共查询到20条相似文献,搜索用时 15 毫秒
1.
A. De Smul J. Dries L. Goethals H. Grootaerd W. Verstraete 《Applied microbiology and biotechnology》1997,48(3):297-303
In a mesophilic (30–35 °C), sulphidogenic, ethanol-fed expanded-granular-sludge-blanket reactor, sulphate, at loading rates
of up to 10.0–12.0 g Sl−1␣day−1, was removed with an average efficiency of more than 80%. The pH was between 7.7 and 8.3 and the maximal total dissolved
sulphide concentration was up to 20 mM S (650 mg S/l). The alkaline pH was maintained by either a pH-control unit with sodium
hydroxide or by stripping part of the sulphide and CO2 from the recycle with nitrogen gas. The superficial upstream liquid velocity (v
up) was 3.0–4.5 m/h. The ratio of ethanol to sulphur was near stoichiometry. At alkaline pH, the activity of the acetotrophic
sulphate-reducing bacteria, growing on acetate, was strongly enhanced, whereas at pH below 7.7 the acetotrophic sulphate-reducing
bacteria were inhibited by aqueous H2S. With regard to the removal efficiency and operational stability, external stripping with N2 and pH control were equally successful.
Received: 2 December 1996 / Received revision: 13 March 1997 / Accepted: 15 March 1997 相似文献
2.
The biodegradation of tributyl phosphate (Bu3-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated
by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu3-P biodegradation by growing cells is described. Growth at the expense of Bu3-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu3-P biodegradation was optimal at 30 °C, reduced at 20 °C and negligible at 4 °C and 37 °C. Incorporation of Cu or Cd inhibited,
and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu3-P biodegradation significantly, but nitrate had no effect. Sulphate (10–100 mM) was inhibitory. When pregrown biomass was used
the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 μmol h−1 mg protein−1 and 37 μmol h−1 mg protein−1 respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate
precipitation at the expense of Bu3-P hydrolysis in the presence of 35 mM SO4
2−. At pH 4.5, 79% of the UO2
2+ was removed at a flow rate of 1.4 ml/h on a 7-ml test column.
Received: 2 June 1997 / Received revision: 15 September 1997 / Accepted: 19 September 1997 相似文献
3.
A number of nutritional factors influencing growth and glucose oxidase (EC 1.1.3.4) production by a newly isolated strain
of Penicillium pinophilum were investigated. The most important factors for glucose oxidase production were the use of sucrose as the carbon source,
and growth of the fungus at non-optimal pH 6.5. The enzyme was purified to apparent homogeneity with a yield of 74%, including
an efficient extraction step of the mycelium mass at pH 3.0, cation-exchange chromatography and gel filtration. The relative
molecular mass (M
r) of native glucose oxidase was determined to be 154 700 ± 4970, and 77 700 for the denatured subunit. Electron-microscopic
examinations revealed a sandwich-shaped dimeric molecule with subunit dimensions of 5.0 × 8.0 nm. Glucose oxidase is a glycoprotein
that contains tightly bound FAD with an estimated stoichiometry of 1.76 mol/mol enzyme. The enzyme is specific for d-glucose, for which a K
m value of 6.2 mM was determined. The pH optimum was determined in the range pH 4.0–6.0. Glucose oxidase showed high stability
on storage in sodium citrate (pH 5.0) and in potassium phosphate (pH 6.0), each 100 mM. The half-life of the activity was
considerably more than 305 days at 4 °C and 30 °C, and 213 days at 40 °C. The enzyme was unstable at temperatures above 40 °C
in the range pH 2.0–4.0 and at a pH above 7.0.
Received: 18 November 1996 / Received revision: 3 March 1997 / Accepted: 7 March 1997 相似文献
4.
H. Okada T. Sekiya K. Yokoyama H. Tohda H. Kumagai Y. Morikawa 《Applied microbiology and biotechnology》1998,49(3):301-308
A cbh2 cDNA encoding Trichoderma reesei QM9414 cellobiohydrolase II, located on the expression vector whose copy number is controlled by the level of gentamicin,
was successfully expressed under the control of a human cytomegalovirus promoter in the fission yeast, Schizosaccharomyces pombe. The 24-amino-acid leader peptide of the cbh2 gene was recognized by the yeast, enabling the efficient secretion of the heterologous cellobiohydrolase. The transformed
S. pombe strain produced over 115 μg cellobiohydrolase proteins/ml rich medium supplemented with malt extract and 100 μg/ml gentamicin.
The molecular masses of the recombinant cellobiohydrolases, secreted as two molecular species, were estimated to be 70 kDa
and 72 kDa by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE). Deglycosylation treatments revealed that
the recombinant enzymes were overglycosylated and scarcely susceptible to α-mannosidase. The recombinant enzymes showed no
carboxymethylcellulase activity, but showed similar characteristics to those of a native enzyme purified from T. reesei in their optimum pH and temperature, pH and temperature stabilities, and V
max values toward phosphoric-acid-swollen cellulose as substrate, except that their K
m values were about fourfold higher than that of the native enzyme.
Received: 4 August 1997 / Received revision: 13 October 1997 / Accepted: 31 October 1997 相似文献
5.
U. Matrubutham J. E. Thonnard G. S. Sayler 《Applied microbiology and biotechnology》1997,47(5):604-609
Pseudomonas fluorescens HK44 is a bioluminescent bioreporter synthesizing light in the presence of naphthalene or salicylate. Upon immobilization,
HK44 is useful as an in situ or on-line biosensor of bioavailable naphthalene and salicylate in waste streams or contaminated
fields. The bioreporting efficacy of alginate/SrCl2-immobilized HK44 was investigated in simulated groundwater with different pH regimes. When induced with complex (salicylate
plus auxiliary energy supplements) and simple (salicylate as the sole energy supplement) inducer solutions, the specific light
response was steadier at pH 6 than at pH 7 in a 35-day study. There was no bioluminescence response from cells incubated in
groundwater samples with pH below 6. The rate of the luminescence reaction was stable at pH 6 irrespective of the type of
inducer solution, indicating the robust physiological status of the bioreporter bacteria. In addition, the quantity of light
synthesized was at least one order of magnitude higher with complex inducer solution than with simple inducer solution. The
numbers of viable and cultivable cells remained constant in groundwater at pH 6 and 7 (approx. 107 g−1 beads). The numbers decreased by four orders of magnitude (107 to 103) to zero in groundwaters with pH below 6. This study suggested that HK44 is useful for long-term biosensor applications in
moderately acidic to neutral groundwater conditions.
Received: 6 August 1996 / Received revision: 12 December 1996 / Accepted: 4 January 1997 相似文献
6.
Various strains of coryneform bacteria, Micrococcaceae and commercial starters of Lactococcus lactis and Leuconostoc were compared for their aptitude to form S-methyl thioesters. Resting cells were incubated with methanethiol alone at pH 7 and in conjunction with a mixture of straight,
branched and hydroxy short-chain fatty acids up to C6 at pH 7 and 5. Results showed that all the strains synthesized at least S-methyl thioacetate, with strains that were low and high producers in each group. This is the only thioester formed in small
amount by Leuconostoc. Brevibacterium linens (six strains) and Micrococcaceae (five strains) were able to form branched-chain thioesters especially from their intracellular
fatty acids at neutral pH, and straight-chain thioesters mostly from exogenous fatty acids at acid pH. Coryneform bacteria
other than B. linens (four strains) and L. lactis (four starters) synthesized thioesters up to S-methyl thiobutyrate from endogenous or exogenous fatty acids but not branched-chain ones, except for one starter which formed
a very little thioisovalerate. Some particular effects of pH and added fatty acids revealed differences between species or
strains in their specific enzymatic systems.
Received: 7 April 1997 / Received revision: 5 June 1997 / Accepted: 7 June 1997 相似文献
7.
In our previous studies, the yeast Endomyces fibuliger LU677 was found to degrade amygdalin in bitter apricot seeds. The present investigation shows that E. fibuliger LU677 produces extracellular β-glycosidase activity when grown in malt extract broth (MEB). Growth was very good at 25 °C
and 30 °C and slightly less at 35 °C. When grown in MEB of pH 5 and pH 6 with addition of 0, 10 or 100 ppm amygdalin, E. fibuliger produced only slightly more biomass at pH 5, and was only slightly inhibited in the presence of amygdalin. Approximately,
60% of the added amygdalin was degraded (fastest at 35 °C) during an incubation period of 5 days. Supernatants of cultures
grown at 25 °C and pH 6 for 5 days were tested for the effects of pH and temperature on activity (using amygdalin, linamarin
and prunasin as substrates). Prunase activity had two pH optima (pH 4 and pH 6), amygdalase and linamarase only one each at
pH 6 and pH 4–5 respectively. The linamarase activity evolved earlier than amygdalase (2 days and 4 days respectively). The
data thus indicate the presence of at least two different glycosidases having different pH optima and kinetics of excretion.
In the presence of amygdalin, lower glycosidase activities were generally produced. However, the amygdalin was degraded from
the start of the growth, strongly indicating an uptake of amygdalin by the cells. The temperature optimum for all activities
was at 40 °C. Activities of amygdalase (assayed at pH 4) and linamarase (at pH 6) evolving during the growth of E. fibuliger were generally higher in cultures grown at 25 °C and 30 °C. TLC analysis of amygdalin degradation products show a two-stage
sequential mechanism as follows: (1) amygdalin to prunasin and (2) prunasin to cyanohydrin.
Received: 16 September 1997 / Received revision: 6 October 1997 / Accepted: 14 October 1997 相似文献
8.
K. Nakamura M. A. Yudiarto N. Kaneko H. Kurosawa Y. Amano 《Applied microbiology and biotechnology》1997,48(6):753-757
A microbial method to determine sulphate concentration in water was developed on the basis of sulphate-dependent acid phosphatase
(APase) in whole cells of Thiobacillus thiooxidans. The activity of the APase was determined colorimetrically by using p-nitrophenylphosphate as substrate. The APase was activated by sulphate. A linear relationship was obtained between the activity
of the APase and the concentration of sulphate in the range 0–0.6 mM. Therefore, the sulphate concentration was estimated
from the APase activity, represented by the absorbance (A
400). The microbial method was applied to the determination sulphate in water. The lower limit of detection was 0.02 mM, the
relative standard deviation being 2% for 10 measurements on a standard sample. As for practical samples, which were taken
from rain, river and tap water, good agreement was obtained between the values measured by the microbial method and those
given by a conventional barium chloranilate method. The relative standard deviation was 2.1% for 12 measurements of tap water.
The activity of the APase was stable over a period of more than 100 days when the cells were stored in 0.1 M sodium acetate/acetic
acid buffer (pH 5.0) at 4 °C.
Received: 21 March 1997 / Received revision: 30 June 1997 / Accepted: 27 July 1997 相似文献
9.
A Saccharomyces-cerevisiae-based simultaneous saccharification and fermentation (SSF) of lignocellulosic biomass is limited to an operating temperature
of about 37 °C, and even a small increase in temperature can have a deleterious effect. This points to a need for a more thermotolerant
yeast. To this end, S. cerevisiae D5A and a thermotolerant yeast, Candida acidothermophilum, were tested at 37 °C, 40 °C, and 42 °C using dilute-acid-pretreated poplar as substrate. At 40 °C, C. acidothermophilum produced 80% of the theoretical ethanol yield, which was higher than the yield from S.cerevisiae D5A at either 37 °C or 40 °C. At 42 °C, C. acidothermophilum showed a slight drop in performance. On the basis of preliminary estimates, SSF with C. acidothermophilum at 40 °C can reduce cellulase costs by about 16%. Proportionately greater savings can be realized at higher temperatures
if such a high-temperature SSF is feasible. This demonstrates the advantage of using thermophilic or thermotolerant yeasts.
Received: 20 February 1997 / Received revision: 24 June 1997 / Accepted: 4 July 1997 相似文献
10.
G. A. da Silva 《Applied microbiology and biotechnology》1996,46(2):112-121
The occurrence of killer toxins amongst yeasts in Brazilian Riesling Italico grape must was investigated by using the sensitive
strain EMBRAPA-26B as a reference strain at 18°C and 28°C. From a total of 85 previously isolated yeasts, 21 strains showed
ability to kill the sensitive strain on unbuffered grape must/agar (MA-MB) and 0.1 M citrate/phosphate-buffered yeast extract/peptone/dextrose/agar
(YEPD-MB) media both supplemented with 30 mg/l methylene blue. The killer activity of only four yeasts depended on the incubation
temperature rather than the medium used. At 28°C, the strains 11B and 53B were not able to show killer action. On the other
hand, strains 49B and 84B did not kill the sensitive yeast at 18°C. The killer strain EMBRAPA-91B and a commercial wine killer
yeast K-1 were employed to examine the sensitivity of the isolated yeasts on YEPD-MB and MA-MB at 18°C. The sensitivity and
neutral characteristics of yeasts were shown to be dependent on the medium and the killer strain. Interactions, including
K- R-, K- R+ and K+ R+ strains, simultaneously, have revealed that some K-R+ strains appear to protect the K- R- strain against the killer toxin. Sensitive dead cells, although to a less extent, also exhibited similar protection. Kinetic
studies have shown that the maximum specific growth rates were higher for the 20B YEPD-MB-sensitive strain (μmax=0.517 h-1) than for both the 91B (μmax=0.428 h-1) and K-1 (μmax= 0.466 h-1) killer strains. The protective capacity of neutral or sensitive cells that contaminate a fermentation, as well as the higher
maximum specific growth rate of sensitive yeasts, besides other factors, may preclude the dominance of a killer strain. This
protective capacity may also reduce the risk of a sensitive inoculum being killed by wild-type killer yeasts in open non-sterile
fermentation.
Received: 3 November 1995/Received revision: 11 March 1996/Accepted: 15 April 1996 相似文献
11.
Growth hormone (GH) enhances the growth rate of aquacultured fish and shellfish, but it is difficult to extract native GH
from fish pituitary glands. However, fish recombinant GH (rGH) can be efficiently synthesized by Escherichia coli cells, although it exists in denatured form in inclusion bodies (IB). We studied the solubilization of IB and the renaturation
of rGH to help facilitate the production of a large amount of biologically active rGH. A 100-ml sample of rGH-producing E. coli produced 73.43 ± 5.47 mg IB (dry weight, n = 3) after 20 h induction by 1 mM isopropyl β-o-thiogalactopyranoside. Interestingly, if the bacteria were induced by 0.1 mM β-lactose, 95.3 ± 3.43 mg of IB was obtained.
The optimal conditions for denaturation and renaturation of rGH were when IB were solubilized in 6 M guanidine hydrochloride
and then dialysed against pH 10 dialysis buffer (50 mM ammonium bicarbonate and 2 mM EDTA) containing 100 mM l-arginine, 2 mM oxidized glutathione and 2 mM reduced glutathione for 24 h at 4 °C in a volume ratio of 3 to 500. At least
20% of the denaturated rGH in IB was renatured. Juvenile black sea bream injected with 0.05 μg/g resultant rGH once every
2 weeks exhibited significant increases (P < 0.05) in weight gain (84%) relative to fish in the control group over a 16-week period. This process is an economical and
effective way to obtain an active form of rGH biosynthesized by a prokaryotic system.
Received: 18 November 1996 / Received revision: 5 March 1997 / Accepted: 7 March 1997 相似文献
12.
M. J. Artolozaga E. Kubátová J. Volc H. M. Kalisz 《Applied microbiology and biotechnology》1997,47(5):508-514
Pyranose 2-oxidase (P2O) was purified 43-fold to apparent homogeneity from the basidiomycete Phanerochaete chrysosporium using liquid chromatography on phenyl Sepharose, Mono Q (twice) and phenyl Superose. The native enzyme has a molecular mass
of about 250 kDa (based on native PAGE) and is composed of four identical subunits of 65 kDa. It contains three isoforms of
isoelectric point (pI) 5.0, 5.05 and 5.15 and does not appear to be a glycoprotein. P2O is optimally stable at pH 8.0 and
up to 60 °C. It is active over a broad pH range (5.0–9.0) with maximum activity at pH 8.0–8.5 and at 55 °C, and a broad substrate
specificity. d-Glucose is the preferred substrate, but 1-β-aurothioglucose, 6-deoxy-d-glucose, l-sorbose, d-xylose, 5-thioglucose, d-glucono-1,5-lactone, maltose and 2-deoxy-d-glucose are also oxidised at relatively high rates. A Ping Pong Bi Bi mechanism was demonstrated for the P2O reaction at
pH 8.0, with a catalytic constant (k
cat) of 111.0 s−1 and an affinity constant (K
m) of 1.43 mM for d-glucose and 83.2 μM for oxygen. Whereas the steady-state kinetics for glucose oxidation were unaffected by the medium at
pH ≥ 7.0, at low pH both pH and buffer composition affected the P2O kinetics with the k
cat/K
m value decreasing with decreasing pH. The greatest effect was observed in acetate buffer (0.1 M, pH 4.5), where the k
cat decreased to 60.9 s−1 and the K
m increased to 240 mM. The activity of P2O was completely inhibited by 10 mM HgCl2, AgNO3 and ZnCl2, and 50% by lead acetate, CuCl2 and MnCl2.
Received: 28 August 1996 / Received revision: 25 November 1996 / Accepted: 29 November 1996 相似文献
13.
Y. Pagot A. Le Clainche J.-M. Nicaud Y. Wache J.-M. Belin 《Applied microbiology and biotechnology》1998,49(3):295-300
γ-Decalactone is a peachy aroma compound resulting from the peroxisomal β-oxidation of ricinoleic acid by yeasts. The expression
levels of acyl-CoA oxidase (gene deletion) and 3-ketoacyl-CoA thiolase activities (gene amplification on replicative plasmids)
were modified in the yeast Yarrowia lipolytica. The effects of these modifications on β-oxidation were measured. Overexpression of thiolase activity did not have any effect
on the overall β-oxidation activity. The disruption of one of the acyl-CoA oxidase genes resulted in an enhanced activity.
The enhancement led to an increase of overall β-oxidation activity but reduced the γ-decalactone production rates. This seemed
to indicate a non-rate-limiting role for β-oxidation in the biotransformation of ricinoleic acid to γ-decalactone by the yeast
Yarrowia lipolytica. All strains produced and then consumed γ-decalactone. We checked the ability of the different strains to consume γ-decalactone
in a medium containing the lactone as sole carbon source. The consumption of the strain overexpressing acyl-CoA oxidase activity
was higher than that of the wild-type strain. We␣concluded that peroxisomal β-oxidation is certainly involved in γ-decalactone
catabolism by the yeast Y.␣lipolytica. The observed production rates probably depend on an equilibrium between production and consumption of the lactone.
Received: 13 June 1997 / Received revision: 2 October 1997 / Accepted: 14 October 1997 相似文献
14.
A. Krastanov 《Applied microbiology and biotechnology》1997,47(5):476-481
A novel immobilized biocatalyst with invertase activity was prepared by adhesion of yeast cells to wool using glutaraldehyde.
Yeast cells could be immobilized onto wool by treating either the yeast cells or wool or both with glutaraldehyde. Immobilized
cells were not desorbed by washing with 1 M KCl or 0.1 M buffers, pH 3.5–7.5. The biocatalyst shows a maximum enzyme activity
when immobilized at pH 4.2–4.6 and 7.5–8.0. The immobilized biocatalyst was tested in a tubular fixed-bed reactor to investigate
its possible application for continuous full-scale sucrose hydrolysis. The influence of temperature, sugar concentration and
flow rate on the productivity of the reactor and on the specific productivity of the biocatalyst was studied. The system demonstrates
a very good productivity at a temperature of 70 °C and a sugar concentration of 2.0 M. The increase of the volume of the biocatalyst
layer exponentially increases the productivity. The productivity of the immobilized biocatalyst decreases no more than 50%
during 60 days of continuous work at 70 °C and 2.0 M sucrose, but during the first 30 days it remains constant. The cumulative
biocatalyst productivity for 60 days was 4.8 × 103kg inverted sucrose/kg biocatalyst. The biocatalyst was proved to be fully capable of continuous sucrose hydrolysis in fixed-bed
reactors.
Received: 8 November 1996 / Received revision: 31 January 1997 / Accepted: 31 January 1997 相似文献
15.
M. Kunioka 《Applied microbiology and biotechnology》1997,47(5):469-475
The biosynthesis and chemical reactions of poly(amino acid)s produced by microorganisms are reviewed. A large amount of γ-poly(glutamic
acid) (PGA) has been produced by Bacillus strains. ε-Polylysine (PL) has been produced by Streptomyces albulus. As a modification of PGA and PL, pH-sensitive hydrogels have been prepared by means of γ irradiation or the addition of
a crosslinking agent to an aqueous solution of PGA and PL.
Received: 4 September 1996 / Received revision: 27 January 1997 / Accepted: 28 January 1997 相似文献
16.
Harald Kosegarten Franz Grolig Andreas Esch Karl-Heinz Glüsenkamp Konrad Mengel 《Planta》1999,209(4):444-452
A fluorimetric ratio technique was elaborated to measure apoplastic pH in the outer root cortex of maize (Zea mays L.) grown hydroponically. A newly synthesized fluorescent probe, fluorescein boronic acid (pKa = 5.48), which covalently binds to the cell wall of the outer cell layers, was used. Under conditions of saturating ion concentrations
the apoplastic pH was determined along the root axis ranging from 1 to 30 mm behind the root tip. Apoplastic pH was recorded
for root segment areas (1 mm2), and pH values of high statistical significance were obtained. With an external solution of pH 5, the apoplastic pH was
about pH 5.1 in the division zone, between pH 4.8 and 4.9 in the elongation region and about pH 4.9 in the root hair zone.
At an external pH of 8.6, the difference between the external pH and the apoplastic pH was considerably more, with a pH of
5.2–5.3 in all root zones. Addition of 1 mM NH4
+ caused a small apoplastic pH decrease (0.05 of a pH unit) in all root zones. Apoplastic alkalization upon application of
6 mM NO3
− was highest (0.3 of a pH unit) in the zone where root hairs emerge; in the division and early elongation zones, apoplastic
pH increased only transiently. In the presence of 10 mM HCO3
−, NO3
− elicited a higher and persistent alkalization (0.06–0.25 of a pH unit) in all root zones. Application of fusicoccin reduced
apoplastic pH from 4.85 to 4.75 in the elongation zone, while inhibition of the H+-ATPase with vanadate alkalized the apoplast in the root hair zone from pH 5.4 to 5.6. The observed pH differences along the
root axis upon differential N supply and application of HCO3
− provide evidence that this new pH technique is a useful tool with which to measure apoplastic pH, and in future may permit
measurements at microsites at the cell level by use of microscope imaging.
Received: 26 August 1998 / Accepted: 4 May 1999 相似文献
17.
Schmitz C Goebel I Wagner S Vomberg A Klinner U 《Applied microbiology and biotechnology》2000,54(1):126-132
An n-alkane-assimilating strain of Candida tropicalis was selected in sandy soil inoculated with microorganisms from contaminated sites. Competition experiments with n-alkane utilizers from different strain collections confirmed that yeasts overgrow bacteria in sandy soil. Acidification of
the soil is one of the colonization factors useful for the yeasts. It can be counteracted by addition of bentonite, a clay
mineral with high ion exchange capacity, but not, however, by kaolin. Strains of different yeast species showed different
levels of competitiveness. Strains of Arxula adeninivorans, Candida maltosa, and Yarrowia lipolytica overgrew strains of C. tropicalis, C. shehatae or Pichia stipitis. Two strains of C. maltosa and Y. lipolytica coexisted during several serial transfers under microcosm conditions.
Received: 20 October 1999 / Received revision: 26 January 2000 / Accepted: 27 January 2000 相似文献
18.
Taniguchi J Hemmi H Tanahashi K Amano N Nakayama T Nishino T 《Applied microbiology and biotechnology》2000,54(4):581-588
A zinc-resistant bacterium, Brevibacterium sp. strain HZM-1 which shows a high Zn2+-adsorbing capacity, was isolated from the soil of an abandoned zinc mine. Kinetic analyses showed that Zn2+ binding to HZM-1 cells follows Langmuir isotherm kinetics with a maximum metal capacity of 0.64 mmol/g dry cells and an apparent
metal dissociation constant of 0.34 mM. The observed metal-binding capacity was one of the highest values among those reported
for known microbial Zn2+ biosorbents. The cells could also adsorb heavy metal ions such as Cu2+. HZM-1 cells could remove relatively low levels of the Zn2+ ion (0.1 mM), even in the presence of large excess amounts (total concentration, 10 mM) of alkali and alkali earth metal
ions. Bound Zn2+ ions could be efficiently desorbed by treating the cells with 10 mM HCl or 10 mM EDTA, and the Zn2+-adsorbing capacity of the cells was fully restored by treatment of the desorbed cells with 0.1 M NaOH. Thus, HZM-1 cells
can serve as an excellent biosorbent for removal of Zn2+ from natural environments. The cells could grow in the presence of significant concentrations of ZnCl2 (at least up to 15 mM) and thus is potentially applicable to in situ bioremediation of Zn2+-contaminated aqueous systems.
Received: 1 February 2000 / Received revision: 31 March 2000 / Accepted: 1 May 2000 相似文献
19.
Overexpression of a cytosolic hydroxymethylglutaryl-CoA reductase leads to squalene accumulation in yeast 总被引:4,自引:0,他引:4
The enzyme 3-hydroxy-3-methylglutaryl-coenzyme-A (HMG-CoA) reductase is known as the rate-limiting enzyme in early sterol
biosynthesis in eukaryotic cells. To eliminate this regulation in the yeast Saccharomyces cerevisiae, a truncated HMG1 gene, producing a form of the enzyme that lacks the membrane-binding region (i.e. amino acids 1–552), was constructed and
overexpressed in this yeast. The transformed strains accumulated large amounts of the sterol precursor squalene, while the
levels of ergosterol and a number of other sterol compounds were only slightly elevated. These findings suggest that HMG-CoA
reductase is not the only rate-limiting step in sterol synthesis and its overexpression cannot significantly influence this
pathway beyond the sterol precursor squalene.
Received: 9 June 1997 / Received revision: 1 September 1997 / Accepted: 19 September 1997 相似文献
20.
Strains of the fission yeast Schizosaccharomyces pombe have been constructed containing single or multiple chromosomally integrated copies of an expression cassette for production
of human gastric lipase. Integrant strains of S. pombe secrete active lipase and are stable for lipase production over a minimum of 50 generations in non-selective media. Lipase
activity levels for integrant strains containing up to three tandem copies of the expression cassette are strongly correlated
with copy number of the cassette in both complete and minimal media. Lipase activity is higher in complete medium than in
minimal medium. Strains carrying three chromosomally integrated expression cassette copies can be grown without selection
in complete medium and are capable of significantly higher lipase activities than strains containing the expression cassette
on a multicopy plasmid.
Received: 27 March 1997 / Received revision: 13 August 1997 / Accepted: 25 August 1997 相似文献