Characterization of the nitrobenzene-degrading strain Pseudomonas sp. a3 and use of its immobilized cells in the treatment of mixed aromatics wastewater

A bacterial strain Pseudomonas sp. a3 capable of degrading nitrobenzene, phenol, aniline, and other aromatics was isolated and characterized. When nitrobenzene was degraded, the release of NH(4) (+) was detected, but not of NO(2) (-). This result implied that nitrobenzene might have a partial reductive metabolic pathway in strain a3. However, aniline appeared as one of the metabolites during the aerobic degradation of nitrobenzene. Moreover, the appearance of 2-aminophenol during aniline degradation by strain a3 indicated that novel initial reactions existed during the degradation of nitrobenzene and aniline by strain a3. Strain a3 was immobilized in the mixed carrier of polyvinyl alcohol and sodium alginate to improve its degrading efficiency. The optimal concentrations of polyvinyl alcohol and sodium alginate in the mixed carrier were 9 and 3 %, respectively. The immobilized cells had stable degradation activity and good mechanical properties in the recycling tests. The immobilized cells also exhibited higher tolerances in acidic (pH 4-5) and highly saline (10 % NaCl) environments than those of free cells. The biodegradation of nitrobenzene mixed with aniline and phenol using immobilized cells of Pseudomonas sp. a3 was also greatly improved compared with those of free cells. The immobilized cells could completely degrade 300 mg L(-1) nitrobenzene within 10 h with 150 mg L(-1) aniline and 150 mg L(-1) phenol. This result revealed that the immobilized cells of Pseudomonas sp. a3 could be a potential candidate for treating nitrobenzene wastewater mixed with other aromatics.     

Transformation of mono- and dichlorinated phenoxybenzoates by phenoxybenzoate-dioxygenase in pseudomonas pseudoalcaligenes POB310 and a modified diarylether-metabolizing bacterium

Pseudomonas pseudoalcaligenes POB310 contains genes that encode phenoxybenzoate dioxygenase. The enzyme transforms mono- and dichlorinated phenoxybenzoates to yield protocatechuate that is used as a growth substrate and chlorophenols that are nonmetabolizable. Mass spectral analysis of (18)O metabolites obtained from the protocatechuate 3,4-dioxygenase-deficient mutant, POB310-B1, suggested that the reaction mechanism is a regioselective angular dioxygenation. A cloning vector containing reaction relevant genes (pD30.9) was transferred into Pseudomonas sp. strain B13 containing a modified ortho-cleavage pathway for aromatic compounds. The resultant Pseudomonas sp. strain B13-D5 (pD30.9) completely metabolized 3-(4-chlorophenoxy)benzoate. During growth on 3-phenoxybenzoate, strain B13-D5 (pD30.9) (K(s) = 0.70+/-0.04 mM, mu(max) = 0.45+/-0.03 h(-1), t(d) = 1.5 h, Y = 0.45+/-0.03 g bio- mass x g substrate(-1)) was better adapted to low substrate concentrations, had a faster rate of growth, and a greater yield than POB310 (K(s) = 1.13+/-0.06 mM, mu(max) = 0.31+/-0.02 h(-1), t(d) = 2.2 h, Y = 0.39+/-0.02 g biomass. g substrate(-1)).     

Characterization of Two Novel Propachlor Degradation Pathways in Two Species of Soil Bacteria

Propachlor (2-chloro-N-isopropylacetanilide) is an acetamide herbicide used in preemergence. In this study, we isolated and characterized a soil bacterium, Acinetobacter strain BEM2, that was able to utilize this herbicide as the sole and limiting carbon source. Identification of the intermediates of propachlor degradation by this strain and characterization of new metabolites in the degradation of propachlor by a previously reported strain of Pseudomonas (PEM1) support two different propachlor degradation pathways. Washed-cell suspensions of strain PEM1 with propachlor accumulated N-isopropylacetanilide, acetanilide, acetamide, and catechol. Pseudomonas strain PEM1 grew on propachlor with a generation time of 3.4 h and a K_s of 0.17 ± 0.04 mM. Acinetobacter strain BEM2 grew on propachlor with a generation time of 3.1 h and a K_s of 0.3 ± 0.07 mM. Incubations with strain BEM2 resulted in accumulation of N-isopropylacetanilide, N-isopropylaniline, isopropylamine, and catechol. Both degradative pathways were inducible, and the principal product of the carbon atoms in the propachlor ring was carbon dioxide. These results and biodegradation experiments with the identified metabolites indicate that metabolism of propachlor by Pseudomonas sp. strain PEM1 proceeds through a different pathway from metabolism by Acinetobacter sp. strain BEM2.     

Continuous production of L-phenylalanine by transamination

L-Phenylalanine was produced continuously from L-as-partate and phenylpyruvate by transaminase from a newly screened Pseudomonas putida strain. The process was carried out with an isolated enzyme in homogeneous phase in an enzyme membrane reactor and with immobilized whole cells in a stirred tank reactor, respectively. Due to the difference in transport resistance, the productivity of the free enzyme in homogeneous phase (72 mmol/L h) was about 3 times higher than the productivity achieved using immobilized cells. However, a better stability of the biocatalyst was observed with immobilized cells.     

Improved degradation of organophosphorus nerve agents and p-nitrophenol by Pseudomonas putida JS444 with surface-expressed organophosphorus hydrolase

Pseudomonas putida JS444, isolated from p-nitrophenol (PNP) contaminated waste sites, was genetically engineered to simultaneously degrade organophosphorus pesticides (OP) and PNP. A surface anchor system derived from the ice-nucleation protein (INP) from Pseudomonas syringae was used to target the organophosphorus hydrolase (OPH) onto the surface of Pseudomonas putida JS444, reducing the potential substrate uptake limitation. Engineered cells were capable of targeting OPH onto the cell surface as demonstrated by western blotting, cell fractionation, and immunofluorescence microscopy. The engineered P. putida JS444 degraded organophosphates as well as PNP rapidly without instability problems associated with the engineered Moraxella sp. The initial hydrolysis rate was 7.90, 3.54, and 1.53 micromol/h/mg dry weight for paraoxon, parathion, and methyl parathion, respectively. The excellent stability in combination with the rapid degradation rate for organophosphates and PNP make this engineered strain an ideal biocatalyst for complete mineralization of organophosphates.     

Fluorene and phenanthrene uptake by Pseudomonas putida ATCC 17514: kinetics and physiological aspects

Pseudomonas putida ATCC 17514 was used as a model strain to investigate the characteristics of bacterial growth in the presence of solid fluorene and phenanthrene. Despite the lower water-solubility of phenanthrene, P. putida degraded this polycyclic aromatic hydrocarbon (PAH) at a maximum observed rate of 1.4 +/- 0.1 mg L(-1) h(-1), higher than the apparent degradation rate of fluorene, 0.8 +/- 0.07 mg L(-1) h(-1). The role of physiological processes on the biodegradation of these PAHs was analyzed and two different uptake strategies were identified. Zeta potential measurements revealed that phenanthrene-grown cells were slightly more negatively charged (-57.5 +/- 4.7 mV) than fluorene-grown cells (-51.6 +/- 4.9 mV), but much more negatively charged than glucose-grown cells (-26.8 +/- 3.3 mV), suggesting that the PAH substrate induced modifications on the physical properties of bacterial surfaces. Furthermore, protein-to-exopolysaccharide ratios detected during bacterial growth on phenanthrene were typical of biofilms developed under physicochemical stress conditions, caused by the presence of sparingly water-soluble chemicals as the sole carbon and energy source for growth, the maximum value for TP/EPS during growth on phenanthrene (1.9) being lower than the one obtained with fluorene (5.5). Finally, confocal laser microscopy observations using a gfp-labeled derivative strain revealed that, in the presence of phenanthrene, P. putida::gfp cells formed a biofilm on accessible crystal surfaces, whereas in the presence of fluorene the strain grew randomly between the crystal clusters. The results showed that P. putida was able to overcome the lower aqueous solubility of phenanthrene by adhering to the solid PAH throughout the production of extracellular polymeric substances, thus promoting the availability and uptake of such a hydrophobic compound.     

Physiology and taxonomy of thiobacillus strain TJ330, which oxidizes carbon disulphide (CS2)

A bacterium (strain TJ330) capable of using carbon disulphide (CS2) as its sole energy source in an acidic environment was isolated from a peat biofilter used in experiments to remove CS2 and hydrogen sulphide (H2S) from air. Its physiology and taxonomy are described here. The strain oxidized CS2, H2S and elemental sulphur to sulphate chemolithotrophically. The rate of sulphate production was highest at pH 2. The maximum growth rate constant (micromax) using CS2 as a substrate was 3.9 x 10(-2) h(-1) (generation time 18 h) and the Monod constant (Ks) was 0.97-2.6 micromol l(-1) CS2 (74-198 microg l(-1)), corresponding to an equilibrium with 15-40 ppm CS2 in the headspace. The optimum growth temperature using elemental sulphur as a substrate was 28 degrees C. The strain bears morphological and physiological similarities to Thiobacillus thiooxidans, but the latter is incapable of oxidizing CS2. The strain TJ330 (DSM 8985) showed only 44.2 + 11.8% DNA homology with the type strain T. thiooxidans ATCC 19377, while its homology with T. ferrooxidans ATCC 23270 was 17.1 + 3.4%. The strain TJ 330 represents a high-affinity bacterium which can effectively remove low CS2 concentrations in an acid environment. These properties can be utilized in biotechnological purification applications.     

Accelerated triacylglycerol turnover kinetics in hearts of diabetic rats include evidence for compartmented lipid storage

Triacylglycerol (TAG) storage and turnover rates in the intact, beating rat heart were determined for the first time using dynamic mode (13)C- NMR spectroscopy to elucidate profound differences between hearts from diabetic rats (DR, streptozotocin treatment) and normal rats (NR). The incorporation of [2,4,6,8,10,12,14,16-(13)C(8)]palmitate into the TAG pool was monitored in isolated hearts perfused with physiological (0.5 mM palmitate, 5 mM glucose) and elevated substrate levels (1.2 mM palmitate, 11 mM glucose) characteristic of the diabetic condition. Surprisingly, although the normal hearts were enriched at a near-linear profile for >or=2 h before exponential characterization, exponential enrichment of TAG in diabetic hearts reached steady state after only 45 min. Consequently, TAG turnover rate was determined by fitting an exponential model to enrichment data rather than conventional two-point linear analysis. In the high-substrate group, both turnover rate (DR 820+/- 330, NR 190 +/-150 nmol.min(-1).g(-1) dry wt; P< 0.001) and [TAG] content (DR 78 +/-10, NR 32+/- 4 micromol/g dry wt; P< 0.001) were greater in the diabetic group. At lower substrate concentrations, turnover was greater in diabetics (DR 530+/-300, NR 160+/- 30; P<0.05). However, this could not be explained by simple mass action, because [TAG] content was similar between groups [DR 34+/- 7, NR 39+/- 9 micromol/g dry wt; not significant (NS)]. Consistent with exponential enrichment data, (13)C fractional enrichment of TAG was lower in diabetics (low- substrate groups: DR 4+/-1%, NR 10+/- 4%, P<0.05; high-substrate groups: DR 8+/- 3%, NR 14+/- 9%, NS), thereby supporting earlier speculation that TAG is compartmentalized in the diabetic heart.     

Nonnutritive flow impairs uptake of fatty acid by white muscles of the perfused rat hindlimb

Triglyceride hydrolysis by the perfused rat hindlimb is enhanced with serotonin-induced nonnutritive flow (NNF) and may be due to the presence of nonnutritive route-associated connective tissue fat cells. Here, we assess whether NNF influences muscle uptake of 0.55 mM palmitate in the perfused hindlimb. Comparisons were made with insulin-mediated glucose uptake. NNF induced during 60 nM insulin infusion inhibited hindlimb oxygen uptake from 22.0 +/- 0.5 to 9.7 +/- 0.8 micromol x g(-1) x h(-1) (P < 0.001), 1-methylxanthine metabolism (indicator of nutritive flow) from 5.8 +/- 0.4 to 3.8 +/- 0.4 nmol x min(-1) x g(-1) (P = 0.004), glucose uptake from 29.2 +/- 1.7 to 23.1 +/- 1.8 micromol x g(-1) x h(-1) (P = 0.005) and muscle 2-deoxyglucose uptake from 82.1 +/- 4.6 to 41.6 +/- 6.7 micromol x g(-1) x h(-1) (P < 0.001). Palmitate uptake, unaffected by insulin alone, was inhibited by NNF in extensor digitorum longus, white gastrocnemius, and tibialis anterior muscles; average inhibition was from 13.9 +/- 1.2 to 6.9 +/- 1.4 micromol x g(-1) x h(-1) (P = 0.02). Thus NNF impairs both fatty acid and glucose uptake by muscle by restricting flow to myocytes but, as shown previously, favors triglyceride hydrolysis and uptake into nearby connective tissue fat cells. The findings have implications for lipid partitioning in limb muscles between myocytes and attendant adipocytes.     

Comparative cytotoxic and cytoprotective effects of taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA) in HepG2 cell line

This study was performed to compare the effects of two hydrophilic bile acids, taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA), on HepG2 cells. Cytotoxicity was evaluated at different times of exposure by incubating cells with increasing concentrations (50-800 micromol/l) of either bile acid, while their cytoprotective effect was tested in comparison with deoxycholic acid (DCA) (350 micromol/l and 750 micromol/l)-induced cytotoxicity. Culture media, harvested at the end of each incubation period, were analyzed to evaluate aspartate transaminase (AST), alanine transaminase and gamma-glutamyltranspeptidase release. In addition, the hemolytic effect of THDCA and TUDCA on human red blood cells was also determined. At 24 h of incubation neither THDCA nor TUDCA was cytotoxic at concentrations up to 200 and 400 micromol/l. At 800 micromol/l both THDCA and TUDCA induced a slight increase in AST release. At this concentration and with time of exposure prolonged up to 72 h, THDCA and TUDCA induced a progressive increase of AST release significantly (P<0.05) higher than that of controls being AST values for THDCA (2.97+/-0.88 time control value (tcv) at 48 h and 4.50+/-1.13 tcv at 72 h) significantly greater than those of TUDCA (1.50+/-0.20 tcv at 48 h and 1.80+/-0.43 tcv at 72 h) (P<0.01). In cytoprotection experiments, the addition of 50 micromol/l THDCA decreased only slightly (-5%) AST release induced by 350 micromol/l DCA, while the addition of 50 micromol/l TUDCA was significantly effective (-23%; P<0.05). Higher doses of THDCA or TUDCA did not reduce toxicity induced by 350 micromol/l DCA, but were much less toxic than an equimolar dose of DCA alone. At the concentration used in this experimental model neither THDCA nor TUDCA was hemolytic; however at a very high concentration (6 mmol/l) both bile acids induced 5-8% hemolysis. We conclude that bile acid molecules with a similar degree of hydrophilicity may show different cytotoxic and cytoprotective properties.     

Thiosulfate elimination and permeability in a sulfide-adapted marine invertebrate.

Oxidation of hydrogen sulfide to thiosulfate is one of the best-characterized mechanisms by which animals adapted to sulfide minimize its toxicity, but the mechanism of thiosulfate elimination in these animals has remained unclear. In this study, we examined the accumulation and elimination of thiosulfate in the sulfide-adapted marine worm Urechis caupo. The coelomic fluid of U. caupo exposed to 50-100 micromol L-1 sulfide in hypoxic seawater (Po2 ca. 10 kPa) accumulated (mean+/-SD) 132+/-41 micromol L-1 thiosulfate after 2 h, reaching 227+/-113 micromol L-1 after an additional 4 h in aerated, sulfide-free seawater. In whole-animal thiosulfate clearance studies, the rate of thiosulfate elimination from the coelomic fluid followed a single exponential time course with a half-life of 6 h. The thiosulfate permeability coefficient of isolated preparations mounted in diffusion chambers was 7.6x10-5+/-7. 7x10-5 cm s-1 for the hindgut and 5.5x10-7+/-2.7x10-7 cm s-1 for the body wall. These rates were independent of the direction of net efflux (mucosal-to-serosal or serosal-to-mucosal). Using a simple mathematical model of U. caupo that incorporates the thiosulfate permeability coefficients, the thiosulfate half-life was calculated to be 23 h without hindgut ventilation but less than 1 h with normal hindgut ventilation. Based on this information, we propose that passive thiosulfate diffusion across the hindgut is adequate to explain the observed rates of thiosulfate elimination.     

Dynamic or inert metabolism? Turnover of N‐acetyl aspartate and glutathione from d‐[1‐13C]glucose in the rat brain in vivo

The rate of (13)C-label incorporation into both aspartyl (NAA C3) and acetyl (NAA C6) groups of N-acetyl aspartate (NAA) was simultaneously measured in the rat brain in vivo for up to 19 h of [1-(13)C]glucose infusion (n = 8). Label incorporation was detected in NAA C6 approximately 1.5 h earlier than in NAA C3 because of the delayed labeling of the precursor of NAA C3, aspartate, compared to that of NAA C6, glucose. The time courses of NAA were fitted using a mathematical model assuming synthesis of NAA in one kinetic compartment with the respective precursor pools of aspartate and acetyl coenzyme A (acetyl-CoA). The turnover rates of NAA C6 and C3 were 0.7 +/- 0.1 and 0.6 +/- 0.1 micromol/(g h) with the time constants 14 +/- 2 and 13 +/- 2 h, respectively, with an estimated pool size of 8 micromol/g. The results suggest that complete label turnover of NAA from glucose occurs in approximately 70 h. Several hours after starting the glucose infusion, label incorporation into glutathione (GSH) was also detected. The turnover rate of GSH was 0.06 +/- 0.02 micromol/(g h) with a time constant of 13 +/- 2 h. The estimated pool size of GSH was 0.8 micromol/g, comparable to the cortical glutathione concentration. We conclude that NAA and GSH are completely turned over and that the metabolism is extremely slow (< 0.05% of the glucose metabolic rate).     

Biodegradation of tert-butyl alcohol and related xenobiotics by a methylotrophic bacterial isolate

A new aerobic bacterial strain, CIP 1-2052, isolated from an activated sludge sample, was able to use tert-butyl alcohol (TBA), a product of methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) degradation, as its sole carbon and energy source. Cobalt ions stimulated TBA mineralization. The maximum growth and TBA degradation rates were 0.032 +/- 0.004 h(-1) and 35.8 +/- 8.5 mg TBA x g(-1) (cell dry mass) per h, respectively. The growth yield on TBA was 0.54 +/- 0.02 g x g(-1). Strain CIP 1-2052 exhibited a particular substrate specificity towards alcohols. It degraded tertiary alcohols, TBA and tert-amyl alcohol (TAA), but neither their primary and secondary alcohol homologues, nor ethanol. However, one-carbon compounds, namely methanol and formate, were degraded by strain CIP 1-2052, showing the methylotrophic nature of this isolate. The properties of this new strain suggest that it could be used for bioremediation of contaminated aquifers.     

Use of stable emulsion to improve stability, activity, and enantioselectivity of lipase immobilized in a membrane reactor

The enantiocatalytic performance of immobilized lipase in an emulsion membrane reactor using stable emulsion prepared by membrane emulsification technology was studied. The production of optical pure (S)-naproxen from racemic naproxen methyl ester was used as a model reaction system. The O/W emulsion, containing the substrate in the organic phase, was fed to the enzyme membrane reactor from shell-to-lumen. The enzyme was immobilized in the sponge layer (shell side) of capillary polyamide membrane with 50 kDa cut-off. The aqueous phase was able to permeate through the membrane while the microemulsion was retained by the thin selective layer. Therefore, the substrate was kept in the enzyme-loaded membrane while the water-soluble product was continuously removed from the reaction site. The results show that lipase maintained stable activity during the entire operation time (more than 250 h), showing an enantiomeric excess (96 +/- 2%) comparable to the free enzyme (98 +/- 1%) and much higher compared to similar lipase-loaded membrane reactors used in two-separate phase systems (90%). The results demonstrate that immobilized enzymes can achieve high stability as well as high catalytic activity and enantioselectivity.     

Modeling reduction of uranium U(VI) under variable sulfate concentrations by sulfate-reducing bacteria

The kinetics for the reduction of sulfate alone and for concurrent uranium [U(VI)] and sulfate reduction, by mixed and pure cultures of sulfate-reducing bacteria (SRB) at 21 +/- 3 degrees C were studied. The mixed culture contained the SRB Desulfovibrio vulgaris along with a Clostridium sp. determined via 16S ribosomal DNA analysis. The pure culture was Desulfovibrio desulfuricans (ATCC 7757). A zero-order model best fit the data for the reduction of sulfate from 0.1 to 10 mM. A lag time occurred below cell concentrations of 0.1 mg (dry weight) of cells/ml. For the mixed culture, average values for the maximum specific reaction rate, V(max), ranged from 2.4 +/- 0.2 micromol of sulfate/mg (dry weight) of SRB. h(-1)) at 0.25 mM sulfate to 5.0 +/- 1.1 micromol of sulfate/mg (dry weight) of SRB. h(-1) at 10 mM sulfate (average cell concentration, 0.52 mg [dry weight]/ml). For the pure culture, V(max) was 1.6 +/- 0.2 micromol of sulfate/mg (dry weight) of SRB. h(-1) at 1 mM sulfate (0.29 mg [dry weight] of cells/ml). When both electron acceptors were present, sulfate reduction remained zero order for both cultures, while uranium reduction was first order, with rate constants of 0.071 +/- 0.003 mg (dry weight) of cells/ml. min(-1) for the mixed culture and 0.137 +/- 0.016 mg (dry weight) of cells/ml. min(-1) (U(0) = 1 mM) for the D. desulfuricans culture. Both cultures exhibited a faster rate of uranium reduction in the presence of sulfate and no lag time until the onset of U reduction in contrast to U alone. This kinetics information can be used to design an SRB-dominated biotreatment scheme for the removal of U(VI) from an aqueous source.     

Glyoxalase II in Saccharomyces cerevisiae: in situ kinetics using the 5,5'-dithiobis(2-nitrobenzoic acid) assay.

The determination of glyoxalase II (S-(2-hydroxyacyl)glutathione hydrolase, EC 3.1.2.6) activity is usually accomplished by monitoring the decrease of absorbance at 240 nm due to the hydrolysis of S-d-lactoylglutathione. However, it was not possible, using this assay, to detect any enzyme activity in situ, in Saccharomyces cerevisiae permeabilized cells. Glyoxalase II activity was then determined by following the formation of GSH at 412 nm using 5,5'-dithiobis(2-nitrobenzoic acid). Using this method we characterized the kinetics of glyoxalase II in situ using S-d-lactoylglutathione as substrate and compared the results with those obtained for cell-free extracts. The specific activity was found to be (4.08 +/- 0.12) x 10(-2) micromol min-1 mg-1 in permeabilized cells and (3.90 +/- 0.04) x 10(-2) micromol min1 mg-1 in cell-free extracts. Kinetic parameters were Km 0.36 +/- 0.09 mM and V (7.65 +/- 0.59) x 10(-4) mM min-1 for permeabilized cells and Km 0.15 +/- 0.10 mM and V (7.23 +/- 1.04) x 10(-4) mM min-1 for cell-free extracts. d-Lactate concentration was also determined and increased in a linear way with permeabilized cell concentration. gamma-Glutamyl transferase (EC 2.3.2.2), which also accepts S-d-lactoylglutathione as substrate and hence could interfere with glyoxalase II assays, was found to be absent in Saccharomyces cerevisiae permeabilized cells.     

Transformation of 2,2'-dichlorodiisopropyl ether in mixed and pure culture

An aerobic enrichment culture derived from a groundwater contaminated with organic and chloroorganic compounds was adapted to the transformation of 2,2'-dichlorodiisopropyl ether (DDE) in a continuous fixed-bed bioreactor. Continuous DDE removal efficiencies over 90% were achieved with a model water containing 3.3 mM methanol as co-substrate at DDE loading rates of up to 150 micromol l(-1) day(-1) with a hydraulic retention time of 24 h. In batch cultures, a stoichiometric release of 2 micromol chloride per micromol DDE transformed was observed. From the mixed culture, a strain was isolated that is able to grow on DDE as the sole energy and carbon source, tolerating DDE concentrations of up to 1 mM. Based on 16S rRNA sequencing, the strain is affiliated with the genus Rhodococcus.     

抗心律失常药RP62719对哺乳动物心室肌K+电流的抑制

使用全细胞膜片箝技术, 研究RP62719对内向整流钾电流(IK1)、瞬时外向钾电流(Ito)和延迟外向整流钾电流(IK)的作用, 并探讨其抗心律失常作用的机制.实验结果表明, 在指令电压为-100 mV时, RP62719可显著抑制豚鼠心室肌细胞IK1, 半数抑制浓度(IC50)为5.0±1.0 μmol/L.RP62719 10 μmol/L在+40 mV时对犬心室肌细胞Ito抑制率为84.0±4.4%, IC50为1.2±0.51 μmol/L.在+40 mV时, 50 μmol/L RP62719还可使豚鼠心室肌细胞IKstep 减少50.0±8.3%, IKtail减少56.0±4.9%, IC50分别为4.2±0.8 μmol/L和3.3±0.75 μmol/L.提示RP62719抗心律失常的离子机制与其对IK1、Ito及IK的抑制有关.     

Biological denitrification in a continuous-flow pilot bioreactor containing immobilized Pseudomonas butanovora cells

Pseudomonas butanovora, a novel denitrifying bacterium, was immobilized in composite beads and filled into a reactor system. The pilot bioreactor average denitrification activity was at ethanol-C:nitrate-N ratios of 3:1 and 1.5:1 0.88 and 0.54 kg NO3(-)-Nm(-3) d(-1), respectively. The denitrification was stable in spite of the relatively low hydraulic retention times of 2.47 and 3 h. The nitrate content of the influent was almost completely reduced at the first level of the bioreactor and the nitrite formed underwent reduction in the upper part of the reactor. The experimentally determined optimum ethanol-C:nitrate-N ratio was 1.41 +/- 0.41. In consequence of the aerobic conditions, the acetic acid produced by the oxygenation of ethanol was also detectable in the reactor effluent. The pH of the effluent (7.58) never exceeded the acceptable maximum (8.5). The nitrate removal efficiency of the cells was nearly 1000% at both C:N ratios, and the nitrite content of the effluent was around the prescribed limit throughout the continuous operation. This continuous-flow pilot bioreactor containing immobilized P. butanovora cells proved an efficient denitrification system with a relatively low retention time.