799
The effects of high manganese [180 μM Mn(II)] concentration and addition of malonate (10 mM) were studied in nitrogen-limited
cultures of the white-rot fungus, Phlebia radiata. High levels of manganese alone showed no systematic influence on the production of lignin peroxidase (LiP), manganese peroxidase
(MnP) or laccase. In contrast, high-manganese containing cultures of P. radiata showed lower efficiency in the mineralization of 14C-ring-labelled synthetic lignin ([14C]DHP). The highest rates of mineralization, up to 30% in 18 days, were reached in low- manganese(2 μM)-containing cultures
when malonate was omitted. Degradation of [14C]DHP was substantially restricted by the addition of malonate. The combination of high manganese and malonate resulted in
increased levels of MnP and laccase production, whereas LiP production was repressed. Also, the profiles of expression of
the MnP and LiP isozymes were affected. A new P. radiata MnP isozyme of pI 3.6 (MnP3) was found in the high-manganese cultures. Addition of malonate alone caused some repression but also stimulating
effects on distinctive MnP and LiP isozymes. The results indicate that manganese and malonate are individual regulators of
MnP and LiP expression and have different roles in the degradation of lignin by P. radiata.
Received: 30 August 1995/Received revision: 10 January 1996/Accepted: 12 February 1996 相似文献
16.
Glucose oxidase from Penicillium amagasakiense was purified to homogeneity by ion-exchange chromatography and deglycosylated with endoglycosidase H. On the basis of gas
chromatography and sodium dodecyl sulphate/polyacrylamide gel electrophoretic (SDS-PAGE) analyses, the protein-bound high-mannose-type
carbohydrate moiety corresponded to 13% of the molecular mass of glycosylated glucose oxidase. A total of six N-glycosylation sites per dimer were determined from the N-acetylglucosamine content. The enzymatically deglycosylated enzyme contained less than 5% of the original carbohydrate moiety.
A molecular mass of 130 kDa (gel filtration) and 133 kDa (native PAGE) was determined for the dimer and 67 kDa (SDS-PAGE)
for the monomer of the deglycosylated enzyme. The N-terminal sequence, which has not been published for glucose oxidase from
P. amagasakiense to date and which showed less than 50% homology to the N terminus of glucose oxidase from Aspergillus niger, and the amino acid composition were not altered by the deglycosylation. Deglycosylation also did not affect the kinetics
of glucose oxidation or the pH and temperature optima. It also did not increase the susceptibility of the enzyme to proteolytic
degradation. However, deglycosylated glucose oxidase exhibited decreased pH and thermal stability. The thermal stability of
both enzymes was shown to be dependent on the buffer concentration and was enhanced by certain additives, particularly 1 M
(NH4)2SO4, which stabilised glucose oxidase 100- to 300-fold at 50 °C and pH 7–8, and 2 M KF, which stabilised the enzyme up to 36-fold
at 60 °C and pH 6. In sodium acetate buffer, changes in pH (4–6) affected the affinity for glucose but had no effect on the
V
max of the reaction. In contrast, in TRIS buffer, pH 8, a 10-fold decrease in V
max and a 2-fold decrease in K
m were observed.
Received: 8 October 1996 / Received revision: 14 January 1997 / Accepted: 17 January 1997 相似文献
17.
A continuous bioreactor packed with a fibrous matrix was set up. Cells of Pediococcus acidilactici PO2 were inoculated and MRS broth was fed gradually until cell growth and immobilization were achieved. Kinetics of fermentation
and production of bacteriocin were investigated at dilution rates ranging from 0.63 day-1 to 1.58 day-1 and at pH values that varied between 4.0 and 5.5. A maximum bacteriocin activity of 6400 AU/ml was detected when the medium
was fermented at dilution rates of at least 1.19 day-1 and the pH controlled at 4.5. The maximum bacteriocin productivity was 1.0×107 AUl-1 day-1 at a dilution rate of 1.58 day-1 and pH 4.5. At this high dilution rate, 1.21 g cells/l medium was produced, 95.9% of the glucose in MRS broth was utilized,
and 15.1 g lactic acid/l accumulated in the bioreactor effluent. The bioreactor was operated continuously for 3 months without
encountering any clogging, degeneration, or contamination problems, indicating good long-term stability of the bioreactor
for bacteriocin production. About 94% of the cells in the bioreactor were immobilized, and the remainder were suspended in
the medium. According to scanning electron microscopic observations, cell immobilization in the fibrous matrix was attained
by natural attachment to fiber surfaces and entrapment in the void volume within the fibrous matrix. In conclusion, conditions
for the optimum continuous production of pediocin were defined; this may facilitate the development of large-scale industrial
processes for production of this bacteriocin.
Received: 25 September 1995/Received revision: 30 November 1995/Accepted: January 1996 相似文献
18.
β-Fructofuranosidase was purified from commercial alkaline protease (Aspergillus oryzae origin). The optimal pH of its transfructosylating activity was more alkaline (pH 8) than that of its hydrolyzing activity
(pH 5). In the case of a 24-h reaction with sucrose, the hydrolysis and transfructosylation reaction were optimal at pH 4–5
and pH 8, respectively. In the reaction at pH 8 1-kestose and nystose were the main fructooligosaccharides produced. The transfer
ratio was hardly different between pH 5 and pH 8 early in the reaction, but the transfer products (1-kestose and nystose)
were decreased at pH 5 as the reaction proceeded because of their hydrolysis.
Received: 18 January 1995/Received last revision: 23 August 1995/Accepted: 13 September 1995 相似文献
19.
Two extracellular isoenzymes of polygalacturonase, isolated from the brown-rot fungus Postia placenta, were purified 342-fold by Mono S cation-exchange chromatography. The temperature optimum ranged from 25 °C to 37 °C, and the pH optimum ranged from 3.2 to 3.9. Apparent pI values of the isoenzymes (3.2 and 3.4) were lower than any previously reported. The estimated molecular mass from a single
band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis (PAGE) was 34 kDa. Isoenzymes of polygalacturonase in native
PAGE and isoelectric focusing gels were identified by substrate/ agar overlays (zymograms). Comparison of viscosity reduction
rates with release of reducing sugars indicated that the enzyme from P. placenta is endo-acting. The objective of this study was to isolate polygalacturonase from the brown-rot fungus P. placenta and characterize the properties of the enzyme.
Received: 31 October 1995/Received revision: 12 February 1996/Accepted: 4 March 1996 相似文献
20.
F. J. M. Verhagen H. J. Swarts T. W. Kuyper J. B. P. A. Wijnberg J. A. Field 《Applied microbiology and biotechnology》1996,45(5):710-718
Recently, several species of basidiomycetes were shown to produce de novo high concentrations of chloroaromatic metabolites. Since these lignocellulose-degrading fungi play a major role in the ecosphere,
the purpose of this study was to determine the ubiquity of organohalogen production among basidiomycetes. A total of 191 fungal
strains were monitored for adsorbable organic halogen (AOX) production when grown on defined liquid media. Approximately 50%
of the strains tested and 55% of the genera tested produced AOX. A low production of 0.1–0.5 mg AOX/l was observed among 25%
of the strains, a moderate production of 0.5–5.0 mg AOX/l was observed among 16% of the strains and 9% of the strains produced
high levels (5–67 mg AOX/l). The latter group was dominated by species belonging to the genera Hypholoma, Mycena and Bjerkandera, showing specific AOX productions in the range 1074–30893 mg AOX/kg dry weight of mycelial biomass. Many highly ecologically
significant fungal species were identified among the moderate to high producers. These species were also able to produce AOX
when cultivated on natural lignocellulosic substrates. Hypholoma fasciculare and Mycena metata respectively produced up to 132 mg and 193 mg AOX/kg dry weight of forest litter substrate in 6 weeks.
Received: 5 October 1995/Received revision: 28 December 1995/Accepted: 12 February 1996 相似文献