Effect of iron concentration on hydrogen fermentation

The effect of the iron concentration in the external environment on hydrogen production was studied using sucrose solution and the mixed microorganisms from a soybean-meal silo. The iron concentration ranged from 0 to 4000 mgFeCl₂ l⁻¹. The temperature was maintained at 37°C. The maximum specific hydrogen production rate was found to be 24.0 mlg⁻¹ VSSh⁻¹ at 4000 mgFeCl₂ l⁻¹. The specific production rate of butyrate increased with increasing iron concentration from 0 to 20 mgFeCl₂ l⁻¹, and decreased with increasing iron concentration from 20 to 4000 mgFeCl₂ l⁻¹. The maximum specific production rates of ethanol (682 mgg⁻¹ VSSh⁻¹) and butanol (47.0 mgg⁻¹ VSSh⁻¹) were obtained at iron concentrations of 5 and 3 mgFeCl₂ l⁻¹, respectively. The maximum hydrogen production yield of 131.9 mlg⁻¹ sucrose was obtained at the iron concentration of 800 mgFeCl₂ l⁻¹. The maximum yields of acetate (389.3 mgg⁻¹ sucrose), propionate (37.8 mgg⁻¹ sucrose), and butyrate (196.5 mg g⁻¹ sucros) were obtained at iron concentrations of 3, 200 and 200 mgFeCl₂ l⁻¹, respectively. The sucrose degradation efficiencies were close to 1.0 when iron concentrations were between 200 and 800 mgFeCl₂ l⁻¹. The maximum biomass production yield was 0.283 gVSSg⁻¹ sucrose at an iron concentration of 3000 mgFeCl₂ l⁻¹.     

Perchlorate and nitrate reductase activity in the perchlorate-respiring bacterium perclace

The perchlorate (ClO₄⁻)-respiring organism, strain perc1ace, can grow using nitrate (NO₃⁻) as a terminal electron acceptor. In resting cell suspensions, NO₃⁻ grown cells reduced ClO₄⁻, and ClO₄⁻ grown cells reduced NO₃⁻. Activity assays showed that nitrate reductase (NR) activity was 1.31 μmol min⁻¹ (mg protein)⁻¹ in ClO₄⁻ grown cells, and perchlorate reductase (PR) activity was 4.24 μmol min⁻¹ (mg protein)⁻¹ in NO₃⁻ grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 μmol min⁻¹ (mg protein)⁻¹. The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO₃⁻ and ClO₄⁻.     

Protoplasts from pectinolytic fungi: isolation, regeneration and pectinolytic enzyme production

S. Solís, M.E. FLORES AND C. HUITRON. 1996. Protoplast release in pectinolytic strain mutants of Aspergillus sp. CH-Y-1043 (A13) and Aspergillus flavipes ATCC-16795 (F7) is described. Optimum yield of protoplasts A13 was obtained in a lapse of 1 h when commercially lytic enzymes of Trichoderma harzanium (2 mg ml⁻¹) were added in 0.05 mol 1⁻¹ citrate-phosphate buffer pH 5.0 containing 0.7 mol 1⁻¹ KCl and 10 mg ml⁻¹ BSA. Best results in F7 were obtained when the protoplasting system of A13 was supplemented with 10 mg ml⁻¹ Aureobasidium sp. lytic enzymes. Isolated protoplasts in A13 and F7 were capable of a high regeneration frequency of 87% and 53% when 0.7 mol 1⁻¹ KCl and sorbitol were used as osmotic stabilizers. Endo-P, Exo-P and pectin lyase production were not modified during the process of regeneration.     

Nitrite effect on nitrous oxide emission from denitrifying activated sludge

Laboratory-scale experiments were conducted to examine the N₂O emission during the denitrification process. For each of the 6 runs carried out, synthetic effluent was fed in a 10 l batch mixed liquor to investigate the effect of nitrite on N₂O emission and Helium was continuously bubbled through the reactor at constant rate (0.12 l/min) to favour N₂O transfer and detection. An increasing COD/NO₃⁻-N influent ratio from 3 to 7 was firstly applied (runs 1–3). Secondly, NO₂⁻ pulse additions were performed during run 4 and 5 (10 and 20 mg N/l, respectively). Finally, the reactor was fed with influent containing both NO₂⁻ and NO₃⁻. We showed that N₂O emission was detected shortly after NO₂⁻ accumulation, few minutes after the substrate feeding. The highest emission occurred at the lower COD/NO₃⁻-N ratio (=3) and at the higher NO₂⁻ addition (20 mg N/l). In addition, the higher nitrogen conversion to N₂O gas (14.4%) was obtained with an influent containing initially both NO₂⁻ and NO₃⁻. Our results suggest a direct effect of the NO₂⁻ concentration on the N₂O emission. We have also confirmed the inhibitory effect of NO₂⁻ concentration on N₂O reduction.     

嗜麦芽寡养单胞菌PX1的降解芘特性及定殖效能

为丰富多环芳烃降解菌菌种库、降低农作物的污染风险,本研究对一株可高效降解多环芳烃(PAHs)的植物内生菌进行筛选鉴定,并初步探究其降解途径以及定殖效能。结果表明: 菌株PX1为嗜麦芽寡养单胞菌。该菌株对多环芳烃的降解具有广谱性,7 d几乎可彻底降解PAH无机盐培养基中的萘,在分别含有50.0 mg·L^-1菲、20.0 mg·L^-1芘、20.0 mg·L^-1荧蒽和10.0 mg·L^-1苯并[a]芘的培养体系中,对菲、芘、荧蒽、苯并[a]芘的降解率分别为72.6%、50.7%、31.9%和12.9%。选取芘作为PAHs模型研究菌株PX1的降解特性。酶活性试验表明,芘可诱导菌株PX1体内邻苯二甲酸双加氧酶、邻苯二酚-1,2-双加氧酶和邻苯二酚-2,3-双加氧酶的活性。在芘降解过程中检测到4,5-环氧化芘、4,5-二羟基芘、龙胆酸/原茶儿酸、水杨酸、顺-己二烯二酸/2-羟粘糠酸半醛、顺-2′-羧基苯丙酮酸、1-羟基-2-萘甲酸、水杨醛等中间产物。浸种定殖试验表明,菌株PX1可高效定殖到空心菜和小麦体内,显著促进空心菜和小麦生长,并能够将空心菜、小麦体内及其生长基质中的芘浓度分别降低29.8%～50.7%、52.4%～67.1%和8.0%～15.3%。表明菌株PX1主要通过“水杨酸途径”和“邻苯二甲酸途径”降解芘,且可以定殖到植物体内,促进植物生长。     

Aerobic biological treatment of black table olive washing wastewaters: effect of an ozonation stage

The present work is a study of oxidative degradation of the organic matter present in the washing waters from the black table olive industry. Pollutant organic matter reduction was studied by an aerobic biological process and by the combination of two successive steps: ozonation pretreatment followed by aerobic biological degradation. In the single aerobic biological process, the evolution of biomass and organic matter contents was followed during each experiment. Contaminant removal was followed by means of global parameters directly related to the concentration of organic compounds in those effluents: chemical oxygen demand (COD) and total phenolic content (TP). A kinetic study was performed using the Contois model, which applied to the experimental data, provides the specific kinetic parameters of this model: 4.81×10⁻² h⁻¹ for the kinetic substrate removal rate constant, 0.279 g VSS g COD⁻¹ for the cellular yield coefficient and 1.92×10⁻² h⁻¹ for the kinetic constant for endogenous metabolism. In the combined process, an ozonation pretreatment is conducted with experiments where an important reduction in the phenolic compounds is achieved. The kinetic parameters of the following aerobic degradation stage are also evaluated, being 5.42×10⁻² h⁻¹ for the kinetic substrate removal rate constant, 0.280 g VSS g COD⁻¹ for the cellular yield coefficient and 9.1×10⁻³ h⁻¹ for the kinetic constant for the endogenous metabolism.     

Multiple deficiencies in antioxidant enzymes in mice result in a compound increase in sensitivity to oxidative stress

To examine the effect of compound deficiencies in antioxidant defense, we have generated mice (Sod2^+/−/Gpx1^−/−) that are deficient in Mn superoxide dismutase (MnSOD) and glutathione peroxidase 1 (Gpx1) by breeding Sod2^+/− and Gpx1^−/− mice together. Although Sod2^+/−/Gpx1^−/− mice showed a 50% reduction in MnSOD and no detectable Gpx1 activity in either mitochondria or cytosol in all tissues, they were viable and appeared normal. Fibroblasts isolated from Sod2^+/−/Gpx1^−/− mice were more sensitive (4- to 6-fold) to oxidative stress (t-butyl hydroperoxide or γ irradiation) than fibroblasts from wild-type mice, and were twice as sensitive as cells from Sod2^+/− or Gpx1^−/− mice. Whole-animal studies demonstrated that survival of the Sod2^+/−/Gpx1^−/− mice in response to whole body γ irradiation or paraquat administration was also reduced compared with that of wild-type, Sod2^+/−, or Gpx1^−/− mice. Similarly, endogenous oxidative stress induced by cardiac ischemia/reperfusion injury led to greater apoptosis in heart tissue from the Sod2^+/−/Gpx1^−/− mice than in that from mice deficient in either MnSOD or Gpx1 alone. These data show that Sod2^+/−/Gpx1^−/− mice, deficient in two mitochondrial antioxidant enzymes, have significantly enhanced sensitivity to oxidative stress induced by exogenous insults and to endogenous oxidative stress compared with either wild-type mice or mice deficient in either MnSOD or Gpx1 alone.     

Arachidonic acid production by Mortierella alpina with growth-coupled lipid synthesis

The fungus Mortierella alpina LPM 301, a producer of arachidonic acid (ARA), was found to possess a unique property of a growth-coupled lipid synthesis. An increase in specific growth rate (μ) from 0.03 to 0.05 h⁻¹ resulted in a two-fold increase in the specific rate of lipid synthesis (milligram lipid (gram per lipid-free biomass) per hour). Under batch cultivation in glucose-containing media with urea or potassium nitrate as nitrogen sources, the ARA content was 46.0 and 60.4% of lipid; 16.4 and 18.8% of dry biomass; and 4.2 and 4.5 g l⁻¹, respectively. Under continuous cultivation of the strain, the productivity of ARA synthesis was 16.2 and 19.2 mg l⁻¹ h⁻¹ at μ=0.05 and 0.03 h⁻¹, respectively.     

Rapid production of thermostable cellulase-free xylanase by a strain of Bacillus subtilis and its properties

A Bacillus subtilis strain isolated from a hot-spring was shown to produce xylanolytic enzymes. Their associative/synergistic effect was studied using a culture medium with oat spelts xylan as xylanase inducer. Optimal xylanase production of about 12 U ml⁻¹ was achieved at pH 6.0 and 50°C, within 18 h fermentation. At 50°C, xylanase productivity obtained after 11 h in shake-flasks, 96,000 U l⁻¹ h⁻¹, and in reactor, 104,000 U l⁻¹ h⁻¹ was similar. Increasing temperature to 55°C a higher productivity was obtained in the batch reactor 45,000 U l⁻¹ h⁻¹, compared to shake-flask fermentations, 12,000 U l⁻¹ h⁻¹. Optimal xylanolytic activity was reached at 60°C on phosphate buffer, at pH 6.0. The xylanase is thermostable, presenting full stability at 60°C during 3 h. Further increase in the temperature caused a correspondent decrease in the residual activity. At 90°C, 20% relative activity remains after 14 min. Under optimised fermentation conditions, no cellulolytic activity was detected on the extract. Protein disulphide reducing agents, such as DTT, enhanced xylanolytic activity about 2.5-fold. When is used xylan as substrate, xylanase production decreased as function of time in contrast, with trehalose as carbon source, xylanase production in maintained constant for at least 80 h fermentation.     

Asparaginase production by a recombinant Pichia pastoris strain harbouring Saccharomyces cerevisiae ASP3 gene

The therapeutic enzyme asparaginase, which is used for the treatment of acute lymphoblastic leukaemia, is industrially produced by the bacteria Escherichia coli or Erwinia crysanthemi. In spite of its effectiveness as a therapeutic agent, the drug causes severe immunological reactions. As asparaginase is also produced by the yeast Saccharomyces cerevisiae, this microorganism could be considered for the production of the enzyme, providing an alternative antitumoral agent. In this study the ASP3 gene, that codes for the periplasmic, nitrogen regulated, asparaginase II from S. cerevisiae, was cloned and expressed in the methylotrophic yeast Pichia pastoris, under the control of the AOX1 gene promoter. Similarly to S. cerevisiae the heterologous enzyme was addressed to the P. pastoris cell periplasmic space. Enzyme yield per dry cell mass reached 800 U g⁻¹, which was seven fold higher than that obtained using a nitrogen de-repressed ure2 dal80 S. cerevisiae strain. High cell density cultures performed with P. pastoris harbouring the ASP3 gene using a 2 l instrumented bioreactor, where biomass concentration reached 107 g l⁻¹, resulted in a dramatic increase in volumetric yield (85,600 U l⁻¹) and global volumetric productivity (1083 U l⁻¹ h⁻¹).     

Effect of chloride ions on the S-state distribution and deactivation kinetics in preparations of the cyanobacterium Anacystis nidulans

The roles of Ca²⁺ and Cl⁻ on the photosynthetic O₂ yield under flash illumination have been examined in EDTA-washed preparations of the cyanobacterium Anacystis nidulans. Especially the effect of Cl⁻ deficiency on the O₂ yield and on the S-state distribution was analyzed. As the results show, omission of both Ca²⁺ and Cl⁻ (Mn²⁺ present) almost totally inhibited O₂ evolution. When Ca²⁺ was replaced by Na⁺, a substantial reduction of the O₂ yield was observed, but only a minor change in the S-state distribution occurred. However, when Cl⁻ was displaced by NO⁻₃, which is equivalent to Cl⁻ deficiency of the water-splitting complex, a substantial reduction of the O₂ yield and in addition a significant change in the S-state distribution was observed. The comparison of deactivation kinetics in NO⁻₃ containing samples with those in control samples indicated that Cl⁻ deficiency allowed accumulation of oxidizing equivalents up to the S₃ state but modified the final step of O₂ evolution. Moreover, those centers which advanced to the S₃ state in the absence of Cl⁻ deactivated in a special way which involved a faster deactivation of S₂ and an increased formation of S₋₁.     

Enhanced production of free trans-astaxanthin by oxidative stress in the cultures of the green microalga Chlorococcum sp

Free trans-astaxanthin accumulated in the alga Chlorococcum sp. was markedly enhanced from 3.664 mg g⁻¹ cell dry weight to 5.724 mg g⁻¹ cell dry weight when the culture was supplemented with hydrogen peroxide (0.1 mM) under mixotrophic conditions of growth. After saponification, a total of 7.086 mg astaxanthin per g cell dry weight was achieved. Similarly, in heterotrophic cultures, the total astaxanthin content was increased from 1.034 mg g⁻¹ cell dry weight without H₂O₂ to 1.782 mg g⁻¹ cell dry weight with 0.1mM H₂O₂. Results indicate that hydrogen peroxide effectively induces the formation of free trans-astaxanthin in Chlorococcum sp.     

Hydrolysis and fermentation of brewer's spent grain by Neurospora crassa

In this study, the ethanol production by the mesophilic fungus Neurospora crassa from BG was studied and optimized concerning the induction of lignocellulose degrading enzymes and the production phase as well. The production of cellulolytic and hemicellulolytic enzymes was studied under solid-state cultivation (SSC). SSC in a laboratory horizontal bioreactor using the optimized medium, WS and BG in the ratio 1:1 and initial moisture level 61.5%, allowed the large scale production of the multienzymatic system. Similar yields with those from flasks experiments, as high as 1073, 56, 4.2, 1.6, 3.1, 5.7 and 0.52 U g⁻¹ carbon source of xylanase, endoglucanase, cellobiohydrolase, β-glucosidase, -l-arabinofuranosidase, acetyl esterase and feruloyl esterase, respectively, were obtained. Chromogenic (fluorogenic) 4-methylumbelliferyl substrates were used to characterize the major activities of the multienzyme component, after the separation by isoelectric focusing (IEF) electrophoresis. Alkali pre-treated BG was used for ethanol production. A yield of about 74 g of ethanol kg⁻¹ dry BG (5, 6 g L⁻¹) was obtained under optimum conditions (aeration 0.1 vvm, pre-treatment with 1 g NaOH 10 g⁻¹ dry BG).     

Induction of specific-locus and dominant lethal mutations in male mice by 1-methyl-1-nitrosourea (MNU)

1-Methyl-1-nitrosourea (MNU) induced specific-locus mutations in mice in all spermatogenic stages except spermatozoa. After intraperitoneal injection of 70 mg/kg body weight of MNU a high yield of specific-locus mutations was observed in spermatids (21.8 × 10⁻⁵ mutations per locus per gamete). The highest mutational yield was induced in differentiating spermatogonia. In 1954 offspring we observed 5 specific-locus mutants (44.8 × 10⁻ mutations per locus per gamete). In addition, 2 mosaics were recovered, which gave a combined mutation rate of 62.7 × 10⁻⁵. In A_s spermatogonia the mutation rate was 3.9 × 10⁻⁵. The same dose of 70 mg/kg of MNU induced dominant lethal mutations 5–48 days post treatment, mainly due to post-implantation loss in spermatids and spermatocytes. It is interesting to compare the induction pattern of mutations by MNU with methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS) and ethylnitrosourea (ENU). Based on the different spermatogenic response of the induction of specific-locus mutations we can characterize the 4 mutagens in the following way: EMS = MMS ≠ MNU ≠ ENU.     

Identification of metabolites from phenanthrene oxidation by phenoloxidases and dioxygenases of Polyporus sp. S133

Phenanthrene degradation by Polyporus sp. S133, a new phenanthrene-degrading strain, was investigated in this work. The analysis of degradation was performed by calculation of the remaining phenanthrene by gas chromatography-mass spectrometry. When cells were grown in phenanthrene culture after 92 h, all but 200 and 250 mg/l of the phenanthrene had been degraded. New metabolic pathways of phenanthrene and a better understanding of the phenoloxidases and dioxygenase mechanism involved in degradation of phenanthrene were explored in this research. The mechanism of degradation was determined through identification of the several metabolites; 9,10-phenanthrenequinone, 2,2'-diphenic acid, salicylic acid, and catechol. 9,10-Oxidation and ring cleavage to give 9,10-phenanthrenequinone is the major fate of phenanthrene in ligninolytic Polyporus sp. S133. The identification of 2,2'-diphenic acid in culture extracts indicates that phenanthrene was initially attacked through dioxigenation at C9 and C10 to give cis-9,10-dihydrodiol. Dehydrogenation of phenanthrene-cis-9,10-dihydrodiol to produce the corresponding diol, followed by ortho-cleavage of the oxygenated ring, produced 2,2'-diphenic acid. Several enzymes (manganese peroxidase, lignin peroxidase, laccase, 1,2-dioxygenase, and 2,3-dioxygenase) produced by Polyporus sp. S133 was detected during the incubation. The highest level of activity was shown at 92 h of culture.     

Production and purification of a novel thermostable phytase by Pichia pastoris FPHY34

A genetically engineered Pichia pastoris FPHY34 strain containing a 1.3 kb thermostable phytase gene (fphy) evolved by DNA shuffling was constructed and screened. Expression and purification conditions for the recombinant phytase were developed in this study. The effect of Pi on recombinant phytase expression and cell growth of P. pastoris FPHY34 was tested in shake flask culture. Optimization of carbon sources for cell growth and methanol feeding strategies for phytase expression in P. pastoris FPHY34 was carried out in a 50-L fermenter by fed-batch fermentation. The purification of phytase was investigated by micro-filtration and ultra-filtration followed by desalting, ion-exchange chromatography, and gel filtration in the ÄKTA system. It showed that the optimum inorganic phosphorus is 13.6 g L⁻¹ and that glucose can be used as a substrate for P. pastoris cell growth instead of glycerol; the biomass yield of glycerol (Y_X/S) is slightly higher than that of glucose. Different profiles of lag phase and respiratory quotient (RQ) displayed between glucose and glycerol as the sole carbon source. The maximum phytase activity in per millimetre reached 2508 U mL⁻¹ at a methanol feed rate of 3.0 mL L⁻¹ h⁻¹ after 80 h period of induction. A purification factor of 41.1 with a 32% yield was achieved after chromatographic purification. The specific enzyme activity was 80 U mg⁻¹ and 3281 U mg⁻¹ in that supernatant fraction and after gel filtration purification, respectively. The strain P. pastoris FPHY34 showed a promising application in phytase industrial production.     

Effect of oxygen transfer rate on levels of key enzymes of xylose metabolism in Debaryomyces hansenii

The titers of key enzymes of xylose metabolism were measured and correlated with the kinetics of xylitol production by Debaryomyces hansenii under different oxygen transfer rates (OTR) in a batch reactor. An OTR change from 2.72 to 4.22 mmol O₂ l⁻¹ min⁻¹ resulted in a decrease in NADPH-dependent xylose reductase (XR) and NAD ± -dependent xylitol dehydrogenase (XDH) activities. For higher values of OTR (12.93 mmol O₂ l⁻¹ min⁻¹, the XDH titer increased twofold whereas the XR titer did not show a significant change. At the lowest OTR (2.72 mmol O₂ l⁻¹ min⁻¹), xylitol (and ethanol) production rates showed the highest values. However, xylitol specific productivity was twice as high as ethanol specific productivity. The titer of the NADPH-forming enzyme, glucose-6-phosphate dehydrogenase (GPDH), increased from 333 to 412 mU mg⁻¹ when the OTR was increased. However, 6-phosphogluconate dehydrogenase (PGDH) activity remained unchanged and at a lower level, which indicates that this enzyme is responsible for the carbon flux control of the oxidative branch of the pentose phosphate pathway. The activity of the alcohol-forming enzyme was repressed at the higher amount of oxygen, decreasing its activity more than 50%. The changes in ADH suggested that two different metabolic regions under oxygen-limited conditions can be hypothesized for xylose metabolism by D. hansenii. For low OTR values (up to 4.22 mmol O₂ l⁻¹ min⁻¹), a fermentative-type activity is displayed. At higher OTR values (above 4.22 mmol O₂ l⁻¹ min⁻¹), no significant fermentative activity is reported.     

Plasmid transfer between strains of Pseudomonas putida, and their survival, within a pilot scale percolating-filter sewage treatment system

Abstract: The effect of Pseudomonas aeruginosa UG2 biosurfactants or UG2 inocula on phenanthrene mineralization in uninoculated nonsterile soil slurries and slurries inoculated with the phenanthrene-mineralizing Pseudomonas sp. UG14r was investigated. In sandy loam and silt loam slurries amended with phenanthrene, inoculation with UG14r alone or in co-culture with UG2Lr reduced the lag period before onset of phenanthrene mineralization by 1 week. The total amount mineralized after 5 weeks was lower or not significantly different from the uninoculated control slurries. Inoculation with P. aeruginosa UG2Lr alone did not improve phenanthrene mineralization. In creosote-contaminated soil slurries, no lag period in phenanthrene mineralization was observed in any treatment. After 4 weeks, the greatest extent of mineralization was observed in creosote-contaminated soil slurries inoculated with the UG14r-UG2Lr co-culture and UG14r alone. In sandy loam and silt loam soil slurries inoculated with Pseudomonas sp. UG14r, addition of UG2 rhamnolipid biosurfactants (100 to 400 mg rhamnose equivalents (RE) · l⁻¹ slurry) inhibited phenanthrene mineralization by 10 to 15%. Mineralization was also inhibited in uninoculated sandy loam slurries. In creosote-contaminated soil slurries inoculated with Pseudomonas sp. UG14r, biosurfactants at 250 mg RE · l⁻¹ slurry enhanced mineralization whereas 400 mg RE · l⁻¹ had no effect, compared to unamended slurries. In uninoculated creosote-contaminated soil slurries, UG2 biosurfactants at 250 and 400 mg RE · l⁻¹ slurry enhanced mineralization, compared to unamended slurries.     

Biodegradaon of phenanthrene in soil microcosms stimulated by an introduced Alcaligenes sp.

Abstract A phenanthrene degrading strain of Alcaligenes sp. was isolated from oil polluted soil. Addition of Alcaligenes sp. to soil microcosms supplemented with phenanthrene (1 mg/g dry soil) resulted in degradation of the added phenanthrene within 11 days. The phenanthrene concentration declined only 12% in uninoculated soil during 42 days. The total phenanthrene degradation potential of Alcaligenes sp. was 2.3 mg/g dry soil during a period of 22 days. The amount of CO₂ evolved during 22 days corresponded to the conversion of 91% of the degraded phenanthrene to CO₂. The Alcaligenes sp. were not able to degrade phenanthrene in sterile soil.     

Poly(methylene co-guanidine) coated alginate as an encapsulation matrix for urease

Urease was encapsulated within alginate beads, coated with poly(methylene co-guanidine) membranes via polyelectrolyte complexation. Membrane thickness increased with reaction time to 53 μm after 80 min, and to 59 μm with an increase in co-guanidine concentration from 2.5 to 20 mg ml⁻¹. A 70% mass and 31% activity yield of urease resulted following encapsulation. Although co-guanidine strongly inhibited freely soluble urease (I_0.5=5.8 μg ml⁻¹ co-guanidine), immobilization stabilized the enzyme against inactivation. Encapsulated activity declined as the polycation concentration used for membrane formation increased; however an activity loss of only 35% was observed when the co-guanidine concentration was as high as 5 mg ml⁻¹. Glucose protected against inactivation, with 0.5 increasing to 28.5 μg ml⁻¹ for the freely soluble enzyme. When the beads were coated with co-guanidine in the presence of glucose, encapsulated urease activity was fully retained.