共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Three different mechanisms can be envisaged that are used by fungi to solubilize coal: the production of alkaline substances,
the extrusion of chelators and, of special interest in the scope of biotechnology, the action of enzymes. Whether these mechanisms
are operating separately or in various combinations has not yet been finally assessed. The two deuteromycetes Fusarium oxysporum and Trichoderma atroviride solubilize coal by synergistic effects of various different mechanisms depending on the cell metabolism. F. oxysporum seems to solubilize coal by increasing the pH of the mycelial surroundings and by the action of chelators induced during
growth in glutamate-containing media (without involvement of enzymes). T. atroviride, on the other hand, appears to use, in addition to an alkaline pH and a high chelator activity, at least two classes of enzyme
activity to attack coal: hydrolytic activity for coal solubilization and ligninolytic activity for degradation of humic acids.
Received: 3 February 1998 / Received revision: 31 August 1998 / Accepted: 3 September 1998 相似文献
3.
Residues and coal fractions that remained after the biosolubilization of Rhenish brown coal by strains of Lentinula edodes and Trametes versicolor have been studied by Curie-point pyrolysis/gas chromatography/mass spectrometry using tetraethylammonium hydroxide (NEt4OH) at 610 °C. To differentiate methyl derivatives of esters and ethers from free or bound hydroxyl and carboxyl groups NEt4OH was used in the thermochemolysis experiments instead the commonly used tetramethylammonium hydroxide. A comparison of humic
acid fractions before and after fungal attack shows considerable alteration of the soluble macromolecules of coal. Depending
on the coal fraction studied and the fungi used, the assortment of fatty acid esters released during the pyrolysis varies
significantly. Furthermore, dicarbonic acid ethyl diesters as well as ethyl derivatives of aromatic ethers and acids yield
information about humic acid structure and the biosolubilization of brown coal. Variations in the mixture produced are possibly
caused by differences in the pattern of extracellular enzymes secreted that attack the macromolecular structural elements
of brown coal. Therefore pyrolysis of native and microbiologically altered geomacromolecules using NEt4OH allows one to differentiate between free hydroxyl groups as well as substances that are attached to humic substances via
ester or ether bridges, and their methylated counterparts.
Received: 13 July 1998 / Received revision: 12 October 1998 / Accepted: 16 October 1998 相似文献
4.
M. Kataoka K. Yamamoto H. Kawabata M. Wada K. Kita H. Yanase S. Shimizu 《Applied microbiology and biotechnology》1999,51(4):486-490
The asymmetric reduction of ethyl 4-chloro-3-oxobutanoate (COBE) to ethyl (R)-4-chloro-3-hydroxybutanoate [(R)-CHBE] using Escherichia coli cells, which coexpress both the aldehyde reductase gene from Sporobolomyces salmonicolor and the glucose dehydrogenase (GDH) gene from Bacillus megaterium as a catalyst was investigated. In an organic solvent-water two-phase system, (R)-CHBE formed in the organic phase amounted to 1610 mM (268 mg/ml), with a molar yield of 94.1% and an optical purity of 91.7%
enantiomeric excess. The calculated turnover number of NADP+ to CHBE formed was 13 500 mol/mol. Since the use of E. coli JM109 cells harboring pKAR and pACGD as a catalyst is simple, and does not require the addition of GDH or the isolation of
the enzymes, it is highly advantageous for the practical synthesis of (R)-CHBE.
Received: 5 October 1998 / Received revision: 16 November 1998 / Accepted: 5 December 1998 相似文献
5.
Two coals of different rank, mined in Russia, were treated by an anaerobic methanogenic enrichment culture. The addition
of alkaline enclosing rock to the lower-rank coal increased the pH of the incubation medium and methane production above that
of the higher-rank coal with addition of its enclosing rock. This effect was accompanied by the leaching of cations from the
incubation medium. The coal was processed without a preliminary chemical treatment in a two-stage aerobic/anaerobic bioreactor
containing an anaerobic methanogenic granulated enrichment culture.
Received: 15 January 1998 / Received revision: 2 October 1998 / Accepted: 2 October 1998 相似文献
6.
Extremophiles as a source of novel enzymes for industrial application 总被引:33,自引:0,他引:33
F. Niehaus C. Bertoldo M. Kähler G. Antranikian 《Applied microbiology and biotechnology》1999,51(6):711-729
Extremophilic microorganisms are adapted to survive in ecological niches such as at high temperatures, extremes of pH, high
salt concentrations and high pressure. These microorganisms produce unique biocatalysts that function under extreme conditions
comparable to those prevailing in various industrial processes. Some of the enzymes from extremophiles have already been purified
and their genes successfully cloned in mesophilic hosts. In this review we will briefly discuss the biotechnological significance
of extreme thermophilic (optimal growth 70–80 °C) and hyperthermophilic (optimal growth 85–100 °C) archaea and bacteria. In
particular, we will focus on selected extracellular-polymer-degrading enzymes, such as amylases, pullulanases, cyclodextrin
glycosyltransferases, cellulases, xylanases, chitinases, proteinases and other enzymes such as esterases, glucose isomerases,
alcohol dehydrogenases and DNA-modifying enzymes with potential use in food, chemical and pharmaceutical industries and in
environmental biotechnology.
Received: 14 August 1998 / Received revision: 17 February 1999 / Accepted: 19 February 1999 相似文献
7.
K. L. Larsen H. J. S. Christensen F. Mathiesen L. H. Pedersen W. Zimmermann 《Applied microbiology and biotechnology》1998,50(3):314-317
The conversion of soluble starch to cyclomaltohexaose (α-CD), cyclomaltoheptaose (β-CD), cyclomaltooctaose (γ-CD) and cyclomaltononaose
(δ-CD) by cyclodextrin glycosyltransferases (E.C. 2.4.1.19) from Bacillus spp. and bacterial isolates was studied. The results show that δ-CD was formed by all the enzymes investigated in the range
of 5%–11.5% of the total amount of α-, β-, γ-, and δ-CD produced.
Received: 17 February 1998 / Received revision: 18 May 1998 / Accepted: 21 May 1998 相似文献
8.
Indirect evidence has suggested that lignin peroxidase (LiP) of the white-rot fungus Phanerochaete chrysosporium catalyses oxidative decolourisation and depolymerisation of macromolecules from brown coal in vivo. In this study we show
that LiP catalyses these transformations in vitro. Unmethylated (USC45 coal) and methylated (MWSC6 coal) fractions of solubilised
macromolecules (M
r > 30 000) from a brown coal were treated with a semi-purified preparation of LiP isozymes from P. chrysosporium. Both coal fractions were decolourised, losing between 26% and 39% of their absorbance at both 280 nm and 400 nm, in reactions
that had an absolute requirement for H2O2 and veratryl alcohol. Neither coal fraction was transformed when the enzyme was heat-inactivated or in the presence of the
LiP inhibitor metavanadate. Gel-permeation chromatography showed that MWSC6 coal but not USC45 was depolymerised and yielded
low-molecular-mass (M
r < 30 000) fragments. Nine monomeric products were identified by GC-MS.
Received: 20 March 1998 / Received revision: 3 September 1998 / Accepted: 3 September 1998 相似文献
9.
H. Ishikawa H. Yamanaka T. Kawamoto A. Tanaka 《Applied microbiology and biotechnology》1999,51(4):470-473
In this study, the enzymatic synthesis of silicon-containing dipeptides with a silicon-containing amino acid, 3-trimethylsilylalanine
(TMS-Ala), was attempted in ethyl acetate, and the effects of TMS-Ala on thermolysin-catalyzed dipeptide synthesis are also
discussed. Benzyloxycarbonyl(Z)-TMS-Ala was recognized by thermolysin as a better substrate than Z-Leu, and various silicon-containing
dipeptides, Z-(TMS-Ala)-Xaa-OMe (Xaa = Leu, Ile, Phe, etc.), could be obtained. The acceleration of the reaction rate in the
synthesis of Z-(TMS-Ala)-Leu-OMe compared with Z-Leu-Leu-OMe synthesis was explained by the higher hydrophobicity of the side-chain
of TMS-Ala containing a trimethylsilyl group. On the other hand, TMS-Ala-OMe was not accepted as the amino component because
of the bulkiness of the trimethylsilyl group. The enantioselectivity of thermolysin was very high. Z-d-TMS-Ala was not a substrate, while Z-l-TMS-Ala served as a good substrate.
Received: 5 October 1998 / Received last revision: 4 December 1998 / Accepted: 26 December 1998 相似文献
10.
Traditional as well as biotechnological processing of coal leads to complex mixtures of products. Besides chemical and physical
characterization, which provides the information for product application, there is a need for bioassays to monitor properties
that are probably toxic, mutagenic or cancerogenic. Investigations carried out focused on the selection, adaptation and validation
of bioassays for the sensitive estimation of toxic effects. Organisms like bacteria, Daphnia magna and Scenedesmus subspicatus, representing different complexities in the biosphere, were selected as test systems for ecotoxicological and mutagenicity
studies. The results obtained indicate that bioassays are, in principle, suitable tools for characterization and evaluation
of coal-derived substances and bioconversion products. Using coal products, coal-relevant model compounds and bioconversion
products, data for risk assessment are presented.
Received: 17 June 1998 / Received revison: 21 October 1998 / Accepted: 24 October 1998 相似文献
11.
Biodegradation of EDTA 总被引:8,自引:0,他引:8
B. Nörtemann 《Applied microbiology and biotechnology》1999,51(6):751-759
The chelating agent ethylenediaminetetraacetate (EDTA) is not degraded by conventional biological and physicochemical methods
for the treatment of wastewater and the purification of drinking water. Of the measurable organic compounds it is the one
present at the highest concentration in many surface and drinking waters. In recent years, however, studies have demonstrated
that EDTA can be degraded by specially enriched bacterial cultures and in wastewater treatment plants receiving EDTA-containing
effluents. The amounts of EDTA released into the aquatic environment could thus be reduced by establishing appropriate biological
wastewater treatment plants. This article describes the degradation of EDTA and its metal chelates by different bacterial
cultures, catabolic steps in EDTA degradation, and biological methods for the removal of this chelating agent from wastewaters.
Received: 14 September 1998 / Received revision: 9 December 1998 / Accepted: 11 December 1998 相似文献
12.
Bacterial magnetosomes: microbiology, biomineralization and biotechnological applications 总被引:20,自引:0,他引:20
Magnetotactic bacteria orient and migrate along geomagnetic field lines. This ability is based on intracellular magnetic
structures, the magnetosomes, which comprise nanometer-sized, membrane-bound crystals of the magnetic iron minerals magnetite
(Fe3O4) or greigite (Fe3S4). Magnetosome formation is achieved by a mineralization process with biological control over the accumulation of iron and
the deposition of the mineral particle with specific size and orientation within a membrane vesicle at specific locations
in the cell. This review focuses on the current knowledge about magnetotactic bacteria and will outline aspects of the physiology
and molecular biology of the biomineralization process. Potential biotechnological applications of magnetotactic bacteria
and their magnetosomes as well as perspectives for further research are discussed.
Received: 2 December 1998 / Received revision: 2 March 1999 / Accepted: 5 March 1999 相似文献
13.
Plant parasitic nematodes are a serious threat for crop production worldwide. This review summarizes our understanding of
plant nematode interactions and presents new alternatives for nematode control in the field. Breeding for resistance has been
a major goal for many important crop species like soybean, potato, tomato and sugar-beet. As a result numerous nematode-resistance
genes have been identified, two of which have been cloned recently, Hs1
pro-1
from sugar-beet, giving resistance to the beet cyst nematode Heterodera schachtii, and Mi from tomato, giving resistance to the root-knot nematode Meloidogyne incognita. Also artificial resistance genes, coding for nematotoxic proteins or causing rapid death of feeding cells, have been elucidated.
In the future, genetic engineering of nematode resistance will become more and more important for plant breeding. Transformation
techniques will allow genes to be quickly introduced into susceptible breeding lines and then combined with each other to
produce plant varieties with durable resistance.
Received: 26 August 1998 / Received revision: 16 December 1998 / Accepted: 21 December 1998 相似文献
14.
Lignite (brown coal) can be liquefied/solubilized with several fungi by different mechanisms. When applied industrially,
only catalytic mechanisms can compete with chemical methods. The well-known fungal ligninolytic peroxidases are at a disadvantage,
in that the relatively expensive hydrogen peroxide must be used as a cofactor. Comparing several fungal strains, we observed
that the fungus Trametes versicolor is able to decolorize coal-derived humic acids, producing a considerable amount of laccase in the process. During this reaction
the amount of humic acids decreases whilst that of fulvic acids increases; this was verified by optical density measurement
and GPC after the two substance classes had been separated.
Received: 27 August 1998 / Received revision: 4 November 1998 / Accepted: 7 November 1998 相似文献
15.
A rapid method for detecting bacterial polyhydroxyalkanoates in intact cells by Fourier transform infrared spectroscopy 总被引:11,自引:0,他引:11
K. Hong S. Sun W. Tian G. Q. Chen W. Huang 《Applied microbiology and biotechnology》1999,51(4):523-526
Polyhydroxyalkanoates (PHA) are synthesized by many bacteria as inclusion bodies, and their biodegradability and structural
diversity have been studied with a view to their potential application as biodegradable materials. In this paper, Fourier-transform
infrared spectroscopy (FT-IR) was used to carry out rapid qualitative analysis of PHA in intact bacterial cells. The FT-IR
spectra of pure PHA containing short-chain-length monomers, such as hydroxybutyrate (HB), medium-chain-length hydroxyalkanoate
(mclHA) monomers including hydroxyoctanoate (HO) and hydroxydecanoate (HD), or both HB and mclHA monomers, showed their strong
characteristic band at 1728 cm−1, 1740 cm−1 or 1732 cm−1 respectively. Other accompanying bands near 1280 cm−1 and 1165 cm−1 helped identify the types of PHA. The intensity of the methylene band near 2925 cm−1 provided additional information for PHA characterization. In comparison, bacterial cells accumulating the above PHA also
showed strong marker bands at 1732 cm−1, 1744 cm−1 or 1739 cm−1, corresponding to intracellular PHB, mclPHA and P(HB + mclHA) respectively. The accompanying bands visible in pure PHA were
also observable in the intact cells. The FT-IR results were further confirmed by gas chromatography analysis.
Received: 14 October 1998 / Received revision: 29 December 1998 / Accepted: 30 December 1998 相似文献
16.
K. Hofvendahl E. W. J. van Niel B. Hahn-Hägerdal 《Applied microbiology and biotechnology》1999,51(5):669-672
Lactococcus lactis ssp. lactis ATCC 19435 is known to produce mixed acids when grown on maltose. A change in fermentation conditions only, elevated temperatures
(up to 37 °C) and reduced pH values (down to 5.0) resulted in a shift towards homolactic product formation. This was accompanied
by decreased growth rate and cell yield. The results are discussed in terms of redox balance and maintenance, and the regulation
of lactate dehydrogenase and pyruvate formate-lyase.
Received: 14 December 1998 / Received revision: 12 January 1999 / Accepted: 22 January 1999 相似文献
17.
High-cell-density cultivation of microorganisms 总被引:29,自引:0,他引:29
High-cell-density cultivation (HCDC) is required to improve microbial biomass and product formation substantially. An overview
of HCDC is given for microorganisms including bacteria, archae and eukarya (yeasts). Problems encountered by HCDC and their
possible solutions are discussed. Improvements of strains, different types of bioreactors and cultivation strategies for successful
HCDC are described. Stirred-tank reactors with and without cell retention, a dialysis-membrane reactor, a gas-lift reactor
and a membrane cyclone reactor used for HCDC are outlined. Recently modified traditional feeding strategies and new ones are
included, in particular those for unlimited growth to very dense cultures. Emphasis is placed on robust fermentation control
because of the growing industrial interest in this field. Therefore, developments in the application of multivariate statistical
control, artificial neural networks, fuzzy control and knowledge-based supervision (expert systems) are summarized. Recent
advances using Escherichia coli– the pioneer organism for HCDC – are outlined.
Received: 20 October 1998 / Received revision: 18 December 1998 / Accepted: 21 December 1998 相似文献
18.
Chemically defined media for commercial fermentations 总被引:13,自引:0,他引:13
The use of chemically defined media is gaining popularity in some commercial fermentations, particularly for the preparation
of biological products. Although these media are still not frequently developed for industrial processes, they do exhibit
favorable characteristics at large scale that are not observed with traditional complex media. This review focuses on the
application, development, and practical considerations, especially process economics, of fermentations in chemically defined
media in an industrial environment.
Received: 3 August 1998 / Received revision: 16 November 1998 / Accepted: 21 November 1998 相似文献
19.
The present work describes investigations on the bacterial degradation of the alicyclic molecule cyclododecane. It represents
a structure where the initial degradative steps have to be similar to a “subterminal” attack as there is no “terminal” part
of the molecule. We were able to show that the gram-positive bacterium Rhodococcus ruber CD4 DSM 44394 oxidizes cyclododecane to the corresponding alcohol and ketone, the latter being subject to ring fission by
a Baeyer-Villiger oxygenase. This key enzyme is an NADPH- and O2-dependent flavoprotein with a substrate specificity for bigger rings. The further metabolism of the resulting lactone gives
rise to an ω-hydroxyalkanoic acid that is susceptible to common β-oxidation. Due to its alicyclic character and its ring size,
cyclododecane is comparable to aliphatic bridge components that are an important element in the coal texture. They contribute
to the three-dimensional coal structure and thus could serve as a valuable target for the oxidative abilities of R. ruber CD4 to reduce the molecular mass of coal.
Received: 2 July 1998 / Received revision: 27 October 1998 / Accepted: 30 October 1998 相似文献
20.
P. Dürre 《Applied microbiology and biotechnology》1998,49(6):639-648
Clostridial acetone/butanol fermentation used to rank second only to ethanol fermentation by yeast in its scale of production
and thus is one of the largest biotechnological processes known. Its decline since about 1950 has been caused by increasing
substrate costs and the availability of much cheaper feedstocks for chemical solvent synthesis by the petrochemical industry.
The so-called oil crisis in 1973 led to renewed interest in novel fermentation and product recovery technologies as well as
in the metabolism and genetics of the bacterial species involved. As a consequence, almost all of the enzymes leading to solvent
formation are known, their genes have been sequenced (in fact, Clostridium acetobutylicum has been recently included in the microbial genome sequencing project), the regulatory mechanisms controlling solventogenesis
have begun to emerge and recombinant DNA techniques have been developed for these clostridia to construct specific production
strains. In parallel, cheap agricultural-waste-based feedstocks have been exploited for their potential as novel substrates,
continuous culture methods have been successfully established and new on-line product recovery technologies are now available,
such as gas stripping, liquid/liquid extraction, and membrane-based methods. In combination with these achievements, a reintroduction
of acetone/butanol fermentation on an industrial scale seems to be economically feasible, a view that is supported by a new
pilot plant in Austria recently coming into operation.
Received: 18 December 1997 / Received revision: 27 January 1998 / Accepted: 27 January 1998 相似文献