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1.
M. Drążkiewicz 《Folia microbiologica》1994,39(4):276-282
The distribution of microorganisms in soil aggregates with different diameters was determined using a “washing and sonic vibration”
method. In humic rendzina the number of bacteria, actinomycetes and fungi located in aggregates measuring 3 to 1 and ≤0.5
mm was greater than in those of 7 to 5 mm.Pseudomonas were more numerous in aggregates of ≤0.5 mm than in those of 3 to 1 mm and spore-forming aerobic bacteria—in aggregates measuring
3 to 1 mm than in those of 7 to 5 mm. The number of microorganisms growing on asparagine agar andArthrobacter-Corynebacterium increased as 7-5<3-1<0.5 and 7-5<0.5<3-1 mm, respectively. In podzolic loess spore-forming aerobic bacteria inhabited preferentially
aggregates measuring 7 to 5 mm,Arthrobacter-Corynebacterium aggregates of ≤0.5 mm. The number of bacteria was greater in aggregates of 3 to 1 than in those measuring ≤0.5 mm. Aggregates
of various diameters differed also in the number of some microorganisms both in the outer and inner parts and the partition
ratio of microorganisms between these parts. Differences were more numerous in the humic rendzina aggregates. 相似文献
2.
A phylogenetic tree was constructed on the basis of the amino acid sequences of the known cyclodextrin glucanotransferases
(CDGTs), including those deduced from the nucleotide sequences ofBacillus sp. strain 6.6.3 andPaenibacillus macerans IB-7 genes encoding α- and β-CDGTs. The tree clearly demonstrates the existence of distinct phylogenetic groups of CDGT-producing
microorganisms and the divergence of the α-, β-, and γ-CDGT produced by microorganisms from the generaBacillus, Paenibacillus, Brevibacillus, andThermoanaerobacter from a common ancestor, whereas the CDGT ofKlebsiella pneumoniae is independent and results from the convergence of different ancestors. The degree of homology of the leader peptide sequences
of CDGTs may serve as a criterion of intraspecies relatedness between CDGT-producing microorganisms. 相似文献
3.
Identification of carotenoids with high antioxidant capacity produced by extremophile microorganisms
F Mandelli VS Miranda E Rodrigues AZ Mercadante 《World journal of microbiology & biotechnology》2012,28(4):1781-1790
In this study, the carotenoids produced by the extremophile microorganisms Halococcus morrhuae, Halobacterium salinarium and Thermus filiformis were separated and identified by high-performance liquid chromatography connected to a diode array detector and a tandem
mass spectrometer. The in vitro scavenging capacity of the carotenoid extracts against radical and non-radical species was
evaluated. In halophilic microorganisms, the following carotenoids were identified: bacterioruberin, bisanhydrobacterioruberin,
trisanhydrobacterioruberin and their derivatives. In the thermophilic bacterium, the carotenoids all-trans-zeaxanthin, zeaxanthin monoglucoside, thermozeaxanthins and thermobiszeaxanthins were identified. The antioxidant capacities
of the carotenoid extracts of H. morrhuae (trolox equivalent antioxidant capacity = 5.07 and IC50 = 0.85 μg mL−1) and H. salinarium (trolox equivalent antioxidant capacity = 5.28 and IC50 = 0.84 μg mL−1) were similar and higher than those of the bacterium T. filiformis (trolox equivalent antioxidant capacity = 2.87 and IC50 = 2.41 μg mL−1). This difference is related to the presence of acyclic carotenoids with both large numbers of conjugated double bounds and
of hydroxyl groups in the major carotenoid of the halophilic microorganisms. 相似文献
4.
Agar degradation by microorganisms and agar-degrading enzymes 总被引:1,自引:0,他引:1
Agar is a mixture of heterogeneous galactans, mainly composed of 3,6-anhydro-l-galactoses (or l-galactose-6-sulfates) d-galactoses and l-galactoses (routinely in the forms of 3,6-anhydro-l-galactoses or l-galactose-6-sulfates) alternately linked by β-(1,4) and α-(1,3) linkages. It is a major component of the cell walls of red
algae and has been used in a variety of laboratory and industrial applications, owing to its jellifying properties. Many microorganisms
that can hydrolyze and metabolize agar as a carbon and energy source have been identified in seawater and marine sediments.
Agarolytic microorganisms commonly produce agarases, which catalyze the hydrolysis of agar. Numerous agarases have been identified
in microorganisms of various genera. They are classified according to their cleavage pattern into three types—α-agarase, β-agarase,
and β-porphyranase. Although, in a broad sense, many other agarases are involved in complete hydrolysis of agar, most of those
identified are β-agarases. In this article we review agarolytic microorganisms and their agar-hydrolyzing systems, covering
β-agarases as well as α-agarases, α-neoagarobiose hydrolases, and β-porphyranases, with emphasis on the recent discoveries.
We also present an overview of the biochemical and structural characteristics of the various types of agarases. Further, we
summarize and compare the agar-hydrolyzing systems of two specific microorganisms: Gram-negative Saccharophagus degradans 2–40 and Gram-positive Streptomyces coelicolor A3(2). We conclude with a brief discussion of the importance of agarases and their possible future application in producing
oligosaccharides with various nutraceutical activities and in sustainably generating stock chemicals for biorefinement and
bioenergy. 相似文献
5.
Sasaki H Nonaka J Sasaki T Nakai Y 《Journal of industrial microbiology & biotechnology》2007,34(2):105-110
We isolated ammonia-assimilating microorganisms from the livestock manure treatment systems and evaluated their ammonia-assimilating
ability. Many isolates utilized ammonia at high rates when they were purely cultivated in a nitrogen-limited medium to which
sterilized lagoon extract had been added. Some isolates that were immobilized in polyvinyl alcohol (PVA) utilized ammonia
present in the media containing viable lagoon microorganisms. Staining with 4′,6′-diamidino-2-phenylindole (DAPI) indicated
that the immobilized high ammonia-assimilating isolates grew dominantly within the PVA beads. High ammonia-assimilating isolates
in the mixed culture containing viable lagoon microorganisms were identified as Pseudomonas spp. and member of Rhizobiaceae species by partial sequencing of the 16S ribosomal DNA. 相似文献
6.
Effects of Thymol on Ruminal Microorganisms 总被引:2,自引:0,他引:2
Thymol (5-methyl-2-isopropylphenol) is a phenolic compound that is used to inhibit oral bacteria. Because little is known
regarding the effects of this compound on ruminal microorganisms, the objective of this study was to determine the effects
of thymol on growth and lactate production by the ruminal bacteria Streptococcus bovis JB1 and Selenomonas ruminantium HD4. In addition, the effect of thymol on the in vitro fermentation of glucose by mixed ruminal microorganisms was investigated.
Neither 45 nor 90 μg/ml of thymol had any significant effect on growth or lactate production by S. bovis JB1, but 180 μg/ml of thymol completely inhibited growth and lactate production. In the case of S. ruminantium HD4, 45 μg/ml of thymol had little effect on growth and lactate production; however, 90 μg/ml of thymol completely inhibited
growth of S. ruminantium HD4. Thymol also decreased glucose uptake by whole cells of both bacteria. When mixed ruminal microorganisms were incubated
in medium that contained glucose, 400 μg/ml of thymol increased final pH and the acetate to propionate ratio and decreased
concentrations of methane, acetate, propionate, and lactate. In conclusion, thymol was a potent inhibitor of glucose fermentation
by S. bovis JB1 and S. ruminantium HD4. Even though thymol treatment decreased methane and lactate concentrations and increased final pH in mixed ruminal microorganism
fermentations of glucose, concentrations of acetate and propionate were also reduced.
Received: 13 May 2000 / Accepted: 14 June 2000 相似文献
7.
The phylogenetic diversity and axial distribution of microorganisms in three sections of the gastrointestinal tracts of the
polychaete Neanthes glandicincta was evaluated using both most probable number method and cloning analyses of 16S rRNA genes in this study. Quantification
of the density of microorganisms in the gut showed that aerobic microorganisms decreased from anterior to posterior, while
anaerobic ones showed a reverse trend. The total numbers of microorganisms decreased significantly (p < 0.05, analysis of variance) but more rapidly from the anterior to the middle segment. Phylogenetic analysis showed that
the dominating phylogenetic groups included Methanomicrobiales I: Methanosaetaceae (up to 66% of archaeal clones), δ-Proteobacteria (up to 42% of bacterial clones), and γ-Proteobacteria (up to 30% of bacterial clones) widely distributed throughout the entire gut. Other microbiota distributed in different gut
sections were Methanomicrobiales II: Methanospirillaceae, Methanomicrobiales III, Thermoplasmatales, Crenarchaea, Methanobacteriaceae, and Methanosarcinales for archaea; and α-Proteobacteria, β-Proteobacteria, Fusobacteria, Clostridia, Chloroflexi, and Planctomycetes for bacteria. The results reveal a difference in microbial community structure along the gut of N. glandicincta. The various phylogenetic diversity and axial distribution of microbes along the gut might indicate an environmental gradient
from anterior to posterior sections affecting the structure of the microbial community. 相似文献
8.
F. Laborda I. F. Monistrol N. Luna M. Fernández 《Applied microbiology and biotechnology》1999,52(1):49-56
Several fundamental aspects of microbial coal liquefaction/solubilization were studied. The liquefied/solubilized products
from coal by microorganisms were analysed. The liquid products analysed by IR titration and UV/visible spectrometry showed
some alterations with regard to the original coal. Humic acids extracted from the liquefied lignite showed a reduction in
the average molecular weight and a increase in the condensation index, probably due to depolymerization caused by microorganisms.
The mechanisms implicated in coal biosolubilization by two fungal strains, M2 (Trichoderma sp.) and M4 (Penicillium sp.) were also studied. Extracellular peroxidase, esterase and phenoloxidase enzymes appear to be involved in coal solubilization.
Received: 15 June 1998 / Received revision: 23 November 1998 / Accepted: 29 November 1998 相似文献
9.
Enhancement of the gas-to-water ethene transfer coefficient by a dispersed water-immiscible solvent: effect of the cells 总被引:1,自引:0,他引:1
M. T. Cesário M. Turtoi S. F. M. Sewalt H. H. Beeftink J. Tramper 《Applied microbiology and biotechnology》1996,46(5-6):497-502
For a mass-transfer-limited system, it was demonstrated that the volumetric ethene transfer coefficient (k
l
a) from gas to water could be enhanced by dispersing adequate amounts of a water-immiscible organic liquid, namely the perfluorocarbon
FC40, in the aqueous phase. When 26% (v/v) FC40 was dispersed in a culture of Mycobacterium parafortuitum an enhancement of k
l
a, calculated on a total liquid volume basis, of 1.8 times was found. Steady-state experiments in the absence of microorganisms,
however, showed a 1.2-fold enhancement of k
l
a at 18.5% (v/v) FC40. At all FC40 volume fractions tested, enhancement factors with cells were higher than enhancements without
cells; apparently the microorganisms or their excretion products affected the interfacial areas or characteristic phase dimensions.
Received: 4 December 1995 / Received revision: 7 June 1996 / Accepted: 10 June 1996 相似文献
10.
High level expression and purification of antimicrobial human cathelicidin LL-37 in Escherichia coli
Ján Krahulec Marcela Hyršová Stanislav Pepeliaev Jana Jílková Zbyněk Černý Jana Machálková 《Applied microbiology and biotechnology》2010,88(1):167-175
The human antimicrobial peptide LL-37 is a cationic peptide with antimicrobial activity against both Gram-positive and Gram-negative
microorganisms. This work describes the development of an expression system based on Escherichia coli capable of high production of the recombinant LL-37. The fusion protein Trx-LL-37 was expressed under control of T7 promoter.
The expression of T7 polymerase in the E. coli strain constructed in this work was controlled by regulation mechanisms of the arabinose promoter. The expression plasmid
was stabilized by the presence of parB locus which ensured higher homology of the culture during cultivation without antibiotic selection pressure. This system
was capable of producing up to 1 g of fusion protein per 1 l of culture. The subsequent semipreparative HPLC allowed us to
isolate 40 mg of pure LL-37. LL-37 showed high antimicrobial activity against both Gram-negative and Gram-positive microorganisms.
Its activity against Candida albicans was practically nonexistent. Minimal Inhibition Concentration (MIC) determined for E. coli was 1.65 μM; for Staphylococcus aureus 2.31 μM, and for Enterococcus faecalis 5.54 μM. The effects of cathelicidin on E. coli included the ability to permeabilize both cell membranes, as could be observed by the increase of β-galactosidase activity
in extracellular space in time. Physiological changes were studied by scanning electron microscopy; Gram-positive microorganisms
did not show any visible changes in cell shapes while the changes observed on E. coli cells were evident. The results of this work show that the herein designed expression system is capable of producing adequate
quantities of active human antimicrobial peptide LL-37. 相似文献
11.
Luciano Polonelli Walter Magliani Tecla Ciociola Laura Giovati Stefania Conti 《Antonie van Leeuwenhoek》2011,99(1):35-41
“Antibiobodies”, antibodies (Abs) with antibiotic activity, internal image of a Pichia anomala killer toxin (PaKT) characterized by microbicidal activity against microorganisms expressing β-glucans cell-wall receptors (PaKTRs), were produced by idiotypic vaccination with a PaKT-neutralizing monoclonal Ab (PaKT-like Abs) or induced by a protein-conjugated β-glucan. Human natural PaKT-like Abs (PaKTAbs) were found in the vaginal fluid of women infected with KT-sensitive microorganisms. Monoclonal and recombinant PaKT-like Abs, and PaKTAbs proved to be protective against experimental candidiasis, cryptococcosis and aspergillosis. A killer decapeptide (KP),
synthesized from the sequence of a recombinant PaKT-like Ab or produced in transgenic plants, showed a microbicidal activity in vitro, neutralized by β-glucans, a therapeutic
effect in vivo, against experimental mucosal and systemic mycoses, and a prophylactic role in planta, against phytopathogenic microorganisms, respectively. KP showed fungicidal properties against all the defective mutants
of a Saccharomyces cerevisiae library, inclusive of strains recognized to be resistant to conventional antifungal drugs. KP inhibited in vitro, ex vivo
and/or in vivo HIV-1 and Influenza A virus replication, owing to down-regulation of CCR5 co-receptors, physical block of the
gp120-receptor interaction and reduction in the synthesis of glycoproteins, HA and M1 in particular. KP modulated the expression
of costimulatory and MHC molecules on murine dendritic cells, improving their capacity to induce lymphocyte proliferation.
KP, proven to be devoid of cytotoxicity on human cells, showed self-assembly-releasing hydrogel-like properties, catalyzed
by β 1,3 glucan. PaKT’s biotechnological derivatives may represent the prototypes of novel antifungal vaccines and anti-infective drugs characterized
by different mechanisms of action. 相似文献
12.
Aline T 《Microbial ecology》2008,55(4):569-580
Spatial and temporal variabilities in species composition, abundance, distribution, and bioeroding activity of euendolithic
microorganisms were investigated in experimental blocks of the massive coral Porites along an inshore–offshore transect across the northern Great Barrier Reef (Australia) over a 3-year period. Inshore reefs
showed turbid and eutrophic waters, whereas the offshore reefs were characterized by oligotrophic waters. The euendolithic
microorganisms and their ecological characteristics were studied using techniques of microscopy, petrographic sections, and
image analysis. Results showed that euendolithic communities found in blocks of coral were mature. These communities were
dominated by the chlorophyte Ostreobium quekettii, the cyanobacterium Plectonema terebrans, and fungi. O. quekettii was found to be the principal agent of microbioerosion, responsible for 70–90% of carbonate removal. In the offshore reefs,
this oligophotic chlorophyte showed extensive systems of filaments that penetrated deep inside coral skeletons (up to 4.1 mm)
eroding as much as 1 kg CaCO3 eroded m−2 year−1. The percentage of colonization by euendolithic filaments at the surface of blocks did not vary significantly among sites,
while their depths of penetration, especially that of O. quekettii (0.6–4.1 mm), increased significantly and gradually with the distance from the shore. Rates of microbioerosion (0.1–1.4 kg
m−2 after 1 year and 0.2–1.3 kg m−2 after 3 years of exposure) showed a pattern similar to the one found for the depth of penetration of O. quekettii filaments. Accordingly, oligotrophic reefs had the highest rates of microbioerosion of up to 1.3 kg m−2 year−1, whereas the development of euendolithic communities in inshore reefs appeared to be limited by turbidity, high sedimentation
rates, and low grazing pressure (rates <0.5 kg m−2 after 3 years). Those results suggest that boring microorganisms, including O. quekettii, have a significant impact on the overall calcium carbonate budget of coral reef ecosystems, which varies according to environmental
conditions. 相似文献
13.
A cellular automata model to simulate penicillin fed-batch fermentation process (CAPFM) was established in this study, based
on a morphologically structured dynamic penicillin production model, that is in turn based on the growth mechanism of penicillin
producing microorganisms and the characteristics of penicillin fed-batch fermentation. CAPFM uses the three-dimensional cellular
automata as a growth space, and a Moore-type neighborhood as the cellular neighborhood. The transition rules of CAPFM are
designed based on mechanical and structural kinetic models of penicillin batch-fed fermentation processes. Every cell of CAPFM
represents a single or specific number of penicillin producing microorganisms, and has various state. The simulation experimental
results show that CAPFM replicates the evolutionary behavior of penicillin batch-fed fermentation processes described by the
structured penicillin production kinetic model accordingly.
__________
Translated from ACTA BIOPHYSICA, 2005, 21(2) [译自: 生物物理学报, 2005,21(2)] 相似文献
14.
The degradation potential of trichloroethene by the aerobic methane- and ammonia-oxidizing microorganisms naturally associated
with wetland plant (Carex comosa) roots was examined in this study. In bench-scale microcosm experiments with washed (soil free) Carex comosa roots, the activity of root-associated methane- and ammonia-oxidizing microorganisms, which were naturally present on the
root surface and/or embedded within the roots, was investigated. Significant methane and ammonia oxidation were observed reproducibly
in batch reactors with washed roots incubated in growth media, where methane oxidation developed faster (2 weeks) compared
to ammonia oxidation (4 weeks) in live microcosms. After enrichment, the methane oxidizers demonstrated their ability to degrade
150 μg l−1 TCE effectively at 1.9 mg l−1 of aqueous CH4. In contrast, ammonia oxidizers showed a rapid and complete inhibition of ammonia oxidation with 150 μg l−1 TCE at 20 mg l−1 of NH4
+-N, which may be attributed to greater sensitivity of ammonia oxidizers to TCE or its degradation product. No such inhibitory
effect of TCE degradation was detected on methane oxidation at the above experimental conditions. The results presented here
suggest that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated
aquatic environments. 相似文献
15.
A. B. Więckowski G. P. Słowik J. A. Gąsiorek P. Gąsiorek F. Domka A. Perkowska 《Applied microbiology and biotechnology》1999,52(1):96-98
A comparison of iron-sulfur proteins obtained from Thiobacillus ferrooxidans was carried out. The microorganisms were grown on iron(II)- or sulfur-containing nutrients. In both cases different, broad
elctron paramagnetic resonance (EPR) lines, originating from an iron(III) compound, were detected. Additional EPR lines of
tetrahedral iron(III) and free radicals were observed. The UV spectra of these compounds also differ.
Received: 15 July 1998 / Received revision: 8 October 1998 / Accepted: 16 October 1998 相似文献
16.
Humic acid effect on pyrene degradation: finding an optimal range for pyrene solubility and mineralization enhancement 总被引:1,自引:0,他引:1
Liang Y Britt DW McLean JE Sorensen DL Sims RC 《Applied microbiology and biotechnology》2007,74(6):1368-1375
The addition of humic acid (HA) to polycyclic aromatic hydrocarbon (PAH) contaminated systems has been shown to enhance, inhibit,
or have no effect on the biodegradation of these PAHs. In this study, the surfactant effects of Elliott soil HA (ESHA) at
two pH values were tested. At pH 7.0, ESHA did not behave as a surfactant. At pH 11.8, ESHA acted as a surfactant, as displayed
by a decrease in surface tension with increasing concentrations of ESHA. The effect of ESHA on pyrene solubility was tested
by adding 0 to 800 μg ESHA/g soil to soil-slurries. Enhancement of pyrene apparent solubility demonstrated a dose- and time-related
effect. Broader doses from 0 to 10,080 μg ESHA/g soil and three higher doses from 3,360 to 10,080 μg ESHA/g soil were tested
for their effects on pyrene mineralization by indigenous soil microorganisms and a novel PAH-degrading Mycobacterium sp. KMS in soil microcosms, respectively. ESHA amendments between 20 and 200 μg ESHA/g soil were found to consistently increase
pyrene mineralization by indigenous microorganisms, while the 10,080 μg ESHA/g soil produced inhibition and all other doses
presented no effects. Pyrene degradation by M. KMS was significantly inhibited by the addition of the highest dose of ESHA. 相似文献
17.
Estuaries are often considered sinks for contaminants and the cleanup of salt marshes, sensitive ecosystems with a major ecological
role, should be carried out by means of least intrusive approaches, such as bioremediation. This study was designed to evaluate
the influence of plant–microorganisms associations on petroleum hydrocarbons fate in salt marshes of a temperate estuary (Lima
River, NW Portugal). Sediments un-colonized and colonized (rhizosediments) by different plants (Juncus maritimus, Phragmites australis, Triglochin striata and Spartina patens) were sampled in four sites of the lower and middle estuary for hydrocarbon degrading microorganisms (HD), total cell counts
(TCC) and total petroleum hydrocarbons (TPHs) assessment. In general, TPHs, HD and TCC were significantly higher (P < 0.05) in rhizosediments than in un-colonized sediments. Also recorded were differences on the abundance of hydrocarbon
degraders among the rhizosediment of the different plants collected at the same site (J. maritimus < P. australis < T. striata), with statistically significant differences (P < 0.05) between J. maritimus and T. striata. Moreover, strong positive correlations—0.81 and 0.84 (P < 0.05), between biotic (HD) and abiotic (organic matter content) parameters and TPHs concentrations were also found. Our
data clearly suggest that salt marsh plants can influence the microbial community, by fostering the development of hydrocarbon-degrading
microbial populations in its rhizosphere, an effect observed for all plants. This effect, combined with the plant capability
to retain hydrocarbons around the roots, points out that salt marsh plant–microorganisms associations may actively contribute
to hydrocarbon removal and degradation in estuarine environments. 相似文献
18.
The heavy metal resistance of yeasts isolated from sugary substrates such as orange, palm wine and pineapple and identified
asSaccharomyces carlsbergensis andS. cerevisiae was studied. The yeast isolates were tested against different concentrations of cadmium, copper, manganese, silver and zinc
salts ranging from 1 to 20 mmol/L. Local yeasts showed resistance to 3–15 mmol/L cadmium, 18–20 copper, 16–20 manganese, 1–9
silver and 16–19 for zinc. The significance of the results is discussed in relation to the effects of heavy metals on growth
of microorganisms and selection of yeasts for the brewing industry in Nigeria. 相似文献
19.
We pyrosequenced the bulk DNA extracted from microorganisms that passed through 0.2-μm-pore-size filters and trapped by 0.1-μm-pore-size
filters in the hydrothermal fluid of the Mariana Trough. Using the 454-FLX sequencer, we generated 202,648 sequences with
an average length of 173.8 bases. Functional profiles were assigned by the SEED Annotation Engine. In the metagenome of the
0.2-μm-passable microorganisms, genes related to membrane function, including potassium homeostasis classified as membrane
transport, and multidrug-resistance efflux pumps classified as virulence, were dominant. There was a higher proportion of
genes pertinent to the subsystem of membrane transport in our metagenomic library than in other oceanic and hydrothermal vent
metagenomes. Genes associated with a RND-type efflux transporter for exogenous substances were specifically identified in
the present study. After a comparative analysis with the genome of the known ultramicrobacterium Sphingopyxis alaskensis RB2256, we discovered 1,542 cases of significant hits (E < 1 × 10−2) in our metagenome, and 1,172 of those were related to the DNA repair protein RadA. In this way, the microbial functional
profile of 0.2-μm-passable fraction in the present study differs from oceanic metagenomes in the 0.2-μm-trapped fractions
and hydrothermal vent metagenomes reported in previous research. 相似文献
20.
The isopenicillin N synthases isolated thus far are related to oxidases from other microorganisms and plants. These enzymes
maintain a non-heme monoferrous-dependent catalytic centre comprising a HisXAsp(53–57)XHis motif and a crucial substrate-binding pocket with an ArgXSer motif for their functionality. The elucidation of these motifs was dependent on information collated from studies on structural
chemistry, structural biology, site-directed engineered mutations and biochemical experiments. It is envisaged that these
enzymes can potentially be improved through molecular breeding and protein engineering.
Received: 15 December 1999 / Received revision: 26 January 2000 / Accepted: 27 January 2000 相似文献