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1.
Simona Romagnoli Alejandro Hochkoeppler Lars Damgaard D. Zannoni 《Archives of microbiology》1997,167(2-3):99-105
The effect of respiration on the positive phototactic movement of swarming agar colonies of the facultative phototroph Rhodospirillum centenum was studied. When the electron flow was blocked at the bc
1
complex level by myxothiazol, the oriented movement of the colonies was totally blocked. Conversely, inhibition of respiration
via the cytochrome c oxidase stimulated the phototactic response. No phototaxis was observed in a photosynthesis deficient mutant (YB707) lacking
bacteriochlorophylls. Analyses of the respiratory activities as monitored by a oxygen microelectrode in single agar colonies
during light/dark transitions showed a close functional correlation between the photosynthetic and respiratory apparatuses.
The respiratory chain of Rsp. centenum was formed by two oxidative pathways: one branch leading to a cytochrome c oxidase inhibited by low cyanide concentrations and a second pathway formed by an oxidase less-sensitive to cyanide that
also catalyzes the light-driven respiration. These results were interpreted to indicate that (1) there is a cyclic electron
transport, and (2) photoinduced cyclic electron flow is required for the phototactic response of Rsp. centenum. Furthermore, under oxic conditions in the light, reducing equivalents may switch from photosynthetic to respiratory components
so as to reduce both the membrane potential and the rate of locomotion.
Received: 25 September 1996 / Accepted: 11 November 1996 相似文献
2.
A novel non-sulfur purple photosynthetic bacterium, designated Rhodospirillum centenum, was isolated from an enrichment culture designed to favor growth of anoxygenic photosynthetic N2-fixing bacteria. R. centenum grows optimally at 40–42° C and has the capacity to produce cytoplasmic R bodies, refractile structures not observed hitherto in photosynthetic prokaryotes. The bacterium is also unusual among photosynthetic bacteria in that it forms desiccation-resistant cysts when grown aerobically in darkness with butyrate as the sole carbon source. 相似文献
3.
The interaction of dinitrogenase reductase-activating glycohydrolase (DRAG) with bacterial membranes and the solubilization
of DRAG in response to nucleotides were characterized. Purified DRAG from Rhodospirillum rubrum reversibly bound bacterial pellet fractions from Rsp. rubrum and other nitrogen-fixing bacteria. DRAG saturated the membrane fraction of Rsp. rubrum at a concentration of 0.2 mol DRAG/mol bacteriochlorophyll, suggesting that the DRAG-binding species is prevalent in the
membrane. DRAG bound poorly to phospholipid vesicles, suggesting a protein requirement for DRAG interaction with the membrane.
Guanosine and uridine tri- and di-nucleotides specifically dissociated DRAG from the pellet fractions of Rsp. rubrum and Azotobacter vinelandii, while adenosine nucleotides had no dissociative effect. Guanosine 5′-triphosphate dissociated DRAG from the membrane at
a concentration causing 50% dissociation (EC50) of 5.0 ± 0.5 mM; guanosine disphosphate had an EC50 of 15.0 ± 2.0 mM. We propose that GTP is a potential participant in the regulation of DRAG, possibly controlling the extent
of DRAG association with the membrane.
Received: 2 November 1998 / Accepted: 6 April 1999 相似文献
4.
Trichloroethylene degradation and mineralization by pseudomonads and Methylosinus trichosporium OB3b 总被引:1,自引:0,他引:1
To examine the trichloroethylene (C2HCl3)-degrading capability of five microorganisms, the maximum rate, extent, and degree of C2HCl3 mineralization were evaluated for Pseudomonas cepacia G4, Pseudomonas cepacia G4 PR1, Pseudomonas mendocina KR1, Pseudomonas putida F1, and Methylosinus trichosporium OB3b using growth conditions commonly reported in the literature for expression of oxygenases responsible for C2HCl3 degradation. By varying the C2HCl3 concentration from 5 μM to 75 μM, V
max and K
m values for C2HCl3 degradation were calculated as 9 nmol/(min mg protein) and 4 μM for P. cepacia G4, 18 nmol/(min mg protein) and 29 μM for P. cepacia G4 PR1, 20 nmol/(min mg protein) and 10 μM for P. mendocina KR1, and 8 nmol/(min mg protein) and 5 μM for P. putida F1. This is the first report of these Michaelis-Menten parameters for P. mendocina KR1, P. putida F1, and P. cepacia G4 PR1. At 75 μM, the extent of C2HCl3 that was degraded after 6 h of incubation with resting cells was 61%–98%; the highest degradation being achieved by toluene-induced
P. mendocina KR1. The extent of C2HCl3 mineralization in 6 h (as indicated by concentration of chloride ion) was also measured and varied from 36% for toluene-induced
P. putida F1 to 102% for M. trichosporium OB3b. Since C2HCl3 degradation requires new bio-mass, the specific growth rate (μmax) of each of the C2HCl3-degradation microorganisms was determined and varied from 0.080/h (M. trichosporium OB3b) to 0.864/h (P. cepacia G4 PR1).
Received: 1 May 1995/Received revision: 11 July 1995/Accepted: 26 July 1995 相似文献
5.
Gerda Oswald Ingo Rombeck B. Song H. Sigel B. Lippert 《Journal of biological inorganic chemistry》1998,3(3):236-245
The synthesis of cis-Pt(NH3)2(dCMP) is reported and by various physico-chemical methods it is demonstrated that it is a macrochelate in which Pt(II) is
bound simultaneously to the N3 site of cytosine in dCMP2– and to a phosphate-oxygen atom. According to the NOESY spectra (cross-peaks between cytosine H6 and H2′ and H3′) the cytosine
ring adopts an anti orientation. Highly unusual is the significant (1 ppm) downfield shift of the sugar proton H5″ in the 1H-NMR spectrum and the sensitivity of the cytosine H6 resonance on the protonation state of the phosphate group. Based on
these three features a geometry for the macrochelate is proposed. The compound is a major product of the reaction of cis-[Pt(NH3)2(H2O)2]2+ with dCMP2– at neutral pH, but it even forms at pH 5. By applying pD-dependent NMR spectroscopy (1H, 31P) and potentiometric pH titration, it is demonstrated that the Pt-coordinated phosphate group can be protonated (pK
a/1=3.21±0.10 and 3.31±0.05, respectively), and 1H- and 31P-NMR spectra also indicate deprotonation (pK
a/2=13.35±0.25) of the exocyclic amino group of the cytosine moiety. The metal ion binding affinity of cis-Pt(NH3)2(dCMP) is very small, as shown for Cu2+ (log K<0.6). The cis-Pt(NH3)2(dCMP) complex reacts with nucleosides and nucleotides (L′) by losing its chelate structure and forming mixed ligand complexes,
cis-Pt(NH3)2(dCMP)(L′); this means that the phosphate group is released from the coordination sphere of Pt(II), indicating that the Pt(II)-O(phosphate)
bond is not very strong.
Received: 23 October 1997 / Accepted: 17 February 1998 相似文献
6.
G. R. V. Babu O. K. Vijaya V. L. Ross J. H. Wolfram K. D. Chapatwala 《Applied microbiology and biotechnology》1996,45(1-2):273-277
Our isolate, Pseudomonas putida, is known to be capable of utilizing cyanides as the sole source of carbon (C) and nitrogen (N) both in the form of free cells
and cells immobilized in calcium alginate. In the present study, the cell-free extract(s) were prepared from the cells of
P. putida grown in the presence of sodium cyanide. The ability of enzyme(s) to convert cyanides, cyanates, thiocyanates, formamide and
cyanide-containing mine waters into ammonia (NH3) was studied at pH 7.5 and pH 9.5. The kinetic analysis of cyanide and formamide conversion into NH3 at pH 7.5 and pH 9.5 by the cell-free extract(s) of P. putida was also studied. The K
m and V
max values for cyanide/formamide were found to be 4.3/8 mM and 142/227 μmol NH3 released mg protein-1 min-1 respectively at pH 7.5 and 5/16.67 mM and 181/434 μmol NH3 released mg protein-1 h-1 respectively at pH 9.5. The study thus concludes that the cell-free extract(s) of P. putida is able to metabolize not only cyanides, cyanates, thiocyanates, and formamide but also cyanide-containing mine waters to
NH3.
Received: 10 April 1995/Received revision: 24 July 1995/Accepted: 22 August 1995 相似文献
7.
G.-J. Shen B. A. Annous R. W. Lovitt M. K. Jain J. G. Zeikus 《Applied microbiology and biotechnology》1996,45(3):355-362
Butyribacterium methylotrophicum produced more butyrate when grown on lactate than when grown on glucose, and only acetate was detected during growth on pyruvate.
Higher levels of NADH were found in butyrate-producing than in acetate-producing cells. The addition of neutral red, an electron-flow
modulator, to cells growing on pyruvate altered the carbon and electron flow from acetate plus H2 synthesis to butyrate synthesis. Enzymatic analysis suggested that pyruvate was produced from glucose via an Embden-Meyerhof-Parnas
pathway. Pyruvate was further metabolized to butyryl-CoA via, β-hydroxybutyryl-CoA and butyryl-CoA dehydrogenases. Lactate
dehydrogenase, unlike butyryl-CoA dehydrogenase, was inducible and detected only in lactate-grown cells. Both of these dehydrogenases
utilized 2,6-dichloroindophenol and other artificial electron acceptors but not NAD(P). Ferredoxin–NAD oxidoreductase levels
were highest in lactate and lowest in pyruvate-grown cells. Cells contained both a ferredoxin–neutral-red reductase activity
and a neutral-red–NAD reductase activity that coupled electron flow to butyrate synthesis. These results showed that butyrate
synthesis by B. methylotrophicum was regulated by the carbon source and was dependent on the cellular NADH/NAD ratios, and the levels and direction of ferredoxin-
and NAD-linked oxidoreductases.
Received: 3 August 1995/Received revision: 31 October 1995/Accepted: 10 November 1995 相似文献
8.
Humoral anti-idiotypic and anti-anti-idiotypic immune response in cancer patients treated with monoclonal antibody 17-1A 总被引:4,自引:0,他引:4
Peter Ragnhammar Maria Liljefors Anna-Lena Hjelm Håkan Mellstedt Jan-Erik Frödin J. Fagersberg 《Cancer immunology, immunotherapy : CII》1996,42(2):81-87
A group of 96 patients with advanced colorectal carcinoma were treated with the mouse (m) or chimeric (c) (mouse variable
regions × human IgG1 constant regions) monoclonal antibody (mAb) 17-1A recognizing the tumour-associated antigen GA733-2.
Eighty-two of the 83 patients treated with mmAb17-1A and 69% of the patients given cmAb17-1A (n = 13) developed anti-idiotypic antibodies (ab2). Auto-antibodies binding to tumour cells expressing GA733-2 were found in 7% of the patients. In a further 38 patients (40%)
antitumour-cell antibodies, i.e. anti-anti-idiotypic antibodies (ab3), were induced by the mAb17-1A therapy. Patients with detectable ab3 after treatment had significantly higher ab2 levels than those not developing ab3. Addition of granulocyte/macrophage-colony-stimulating factor (GM-CSF) to mmAb17-1A significantly enhanced the induction
of ab2 as well as induction of anti-anti-idiotypic antibodies (ab3), compared to mmAb17-1A alone. Patients with a high increase in antitumour-cell antibodies (ab3) induced by the therapy lived significantly longer than patients with no or a low level of induction of ab3 (P = 0.016). The results indicate that induction of an idiotypic network response might be an important effector mechanism in
mAb therapy.
Received: 20 October 1995 / Accepted: 18 December 1995 相似文献
9.
Ryszard Russa Maud Bruneteau Alexander S. Shashkov Teresa Urbanik-Sypniewska Hubert Mayer 《Archives of microbiology》1996,165(1):26-33
Lipopolysaccharides from the Rhizobium meliloti wild-type strain 102F51, which is effective in symbiosis with alfalfa, and from the nonnodulating mutant WL113, defective
in root hair adhesion, derived thereof, were isolated and comparatively analyzed. Both preparations were composed of galactose,
glucose, glucuronic acid, galacturonic acid, glucosamine, 3-deoxyheptulosaric acid, and 2-keto-3-deoxyoctonic acid as the
major sugar constitutents. After a modified methylation analysis (consisting of the following consecutive steps: methylation,
carboxyl reduction, remethylation, mild acid hydrolysis, reduction, and trideuterio-methylation), all of the 3-deoxyheptulosaric
and some of the 2-keto-3-deoxyoctonic acid residues were converted into their corresponding 3-deoxyalditol derivatives, which
carried trideuteriomethyl groups at positions C-2, C-4, and C-6. Another part of the permethylated 3-deoxyoctitol was also
found as 2,5,6- and 2,6,8-tri-O-trideuteriomethyl derivatives. NMR data obtained with the separated oligosaccharides and the results of methylation analysis
indicated that the majority of 2-keto-3-deoxyoctonate was present in the fraction of permethylated disaccharide alditols,
namely as 6-O-CD3-aGlc(1→5)3-deoxyoctitol, 6-O-CD3-βGlcNMeAcyl(1→4)3-deoxyoctitol, and as the permethylated trisaccharide alditol, αGalA(1→3)-[6-O-CD3]-β-Glc(1→5)-[4-O-CD3]-3-deoxyoctitol. The presence of trideuteriomethyl groups at C-4 of both 3-deoxyalditols and at C-6 of the glucosaminyl or
glucosyl residues indicated the linkage points of the released acid-labile ketosidic substituents, such as 3-deoxyheptulosarate
and 2-keto-3-deoxyoctonate, in these oligosaccharides. The main differences between the preparations from the wild-type 102F51
and its mutant strain WL 113 were found in the higher content (in strain 102F51) of the following oligosaccharides: α-glucuronosyl(1→4)2-keto-3-deoxyoctonate
and α-galacturonosyl-(1→3)α-glucosyl-(1→5)2-keto-3-deoxyoctonate and in the decreased content of β-glucosaminyl(1→4)2-keto-3-deoxy-octonate.
Received: 21 July 1995 / Accepted: 25 October 1995 相似文献
10.
M. Kato H. J. Bao C.-K. Kang T. Fukui Y. Doi 《Applied microbiology and biotechnology》1996,45(3):363-370
Pseudomonas sp. 61-3 (isolated from soil) produced a polyester consisting of 3-hydroxybutyric acid (3HB) and of medium-chain-length 3-hydroxyalkanoic
acids (3HA) of C6, C8, C10 and C12, when sugars of glucose, fructose and mannose were fed as the sole carbon source. The polyester produced was a blend of homopolymer
and copolymer, which could be fractionated with boiling acetone. The acetone-insoluble fraction of the polyester was a homopolymer
of 3-hydroxybutyrate units [poly (3HB)], while the acetone-soluble fraction was a copolymer [poly(3HB-co-3HA)] containing both short- and medium-chain-length 3-hydroxyalkanoate units ranging from C4 to C12:44 mol% 3-hydroxybutyrate, 5 mol% 3-hydroxyhexanoate, 21 mol% 3-hydroxyoctanoate, 25 mol% 3-hydroxydecanoate, 2 mol% 3-hydroxydodecanoate
and 3 mol% 3-hydroxy-5-cis-dodecenoate. The copolyester was shown to be a random copolymer of 3-hydroxybutyrate and medium-chain-length 3-hydroxyalkanoate
units by analysis of the 13C-NMR spectrum. The poly(3HB) homopolymer and poly (3HB-co-3HA) copolymer were produced simultaneously within cells from glucose in the absence of any nitrogen source, which suggests
that Pseudomonas sp. 61-3 has two types of polyhydroxy-alkanoate syntheses with different substrate specificities.
Received: 9 June 1995/Received last revision: 30 October 1995/Accepted: 6 November 1995 相似文献
11.
B. A. Annous J.-S. Shieh G.-J. Shen M. K. Jain J. G. Zeikus 《Applied microbiology and biotechnology》1996,45(6):804-810
Exogenous H2/CO2 and glucose were consumed simultaneously by Butyribacterium methylotrophicum when grown under glucose-limited conditions. CO2 reduction to acetate was coupled to H2 consumption. The addition of either H2 or CO2 to glucose batch fermentation resulted in an increase in cell density, hydrogenase (H2-consuming and -producing) activities and fatty acid production by B. methylotrophicum as compared to when N2 was the feed gas. Hydrogenase activities appeared to be tightly regulated and were produced at higher rates during the exponential
phase when CO2 was the feed gas as compared to H2 or N2. The increase in H2-consuming activity and decrease in H2-producing activity was correlated with an increase in butyrate synthesis. H2-consuming and ferredoxin (Fd)–NAD reductase activities increased while H2-producing and NADH–Fd reductase activities decreased in cells grown at pH 5.5 compared to those at pH 7.0. The molar ratio
of butyrate/acetate was shifted from 0.35 at pH 7.0 to 1.22 at pH 5.5. The addition of exogenous H2 did not decrease the butyrate/acetate ratio at pH 7.0 nor at pH 5.5. The results indicated that growth pH values regulated
both hydrogenase and Fd–NAD oxidoreductase activities such that, at acid pH, more intermediary electron flow was directed
towards butyrate synthesis than H2 production.
Received: 22 August 1995/Received revision: 18 December 1995/Accepted: 22 January 1996 相似文献
12.
The photosynthetic bacterium, Rhodospirillum centenum, has a flexible life cycle that permits it to survive starvation as dormant cyst cells. Previous studies have identified
some of the key regulators for encystment and demonstrated that the control of development is intricate. This complexity may
arise from the need to integrate several environmental signals to mediate a switch from one mode of energy metabolism to another
and to ensure that a transition to dormancy is initiated only when necessary. We searched for additional regulators of development
by screening for encystment deficient strains after subjecting wild type R. centenum to mini-Tn5 mutagenesis. Analysis of “hypo-cyst” strains led to the identification of two genes that encode putative hybrid
histidine kinases (cyd1 and cyd2). Cells with deletions of either gene fail to form cysts under conditions that normally induce development. Furthermore,
the deletion strains exhibit altered swarming behavior suggesting that Cyd1 and Cyd2 affect behaviors utilized when the organism
is attached to a substrate. 相似文献
13.
Transformation of 1,2,3- and 1,2,4-trichlorobenzene in the presence of 20 mM sodium formate, by the methanotrophic bacterium
Methylosinus trichosporium OB3b, was studied using cells grown in batch and continuous culture. Only 1,2,3-trichlorobenzene was transformed and transformation
was strictly co-metabolic, only catalysed in the presence of the soluble form of methane monooxygenase. The kinetics of transformation
could be described by simple first-order kinetics (0.00193 l min-1 g-1). Also the kinetics of transformation were found to be linearly proportional to cell density. No chloride ion release was
observed during the reaction and the products of transformation (2,3,4- and 3,4,5-trichlorophenol) were identified by gas
chromatography/mass spectroscopy and 1H-NMR and a 1.84:1 ratio of products in favour of para hydroxylation was observed. It was also observed that the relationship between mass of substrate transformed and cell density
was linear giving a transformation capacity of 88.8±11.8 μmol g-1, after which the transformation of 1,2,3-trichlorobenzene was inhibited. This inhibition was not due to O2 limitation, co-substrate (CHOONa) limitation or product inhibition. Recovery and washing of the cells did not reverse this
inhibition, indicating that inhibition was irreversible. During transformation a substantial decrease in the endogenous and
formate-dependent O2 consumption rates was observed, although the methanol-dependent O2 consumption rate varied little between fresh cell samples and samples that had been used to transform 1,2,3-trichlorobenzene.
Received: 22 June 1995 / Received last revision: 26 October 1995 / Accepted: 30 October 1995 相似文献
14.
We tested whether treatment with an inhibitor of nitric oxide synthesis (N
G-methyl-L-arginine, MeArg) can ameliorate interleukin-2(IL-2)-therapy-induced capillary leak syndrome in healthy or tumor-bearing mice
without compromising the antitumor effects of IL-2 therapy. Healthy or C3-L5-mammary-adenocarcinoma-bearing C3H/HeJ mice were
treated with one or two rounds of various doses of IL-2 (ten injections, i. p., every 8 h) or MeArg (ten injections s. c.,
every 8 h) or their combination. In an additional experiment, MeArg was given chronically in the drinking water, rather than
s. c. to healthy mice subjected to one round of therapy as above. Mice were killed 1 h after their last IL-2 injection to
measure the water content of the lungs and pleural cavities (markers of capillary leakage), NO production (given by NO2
– and NO3
– levels in the serum and pleural effusion), as well as the effect of therapies on the primary tumor size and number of spontaneous
lung metastatic nodules. Results revealed that all doses of IL-2 (7500 – 35 000 Cetus U/injection), as well as both rounds
of IL-2 therapy, caused capillary leakage. However, no pleural effusion was seen after the second round in any of the IL-2-treated
groups. MeArg therapy, given subcutaneously (5 – 20 mg kg–1 injection–1 in healthy and 20 mg kg–1 injection–1 in tumor-bearing mice), did not ameliorate IL-2-induced capillary leakage in either group of mice, and did not compromise
antitumor effects of IL-2. However, subcutaneous MeArg therapy alone reduced the growth of the primary tumors, the occurrence
of spontaneous lung metastases and the amount of tumor-induced pulmonary edema. When MeArg therapy was given orally (1 mg/ml
drinking water), a substantial drop in NO production, as well as reduction in capillary leakage was noted in IL-2-treated
healthy mice. These findings suggest that NO inhibitors could be a valuable adjunct to IL-2 therapy of cancer and infectious
diseases.
Received: 23 October 1995 / Accepted: 22 November 1995 相似文献
15.
Mutants having impaired protein synthesis, that is cycloheximide-sensitive mutants of a citric-acid-hyper-accumulating strain,
were induced from Aspergillus niger WU-2223L. Selection was on the basis of a presumption that the mutants should be more sensitive to cycloheximide than WU-2223L.
In shake culture without methanol as a promotor substance, seven mutants accumulated approximately 1.8–3.5 times as much citric
acid as WU-2223L. The best mutant, CHM I-C3, accumulated 69.4 mg citric acid/ml from 120 mg glucose/ml in shake culture without
methanol, this amount being 1.1 times the amount accumulated by WU-2223L with methanol. Furthermore, under the conditions
without methanol the mutants appeared to be more efficient than WU-2223L in employing the consumed glucose for the accumulation
of citric acid. It was also confirmed that CHM I-C3 exhibited a significantly increased level of intracellular NH+
4 accumulation. The addition of 2% (v/v) methanol or 20 μg cycloheximide/ml to the medium caused a remarkable increase of citric
acid accumulation by WU-2223L: about 3.1 and 2.4 times respectively. However, the addition of these substances produced negative
effects on citric acid accumulation by the mutants. With 2% (v/v) methanol, WU-2223L showed a remarkably decreased level of
protein accumulation but a substantially increased level of intracellular NH+
4 accumulation. However, these phenomena were also observed in CHM I-C3 without methanol. These results indicate that the intracellular
circumstances of the cycloheximide-sensitive mutants without methanol were similar to those of WU-2223L with methanol, and
that the impairment of protein synthesis contributed to increased citric acid accumulation by the mutants in the absence of
methanol.
Received: 21 November 1994 / Received last revision: 10 July 1995 / Accepted: 26 July 1995 相似文献
16.
A.-K. Duhme R. C. Hider M. J. Naldrett R. N. Pau 《Journal of biological inorganic chemistry》1998,3(5):520-526
Azotobacter vinelandii produces five siderophores with different metal binding properties, depending on the concentrations of Fe(III) and molybdate
in the growth medium. The three lower protonation constants of the unusual bis(catecholamide) siderophore azotochelin (L)
were determined by a simultaneous spectrophotometric and potentiometric titration as log K
5=3.65(5), log K
4=7.41(3) and log K
3=8.54(4). The metal-ligand equilibrium constant for [MoO2(L)]3– was obtained from analysis of the absorbance concentration data: at 20 °C and pH 6.6, log K
eq=4(1). Based on an average log K
a value of 12.1 for the two basic phenolic oxygens of azotochelin, the equilibrium formation constant was converted into the
conventional formation constant K
f(MoL) = [MoO2L3
–]/[MoO2
2+][L5
–] = 1035 M–1. To assess the influence of molybdenum-siderophore interactions on metal uptake in A. vinelandii, the dose-response effect of molybdate in the growth medium on siderophore biosynthesis was followed by UV-vis spectroscopy
and HPLC. It could be shown that the formation of molybdenum siderophore complexes clearly reduces the concentration of free
siderophores available for iron solubilization. Furthermore, in media with initial molybdate concentrations up to 100 μM,
the molybdenum azotochelin complex is the predominant molybdenum species, suggesting that azotochelin might also possess sequestering
activity towards molybdenum. Even higher molybdate levels result in a complete repression of the synthesis of the tetradentate
siderophore azotochelin, while they initiate the alternative release of the more efficient iron chelator, the hexadentate
siderophore protochelin.
Received: 20 April 1998 / Accepted: 29 June 1998 相似文献
17.
C. Kuek 《Applied microbiology and biotechnology》1996,45(3):319-326
Large-scale exploitation of the potential benefits of ectomycorrhizal fungi in improving plantation yields means that fermentation
techniques for these fungi will be required. Starting with a base performance on a rich, complex medium, the effect of variations
in some physicochemical culture parameters on biomass yield was studied. It was possible to reduce the amount of phosphate
salts (to 1/9th) and other ingredients (to 1/3rd) in the medium. A shaking speed of either 100 rpm or 200 rpm in an orbital
incubator was satisfactory and biomass yield responded to an increase in carbon substrate (glucose, from 10 g l-1 and 20 g l-1) though Y
x/s declined. An increase in inoculum size shortened culture time but decreased biomass yield. The upper limit of the incubation
temperature was between 25°C and 30°C. Biomass yields were about 12 g l-1 dry weight (Y
x/s=0.63) when 20 g l-1 glucose was supplied, and about 7 g l-1 (Y
x/s=0.74) when 10 g l-1 glucose was supplied.
Received: 9 October 1995/Accepted: 4 December 1995 相似文献
18.
Elena Antoshina Lawrence E. Ostrowski 《In vitro cellular & developmental biology. Animal》1997,33(3):212-217
Summary We are studying the regulation of ciliated cell differentiation using an in vitro model of tracheal regeneration. Previously, we reported that removal of growth stimulating compounds such as epidermal growth
factor (EGF) and cholera toxin reduced DNA synthesis and cell number while increasing ciliated cell differentiation (Clark
et al., 1995). This result suggested that the induction of growth arrest may stimulate terminal differentiation of airway
epithelial cells into ciliated cells. Transforming growth factor βs (TGFβs) inhibit epithelial cell proliferation and have
also been shown to stimulate epithelial cell differentiation. In this study, the effect of TGFβ1 on growth and ciliated cell differentiation of rat tracheal epithelial (RTE) cells was examined. TGFβ1 inhibited [3H]thymidine incorporation by RTE cells in a dose-dependent manner. A 40% inhibition was observed after a 24-h incubation with
10 pM TGFβ1. Continuous treatment with TGFβ1 (1–50 pM) also reduced cell number during the time when ciliogenesis occurs. This reduction resulted in part from a loss of cells
through exfoliation, in addition to the inhibition of proliferation. The exfoliated cells exhibited several morphological
features characteristic of apoptosis, including shrunken cells, condensed and fragmented nuclei, and intact organelles. In
addition, electrophoretic analysis of genomic DNA analysis isolated from exfoliated cells demonstrated the presence of a nucleosomal
ladder. However, in contrast to the removal of EGF, treatment with TGFβ1 for 7 d did not increase ciliated cell differentiation. TGFβ1 is, therefore, capable of inhibiting proliferation and increasing
apoptosis in RTE cells without stimulating ciliated cell differentiation. 相似文献
19.
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
20.
The biofiltration of dimethyl sulphide (Me2S) and other volatile sulphur compounds results in the accumulation of the metabolite sulphuric acid in the carrier material.
Regeneration of an acidified (pH 4.7), Hyphomicrobium-MS3-inoculated compost biofilter degrading Me2S was not possible by trickling tap water (days 0–28) or a KH2PO4/K2HPO4 buffer solution (1.26 g PO3-
4 l-1, pH 7) (days 29–47) over the bioreactor at a superficial liquid flow rate of 34 lm-2 day-1. Since the protons produced displaced nutrient cations (Na+, K+, Ca2+, Mg2+, NH+
4) from the cation-exchange sites on the compost material, 95% of the SO2-
4 was leached as the corresponding sulphate salts and not as sulphuric acid. Concomitantly, the pH of the compost material
decreased from 4.7 to 3.9 over the 47 days rinsing period. Moreover, the rinsing procedure resulted in the leaching of essential
microbial nutrients from the compost material, such as NH+
4 (22.3% wash-out over the 47-day rinsing period) and PO3-
4 (39.3% washout over the 28-day tap-water rinsing period). However, mixing limestone powder into the Me2S-degrading compost biofilter was a successful approach to controlling the pH in the optimal range for the inoculum Hyphomicrobium MS3 (pH 6–7). A stoichiometric neutralisation reaction (molar ratio CaCO3/H2SO4=1.1) was observed between the CaCO3 added and the metabolite of the Me2S degradation, while high elimination capacities (above 100 g Me2S m-3 day-1) were obtained over a prolonged (more than 100 days) period.
Received: 1 December 1995/Received revision: 26 April 1995 Accepted: 29 April 1996 相似文献