Mathematical analysis of trickling filter response to pentachlorophenol shock load

The response of a laboratory trickling filter to a step increase in pentachlorophenol (PCP) feed concentration was analyzed using continuous stirred tank (CSTR) and plug flow reactor (PFR) models. The CSTR model provided a slightly better fit to experimental data than the plug flow model when specific growth rate, μ, and PCP-degrading biomass concentration before the shock load, X₀, were variable parameters but was clearly superior when the mean residence time, τ, was added as a third parameter. The three-parameter CSTR model accurately represented six of seven concentration response curves corresponding to step increases in PCP feed concentration of 12–165 mg l⁻¹ and 20–150 mg l⁻¹. The continuing improvement in system response to repetitive 20–150 mg l⁻¹ shock loads was reflected by a monotonic increase in the optimal estimates of initial rate of biomass production.     

Evaluation of the association of mercury(II) with some dicysteinyl tripeptides

The present study was undertaken to gain insight into the associations of mercury(II) with dicysteinyl tripeptides in buffered media at pH 7.4. We investigated the effects of increasing the distance between cysteinyl residues on mercury(II) associations and complex formations. The peptide–mercury(II) formation constants and their associated thermodynamic parameters in 3-(N-morpholino)propanesulfonic acid (MOPS) buffered solutions were evaluated by isothermal titration calorimetry. Complexes formed in different relative ratios of mercury(II) to cysteinyl peptides in ammonium formate buffered solutions were characterized by LTQ Orbitrap mass spectrometry. The results from these studies show that n-alkyl dicysteinyl peptides (CP 1–4), and an aryl dicysteinyl peptide (CP 5) can serve as effective “double anchors” to accommodate the coordination sites of mercury(II) to form predominantly one-to-one Hg(peptide) complexes. The aryl dicysteinyl peptide (CP 5) also forms the two-to-two Hg₂(peptide)₂ complex. In the presence of excess peptide, Hg(peptide)₂ complexes are also detected. Notably, increasing the distance between the ligating groups or “anchor points” in CP 1–5 does not significantly affect their affinity for mercury(II). However, the enthalpy change (ΔH) values (ΔH₁ ∼ −91 kJ mol⁻¹ and ΔH₂ ∼ −66 kJ mol⁻¹) for complex formation between CP 4 and 5 with mercury(II) are about one and a half times larger than the related values for CP 1, 2 and 3 (ΔH₁ ∼ −66 kJ mol⁻¹ and ΔH₂ ∼ 46 kJ mol⁻¹). The corresponding entropy change (ΔS) values (ΔS₁ ∼ −129 J K⁻¹ mol⁻¹ and ΔS₂ ∼ −116 J K⁻¹ mol⁻¹) of the structurally larger dicysteinyl peptides CP 4 and 5 are less entropically favorable than for CP 1, 2 and 3 (ΔS₁ ∼ −48 J K⁻¹ mol⁻¹ and ΔS₂ ∼ −44 J K⁻¹ mol⁻¹). Generally, these associations result in a decrease in entropy, indicating that these peptide–mercury complexes potentially form highly ordered structures. The results from this study show that dicysteinyl tripeptides are effective in binding mercury(II) and they are promising motifs for the design of multi-cysteinyl peptides for binding more than one mercury(II) ion per peptide.     

Decolorization of azo dye by immobilized Pseudomonas luteola entrapped in alginate–silicate sol–gel beads

Pseudomonas luteola was immobilized by entrapment in alginate–silicate sol–gel beads for decolorization of the azo dye, Reactive Red 22. The influences of biomass loading and operating conditions on specific decolorization rate and dye removal efficiency were studied in details. The immobilized cells were found to be less sensitive to changes in agitation rates (dissolved oxygen levels) and pH values. Michaelis–Menten kinetics could be used to describe the decolorization kinetics with the kinetic parameters being 36.5 mg g⁻¹ h⁻¹, 300.1 mg l⁻¹ and 18.2 mg g⁻¹ h⁻¹, 449.8 mg l⁻¹ for free and immobilized cells, respectively. After five repeated batch cycles, the decolorization rate of the free cells decreased by nearly 54%, while immobilized cells still retained 82% of their original activity. The immobilized cells exhibited better thermal stability during storage and reaction when compared with free cells. From SEM observation, a dense silicate gel layer was found to surround the macroporous alginate–silicate core, which resulted in much improved mechanical stability over that of alginate beads when tested under shaking conditions. Alginate–silicate matrices appeared to be the best matrix for immobilization of P. luteola in decolorization of Reactive Red 22 when compared with previous results using synthetic or natural polymer matrices.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

The effects of light intensity on the growth of Japanese Gambierdiscus spp. (Dinophyceae)

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (L_max) and the semi-optimum light intensity range (L_s-opt) that resulted in the maximum growth rate (μ_max) and ≥80% μ _max values of the four species/phylotypes, respectively, were as follows: (1) the L_max and L_s-opt of G. australes were 208 μmol photons m⁻² s⁻¹ and 91–422 μmol photons m⁻² s⁻¹, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m⁻² s⁻¹, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m⁻² s⁻¹, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m⁻² s⁻¹, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m⁻² s⁻¹ to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m⁻¹. The values 1700 μmol photons m⁻² s⁻¹, 500 μmol photons m⁻² s⁻¹, and 200 μmol photons m⁻² s⁻¹ were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of L_max and L_s-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.     

Hydrogen sulphide removal from air by biotrickling filter using open-pore polyurethane foam as a carrier

A study was conducted on H₂S removal in a biotrickling filter packed with open-pore polyurethane foam. Thiobacillus denitrificans was used as inoculum and a mixed culture population was developed during the process. The inhibitory effect of sulphate concentration (1.8–16.8 g L⁻¹), pH (6.9–8.6), trickling liquid velocity (TLV, 9.1–22.8 m h⁻¹), H₂S inlet concentration (20–157 ppmv) and the empty bed residence time (EBRT, 9–57 s) on the H₂S removal efficiency (RE) were thoroughly investigated. An increase in pH from 6.9 to 8.5 led to a corresponding increase in H₂S removal. In addition, an inhibitory effect of sulphate concentration was observed from 16.8 g L⁻¹ and the maximum elimination capacity was found to be 22 gS m⁻³ h⁻¹ (RE 98%). The RE was constant (98.8 ± 0.30%) for EBRT ≥ 16 s, but a decrease in the EBRT from 16 to 9 s led to a corresponding decrease in RE from 98.2 to 89.6% for a TLV of 9.1 m h⁻¹ and from 97.9 to 94.9% for a TLV of 22.8 m h⁻¹ (inlet load of 11.0 ± 0.2 gS m⁻³ h⁻¹). The sulphur oxidation capacity in the biotrickling filter was not diminished by the presence of other bacteria.     

Biosynthesis of ethyl caproate and other short ethyl esters catalyzed by cutinase in organic solvent

The main objective of this work was to study the enzymatic synthesis of short chain ethyl esters, a group of relevant aroma molecules, by Fusarium solani pisi cutinase in an organic solvent media (iso-octane), and to assess the influence of different parameters on the reaction yield.Cutinase displayed high initial esterification rates in iso-octane, which amounted to 1.15 μmol min⁻¹ mg⁻¹ for ethyl butyrate (C₄ acid chain) and 1.06 μmol min⁻¹ mg⁻¹ for ethyl valerate (C₅ acid chain). High product yields, 84% for ethyl butyrate and 96% for ethyl valerate, were observed after 6 h of reaction, for an initial equimolar concentration of substrates (0.1 M).The highest product yield (97%) was observed for ethyl caproate (C₆) synthesis, a compound which is a part of natural apple and pineapple flavour, for an alcohol:acid molar ratio of 2 (0.2 M ethanol concentration).Cutinase affinity for short chain length carboxylic acids (C₄–C₆) in ester synthesis in iso-octane confirmed previous observations in reversed micellar system.     

Cloning and characterization of a NADH-dependent aldo-keto reductase from a newly isolated Kluyveromyces lactis XP1461

An aldo-keto reductase gene (klakr) from Kluyveromyces lactis XP1461 was cloned and heterologously expressed in Escherichia coli. The aldo-keto reductase KlAKR was purified and found to be NADH-dependent with a molecular weight of approximately 36 kDa. It is active and stable at 30 °C and pH 7.0. The maximal reaction rate (v_max), apparent Michaelis–Menten constant (K_m) for NADH and t-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate (1a) and catalytic number (k_cat) were calculated as 7.63 U mg⁻¹, 0.204 mM, 4.42 mM and 697.4 min⁻¹, respectively. Moreover, the KlAKR has broad substrate specificity to a range of aldehydes, ketones and keto-esters, producing chiral alcohol with e.e. or d.e. >99% for the majority of test substrates.     

Effect of nutrient pulses on photosynthesis of Chaetomorpha linum from a shallow Mediterranean coastal lagoon

The influence of nitrogen and phosphorus pulses on Chaetomorpha linum (Muller) Kutzing growth and photosynthesis was studied in laboratory experiments. Photosynthesis and growth of C. linum from Tancada lagoon seems limited by both nitrogen and phosphorus, as indicated by the high rate (4.7–11.6 mg O₂ g⁻¹ dry weight h⁻¹) of light-saturated photosynthesis (P_m) and growth rates observed under nitrogen plus phosphorus enrichment in relation to enrichment by nitrogen alone (2.9–7.6 mg O₂ g⁻¹ dry weight h⁻¹). Significant increase in nitrogen and phosphorus content as percentage of dry weight was observed in C. linum fertilized with a single nutrient or with nitrogen plus phosphorus. In Tancada lagoon, when availability of nitrogen to primary producers is by pulses, an increase of nitrate concentration in the water column (from 6 to 100 μM) has a greater effect on growth of C. linum (growth rate: 0.13 day⁻¹) than an increase in ammonium concentration (from 20 to 100 μM and growth rate: 0.11 day⁻¹). For a given thallus nitrogen content (0.6–1.4% N), both P_m and the photosynthetic efficiency (α) normalized to dry weight were correlated (r² = 0.73, p < 0.005) indicating that variations in electron transport were coupled to variations in C-fixation capacity. Optimizing both α and P_m may be a general characteristic of thin-structured opportunistic algae in more variable estuarine environments.     

Investigation on the properties and kinetics of glucose-fed aerobic granular sludge

Aerobic granulation is a process in which suspended biomass aggregate and form discrete well-defined granules in aerobic systems. To investigate the properties and kinetics of aerobic granular sludge, aerobic granules were cultivated with glucose synthetic wastewater in a series of sequencing batch reactors (SBR). The spherical shaped granules were observed on 8th day with the mean diameter of 0.1 mm. With the organic loading rate (OLR) being increased to 4.0 g COD L⁻¹ d⁻¹, aerobic granules grew matured with spherical shape. The size of granules ranged from 1.2 to 1.8 mm, and the corresponding settling velocity of individual granule was 24.2–36.4 m h⁻¹. The oxygen utilization rate (OUR) of mature granules was 41.90 g O₂ kg MLSS⁻¹ h⁻¹, which was two times higher than that of activated sludge (18.32 g O₂ kg MLSS⁻¹ h⁻¹). The experimental data indicated that the substrate utilization and biomass growth kinetics generally followed Monod's kinetics model. The corresponding kinetic coefficients of k (maximum specific substrate utilization rate), K_s (half velocity coefficient), Y (growth yield coefficient) and K_d (decay coefficient) were determined as follows, k_c = 23.65 d⁻¹, K_c = 3367.05 mg L⁻¹, K_N = 0.038 d⁻¹, K_N = 29.65 mg L⁻¹, Y = 0.1927–0.2022 mg MMLS (mg COD)⁻¹ and K_d = 0.00845–0.0135 d⁻¹, respectively. Those properties of aerobic granules made aerobic granules system had a short setup period, high substrate utilization rate and low sludge production.     

Investigation on the formation and kinetics of glucose-fed aerobic granular sludge

Aerobic granular sludge was cultivated in a glass sequencing batch reactor (SBR) with glucose synthetic wastewater. The spherical shaped granules were observed on 4th day with the mean diameter of 0.1 mm. With the increase of chemical oxygen demand (COD) concentration of the influent, aerobic granules grew matured, the size of which ranged from 1.2 to 1.9 mm. The aerobic granular sludge could sustain high organic loading rate (about 4.0 g COD L⁻¹ d⁻¹), with good settling ability (settling velocity 36 m/h) and high biomass concentration (MLSS 6.7 ±0.2 g/L). Experimental data indicated that the substrate utilization and biomass growth kinetics followed Monod's kinetics model approximately. The corresponding kinetic coefficients of maximum specific substrate utilization rate (k), half velocity coefficient (K_s), growth yield coefficient (Y) and decay coefficient (K_d) were 13.2 d⁻¹, 275.8 mg/L, 0.183–0.250 mg MLSS/mg COD and 0.023–0.075 d⁻¹, respectively, which made aerobic granules have short setup period, high rate of substrate utilization and little surplus sludge.     

Effect of the aeration rate and agitation speed on β-carotene production and morphology of Blakeslea trispora in a stirred tank reactor: mathematical modeling

The effect of aeration rate and agitation speed on β-carotene production and morphology of Blakeslea trispora in a stirred tank reactor was investigated. B. trispora formed hyphae, zygophores and zygospores during the fermentation. The zygospores were the morphological form responsible for β-carotene production. Both aeration and agitation significantly affected β-carotene concentration, productivity, biomass and the volumetric mass transfer coefficient (K_La). The highest β-carotene concentration (1.5 kg m⁻³) and the highest productivity (0.08 kg m⁻³ per day) were obtained at low impeller speed (150 rpm) and high aeration rate (1.5 vvm). Also, maximum productivity (0.08 kg m⁻³ per day) and biomass dry weight (26.4 kg m⁻³) were achieved at high agitation speed (500 rpm) and moderate aeration rate (1.0 vvm). Conversely, the highest value of K_La (0.33 s⁻¹) was observed at high agitation speed (500 rpm) and high aeration rate (1.5 vvm). The experiments were arranged according to a central composite statistical design. Response surface methodology was used to describe the effect of impeller speed and aeration rate on the most important fermentation parameters. In all cases, the fit of the model was found to be good. All fermentation parameters (except biomass concentration) were strongly affected by the interactions among the operation variables. β-Carotene concentration and productivity were significantly influenced by the aeration, agitation, and by the positive or negative quadratic effect of the aeration rate. Biomass concentration was principally related to the aeration rate, agitation speed, and the positive or negative quadratic effect of the impeller speed and aeration rate, respectively. Finally, the volumetric mass transfer coefficient was characterized by the significant effect of the agitation speed, while the aeration rate had a small effect on K_La.     

Bench-scale fermentation of Trichoderma viride on wastewater sludge: Rheology,lytic enzymes and biocontrol activity

Conidiation and lytic enzyme production by Trichoderma viride at different solids concentration of pre-treated municipal wastewater sludge was examined in a 15-L fermenter. The maximum conidia concentration (5.94 × 10⁷ CFU mL⁻¹ at 96 h) was obtained at 30 g L⁻¹ suspended solids. The maximum lytic enzyme activities were achieved around 12–30 h of fermentation. Bioassay against a fungal phytopathogen, Fusarium sp. showed maximum activity in the sample drawn around 96 h of fermentation at 30 g L⁻¹ suspended solids concentration. Entomotoxicity against spruce budworm larvae showed maximum value ≈17290 SBU μL⁻¹ at 30 g L⁻¹ suspended solids concentration at the end of fermentation (96 h). Plant bioassay showed dual action of T. viride, i.e., disease prevention and growth promotion. The rheological analyses of fermentation sludges showed the pseudoplastic behaviour. In order to maintain required dissolved oxygen concentration ≥30%, the agitation and aeration requirements significantly increased at 35 g L⁻¹ compared to 30 and 25 g L⁻¹. The oxygen uptake rate and volumetric oxygen mass transfer coefficient, k_La at 35 g L⁻¹ did not increase in comparison to 30 g L⁻¹ due to rheological complexity of the broth during fermentation. Thus, the successful fermentation operation of the biocontrol fungus T. viride is a rational indication of its potential for mass-scale production for agriculture and forest sector as a biocontrol agent.     

Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l⁻¹). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy (E_a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (ΔG°) and heat of adsorption (ΔH_r) were calculated. The ΔG° and ΔH_r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l⁻¹.     

Purification and characterization of a new carbonyl reductase from Leifsonia xyli HS0904 involved in stereoselective reduction of 3,5-bis(trifluoromethyl) acetophenone

Leifsonia xyli HS0904 can stereoselectively catalyze the bioreduction of 3,5-bis(trifluoromethyl) acetophenone (BTAP) to its corresponding alcohol, which is a valuable chiral intermediate in the pharmaceuticals. In this study, a new carbonyl reductase derived from L. xyli HS0904 was purified and its biochemical properties were determined in detail. The carbonyl reductase was purified by 530-fold with a specific activity of 13.2 U mg⁻¹ and found to be a homodimer with a molecular mass of 49 kDa, in which the subunit molecular-weight was about 24 kDa. The purified enzyme exhibited a maximum enzyme activity at 34 °C and pH 7.2, and retained over 90% of its initial activity at 4 °C and pH 7.0 for 24 h. The addition of various additives, such as Ca²⁺, Mg²⁺, Mn²⁺, l-cysteine, l-glutathione, urea, PEG 1000 and PEG 4000, could enhance the enzyme activity. The maximal reaction rate (V_max) and apparent Michaelis–Menten constant (K_m) of the purified carbonyl reductase for BTAP and NADH were confirmed as 33.9 U mg⁻¹, 0.383 mM and 69.9 U mg⁻¹, 0.412 mM, respectively. Furthermore, this enzyme was found to have a broad spectrum of substrate specificity and can asymmetrically catalyze the reduction of a variety of ketones and keto esters.     

Plasma levels of intermedin (adrenomedullin-2) in healthy human volunteers and patients with heart failure

Intermedin/adrenomedullin-2 (IMD) is a member of the adrenomedullin/CGRP peptide family. Less is known about the distribution of IMD than for other family members within the mammalian cardiovascular system, particularly in humans. The aim was to evaluate plasma IMD levels in healthy subjects and patients with chronic heart failure. IMD and its precursor fragments, preproIMD_25–56 and preproIMD_57–92, were measured by radioimmunoassay in 75 healthy subjects and levels of IMD were also compared to those of adrenomedullin (AM) and mid-region proadrenomedullin_45–92 (MRproAM_45–92) in 19 patients with systolic heart failure (LVEF < 45%). In healthy subjects, plasma levels (mean + SE) of IMD (6.3 + 0.6 pg ml⁻¹) were lower than, but correlated with those of AM (25.8 + 1.8 pg ml⁻¹; r = 0.49, p < 0.001). Plasma preproIMD_25–56 (39.6 + 3.1 pg ml⁻¹), preproIMD_57–92 (25.9 + 3.8 pg ml⁻¹) and MRproAM_45–92 (200.2 + 6.7 pg ml⁻¹) were greater than their respective bioactive peptides. IMD levels correlated positively with BMI but not age, and were elevated in heart failure (9.8 + 1.3 pg ml⁻¹, p < 0.05), similarly to MRproAM_45–92 (329.5 + 41.9 pg ml⁻¹, p < 0.001) and AM (56.8 + 10.9 pg ml⁻¹, p < 0.01). IMD levels were greater in heart failure patients with concomitant renal impairment (11.3 + 1.8 pg ml⁻¹) than those without (6.5 + 1.0 pg ml⁻¹; p < 0.05). IMD and AM were greater in patients receiving submaximal compared with maximal heart failure drug therapy and were decreased after 6 months of cardiac resynchronization therapy. In conclusion, IMD is present in the plasma of healthy subjects less abundantly than AM, but is similarly correlated weakly with BMI. IMD levels are elevated in heart failure, especially with concomitant renal impairment, and tend to be reduced by high intensity drug or pacing therapy.     

Forming nanoparticles of α-amylase and embedding them into solid surfaces

In the current work nanoparticles (NPs) of α-amylase were generated in an aqueous solution using high-intensity ultrasound, and were subsequently immobilized on polyethylene (PE) films, or polycarbonate (PC) plates, or on microscope glass slides. The α-amylase NPs coated on the solid surfaces have been characterized by ESEM, TEM, FTIR, XPS and AFM. The substrates immobilized with α-amylase were used for hydrolyzing soluble potato starch to maltose. The amount of enzyme introduced in the substrates, leaching properties, and the catalytic activity of the immobilized enzyme were compared. The catalytic activity of the amylase deposited on the three solid surfaces was compared to that of the same amount of free enzyme at different pHs and temperatures. α-Amylase coated on PE showed the best catalytic activity in all the examined parameters when compared to native amylase, especially at high temperatures. When immobilized on glass, α-amylase showed better activity than the native enzyme over all pH and temperature values studied. However, the immobilization on PC did not improve the enzyme activity at any pH and any temperature compared to the free amylase. The kinetic parameters, K_m and V_max were also calculated. The amylase coated PE showed the most favorable kinetic parameters (K_m = 5 g L⁻¹ and V_max = 5E−07 mol mL⁻¹ min⁻¹). In contrast, the anchored enzyme-PC exhibited unfavorable kinetic parameters (K_m = 16 g L⁻¹, V_max = 4.2E−07 mol mL⁻¹ min⁻¹). The corresponding values for amylase-glass were K_m = 7 g L⁻¹, V_max = 1.8E−07 mol mL⁻¹ min⁻¹, relative to those obtained for the free enzyme (K_m = 6.6 g L⁻¹, V_max = 3.3E−07 mol mL⁻¹ min⁻¹).     

Effects of flooding on photosynthesis and root respiration in saltcedar (Tamarix ramosissima), an invasive riparian shrub

The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO₂, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500 μmol quanta m⁻² s⁻¹ (A₁₅₀₀) in flooded plants ranged from 2.3 to 6.2 μmol CO₂ m⁻² s⁻¹ during the first week, but A₁₅₀₀ increased to 6.4–12.7 μmol CO₂ m⁻² s⁻¹ by the third week of flooding. Stomatal conductance (g_s) at 1500 μmol quanta m⁻² s⁻¹ also decreased initially during flooding, where g_s was 0.018 to 0.099 mol H₂O m⁻² s⁻¹ during the first week, but g_s increased to 0.113–0.248 mol H₂O m⁻² s⁻¹ by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ¹³C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.     

Effects of feed sugar concentration on continuous ethanol fermentation of cheese whey powder solution (CWP)

Cheese whey powder (CWP) solution with different CWP or sugar concentrations was fermented to ethanol in a continuous fermenter using pure culture of Kluyveromyces marxianus (DSMZ 7239). Sugar concentration of the feed CWP solution varied between 55 and 200 g l⁻¹ while the hydraulic residence time (HRT) was kept constant at 54 h. Ethanol formation, sugar utilization and biomass formation were investigated as functions of the feed sugar concentration. Percent sugar utilization and biomass concentrations decreased and the effluent sugar concentration increased with increasing feed sugar concentrations especially for the feed sugar contents above 100 g l⁻¹. Ethanol concentration and productivity (DP) increased with increasing feed sugar up to 100 g l⁻¹ and then decreased with further increases in the feed sugar content. The highest ethanol concentration (3.7%, v v⁻¹) and productivity (0.54 gE l⁻¹ h⁻¹) were obtained with the feed sugar content of 100 g l⁻¹ or 125 g l⁻¹. The ethanol yield coefficient (Y_P/S) was also maximum (0.49 gE gS⁻¹) when the feed sugar was between 100 and 125 g l⁻¹. The growth yield coefficient (Y_X/S) decreased steadily from 0.123 to 0.063 gX gS⁻¹ when the feed sugar increased from 55 to 200 g l⁻¹ due to adverse effects of high sugar contents on yeast growth. The optimal feed sugar concentration maximizing the ethanol productivity and sugar utilization was between 100 and 125 g l⁻¹ under the specified experimental conditions.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.