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1.
Active excretion of ammonia across the gills of the shore crab Carcinus maenas and its relation to osmoregulatory ion uptake 总被引:1,自引:0,他引:1
D. Weihrauch W. Becker U. Postel S. Riestenpatt D. Siebers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):364-376
The mechanism of transbranchial excretion of total ammonia of brackish-water acclimated shore crabs, Carcinus maenas was examined using isolated, perfused gills. Applying physiological gradients of NH4Cl (100–200 μmol · l−1) directed from the haemolymph space to the bath showed that the efflux of total ammonia consisted of two components. The
saturable component (excretion of NH4
+) greatly exceeded the linear component (diffusion of NH3). When an outwardly directed gradient (200 μmol · l−1) was applied, total ammonia in the perfusate was reduced by more than 50% during a single passage of saline through the gill.
Effluxes of ammonia along the gradient were sensitive to basolateral dinitrophenol, ouabain, and Cs+ and to apical amiloride. Acetazolamide (1 mmol · l−1 basolateral) or Cl−-free conditions had no substantial effects on ammonia flux, which was thus independent of both carbonic anhydrase mediated
pH regulation and osmoregulatory NaCl uptake. When an inwardly directed gradient (200 μmol · l−1) was employed, influx rates were about 10-fold smaller and unaffected by basolateral ouabain (5 mmol · l−1) or dinitrophenol (0.5 mmol · l−1). Under symmetrical conditions (100 μmol · l−1 NH4Cl on both sides) ammonia was actively excreted against the gradient of total ammonia, which increased strongly during the
experiment and against the gradient of the partial pressure of NH3. The active excretion rate was reduced to 7% of controls by basolateral dinitrophenol (0.5 mmol · l−1), to 44% by basolateral ouabain (5 mmol · l−1), to 46% by Na+-free conditions and to 42% by basolateral Cs+ (10 mmol · l−1), indicating basolateral membrane transport of NH4
+ via the Na+/K+-ATPase and K+-channels and a second active, apically located, Na+ independent transport mechanism of NH4
+. Anterior gills, which are less capable of active ion uptake than posterior gills, exhibited even increased rates of active
excretion of ammonia. We conclude that, under physiological conditions, branchial excretion of ammonia is a directed process
with a high degree of effectiveness. It even allows active extrusion against an inwardly directed gradient, if necessary.
Accepted: 11 March 1998 相似文献
2.
An DS Cui CH Sung BH Yang HC Kim SC Lee ST Im WT Kim SG 《Applied microbiology and biotechnology》2012,94(3):673-682
The gene encoding an α-l-arabinofuranosidase that could biotransform ginsenoside Rc {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-[α-l-arabinofuranosyl-(1–6)-β-d-glucopyranosyl]-20(S)-protopanaxadiol} to ginsenoside Rd {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-β-d-glucopyranosyl-20(S)-protopanaxadiol} was cloned from a soil bacterium, Rhodanobacter ginsenosidimutans strain Gsoil 3054T, and the recombinant enzyme was characterized. The enzyme (AbfA) hydrolyzed the arabinofuranosyl moiety from ginsenoside
Rc and was classified as a family 51 glycoside hydrolase based on amino acid sequence analysis. Recombinant AbfA expressed
in Escherichia coli hydrolyzed non-reducing arabinofuranoside moieties with apparent K
m values of 0.53 ± 0.07 and 0.30 ± 0.07 mM and V
max values of 27.1 ± 1.7 and 49.6 ± 4.1 μmol min−1 mg−1 of protein for p-nitrophenyl-α-l-arabinofuranoside and ginsenoside Rc, respectively. The enzyme exhibited preferential substrate specificity of the exo-type
mode of action towards polyarabinosides or oligoarabinosides. AbfA demonstrated substrate-specific activity for the bioconversion
of ginsenosides, as it hydrolyzed only arabinofuranoside moieties from ginsenoside Rc and its derivatives, and not other sugar
groups. These results are the first report of a glycoside hydrolase family 51 α-l-arabinofuranosidase that can transform ginsenoside Rc to Rd. 相似文献
3.
Castor bean (Ricinus communis L.) plants were grown for 5–7 weeks in a controlled environment at 350 μl l−1 or 700 μl l−1 CO2. Carbon assimilation, assimilate deposition, dark respiration and assimilate mobilization were measured in leaves 2, 3 and
4 (counted from the base of the plant), and a balance sheet of carbon input and export was elaborated for both CO2 concentrations. Carbon dioxide assimilation was nearly constant over the illumination period, with only a slight depression
occurring at the end of the day in mature source leaves, not in young source leaves. Assimilation was ca. 40% higher at 700 μl l−1 than at 350 μl l−1 CO2. The source leaves increased steadily in weight per unit area during the first 3 weeks, more at 700 μl l−1 than at 350 μl l−1 CO2. On top of an irreversible weight increase, there was a large gain in dry weight during the day, which was reversed during
the night. This reversible weight gain was constant over the life time of the leaf and ca. 80% higher at 700 μl l−1 than at 350 μl l−1. Most of it was due to carbohydrates. The carbon content (as a percentage) was not altered by the CO2 treatment. Respiration was 25% higher in high-CO2 plants when based on leaf area, but the same when based on dry weight. The rate of carbon export via the phloem was the same
during the daytime in plants grown at 350 μl l−1 and 700 μl l−1 CO2. During the night the low-CO2 plants had only 50% of the daytime export rate, in contrast to the high-CO2 plants which maintained the high export rate. It was concluded that the phloem loading system is saturated during the daytime
in both CO2 regimes, whereas during the night the assimilate supply is reduced in plants in the normal CO2 concentration. Two-thirds of the carbon exported from the leaves was permanently incorporated as plant dry matter in the
residual plant parts. This “assimilation efficiency” was the same for both CO2 regimes. It is speculated that under 350 μl l−1 CO2 the growing Ricinus plant operates at sink limitation during the day and at source limitation during the night.
Received: 2 February 1999 / Accepted: 19 April 1999 相似文献
4.
Hogstrand C Ferguson EA Galvez F Shaw JR Webb NA Wood CM 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):461-573
Physiological effects of exposure to silver (AgCln
n−1; 250 μg Ag l−1 or 1000 μg Ag l−1) in seawater fish were investigated using adult starry flounders. While all fish survived up to 10 days in 250 μg Ag l−1, flounders started to die after day 4 in 1000 μg l−1. Dose-dependent increases in plasma and hepatic silver concentrations showed that silver was available for uptake. There
were minimal negative effects on hematological parameters, acid-base status, and blood gases. Plasma ammonia showed a pronounced
(three- to four-fold), but transient increase in flounders exposed to either 250 μg Ag l−1 or 1000 μg Ag l−1. Whole body ammonia and acid equivalent efflux measurements indicated that ammonia retention was due to a combination of
stimulated production and inhibited excretion. In the 1000-μg Ag l−1 group there was a similar transient increase in plasma [magnesium], which was restored by day 4. In contrast, plasma chloride
and sodium levels increased gradually towards the point when fish began to die. At 250 μg Ag l−1, the Na+/K+-ATPase activity of the intestine was unaffected but there was a two-fold increase in branchial Na+/K+-ATPase activity. The latter effect was interpreted as compensation for an elevated chloride and sodium load. The increases
in plasma chloride and sodium concentrations were accompanied by a marked suppression of drinking, thereby indicating that
acute silver toxicity was likely caused by a combination of elevated electrolyte concentrations and dehydration.
Accepted: 9 June 1999 相似文献
5.
The culture-medium composition was optimised, on a shake-flask scale, for simultaneous production of high activities of endoglucanase
and β-glucosidase by Thermoascus aurantiacus using statistical factorial designs. The optimised medium containing 40.2 g l−1 Solka Floc as the carbon source and 9 g l−1 soymeal as the organic nitrogen source yielded 1130 nkat ml−1 endoglucanase and 116 nkat ml−1β-glucosidase activities after 264 h as shake cultures. In addition, good levels of β-xylanase (3479 nkat ml−1) and low levels of filter-paper cellulase, β-xylosidase, α-l-arabinofuranosidase, β-mannanase, β-mannosidase, α-galactosidase and β-galactosidase were detected. Batch fermentation in
a 5-l laboratory fermentor using the optimised medium allowed the production of 940 nkat ml−1 endoglucanase and 102 nkat ml−1β-glucosidase in 192 h. Endoglucanase and β-glucosidase showed optimum activity at pH 4.5 and pH 5, respectively, and they
displayed optimum activity at 75 °C. Endoglucanase and β-glucosidase showed good stability at pH values 4–8 and 4–7, respectively,
after a prolonged incubation (48 h at 50 °C). Endoglucanase had half-lives of 98 h at 70 °C and 4.1 h at 75 °C, while β-glucosidase
had half-lives of 23.5 h at 70 °C and 1.7 h at 75 °C. Alkali-treated bagasse, steam-treated wheat straw, Solka floc and Sigmacell
50 were 66, 48.5, 33.5 and 14.4% hydrolysed by a crude enzyme complex of T. aurantiacus in 50 h.
Received: 12 November 1999 / Accepted: 14 November 1999 相似文献
6.
L. E. M. Nery M. A. da Silva A. M. Lauro Castrucci 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):624-630
The participation of cyclic nucleotide-dependent intracellular signalling pathways in the pigment translocation induced by
pigment-dispersing hormone (α -PDH) or pigment-concentrating hormone (PCH) was investigated in the erythrophores of the freshwater
shrimp, Macrobrachium potiuna. Cholera toxin, forskolin and dibutyryl cyclic adenosine 3′5′ monophosphate (dbcAMP) were able to induce pigment dispersion
with effective agonist concentrations for half maximal response (EC50 s) of 2.8 · 10−11 mol · l−1, 7.0 · 10−7 mol · l−1 and 3.3 · 10−7 mol · l−1, respectively. KT5720 (10−7 mol · l−1 and 10−6 mol · l−1) significantly shifted the dose response curve to α -PDH to the right. Dibutyryl cyclic guanosine 3′5′ monophosphate (dbcGMP)
was ineffective in inducing either pigment aggregation or dispersion. 2′5′ dideoxyadenosine (DDA) and SQ22,536 essentially
elicit a pigment-aggregating response in a dose-dependent manner. These effects were not due to the activation of purinergic
receptors, since concentrations up to 10−4 mol · l−1 of adenosine and adenosine triphosphate (ATP), and up to 10−3 mol · l−1 of uracil triphosphate (UTP) did not elicit pigment aggregation. In order to verify if PCH decreased cyclic adenosine 3′5′
monophosphate (cAMP) levels, cumulative dose-response curves to PCH in the absence and presence of pertussis toxin and 8-MOM-IBMX
were determined. However, neither drug significantly affected PCH activity. The levels of cAMP in the integument cells of
M. potiuna were significantly increased (P < 0.05) by α -PDH (10−7 mol · l−1) and forskolin (10−6 mol · l−1), but were not affected by PCH (10−7 or 10−10 mol · l−1). In conclusion, α -PDH seems to elicit pigment dispersion through the activation of a Gs-protein coupled receptor resulting
in cAMP increase and cAMP-dependent protein kinase (PKA) activation. Furthermore, although a decrease in cAMP was assumed
to be responsible in turn for the action of PCH, such a decrease could not be directly demonstrated.
Accepted: 11 August 1998 相似文献
7.
The effects of temperature (20, 24 and 28 °C) and irradiance (15 and 40 μmol photon m−2 s−1) on the nitrate and ammonium uptake rates of the subtropical red alga, Laurencia brongniartii, were investigated to prepare for tank cultivation. Nitrate uptake followed saturation kinetics and was faster at higher
irradiances and temperatures. In contrast, ammonium uptake was linear over the experimental range and was not affected by
an increase in temperature. A parameter, β, was calculated to compare substrate uptake rates of nitrate along the linear portion
of the uptake curve with that of ammonium. For nitrate, β was lower at low irradiance and higher at high irradiance (β = 0.007
± 0.003 and 0.030 ± 0.002 [μmol N L−1 (μmol N gww−1 d−)−1], respectively). However, β was 0.023 ± 0.002 and 0.034 ± 0.002 [μmol N L−1 (μmol N gww−1 d−1)−1] for ammonium, suggesting a preference for ammonium over nitrate. 相似文献
8.
The effects of elevated CO2 concentrations on stomatal movement, anion- and K+-channel activities were examined in guard cells from epidermal strips of Vicia faba. Membrane voltage was measured using intracellular, double-barrelled microelectrodes and ion-channel currents were recorded
under voltage clamp during exposure to media equilibrated with ambient (350 μl · l−1), 1000 μl · l−1 and 10 000 μl · l−1 CO2 in 20% O2 and 80% N2. The addition of 1000 μl · l−1 CO2 to the bathing solution caused stomata to close with a halftime of approx. 40 min, and with 10 000 μl · l−1 CO2 closure occurred with a similar time course. Under voltage clamp, exposure to 1000 μl · l−1 and 10 000 μl · l−1 CO2 resulted in a rapid increase (mean, 1.5 ± 0.2-fold, n = 8; range 1.3- to 2.5-fold) in the magnitude of current carried by outward-rectifying K+ channels (IK,out). The effect of CO2 on IK,out was essentially complete within 30 s and was independent of clamp voltage, but was associated with 25–40% (mean, 30 ± 4%)
decrease in the halftime for current activation. Exposure to CO2 also resulted in a four-fold increase in background current near the free-running membrane voltage, recorded as the instantaneous
current at the start of depolarising and hyperpolarising voltage steps, and a decrease in the magnitude of current carried
by inward-rectifying K+ channels (IK,in). The effect of CO2 on IK,in was generally slower than on IK,out; it was allied with a transient acceleration of its activation kinetics during the first 60–120 s of treatment; and it was
associated with a negative shift in the voltage-sensitivity of gating over a period of 3–5 min. Measurements carried out to
isolate the background currents attributable to anion channels (ICl), using tetraethylammonium chloride and CsCl, showed that CO2 also stimulated ICl and dramatically altered its relaxation kinetics. Within the timeframe of CO2 action at the membrane, no significant effect was observed on cytosolic pH, measured using the fluorescent dye 2′,7′-bis-(2-carboxyethyl)-5,6-carboxyflourescein
(BCECF) and ratio fluorescence microphotometry. These results are broadly consistent with the pattern of guard-cell response
to abscisic acid, and indicate that guard cells control both anion and K+ channels to achieve net solute loss in CO2. By contrast with the effects of abscisic acid, however, the data indicate that CO2 action is not mediated through changes in cytosolic pH and thereby implicate new and, as yet, unidentified pathway(s) for
channel regulation in the guard cells.
Received: 8 January 1997 / Accepted: 28 February 1997 相似文献
9.
Inhibition of Clostridium butyricum by 1,3-propanediol and diols during glycerol fermentation 总被引:3,自引:0,他引:3
1,3-Propanediol inhibition during glycerol fermentation to 1,3-propanediol by Clostridium butyricum CNCM 1211 has been studied. The initial concentration of the 1,3-propanediol affected the growth of the bacterium more than
the glycerol fermentation. μ
max was inversely proportional to the initial concentration of 1,3-propanediol (0–65 g l−1). For glycerol at 20 g l−1, the growth and fermentation were completely stopped at an initial 1,3-propanediol concentration of 65 g l−1. However, for an initial 1,3-propanediol concentration of 50 g l−1 and glycerol at 70 g l−1, the final concentration (initial and produced) of 1,3-propanediol reached 83.7 g l−1(1.1 M), with complete consumption of the glycerol. Therefore, during the fermentation, the strain tolerated a 1,3-propanediol
concentration higher than the initial inhibitory concentration (65 g l−1). The addition of 1,2-propanediol or 2,3-butanediol (50 g l−1) in the presence of glycerol (50–100 g l−1), showed that 2-diols reduced the μ
max in a similar way to 1,3-propanediol. The measurement of the osmotic pressure of glycerol solutions, diols and diol/glycerol
mixtures did not indicate any differences between these compounds. The hypothesis of diol inhibition was discussed. Taking
into account the strain tolerance of highly concentrated 1,3-propanediol during fermentation, the fermentation processes for
optimising production were considered.
Received: 15 November 1999 / Revision received: 1 February 2000 / Accepted: 4 February 2000 相似文献
10.
J. Gerritse G. Kloetstra A. Borger G. Dalstra A. Alphenaar J. C. Gottschal 《Applied microbiology and biotechnology》1997,48(4):553-562
Anaerobic tetrachloroethene(C2Cl4)-dechlorinating bacteria were enriched in slurries from chloroethene-contaminated soil. With methanol as electron donor,
C2Cl4 and trichloroethene (C2HCl3) were reductively dechlorinated to cis-1,2-dichloroethene (cis-C2H2Cl2), whereas, with l-lactate or formate, complete dechlorination of C2Cl4 via C2HCl3, cis-C2H2Cl2 and chloroethene (C2H3Cl) to ethene was obtained. In oxic soil slurries with methane as a substrate, complete co-metabolic degradation of cis-C2H2Cl2 was obtained, whereas C2HCl3 was partially degraded. With toluene or phenol both of the above were readily co-metabolized. Complete degradation of C2Cl4 was obtained in sequentially coupled anoxic and oxic chemostats, which were inoculated with the slurry enrichments. Apparent
steady states were obtained at various dilution rates (0.02–0.4 h−1) and influent C2Cl4-concentrations (100–1000 μM). In anoxic chemostats with a mixture␣of␣formate and glucose as the carbon and electron source,
C2Cl4 was transformed at high rates (above␣140 μmol l−1 h−1, corresponding to 145 nmol Cl− min−1 mg protein−1) into cis-C2H2Cl2 and C2H3Cl. Reductive dechlorination was not affected by addition of 5 mM sulphate, but strongly inhibited after addition of 5 mM
nitrate. Our results (high specific dechlorination rates and loss of dechlorination capacity in the absence of C2Cl4) suggest that C2Cl4-dechlorination in the anoxic chemostat was catalysed by specialized dechlorinating bacteria. The partially dechlorinated
intermediates, cis-C2H2Cl2 and C2H3Cl, were further degraded by aerobic phenol-metabolizing bacteria. The maximum capacity for chloroethene (the sum of tri-,
di- and monochloro derivatives removed) degradation in the oxic chemostat was 95 μmol l−1 h−1 (20 nmol min−1 mg protein−1), and that of the combined anoxic → oxic reactor system was 43.4 μmol l−1 h−1. This is significantly higher than reported thus far.
Received: 17 April 1997 / Received revision: 6 June 1997 / Accepted: 7 June 1997 相似文献
11.
During January 1989, phytoplankton biomass and species composition were studied in a north / south transect at the Weddell / Scotia
Confluence (47°W), between 57° and 61°30′S. Results showed a diatom bloom in the Scotia Sea (chlorophyll a 1.9 μg l−1, particulate organic carbon 239 μg l−1), dominated by Fragilariopsis cylindrus, Dactyliosolen antarcticus and Chaetoceros dichaeta. Low chlorophyll a / phaeopigments ratios (about 1.4) and silicate concentrations (15 μmol l−1) suggested that this was an advanced bloom phase, probably linked to high grazing pressure. Minimum chlorophyll a values of 0.1–0.2 μg l−1 and particulate organic carbon 46 μg l−1 were found at the Weddell / Scotia Front and in a subsurface layer of the Weddell Sea Water. In the southern part of the
transect (61°30′S), in the Weddell Sea, a second surface maximum was found (chlorophyll a 0.9 μg l−1, particulate organic carbon 120 μg l−1), but with a different species composition, with Cryptomonas sp. dominant. Our results show a succession within the diatom community in the Weddell / Scotia Confluence Waters when comparing
the three EPOS legs. In the Weddell Sea from spring to summer, nanoflagellates, with only a minor contribution from diatoms,
persist over a long period with little change in the community structure. We suggest that the frontal system, together with
the receding ice edge and the grazing pressure of either krill or protozooplankton, are mainly responsible for the phytoplankton
distribution patterns found.
Received: 3 July 1996 / Accepted: 3 November 1996 相似文献
12.
CO2 exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO2 concentration. The species had low CO2 exchange rates (maximum net photosynthesis: c. 0.45 μmol CO2 m−2 s−1; maximum dark respiration: c. 0.3 μmol CO2 m−2 s−1) and a very low light compensation point (7 μmol photons m−2 s−1 at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9–15°C. Photosynthetic activity was affected only
after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under
different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant.
Low photosynthetically active radiation (normally below 40 μmol photons m−2 s−1), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO2 assimilation were often measured in the absence of condensation phenomena.
Received: 22 September 1996 / Accepted: 26 April 1997 相似文献
13.
The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol 总被引:5,自引:0,他引:5
A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam
(PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR),
packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation
rate of phenol (q
s
max) decreased in the order: PBRC (598 mg l−1 h−1) > PBR (PU, 471 mg l−1 h−1) > PBR (SG, 394 mg l−1 h−1) > FBR (PU, 161 mg l−1 h−1) > FBR (SG, 91 mg l−1 h−1). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100–200 μm thick
layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed
to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized
in colloidal SiO2 enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic
packing.
Received: 2 December 1999 / Revision received: 2 February 2000 / Accepted: 4 February 2000 相似文献
14.
Wood CM Pärt P 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(3):175-184
The influence of a CO2/HCO−
3-buffered medium on intracellular pH regulation of gill pavement cells from freshwater rainbow trout was examined in monolayers
grown in primary culture on glass coverslips; intracellular pH (pHi) was monitored by continuous spectrofluorometric recording from cells loaded with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxy-fluoroscein. When cells in HEPES-buffered medium at normal pH=7.70 were transferred to normal
CO2/HCO−
3-buffered medium {P
CO2=3.71 mmHg, [HCO−
3]= 6.1 mmol l−1, extracellular pH (pHe)=7.70}, they exhibited a brief acidosis but subsequently regulated the same pHi (∼7.41) as in HEPES. Buffer capacity (β)
increased by the expected amount (5.5–8.0 slykes) based on intracellular [HCO−
3], and was unaffected by most drugs and treatments. However, after transfer to high P
CO2=11.15 mmHg, [HCO−
3]= 18.2 mmol l−1 at the same pHe=7.70, the final regulated pHi was elevated (∼7.53). The rate of correction of alkalosis caused by washout of this high P
CO2, high-HCO−
3 medium was unaffected by removal of extracellular Cl−. Removal of extracellular Na+ lowered resting pHi and greatly inhibited the rate of pHi recovery from acidosis. Bafilomycin A1 (3 μmol l−1) had no effect on these responses. However amiloride (0.2 mmol l−1) inhibited recovery from acidosis caused by washout of an ammonia prepulse, but did not affect resting pHi, the latter differing from the response in HEPES where amiloride also lowered resting pHi. Similarly 4-acetamido-4′- isothiocyanatostilbene-2,2′-disulfonic acid, sodium salt (0.1 mmol l−1) did not affect resting pHi but slowed the rate of recovery from acidosis, though to a lesser extent than amiloride. Removal of extracellular Cl− also slowed the rate of recovery but greatly increased β by an unknown mechanism; when this was taken into account, H+ extrusion rate was unaffected. These results are consistent with the presence of Na+-(HCO−
3)N co-transport and/or Na+-dependent HCO−
3/Cl− exchange, in addition to Na+/H+ exchange, as mechanisms contributing to “housekeeping” pHi regulation in gill cells in CO2/HCO−
3 media, whereas only Na+/H+ exchange is seen in HEPES. Both Na+-independent Cl−/HCO−
3 exchange and V-type H+-ATPase mechanisms appear to be absent from these cells cultured in isotonic media.
Accepted: 30 November 1999 相似文献
15.
A fluidized-bed reactor (FBR) was used to enrich an aerobic chlorophenol-degrading microbial culture. Long-term continuous-flow
operation with low effluent concentrations selected oligotrophic microorganisms producing good-quality effluent for pentachlorophenol(PCP)-contaminated
water. PCP biodegradation kinetics was studied using this FBR enrichment culture. The results from FBR batch experiments were
modeled using a modified Haldane equation, which resulted in the following kinetic constants: q
max = 0.41 mg PCP mg protein−1 day−1, K
S = 16 μg l−1, K
i = 5.3 mg l−1, and n = 3.5. These results show that the culture has a high affinity for PCP but is also inhibited by relatively low PCP concentrations
(above 1.1 mg PCP l−1). This enrichment culture was maintained over 1 year of continuous-flow operation with PCP as the sole source of carbon and
energy. During continuous-flow operation, effluent concentrations below 2 μg l−1 were achieved at 268 min hydraulic retention time (t
HR) and 2.5 mg PCP l−1 feed concentration. An increase in loading rate by decreasing t
HR did not significantly deteriorate the effluent quality until a t
HR decrease from 30 min to 21 min resulted in process failure. Recovery from process failure was slow. Decreasing the feed PCP
concentration and increasing t
HR resulted in an improved process recovery.
Received: 10 October 1996 / Received revision: 21 January 1997 / Accepted: 24 January 1997 相似文献
16.
In order to provide a better understanding of the dynamics of phytoplankton in the coastal regions of high latitudes, a study
was carried out to estimate the dynamics of carbon biomass of autotrophic and heterotrophic algal groups over the austral
spring-summer 1997/1998 period. At a fixed station located in the central basin (Paso Ancho) of the Straits of Magellan (53°S),
surface water samples were collected at least once a week from September 1997 (early spring) to March 1998 (late summer).
Quantitative analysis of biomass of phytoplankton was estimated from geometric volumes, using non-linear equations, and converted
to biomass. The pattern of chlorophyll a showed a strong temporal variability, with maximum values (mean 2.8 mg m−3) at the austral spring phytoplankton increase or bloom (October/November) and minimum values during early spring (September:
<0.5 mg m−3) and summer (January/March: 0.5–1.0 mg m−3). During the spring bloom, diatoms made up to 90% of the total phytoplankton carbon (0.01–189 μg l−1), followed by a maximum of thecate dinoflagellates (0.08–34 μg l−1), and sporadic high biomass of phytoflagellates during summer. Heterotrophic algal groups such as Gymnodinium and Gyrodinium spp. dominated (70%, in the 5- to 25-μm size range) shortly before the main diatom bloom, and small peaks were observed within
spring and early summer periods (0–0.4 μg l−1). Phytoflagellates dominated earlier (spring) with higher carbon biomass (8 μg l−1) and post-bloom periods (summer) when carbon biomass ranged between 1 and 4 μg l−1.
Accepted: 6 September 2000 相似文献
17.
S A Shaikh J M Khire M I Khan 《Journal of industrial microbiology & biotechnology》1997,19(4):239-245
A thermostable β-galactosidase was produced extracellularly by a thermophilic Rhizomucor sp, with maximum enzyme activity (0.21 U mg−1) after 4 days under submerged fermentation condition (SmF). Solid state fermentation (SSF) resulted in a nine-fold increase
in enzyme activity (2.04 U mg−1). The temperature range for production of the enzyme was 38–55°C with maximum activity at 45°C. The optimum pH and temperature
for the partially purified enzyme was 4.5 and 60°C, respectively. The enzyme retained its original activity on incubation
at 60°C up to 1 h. Divalent cations like Co2+, Mn2+, Fe2+ and Zn2+ had strong inhibitory effects on the enzyme activity. The K
m and V
max for p-nitrophenyl-β- D-galactopyranoside and o-nitrophenyl-β - D-galactopyranoside were 0.39 mM, 0.785 mM and 232.1 mmol min−1 mg−1 respectively. The K
m and V
max for the natural substrate lactose were 66.66 μM and 0.20 μ mol min−1 mg−1.
Received 10 March 1997/ Accepted in revised form 17 July 1997 相似文献
18.
Jennings BL Bell JD Hyodo S Toop T Donald JA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(5):557-567
This study investigated vasodilator mechanisms in the dorsal aorta of the elephant fish, Callorhinchus milii, using anatomical and physiological approaches. Nitric oxide synthase could only be located in the perivascular nerve fibres
and not the endothelium of the dorsal aorta, using NADPH histochemistry and immunohistochemistry. In vitro organ bath experiments
demonstrated that a NO/soluble guanylyl cyclase (GC) system appeared to be absent in the vascular smooth muscle, since the
NO donors SNP (10−4 mol l−1) and SIN-1 (10−5 mol l−1) were without effect. Nicotine (3 × 10−4 mol l−1) mediated a vasodilation that was not affected by ODQ (10−5 mol l−1), l-NNA (10−4 mol l−1), indomethacin (10−5 mol l−1), or removal of the endothelium. In contrast, the voltage-gated sodium channel inhibitor, tetrodotoxin (10−5 mol l−1), significantly decreased the dilation induced by nicotine, suggesting that it contained a neural component. Pre-incubation
of the dorsal aorta with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP8–37 (10−6 mol l−1) also caused a significant decrease in the nicotine-induced dilation. We propose that nicotine is mediating a neurally-derived
vasodilation in the dorsal aorta that is independent of NO, prostaglandins and the endothelium, and partly mediated by CGRP. 相似文献
19.
Chavan SP Lokhande VH Nitnaware KM Nikam TD 《Applied microbiology and biotechnology》2011,89(6):1701-1707
The present study examined the effects of plant growth hormones, incubation period, biotic (Trametes versicolor, Mucor sp., Penicillium notatum, Rhizopus stolonifer, and Fusarium oxysporum) and abiotic (NaCl, MgSO4, FeSO4, ZnSO4, and FeCl3) elicitors on cell growth and α-tocopherol and pigment (red and yellow) productions in Carthamus tinctorius cell cultures. The cell growth and α-tocopherol and pigment contents improved significantly on Murashige and Skoog (MS) liquid
medium containing 50.0 μM α-naphthalene acetic acid (NAA) and 2.5 μM 6-Benzyladenine (BA) at 28 days of incubation period.
Incorporation of T. versicolor (50 mg l−1) significantly enhanced the production of α-tocopherol (12.7-fold) and red pigment (4.24-fold). Similarly, supplementation
of 30 mg l−1
T. versicolor (7.54-fold) and 70 mg l−1
Mucor sp. (7.40-fold) significantly increased the production of yellow pigment. Among abiotic elicitors, NaCl (50–70 mg l−1) and MgSO4 (10–30 mg l−1) significantly improved production of α-tocopherol (1.24-fold) and red pigment (20-fold), whereas yellow pigment content
increased considerably by all the abiotic elicitor treatments. Taken together, the present study reports improved productions
of α-tocopherol and the pigment as a stress response of safflower cell cultures exposed to these elicitors. 相似文献
20.
Batch experiments were conducted to evaluate the biodegradation rates of limonene, α-pinene, γ-terpinene, terpinolene and
α-terpineol at 23 °C under aerobic conditions. Biodegradation was demonstrated by the depletion of monoterpene mass, CO2 production and a corresponding increase in biomass. Monoterpene degradation in liquid cultures devoid of soil followed Monod
kinetics. The maximum specific growth rate (μmax) was 0.02 h−1 and 0.06 h−1 and the half-velocity constant (K
s ) varied from 32 mg/l to 3 mg/l for the limonene and α-terpineol respectively. The recovery of monoterpenes by solvent extraction
from autoclaved and azide-amended soil-slurry samples decreased over time and ranged from 69% to 73% for 120 h of incubation
period. Although a significant fraction of monoterpene hydrocarbon could not be extracted, mineralization of these compounds
in the soil-slurry systems took place, as shown by CO2 production. The soil-normalized degradation rates for the hydrocarbon monoterpenes ranged from 0.6 μg g−1 h−1 to 2.1 μg g−1 h−1. A kinetic model – which combined monoterpene biodegradation in the liquid phase and net desorption – was developed and applied
to data obtained from soil-slurry assays.
Received: 10 September 1996 / Received revision: 16 December 1996 / Accepted: 10 January 1997 相似文献