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1.
Targeted alteration of the substrate specificity of peptide synthetases by rational module swapping 总被引:7,自引:0,他引:7
Analysis of the primary structure of peptide synthetases involved in the non-ribosomal synthesis of peptide antibiotics has
revealed a highly conserved and ordered modular arrangement. A module contains at least two domains, involved in ATP-dependent
substrate activation and thioester formation. The occurrence and arrangement of these functional building blocks is associated
with the number and order of the amino acids incorporated in the peptide product. In this study, we present data on the targeted
exchange of the leucine-activating module within the three-module surfactin synthetase 1 (SrfA-A) of Bacillus subtilis. This was achieved by engineering several hybrid srfA-A genes, which were introduced into the surfactin biosynthesis operon by in vivo recombination. We examined the hybrid genes
for expression and investigated the enzymatic activities of the resulting recombinant peptide synthetases. For the first time,
we demonstrate directly that an individual minimal module, of bacterial or fungal origin, confers its amino acid-specific
activity on a multi-modular peptide synthetase. Furthermore, it is shown that directed incorporation of ornithine at the second
position of the peptide chain induces a global alteration in the conformation of surfactin and may result in premature cyclization
or a branched cyclic structure.
Received: 10 July 1997 / Accepted: 11 September 1997 相似文献
2.
Candida bombicola produces glycolipids containing sophorose and a glycosidically/esterically bound ω- or (ω−1)-hydroxy C16(18) acid. Here we describe novel glycolipids from this source. Glucose and 2-dodecanol were used for the cultivation of the yeast,
one part of the racemic secondary alcohol being connected directly with a glucose or a sophorose unit. A relatively high content
of yeast extract, up to 4 g l−1, and subsequently higher biomass concentrations favoured the production of novel products. The provision of 150 g l−1 glucose and 15 g l−1 2-dodecanol resulted in maximum production of 22 g l−1 novel alkyl glycosides (more than 90% novel products). The molecular structures were analysed by gas chromatography, fast
atom bombardment/mass spectrometry, 1H- and 13C-nuclear magnetic resonance and optical rotation studies. Sophorose and glucose were detected as carbohydrate moieties, (S)-(+)-2-dodecanol (88%) was found to be the major lipid moiety. The new glycolipids are suitable biosurfactants, reducing
the surface tension of water from 72 mN m−1 to 32–38 mN m−1.
Received: 8 December 1997 / Received revision: 19 March 1998 / Accepted: 20 March 1998 相似文献
3.
Production of sophorolipids from whey 总被引:5,自引:0,他引:5
Otto RT Daniel HJ Pekin G Müller-Decker K Fürstenberger G Reuss M Syldatk C 《Applied microbiology and biotechnology》1999,52(4):495-501
Sophorolipids, obtained by a two-stage process starting from deproteinized whey concentrate using Cryptococcus curvatus ATCC 20509 and Candida bombicola ATCC 22214, were compared to products from one-stage processes, using different lipidic compounds as substrates. Results
showed that above all carbon source and not cultivation conditions had a distinct influence on the composition of the crude
product mixture and therefore on the physicochemical and biological properties of the sophorolipids, such as, for example,
surface activity, cytotoxicity and stability against hydrolases. The results were completed by corresponding data for purified
mono- and diacetylated (17-hydroxyoctadecenoic)-1′,4′′-lactonized sophorolipids. Crude sophorolipid mixtures showed moderate
to good surface active properties (SFTmin 39 mN m−1, CMC 130 mg l−1), water solubilities (2–3 g l−1) and low cytotoxicities (LC50 300–700 mg l−1). In contrast, purified sophorolipids were more surface active (SFTmin 36 mN m−1, CMC 10 mg l−1), less water soluble (max. 70 mg l−1) and showed stronger cytotoxic effects (LC50 15 mg l−1). Incubation of crude sophorolipid mixtures with different hydrolases demonstrated that treatment with commercially available
lipases such as from Candida rugosa and Mucor miehei distinctly reduced the surface active properties of the sophorolipids, while treatment with porcine liver esterase and glycosidases
had no effect.
Received: 23 February 1999 / Received revision: 27 May 1999 / Accepted: 28 May 1999 相似文献
4.
Koizumi S Yonetani Y Maruyama A Teshiba S 《Applied microbiology and biotechnology》2000,53(6):674-679
Improved strains for the production of riboflavin (vitamin B2) were constructed through metabolic engineering using recombinant DNA techniques in Corynebacterium ammoniagenes. A C. ammoniagenes strain harboring a plasmid containing its riboflavin biosynthetic genes accumulated 17-fold as much riboflavin as the host
strain. In order to increase the expression of the biosynthetic genes, we isolated DNA fragments that had promoter activities
in C. ammoniagenes. When the DNA fragment (P54-6) showing the strongest promoter activity in minimum medium was introduced into the upstream
region of the riboflavin biosynthetic genes, the accumulation of riboflavin was 3-fold elevated. In that strain, the activity
of guanosine 5′-triphosphate (GTP) cyclohydrolase II, the first enzyme in riboflavin biosynthesis, was 2.4-fold elevated whereas
that of riboflavin synthase, the last enzyme in the biosynthesis, was 44.1-fold elevated. Changing the sequence containing
the putative ribosome-binding sequence of 3,4-dihydroxy-2-butanone 4-phosphate synthase/GTP cyclohydrolase II gene led to
higher GTP cyclohydrolase II activity and strong enhancement of riboflavin production. Throughout the strain improvement,
the activity of GTP cyclohydrolase II correlated with the productivity of riboflavin. In the highest producer strain, riboflavin
was produced at the level of 15.3 g l−1 for 72 h in a 5-l jar fermentor without any end product inhibition.
Received: 23 August 1999 / Received revision: 13 October 1999 / Accepted: 5 November 1999 相似文献
5.
Atomic force microscopy (AFM) enables the topographical structure of cells and biological materials to be resolved under
natural (physiological) conditions, without fixation and dehydration artefacts associated with imaging methods in vacuo. It
also provides a means of measuring interaction forces and the mechanical properties of biomaterials. In the present study,
AFM has been applied for the first time to the study of the mechanical properties of a natural adhesive produced by a green
plant cell. Swimming spores of the green alga Enteromorpha linza (L.) J. Ag. (7–10 μm) secrete an adhesive glycoprotein which provides firm anchorage to the substratum. Imaging of the adhesive in its
hydrated state revealed a swollen gel-like pad, approximately 1 μm thick, surrounding the spore body. Force measurements revealed
that freshly released adhesive has an adhesion strength of 173 ± 1.7 mN m−1 (mean ± SE; n=90) with a maximum value for a single adhesion force curve of 458 mN m−1. The adhesive had a compressibility (equivalent to Young's modulus) of 0.54 × 106 ± 0.05 × 106 N m−2 (mean ± SE; n=30). Within minutes of release the adhesive underwent a progressive `curing' process with a 65% reduction in mean adhesive
strength within an hour of settlement, which was also reflected in a reduction in the average length of the adhesive polymer
strands (polymer extension) and a 10-fold increase in Young's modulus. Measurements on the spore surface itself revealed considerably
lower adhesion-strength values but higher polymer-extension values than the adhesive pad, which may reflect the deposition
of different polymers on this surface as a new cell wall is formed. The study demonstrates the value of AFM to the imaging
of plant cells in the absence of fixation and dehydration artefacts and to the characterisation of the mechanical properties
of plant glycoproteins that have potential utility as adhesives.
Received: 22 February 2000 / Accepted: 20 April 2000 相似文献
6.
Biosurfactants containing rhamnose and β-hydroxydecanoic acid and called rhamnolipids are reviewed with respect to microbial
producers, their physiological role, biosynthesis and genetics, and especially their microbial overproduction, physicochemical
properties and potential applications. With Pseudomonas species, more than 100 g l−1 rhamnolipids were produced from 160 g l−1 soybean oil at a volumetric productivity of 0.4 g l−1 h−1. The individual rhamnolipids are able to lower the surface tension of water from 72 mN m−1 to 25–30 mN m−1 at concentrations of 10–200 mg l−1. After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution, removing oil
from sand and in combating zoosporic phytopathogens. Rhamnolipids are also a source of l-rhamnose, which is already used for the industrial production of high-quality flavor components.
Received: 1 July 1998 / Received revision: 11 September 1998 / Accepted: 13 September 1998 相似文献
7.
Poly-(3-hydroxybutyrate) production from whey by high-density cultivation of recombinant Escherichia coli 总被引:2,自引:0,他引:2
Recombinant Escherichia coli strain GCSC 6576, harboring a high-copy-number plasmid containing the Ralstonia eutropha genes for polyhydroxyalkanoate (PHA) synthesis and the E. coli ftsZ gene, was employed to produce poly-(3-hydroxybutyrate) (PHB) from whey. pH-stat fed-batch fermentation, using whey powder
as the nutrient feed, produced cellular dry weight and PHB concentrations of 109 g l−1 and 50 g l−1 respectively in 47 h. When concentrated whey solution containing 210 g l−1 lactose was used as the nutrient feed, cellular dry weight and PHB concentrations of 87 g l−1 and 69 g l−1 respectively could be obtained in 49 h by pH-stat fed-batch culture. The PHB content was as high as 80% of the cellular dry
weight. These results suggest that cost-effective production of PHB is possible by fed-batch culture of recombinant E. coli using concentrated whey solution as a substrate.
Received: 19 December 1997 / Received revision: 17 March 1998 / Accepted: 20 March 1998 相似文献
8.
Tudzynski P Hölter K Correia T Arntz C Grammel N Keller U 《Molecular & general genetics : MGG》1999,261(1):133-141
A gene (cpd1) coding for the dimethylallyltryptophan synthase (DMATS) that catalyzes the first specific step in the biosynthesis of ergot
alkaloids, was cloned from a strain of Claviceps purpurea that produces alkaloids in axenic culture. The derived gene product (CPD1) shows only 70% similarity to the corresponding
gene previously isolated from Claviceps strain ATCC 26245, which is likely to be an isolate of C. fusiformis. Therefore, the related cpd1 most probably represents the first C. purpurea gene coding for an enzymatic step of the alkaloid biosynthetic pathway to be cloned. Analysis of the 3′-flanking region of cpd1 revealed a second, closely linked ergot alkaloid biosynthetic gene named cpps1, which codes for a 356-kDa polypeptide showing significant similiarity to fungal modular peptide synthetases. The protein
contains three amino acid-activating modules, and in the second module a sequence is found which matches that of an internal
peptide (17 amino acids in length) obtained from a tryptic digest of lysergyl peptide synthetase 1 (LPS1) of C. purpurea, thus confirming that cpps1 encodes LPS1. LPS1 activates the three amino acids of the peptide portion of ergot peptide alkaloids during D-lysergyl peptide
assembly. Chromosome walking revealed the presence of additional genes upstream of cpd1 which are probably also involved in ergot alkaloid biosynthesis: cpox1 probably codes for an FAD-dependent oxidoreductase (which could represent the chanoclavine cyclase), and a second putative
oxido-reductase gene, cpox2, is closely linked to it in inverse orientation. RT-PCR experiments confirm that all four genes are expressed under conditions
of peptide alkaloid biosynthesis. These results strongly suggest that at least some genes of ergot alkaloid biosynthesis in C. purpurea are clustered, opening the way for a detailed molecular genetic analysis of the pathway.
Received: 26 August 1998 / Accepted: 19 October 1998 相似文献
9.
A quantitative study of indole-3-acetic acid (IAA) turnover, and the contribution of tryptophan-dependent and tryptophan-independent
IAA-biosynthesis pathways, was carried out using protoplast preparations and shoot apices obtained from wild-type and transgenic,
IAA-overproducing tobacco (Nicotiana tabacum L.) plants, during a phase of growth when the level of endogenous IAA was stable. Based on the rate of disappearance of [13C6]IAA, the half-life of the IAA pool was calculated to be 1.1 h in wild-type protoplasts and 0.8 h in protoplasts from the
IAA-overproducing line, corresponding to metabolic rates of 59 and 160 pg IAA (μg Chl)−1 h−1, respectively. The rate of conversion of tryptophan to IAA was 15 pg IAA (μg Chl)−1 h−1 in wild-type protoplasts and 101 pg IAA (μg Chl)−1 h−1 in protoplasts from IAA-overproducing plants. In both instances, IAA was metabolised more rapidly than it was synthesised
from tryptophan. As the endogenous IAA pools were in a steady state, these findings indicate that IAA biosynthesis via the
tryptophan-independent pathway was 44 pg IAA (μg Chl)−1 h−1 and 59 pg IAA (μg Chl)−1 h−1, respectively, in the wild-type and transformed protoplast preparations. In a parallel study with apical shoot tissue, the
presumed site of IAA biosynthesis, the rate of tryptophan-dependent IAA biosynthesis exceeded the rate of metabolism of [13C6]IAA despite the steady state of the endogenous IAA pool. The most likely explanation for this anomaly is that, unlike the
protoplast system, injection of substrates into the apical tissues did not result in uniform distribution of label, and that
at least some of the [2H5]tryptophan was metabolised in compartments not normally active in IAA biosynthesis. This demonstrates the importance of using
experimental systems where labelling of the precursor pool can be strictly controlled.
Received: 18 January 2000 / Accepted 24 February 2000 相似文献
10.
Effects of over-expression of strictosidine synthase and tryptophan decarboxylase on alkaloid production by cell cultures of Catharanthus roseus 总被引:1,自引:0,他引:1
Camilo Canel M. Inês Lopes-Cardoso Serap Whitmer Leslie van der Fits Giancarlo Pasquali Robert van der Heijden J. Harry C. Hoge Robert Verpoorte 《Planta》1998,205(3):414-419
Cells of Catharanthus roseus (L.) G. Don were genetically engineered to over-express the enzymes strictosidine synthase (STR; EC 4.3.3.2) and tryptophan
decarboxylase (TDC; EC 4.1.1.28), which catalyze key steps in the biosynthesis of terpenoid indole alkaloids (TIAs). The cultures
established after Agrobacterium-mediated transformation showed wide phenotypic diversity, reflecting the complexity of the biosynthetic pathway. Cultures
transgenic for Str consistently showed tenfold higher STR activity than wild-type cultures, which favored biosynthetic activity through the
pathway. Two such lines accumulated over 200 mg · L−1 of the glucoalkaloid strictosidine and/or strictosidine-derived TIAs, including ajmalicine, catharanthine, serpentine, and
tabersonine, while maintaining wild-type levels of TDC activity. Alkaloid accumulation by highly productive transgenic lines
showed considerable instability and was strongly influenced by culture conditions, such as the hormonal composition of the
medium and the availability of precursors. High transgene-encoded TDC activity was not only unnecessary for increased productivity,
but also detrimental to the normal growth of the cultures. In contrast, high STR activity was tolerated by the cultures and
appeared to be necessary, albeit not sufficient, to sustain high rates of alkaloid biosynthesis. We conclude that constitutive
over-expression of Str is highly desirable for increased TIA production. However, given its complexity, limited intervention in the TIA pathway
will yield positive results only in the presence of a favorable epigenetic environment.
Received: 12 June 1997 / Accepted: 24 October 1997 相似文献
11.
Shaw-Reid CA McCormick MM Sinskey AJ Stephanopoulos G 《Applied microbiology and biotechnology》1999,51(3):325-333
The N-succinyl-ll-diaminopimelate desuccinylase gene (dapE) in the four-step succinylase branch of the l-lysine biosynthetic pathway of Corynebacterium glutamicum was disrupted via marker-exchange mutagenesis to create a mutant strain that uses only the one-step meso-diaminopimelate dehydrogenase branch to overproduce lysine. This mutant strain grew and utilized glucose from minimal medium
at the same rate as the parental strain. In addition, the dapE
−
strain produced lysine at the same rate as its parent strain. Transformation of the parental and dapE
−
strains with the amplified meso-diaminopimelate dehydrogenase gene (ddh) on a plasmid did not affect lysine production in either strain, despite an eightfold amplification of the activity of the
enzyme. These results indicate that the four-step succinylase pathway is dispensable for lysine overproduction in shake-flask
culture. In addition, the one-step meso-diaminopimelate dehydrogenase pathway does not limit lysine flux in Corynebacterium under these conditions.
Received: 20 May 1998 / Received revision: 12 August 1998 / Accepted: 3 September 1998 相似文献
12.
Carmen Lapadatescu Gilles Feron Catherine Vergoignan Aleth Djian Alain Durand Pascal Bonnarme 《Applied microbiology and biotechnology》1997,47(6):708-714
Three white-rot basidiomycetes, Bjerkandera adusta, Ischnoderma benzoinum and Dichomitus squalens, were cultivated on a liquid medium supplemented with l-phenylalanine, a precursor for benzaldehyde (bitter almond aroma) and benzyl alcohol. Remarkable amounts of benzaldehyde
(587 mg l−1) were found in cultures of B. adusta. Immobilization of this fungus on polyurethane foam cubes allowed an 8.3-fold increase of the production of benzaldehyde
and a 15-fold increase of the productivity as compared with non-immobilized cells. Aryl-alcohol oxidase activity was only
detected in B. adusta. This activity was also significantly enhanced in immobilized cells, suggesting that it plays an important role in benzaldehyde
biosynthesis. Conversely, consistent amounts of benzyl alcohol (340 mg l−1 for B. adusta and I. benzoinum and 100 mg l−1 for D. squalens) were produced by the three fungi when immobilized. Laccase activity was found only in the strains I. benzoinum and D. squalens. This activity was markedly enhanced in free cells cultures. Immobilization of the fungi did not promote benzyl alcohol production
by comparison with free cell cultures (500 mg l−1).
Received: 10 December 1996 / Received revision: 17 February 1997 / Accepted: 22 February 1997 相似文献
13.
A heat shock following electroporation induces highly efficient transformation of Corynebacterium glutamicum with xenogeneic plasmid DNA 总被引:10,自引:0,他引:10
An improved method for the electrotransformation of wild-type Corynebacterium glutamicum (ATCC 13032) is described. The two crucial alterations to previously developed methods are: cultivation of cells used for
electrotransformation at 18 °C instead of 30 °C, and application of a heat shock immediately following electrotransformation.
Cells cultivated at sub optimal temperature have a 100-fold improved transformation efficiency (108 cfu μg−1) for syngeneic DNA (DNA isolated from the same species). A heat shock applied to these cells following electroporation improved
the transformation efficiency for xenogeneic DNA (DNA isolated from a different species). In combination, low cultivation
temperature and heat shock act synergistically and increased the transformation efficiency by four orders of magnitude to
2.5 × 106 cfu μg−1 xenogeneic DNA. The method was used to generate gene disruptions in C. glutamicum.
Received: 26 March 1999 / Received revision: 9 June 1999 / Accepted: 11 June 1999 相似文献
14.
N. Frankenberg T. Kittel C. Hungerer U. R?mling D. Jahn 《Molecular & general genetics : MGG》1998,257(4):485-489
During tetrapyrrole biosynthesis 5-aminolevulinic acid dehydratase (ALAD) catalyzes the condensation of two molecules of
5-aminolevulinic acid (ALA) to form one molecule of the pyrrole derivative porphobilinogen. In Escherichia coli, the enzyme is encoded by the gene hemB. The hemB gene was cloned from Pseudomonas aeruginosa by functional complementation of an E. coli hemB mutant. An open reading frame of 1011 bp encoding a protein of 336 amino acids (Mr = 37 008) was identified. The gene was mapped to SpeI fragment G and DpnI fragment G of the P. aeruginosa chromosome, corresponding to the 10 to 12 min region of the new map or 19 to 22 min interval of the old map. The 5′ end of
the hemB mRNA was determined and the −10 and −35 regions of a potential σ70-dependent promoter were localized. No obvious regulation of the hemB gene by oxygen, nitrate, heme or iron was detected. Alignment of the amino acid sequences deduced from hemB revealed a potential metal-binding site and indicated that the enzyme is Mg2+-dependent. P. aeruginosa hemB was overexpressed in an E. coli hemB mutant using the phage T7 RNA polymerase system and its Mg2+-dependent activity was directly demonstrated.
Received: 11 July 1997 / Accepted: 9 October 1997 相似文献
15.
Batch and continuous cultivation of Anaerobiospirillum succiniciproducens for the production of succinic acid from whey 总被引:3,自引:0,他引:3
Batch and continuous cultivation of Anaerobiospirillum succiniciproducens were systematically studied for the production of succinic acid from whey. Addition of 2.5 g l−1 yeast extract and 2.5 g l−1 polypeptone per 10 g l−1 whey was most effective for succinic acid production from both treated and nontreated whey. When 20 g l−1 nontreated whey and 7 g l−1 glucose were used as cosubstrates, the yield and productivity of succinic acid reached at the end of fermentation were 95%
and 0.46 g (l h)−1, respectively. These values were higher than those obtained using nontreated whey alone [93% and 0.24 g (l h)−1 for 20 g l−1 whey]. Continuous fermentation of A. succiniciproducens at an optimal dilution rate resulted in the production of succinic acid with high productivity [1.35 g (l h)−1], high conversion yield (93%), and higher ratio of succinic acid to acetic acid (5.1:1) from nontreated whey.
Received: 23 July 1999 / Received revision: 17 November 1999 / Accepted: 24 December 1999 相似文献
16.
This is the first report describing the gene structure and the enzymatic properties of a β-fructosidase of a hyperthermophilic
organism. The bfrA gene of the ancestral bacterium Thermotoga maritima MSB8 codes for a 432-residue, polypeptide of about 50 kDa, with significant sequence similarity to other β-fructosidases.
On the basis of its primary structure, BfrA can be assigned to glycosyl hydrolase family 32. The bfrA gene was expressed in Escherichia coli and the recombinant enzyme was purified and characterised. BfrA was specific for the fructose moiety and the β-anomeric configuration
of the glycosidic linkages of its substrates. The enzyme released fructose from sucrose and raffinose, and the fructose polymer
inulin was hydrolysed quantitatively in an exo-type fashion. BfrA displayed similar catalytic efficiencies for the hydrolysis
of sucrose and inulin with k
cat/K
m values (at 75 °C, pH 5.5) of about 4.1 × 104 M−1s−1 and 3.1 × 104 M−1s−1 respectively. BfrA had an optimum temperature of 90–95 °C (10-min assay) and was extremely insensitive to thermo-inactivation.
During 5 h at temperatures up to 80 °C at pH 7, the enzyme retained at least 85% of its initial activity. Thus, BfrA is the
most thermostable β-fructosidase and also the most thermostable inulinase described to date. In conclusion, the T. maritima enzyme can be classified as an exo-β-d-fructofuranosidase (EC 3.2.1.26) with invertase and inulinase activity. Its catalytic properties along with the extreme thermostability
recommend it for use in biotechnology.
Received: 28 August 1997 / Received revision: 19 January 1998 / Accepted: 24 January 1998 相似文献
17.
The Aspergillus niger strain BO-1 was grown in batch, continuous (chemostat) and fed-batch cultivations in order to study the production of the
extracellular enzyme glucoamylase under different growth conditions. In the pH range 2.5–6.0, the specific glucoamylase productivity
and the specific growth rate of the fungus were independent of pH when grown in batch cultivations. The specific glucoamylase
producivity increased linearly with the specific growth rate in the range 0–0.1 h−1 and was constant in the range 0.1–0.2 h−1. Maltose and maltodextrin were non-inducing carbon sources compared to glucose, and the maximum specific growth rate was
0.19 ± 0.02 h−1 irrespective of whether glucose or maltose was the carbon source. In fed-batch cultivations, glucoamylase titres of up to
6.5 g l−1 were obtained even though the strain contained only one copy of the glaA gene.
Received: 5 May 1999 / Received revision: 7 September 1999 / Accepted: 17 September 1999 相似文献
18.
Dilsen S Paul W Sandgathe A Tippe D Freudl R Thömmes J Kula MR Takors R Wandrey C Weuster-Botz D 《Applied microbiology and biotechnology》2000,54(3):361-369
A pH-auxostatic fed-batch process was developed for the secretory production of a fusion protein consisting of the pro-part
of Staphylococcus hyicus lipase and two synthetic human calcitonin (hCT) precursor repeats under the control of a xylose-inducible promotor from Staphylococcus xylosus. Using glycerol as the energy source and pH-controlled addition of yeast extract resulted in the production of 2000 mg l−1 of the fusion protein (420 mg l−1 of the recombinant hCT precursor) within 14 h, reaching 45 g l−1 cell dry mass with Staphylococcus carnosus in a stirred-tank reactor. Product titer and space-time yield (30 mg calcitonin precursor l−1 h−1) were thus improved by a factor of 2, and 4.5, respectively, compared to Escherichia coli expression-secretion systems for the production of calcitonin precursors. Two hundred grams of the fusion protein was secreted
by the recombinant S. carnosus on a 150-l scale (scale-up factor of 50) with a minimum use of technical-grade yeast extract (40 mg fusion protein g−1 yeast extract).
Received: 18 January 2000 / Received revision: 14 April 2000 / Accepted: 14 April 2000 相似文献
19.
Mode of depolymerisation of hemicellulose by various mannanases and xylanases in relation to their ability to bleach softwood pulp 总被引:2,自引:0,他引:2
G. M. Gübitz D. Haltrich B. Latal W. Steiner 《Applied microbiology and biotechnology》1997,47(6):658-662
Endo-mannanases and endo-xylanases cleave different heteromannans and xylans yielding mainly dimers and trimers of the corresponding
sugars as end-products. However, in the early stages of hydrolysis, four purified mannanases and four xylanases from fungal
and bacterial origin, examined in this study, showed a different pattern of released oligomers (determined up to the pentamers).
Furthermore, some of these enzymes showed a preference for cleaving the polysaccharides in the middle of the chain while others
acted more at the end. When the increase in the specific fluidity of mannan and xylan solutions per reducing sugar released
(K
v) was measured against the bleaching effect of the enzymes on softwood kraft pulp, a correlation was found. A xylanase from
Penicillium simplicissimum (K
v = 0.15 l mPa−1s−1g−1) and a mannanase from Sclerotium rolfsii (K
v = 0.12 l mPa−1s−1g−1) applied in a O(QX)P bleaching sequence (O = oxygen delignification, X = treatment with hemicellulolytic enzymes, Q = chelation
of metals, P = treatment with hydrogen peroxide in alkaline solution) gave a high brightness increase of 3.0% and 1.9% ISO
respectively. A less significant brightness increase was obtained with enzymes showing lower K
v values, such as a xylanase from Schizophyllum commune (Kv = 0.051 l mPa−1s−1g−1, 0.2% ISO) and a bacterial mannanase (K
v = 0.061 l mPa−1s−1g−1,0.5% ISO).
Received: 19 December 1996 / Received revision: 20 February 1997 / Accepted: 22 February 1997 相似文献
20.
J. S. Potekhina N. G. Sherisheva L. P. Povetkina A. P. Pospelov T. A. Rakitina F. Warnecke G. Gottschalk 《Applied microbiology and biotechnology》1999,51(5):639-646
In acetate-limited chemostat cultures of Acinetobacter johnsonii 210A at a dilution rate of 0.1 h−1 the polyphosphate content of the cells increased from 13% to 24% of the biomass dry weight by glucose (100 mM), which was
only oxidized to gluconic acid. At this dilution rate, only about 17% of the energy from glucose oxidation was calculated
to be used for polyphosphate synthesis, the remaining 83% being used for biomass formation. Suspensions of non-growing, phosphate-deficient
cells had a six- to tenfold increased uptake rate of phosphate and accumulated polyphosphate aerobically up to 53% of the
biomass dry weight when supplied with only orthophosphate and Mg2+. The initial polyphosphate synthesis rate was 98 ± 17 nmol phosphate min−1 mg protein−1. Intracellular poly-β-hydroxybutyrate and lipids served as energy sources for the active uptake of phosphate and its subsequent
sequestration to polyphosphate. The H+-ATPase inhibitor N,N′-dicyclohexylcarbodiimide caused low ATP levels and a severe inhibition of polyphosphate formation, suggesting the involvement
of polyphosphate kinase in polyphosphate synthesis. It is concluded that, in A. johnsonii 210A, (i) polyphosphate is accumulated as the energy supply is in excess of that required for biosynthesis, (ii) not only
intracellular poly-β-hydroxybutyrate but also neutral lipids can serve as an energy source for polyphosphate-kinase-mediated
polyphosphate formation, (iii) phosphate-deficient cells may accumulate as much polyphosphate as activated sludges and recombinants
of Escherichia coli designed for polyphosphate accumulation.
Received: 23 October 1998 / Received revision: 18 January 1999 / Accepted: 22 January 1999 相似文献