Degradation of <Emphasis Type="Italic">p</Emphasis>-Toluenesulfonate by Immobilized <Emphasis Type="Italic">Comamonas testosteroni</Emphasis> BS1310 (pBS1010) Cells

Parameters of degradation of p-toluenesulfonate (TS) by free and agar-embedded Comamonas testosteroni BS1310 (pBS1010) cells were determined. The maximum rate of TS degradation was 25% lower in immobilized than free cells, equaling 11 nmol min^?1 mg^?1 cells. Degradation of TS by both free and immobilized cells was associated with molecular oxygen consumption (molar ratio 1 : 2). In a plug-flow reactor, the degradation rate was 10.4 nmol min^?1 mg^?1 cells. The results can be applied to designing reactors for TS degradation in sewage and developing biosensors.     

Degradation of 2,4-dinitrophenol by free and immobilized cells of Rhodococcus erythropolis HL PM-1

Degradation of 2,4-dinitrophenol (2,4-DNP) by the cells of Rhodococcus erythropolis HL PM-1 was studied. The enzymes involved in 2,4-DNP degradation were inducible, and their resynthesis took place during the process. Cell immobilization by embedding into agar gels decreased the degrader activity. Maximum rates of 2,4-DNP degradation by free and immobilized cells were 10.0 and 5.4 nmol/min per mg cells, respectively. The concentration dependence of 2,4-DNP degradation was typical of substrate inhibition kinetics. The immobilized cells were used in a model reactor designed for 2,4-DNP biodegradation. Its maximum capacity was 0.45 nmol/min per mg cells at a volumetric flow rate of 20 h-1. The reactor operated for 14 days without losing capacity; its half-lifetime equaled 16 days.     

Degradation of 2,4-Dinitrophenol by Free and Immobilized Cells of Rhodococcus erythropolis HL PM-1

The degradation of 2,4-dinitrophenol (2,4-DNP) by Rhodococcus erythropolis HL PM-1 was studied. The enzymes involved in 2,4-DNP degradation were inducible, and their resynthesis took place during the process. Cell immobilization by embedding into agar gels decreased the degrader activity. The maximum rates of 2,4-DNP degradation by free and immobilized cells were 10.0 and 5.4 nmol/min per mg cells, respectively. The concentration dependence of 2,4-DNP degradation was typical of substrate inhibition kinetics. The immobilized cells were used in a model reactor designed for 2,4-DNP biodegradation. Its maximum capacity was 0.45 nmol/min per mg cells at a volumetric flow rate of 20 h^–1. The reactor operated for 14 days without losing capacity; its half-life equaled 16 days.     

Metabolic pathway engineering to enhance aerobic degradation of chlorinated ethenes and to reduce their toxicity by cloning a novel glutathione S-transferase, an evolved toluene o-monooxygenase, and gamma-glutamylcysteine synthetase

Aerobic, co-metabolic bioremediation of trichloroethylene (TCE), cis-1,2-dichloroethylene (cis-DCE) and other chlorinated ethenes with monooxygenase-expressing microorganisms is limited by the toxic epoxides produced as intermediates. A recombinant Escherichia coli strain less sensitive to the toxic effects of cis-DCE, TCE and trans-1,2-dichloroethylene (trans-DCE) degradation has been created by engineering a novel pathway consisting of eight genes including a DNA-shuffled toluene ortho-monooxygenase from Burkholderia cepacia G4 (TOM-Green), a newly discovered glutathione S-transferase (GST) from RhodococcusAD45 (IsoILR1), found to have activity towards epoxypropane and cis-DCE epoxide, and an overexpressed E. coli mutant gamma-glutamylcysteine synthetase (GSHI*). Along with IsoILR1, another new RhodococcusAD45 GST, IsoILR2, was cloned that lacks activity towards cis-DCE epoxide and differs from IsoILR1 by nine amino acids. The recombinant strain in which TOM-Green and IsoILR1 were co-expressed on separate plasmids degraded 1.9-fold more cis-DCE compared with a strain that lacked IsoILR1. In the presence of IsoILR1 and TOM-Green, the addition of GSH1* resulted in a sevenfold increase in the intracellular GSH concentration and a 3.5-fold improvement in the cis-DCE degradation rate based on chloride released (2.1 +/- 0.1 versus 0.6 +/- 0.1 nmol min(-1) mg(-1) protein at 540 microM), a 1.8-fold improvement in the trans-DCE degradation rate (1.29 +/- 0.03 versus 0.71 +/- 0.04 nmol x min(-1) mg(-1) protein at 345 microM) and a 1.7-fold improvement in the TCE degradation rate (6.8 +/- 0.24 versus 4.1 +/- 0.16 nmol x min(-1) mg(-1) protein at 339 microM). For cis-DCE degradation with TOM-Green (based on substrate depletion), V(max) was 27 nmol x min(-1) mg(-1) protein with both IsoILR1 and GSHI* expressed compared with V(max) = 10 nmol x min(-1) mg(-1) protein for the GST(-)GSHI*(-) strain. In addition, cells expressing IsoILR1 and GSHI* grew 78% faster in rich medium than a strain lacking these two heterologous genes.     

阿维菌素在土壤中的微生物降解研究

运用恒温培养法研究了阿维菌素在土壤中的降解动力学．结果表明,非生物+微生物降解、非生物降解及微生物降解的半衰期分别为34．8、277．3和49．9d,说明阿维菌素在土壤中的降解主要由微生物引起．从试验土壤中分离到1株高效降解阿维菌素的菌株,经16S rDNA鉴定为嗜麦芽寡养单胞菌(Stenotrophomonas maltrophilia)．从该降解菌中提取的粗酶液米氏常数(Km)为6．78nmol·ml^-1,最大降解速率为81．5nmol·min^-1·mg^-1。     

Biphenyl uptake by psychrotolerant Pseudomonas sp. strain Cam-1 and mesophilic Burkholderia sp. strain LB400

We investigated the uptake of biphenyl by the psychrotolerant, polychlorinated biphenyl (PCB)-degrader, Pseudomonas sp. strain Cam-1 and the mesophilic PCB-degrader, Burkholderia sp. strain LB400. The effects of growth substrates, metabolic inhibitors, and temperature on [14C]biphenyl uptake were studied. Biphenyl uptake by both strains was induced by growth on biphenyl, and was inhibited by dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP), which are metabolic uncouplers. The Vmax and Km for biphenyl uptake by Cam-1 at 22 degrees C were 5.4 +/- 1.7 nmol x min(-1) x (mg of cell protein)(-1) and 83.1 +/- 15.9 micromol x L(-1), respectively. The Vmax and Km for biphenyl uptake by LB400 at 22 degrees C were 3.2 +/- 0.3 nmol x min(-1) x (mg of cell protein(-1)) and 51.5 +/- 9.6 micromol x L(-1), respectively. At 15 degrees C, the maximum rate for biphenyl uptake by Cam-1 and LB400 was 3.1 +/- 0.3 nmol x min(-1) x (mg of cell protein)(-1) and 0.89 +/- 0.1 nmol x min(-1) x (mg of cell protein)(-1), respectively. Thus, the maximum rate for biphenyl uptake by Cam-1 at 15 degrees C was more than 3 times higher than that for LB400.     

Methyl mercury uptake by free and immobilized cyanobacterium

Methyl mercury uptake in free cells and different immobilizates of the cyanobacteriumNostoc calcicola has been examined. The general growth of the immobilized cyanobacterial cells could be negatively correlated with methyl mercury uptake. Alginate spheres proved most efficient in terms of uptake rate (0.48 nmol mg protein^–1 min^–1, 10 min) and total bioaccumulation (10.71 nmol mg protein^–1, 1 h) with a bioconcentration factor of 3.3×10³. Alginate biofilms showed a faster methyl mercury accumulation rate (0.83 nmol mg protein^–1 min^–1, 10 min) with a saturation of 10.28 nmol mg protein^–1 reached within only 30 min (bioconcentration factor, 3.1×10³). Foam preparations with a slow initial uptake approximated biofilms but were characterized by a lower bioconcentration factor (2.8×10³). Free cells, in comparison, maintained the initial slow rate of uptake (0.62 nmol mg protein^–1 min^–1, 10 min), saturating at 30 min (8.81 nmol mg protein^–1), and the resultant lowest bioconcentration factor (2.7×10³). Cell ageing (30 days) brought a drastic reduction (3-fold) in organomercury uptake by free cells while alginate spheres maintained the same potential. Foam preparations of the same age showed a significant improvement in methyl mercury uptake followed by only a marginal decline in alginate biofilms. Data are discussed in the light of the physiological efficiency and longevity of immobilized cells.     

Striatal dopamine-NMDA receptor interactions in the modulation of glutamate release in the substantia nigra pars reticulata in vivo: opposite role for D1 and D2 receptors

To investigate the antioxidative capacities of oligodendrocytes, rat brain cultures enriched for oligodendroglial cells were prepared and characterized. These cultures contained predominantly oligodendroglial cells as determined by immunocytochemical staining for the markers galactocerebroside and myelin basic protein. If oligodendroglial cultures were exposed to exogenous hydrogen peroxide (100 micro m), the peroxide disappeared from the incubation medium following first order kinetics with a half-time of approximately 18 min. Normalization of the disposal rate to the protein content of the cultures by calculation of the specific hydrogen peroxide detoxification rate constant revealed that the cells in oligodendroglial cultures have a 60% to 120% higher specific capacity to dispose of hydrogen peroxide than cultures enriched for astroglial cells, microglial cells or neurones. Oligodendroglial cultures contained specific activities of 133.5 +/- 30.4 nmol x min(-1) x mg protein(-1) and 27.5 +/- 5.4 nmol x min(-1) x mg protein(-1) of glutathione peroxidase and glutathione reductase, respectively. The specific rate constant of catalase in these cultures was 1.61 +/- 0.54 min(-1) x mg protein(-1). Comparison with data obtained by identical methods for cultures of astroglial cells, microglial cells and neurones revealed that all three of the enzymes which are involved in hydrogen peroxide disposal were present in oligodendroglial cultures in the highest specific activities. These results demonstrate that oligodendroglial cells in culture have a prominent machinery for the disposal of hydrogen peroxide, which is likely to support the protection of these cells in brain against peroxides when produced by these or by surrounding brain cells.     

Uptake and Metabolism of Serotonin by Ependymal Primary Cultures

Serotonin uptake and metabolism was studied in ependymal primary cultures. Serotonin uptake was facilitated by two different systems, one of which was the neuronal serotonin transporter SERT, exhibiting a Vmax value of 3.8+/-0.1 pmol x min(-1) x (mg protein)(-1) and an apparent Michaelis-Menten constant of 0.41+/-0.03 microM. The main product of metabolism was 5-hydroxyindole acetic acid, which resulted from the action of monoamine oxidase A. This enzyme showed a maximal rate of 0.85+/-0.02 nmol x min(-1) x (mg protein)(-1) and a Michaelis-Menten constant of 78+/-5 microM. Ependymal cells were able to dispose of extracellular serotonin with initial rates of approximately 600 pmol x min(-1) x (mg protein)(-1) and of 4 pmol x min(-1) x (mg protein)(-1) when challenged with 500 microM and 1 microM extracellular serotonin, respectively. Ependymal cells are concluded to facilitate the "sink" action of the CSF by removing waste compounds upon passing of the fluid from the parenchymal extracellular space into the ventricular system.     

Investigations into enzymes of nitrogen metabolism of the ectomycorrhizal basidiomycete, Suillus bovinus

Axenic mycelia of the ectomycorrhizal basidiomycete, Suillus bovinus, were grown in liquid media under continuous aeration with compressed air at 25 degrees C in darkness. Provided with glucose as the only carbohydrate source, they produced similar amounts of dry weight with ammonia, with nitrate or with alanine, 60-80% more with glutamate or glutamine, but about 35% less with urea as the respectively only exogenous nitrogen source. In crude extracts of cells from NH4(+)-cultures, NADH-dependent glutamate dehydrogenase exhibited high aminating (688 nmol x mg protein(-1) x min(-1)) and low deaminating (21 nmol x mg protein(-1) x min(-1)) activities. Its Km-values for 2-oxoglutarate and for glutamate were 1.43 mM and 23.99 mM, respectively. pH-optimum for amination was about 7.2, that for deamination about 9.3. Glutamine synthetase activity was comparatively low (59 nmol x mg protein(-1) x min(-1)). Its affinity for glutamate was poor (Km = 23.7 mM), while that for the NH4+ replacing NH2OH was high (Km = 0.19 mM). pH-optimum was found at 7.0. Glutamate synthase (= GOGAT) revealed similar low activity (62 nmol x mg protein(-1) x min(-1)), Km-values for glutamine and for 2-oxoglutarate of 2.82 mM and 0.28 mM, respectively, and pH-optimum around 8.0. Aspartate transaminase (= GOT) exhibited similar affinities for aspartate (Km = 2.55 mM) and for glutamate (Km = 3.13 mM), but clearly different Km-values for 2-oxoglutarate (1.46 mM) and for oxaloacetate (0.13 mM). Activity at optimum pH of about 8.0 was 506 nmol x mg protein(-1) x min(-1) for aspartate conversion, but only 39 nmol x mg protein(-1) x min(-1) at optimum pH of about 7.0 for glutamate conversion. Activity (599 nmol x mg protein(-1) x min(-1)), substrate affinities (Km for alanine = 6.30 mM, for 2-oxoglutarate = 0.45 mM) and pH-optimum (6.5-7.5) proved alanine transaminase (= GPT) also important in distribution of intracellular nitrogen. There was comparatively low activity of the obviously constitutive enzyme, urease, (42 nmol x mg protein(-1) x min(-1)) whose substrate affinity was rather high (Km = 0.56 mM). Nitrate reductase proved substrate induced; activity could only be measured after exposure of the mycelia to exogenous nitrate. Routes of entry of exogenous nitrogen and tentative significance of the various enzymes in cell metabolism are discussed.     

Degradation of methyl tert-butyl ether by gel immobilized Methylibium petroleiphilum PM1

Cells of Methylibium petroleiphilum PM1 were immobilized in gel beads to degrade methyl tert-butyl ether (MTBE). Calcium alginate, agar, polyacrylamide and polyvinvyl alcohol were screened as suitable immobilization matrices, with calcium alginate demonstrating the fastest MTBE-degradation rate. The rate was accelerated by 1.8-fold when the beads had been treated in physiological saline for 24h at 28 degrees C. MTBE degradation in mineral salts medium (MSM) was accompanied by the increase of biomass. The half-life of MTBE-degradation activity for the encapsulated cells stored at 28 degrees C was about 120 h, which was obviously longer than that of free cells (approximately 36 h). Efficient reusability of the beads up to 30 batches was achieved in poor nutrition solution as compared to only 6 batches in MSM. The immobilized cells could be operated in a packed-bed reactor for degradation of 10 mg L(-1) MTBE in groundwater with more than 99% removal efficiency at hydraulic retention time of 20 min. These results suggested that immobilized cells of PM1 in bioreactor might be applicable to a groundwater treatment system for the removal of MTBE.     

Preeclampsia-associated decrease of potential collagenolytic and gelatinolytic activities in the wall of the umbilical cord vein.

Preeclampsia is the most common pathological syndrome associated with pregnancy. It is accompanied by remodelling of the extracellular matrix of the umbilical cord. A decrease of collagen content in the umbilical cord vein was described. This decrease may result from reduced collagen biosynthesis or enhanced collagen degradation. It was decided to evaluate whether or not this phenomenon is associated with alterations in the activities of collagenolytic, gelatinolytic and non-specific proteolytic enzymes that may be involved in collagen degradation, as well as the activity of prolidase which provides proline as a substrate for collagen biosynthesis. Studies were performed on the umbilical cord veins of newborns delivered by healthy mothers and those with preeclampsia. The control vein extract, activated with trypsin, degraded reconstituted collagen fibres (64.4+/-2.9 nmol Hyp x mg(-1) protein), whereas the preeclamptic material demonstrated only a trace activity. The venous wall extract contained a latent form of gelatinase that might have been activated by trypsin and 4-aminophenylmercuric acetate. A decrease in the gelatinolytic and proteolytic activities of preeclamptic vein extract at neutral pH was found. Prolidase activity was almost 3-fold lower in the preeclamptic extract (240.6+/-29.3 nmol Pro x min(-1) x mg(-1) protein) in comparison to the control (608.2+/-63.7 nmol Pro x min(-1) x mg(-1)protein). It was concluded that the umbilical cord vein contains a latent form of gelatinase A. The decrease in prolidase activity may reduce collagen biosynthesis, resulting in a decrease of this protein in the preeclamptic umbilical cord vein.     

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.     

Immobilization of S-methyltransferase

S-methyltransferase was solubilized from pig liver microsomes by treatment with N-dodecyl-N,N-dimethyl-3-ammonio-1-sulfonate (Zwittergent). The soluble enzyme was immobilized by covalent binding to agarose and by copolymerization with acrylamide. The specific activity for the agarose-bound enzyme towards the substrate ethane thiol was 0.87 nmol/min/mg and for the acrylamide-bound enzyme 0.55 nmol/min/mg. The specific activity of the soluble enzyme was found to vary with increasing chain length of the substrate molecules from 0.5 nmol/min/mg for methane thiol (C1) to 6.3 nmol/min/mg for n-heptane thiol (C7). After binding of the enzyme to agarose beads, the increase in specific activity towards substrates with increasing chain length was no longer detectable. Instead, a relatively constant specific activity of 1.1 nmol/min/mg was observed for the whole range of substrates tested from C1 to C7. The stability of the agarose immobilized enzyme at -20 degrees C is twice as good as the soluble enzyme. The acrylamide immobilized enzyme is less stable than the soluble enzyme.     

Presence of ectonucleotidases in cultured chromaffin cells: hydrolysis of extracellular adenine nucleotides

The granular ATP released from chromaffin cells during the secretory response can be hydrolyzed by ectonucleotidases that are present in the plasma membrane of these cells. The ecto-ATPase activity showed a Km for ATP of 250 +/- 18 microM and a VMAX value of 167 +/- 25 nmol/10(6) cells x min (1.67 mumol/mg protein x min) for cultured chromaffin cells, while the ecto-ADPase activity showed a Km value for ADP of 375 +/- 40 microM and a VMAX of 125 +/- 20 nmol/10(6) cells x min (1.25 mumol/mg protein x min). The ecto 5'-nucleotidase activity of cultured chromaffin cells was more specific for the purine nucleotides, AMP and IMP, than for the pirimidine nucleotides, CMP and TMP. The Km for AMP was 55 +/- 5 microM and the VMAX value was 4.3 +/- 0.8 nmol/10(6) cells x min (43 nmol/mg protein x min). The nonhydrolyzable analogs of ADP and ATP, alpha, beta-methylene-adenosine 5'-diphosphate and adenylyl-(beta, gamma-methylene)-diphosphonate were good inhibitors of ecto 5'-nucleotidase activity, the KI values being 73.3 +/- 3.5 nM and 193 +/- 29 nM, respectively. The phosphatidylinositol-specific phospholipase C released the ecto-5'-nucleotidase from the chromaffin cells in culture, thus suggesting an anchorage through phosphatidylinositol to plasma membranes. The presence of ectonucleotidases in chromaffin cells may permit the recycling of the extracellular ATP exocytotically released from these neural cells.     

Degradation kinetics of phenol by immobilized cells of Candida tropicalis in a fluidized bed reactor

Degradation kinetics of phenol by free and agar-entrapped cells of Candida tropicalis was studied in batch cultures. The initial phenol degradation rate achieved with free cells was higher than that obtained with immobilized cells, when phenol concentrations up to 1000 mg l^–1 were used. However, at higher phenol concentrations, the behaviour was quite different. The initial degradation rate of the immobilized yeast cells was about 10 times higher than that of the free cells, at a phenol concentration of 3500 mg l^–1. The semicontinuous and continuous degradation of phenol by immobilized yeast cells was also investigated in a multi-stage fluidized bed reactor. The highest phenol removal efficiencies and degradation rates as well as the lowest values of residual phenol and chemical oxygen demand were obtained in the semicontinuous culture when phenol concentrations up to 1560 mg l^–1 were used.     

Uptake of 4-toluene sulfonate by Comamonas testosteroni T-2.

The mechanism of transport of the xenobiotic 4-toluene sulfonate (TS) in Comamonas testosteroni T-2 was investigated. Rapid uptake of TS was observed only in cells grown with TS or 4-methylbenzoate as a carbon and energy source. Initial uptake rates under aerobic conditions showed substrate saturation kinetics, with an apparent affinity constant (Kt) of 88 microM and a maximal velocity (Vmax) of 26.5 nmol/min/mg of protein. Uptake of TS was inhibited completely by uncouplers and only marginally by ATPase inhibitors and the phosphate analogs arsenate and vanadate. TS uptake was also studied under anaerobic conditions, which prevented intracellular TS metabolism. TS was accumulated under anaerobic conditions in TS-grown cells upon imposition of an artificial transmembrane pH gradient (delta pH, inside alkaline). Uptake of TS was inhibited by structurally related methylated and chlorinated benzenesulfonates and benzoates. The results provide evidence that the first step in the degradation of TS by C. testosteroni T-2 is uptake by an inducible secondary proton symport system.     

Capacity of enzymes of the euphorbiacea Aleurites montana involved in CO2-fixation, compared to plants having C3-, C4- and Crassulacean acid metabolism

Capacities of phosphoenolpyruvate carboxylase (PEP-Co), ribulose bisphosphate carboxylase (Rubisco), NADP+ malic enzyme (ME) and of malate dehydrogenase (MDH) were measured in the Euphorbiacea Aleurites montana, grown under 700 ppm CO2 for four weeks prior to enzyme extraction. For comparison Bryophyllum daigremontiana (CAM). Saccharum officinarum (C4) and Capsicum frutescens (C3) were treated in the same way. PEP-Co capacity of Aleurites was in the range of 12-, that of Capsicum approx. 26 nmol x min(-1) x mg protein(-1), without significant influence of the light period or CO2-treatment. In contrast, the activity of the enzyme from Saccharum was, depending on the duration of light, 160- respectively 96 times higher than that of the tung-oil tree. In Bryophyllum a rather low activity in the morning was increased during the day to approx. 230 nmol x min(-1) x mg protein(-1) in plants grown in the greenhouse and to approx. 115 nmol x min(-1) x mg protein(-1) in those from the growth chamber. Malate was hardly detectable in extracts of Aleurites, whereas it was high in Bryophyllum, depending on the light period. The ratio of average PEP-Co to Rub-Co capacity was high for the CAM-plant (20:1), somewhat lower for sugar cane (10:1), but almost at equality for Aleurites (0.9:1) and chilli (0.8:1). For the NADP+ malic enzyme, low capacity (20 to 28 nmol x min(-1) x mg protein(-1)) was found for Aleurites and for Capsicum, whereas it was 10 to 17 times higher in Saccharum. In Bryophyllum, the activity was up to 80 nmol x min(-1) x mg protein, dependent on light period. MDH capacity was extremely high in all plants investigated. Highest rates (10-20 micromol x min(-1) x mg protein(-1)), were obtained for Bryophyllum, followed by sugar cane and Capsicum with 5-8 micromol x min(-1) x mg protein(-1). Again, the lowest capacity was found in extracts of Aleurites with approx. 1.3 to 1.6 micromol x min(-1) x m protein(-1). Thus, in Aleurites montana no indication for C4- or Crassulacean acid metabolism was obtained. Therefore, the earlier observed very efficient uptake of CO2 cannot be explained by a high expression of the PEP-Co protein, known to occur in CAM- and C4-plants.     

Biodegradation of benzene,toluene, ethylbenzene,and o-xylene by a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in a fibrous-bed bioreactor

A fibrous-bed bioreactor containing the coculture of Pseudomonas putida and P. fluorescens immobilized in a fibrous matrix was developed to degrade benzene (B), toluene (T), ethylbenzene (E), and o-xylene (X) in synthetic waste streams. The kinetics of BTEX biodegradation by immobilized cells adapted in the fibrous-bed bioreactor and free cells grown in serum bottles were studied. In general, the BTEX biodegradation rate increased with increasing substrate concentration and then decreased after reaching a maximum, showing substrate-inhibition kinetics. However, for immobilized cells, the degradation rate was much higher than that of free cells. Compared to free cells, immobilized cells in the bioreactor tolerated higher concentrations (>1000 mg l⁻¹) of benzene and toluene, and gave at least 16-fold higher degradation rates for benzene, ethylbenzene, and o-xylene, and a 9-fold higher degradation rate for toluene. Complete and simultaneous degradation of BTEX mixture was achieved in the bioreactor under hypoxic conditions. Cells in the bioreactor were relatively insensitive to benzene toxicity; this insensitivity was attributed to adaptation of the cells in the bioreactor. Compared to the original seeding culture, the adapted cells from the fibrous-bed bioreactor had higher specific growth rate, benzene degradation rate, and cell yield when the benzene concentration was higher than 100 mg l⁻¹. Cells in the fibrous bed had a long, slim morphology, which is different from the normal short-rod shape found for suspended cells in solution.     

Copper uptake by free and immobilized cyanobacterium

Abstract Copper uptake in free and immobilized cells of the cyanobacterium Nostoc calcicola has been examined. The immobilized cells invariably maintained a higher profile of Cu intake rate (12.7 nmol mg⁻¹ protein min⁻¹) over the free cells (6.0 nmol mg⁻¹ protein min⁻¹). The total Cu uptake in immobilized cells was almost two and a half-times more than their free cell counterpart under identical experimental conditions. Also, the immobilized cells showed a stronger positive correlation between Cu adsorption and uptake. The results have been discussed in terms of improved metabolic efficiency of immobilized cells.