Granulation in anaerobic sludge bed reactors treating food industry wastes

Three parallel laboratory reactors, R1, R2 and R3, received food industry wastewater: R1 unadulterated; R2 supplemented with calcium and phosphate; R3 supplemented with ferric chloride and traces of nickel and cobalt. Reactors were packed with active granular sludge from a large scale pilot reactor treating the same wastewater. Addition of calcium and phosphate was found to be detrimental to the granule formation at naturally established reactor pH = 6·9–7·4 in R2 while iron promoted granulation in R3. Conditions of upflow velocities of 1·5–6 m h⁻¹, rapid increase of loads up to 15 kg COD m⁻³ day⁻¹ and ratios of recycle to raw waste feed of 20:1–80:1 were imposed on all reactors. The granules in R1 and R2 disintegrated, from 70–100 g liter⁻¹ VSS to a flocculant sludge at 1·5–3 g liter⁻¹. In spite of such severe washout, reactors R1 and R2 were able to maintain a steady COD removal of over 90% at a load of 10kg m⁻³ day⁻¹. R3 retained a VSS concentration around 100 g liter⁻¹ and maintained COD removal at over 95%. R3 exhibited a more stable performance and was less vulnerable to the shock treatment to which all reactors were subjected.     

Glutamine synthetase activity and free amino acid pools of eelgrass (Zostera marina L.) roots

Activity of the enzyme glutamine synthetase (GS, EC 6.3.1.2) was determined in vitro for roots of the marine angiosperm Zostera marina L. (eelgrass) collected from a population in Great Harbor, Woods Hole, Massachusetts, U.S.A. The GS synthetase activity was lowest in roots of plants collected from the shallow region of the eelgrass bed (12.0 μmol·g⁻¹ (fresh wt)· h⁻¹) and increased in the mid (3.0 m, 40.3 μmol·g⁻¹ (fresh wt)·h⁻¹) and deep (5.0 m, 72.3 μmol·g⁻¹ (fresh wt)·h⁻¹) plant collection depths. GS transferase activity increased with collection depth in a similar manner: shallow, 28.6 μmol·g⁻¹ (fresh wt)·h⁻¹; mid, 52.0 μmol·g⁻¹ (fresh wt)·h⁻¹; deep, 92.8 μmol·g⁻¹ (fresh wt)·h⁻¹. When sediment-embedded plants were held in continuous darkness for 2 days to create extended root anoxia, root GS activities nearly doubled. In contrast, in vivo incorporation of ¹⁴C-glutamate into glutamine and protein residue remained constant or declined under short-term hypoxia and anoxia. During aerobic recovery from anoxia, root labelling of glutamine and protein increased markedly. Free amino acid patterns of eelgrass roots growing in situ were determined over a diurnal cycle. Total free amino acid content was maximal at dawn and decreased 50% by noon. In contrast, the proportion of glutamine was lowest at dawn and maximal at noon for both shallow and deep-growing plants. Despite differences in depth-specific plant sizes, root/rhizome/shoot ratios, and relative growth rates, the daily whole plant nitrogen demand of shallow and deep growing plants were equivalent. When corrected for assay temperature response, the enzyme synthetase activities measured in vitro suggest that all of the plant nitrogen assimilation requirements can be met within daylight hours during the period of peak summer biomass.     

Short Term Bioturbation Activity in the Lagoonal Sediments of Tikehau Atoll (Tuamotu Archipelago,French Polynesia)

To quantify bioturbation activity in Tikehau lagoon, a tracer made of black basaltic sand was poured over the natural white calcareous sediment surface. Three stations respectively located on the inner flat (-3m), the inner slope (-9m), and the lagoon floor (-19m), were studied for short periods of time (48 hours). Bioturbation by macrofauna was quantified by volume of sediment ejected onto the experimental surface and by volume of tracer incorporated into sediment. The results showed a rapid incorporation of sedimented particles at the interface by way of the funnels and burrows of surface deposit feeders and carnivores. Expelled quantities varied with respect to site location: 213 cm³ · m⁻² · 24 h⁻¹ in the inner flat; 98.9 cm³ · m⁻² · 24 h⁻¹ in the inner slope; 7.9 m³ · m⁻² · 24 h⁻¹ in the lagoon floor. Bioturbation by decapod megafauna appeared to be important in the dynamics of the sediments in the deepest areas of the lagoon. In these areas, with almost no hydrodynamical impacts on sediments, bioturbating events were responsible for sediment mixing (despite lower absolute rates than in shallow area). Hydrodynamics controlled the spatial distribution of macroinvertebrate trophic groups by its effects on sedimentation.     

Auxin Synthesis in Crown Gall Tumor Tissue: A Comparison of Three Putative Precursors

Axenic crown gall tumor callus (from Vinca rosea L.) which is known to synthesize its own auxin is able to convert exogenous ¹⁴C-indole or tryptamine to indoleacetic acid [5.4 and 10 × 10⁻⁶μmol × h⁻¹× (g fr wt)⁻¹ respectively], but little or no ³H-tryptophan is converted [less than 6.4 × 10⁻⁸×μmol × h⁻¹× (g fr wt)⁻¹].     

Quasi-continuous fermentation in a reverse-flow diafiltration bioreactor

Heterogeneities occur in various bioreactor designs including cell retention devices. Whereas in external devices changing environmental conditions cannot be prevented, cells are retained in their optimal environment in internal devices. Conventional reverse-flow diafiltration utilizes an internal membrane device, but pulsed feeding causes spatial heterogeneities. In this study, the influence of conventional reverse-flow diafiltration on the yeast Hansenula polymorpha is investigated. Alternating 180 s of feeding with 360 s of non-feeding at a dilution rate of 0.2 h⁻¹ results in an oscillating DOT signal with an amplitude of 60%. Thereby, induced short-term oxygen limitations result in the formation of ethanol and a reduced product concentration of 25%. This effect is enforced at increased dilution rate. To overcome this cyclic problem, sequential operation of three membranes is introduced. Thus, quasi-continuous feeding is achieved reducing the oscillation of the DOT signal to an amplitude of 20% and 40% for a dilution rate of 0.2 h⁻¹ and 0.5 h⁻¹, respectively. Fermentation conditions characterized by complete absence of oxygen limitation and without formation of overflow metabolites could be obtained for dilution rates from 0.1 h⁻¹ to 0.5 h⁻¹. Thus, sequential operation of three membranes minimizes oscillations in the DOT signal providing a nearly homogenous culture over time.     

Factors affecting l-arginine production in the continuous culture of an l-arginine producer of Corynebacterium acetoacidophilum

The effects of culture conditions on l-arginine production by continuous culture were studied using a stable l-arginine hyperproducing strain of Corynebacterium aceto-acidophilum, SC-190. Strain SC-190 demonstrated a volumetric productivity of 35 g l⁻¹·h⁻¹ at a dilution rate of 0.083h⁻¹ and feeding sugar concentration of 8%, and a product yield of 29.2% at a dilution rate 0.021h⁻¹ and feeding sugar concentration of 15%. The corresponding values for fed-batch culture are 0.85 g·l⁻¹·h⁻¹ and 26%. However, the product yield decreased with an increase in the volumetric productivity. To achieve stable l-arginine production, aeration and agitation conditions sufficient to maintain an optimal level of redox potential (>−100 mV) were necessary. The addition of phosphate to the feeding medium led to a decrease in l-arginine production. It was confirmed in the steady state that growth and l-arginine formation were inhibited by a high concentration of l-arginine.     

GRAZING AND GROWTH OF THE MIXOTROPHIC CHRYSOMONAD POTERIOOCHROMONAS MALHAMENSIS (CHRYSOPHYCEAE) FEEDING ON ALGAE

The growth and grazing characteristics of Poterioochromonas malhamensis (Pringsheim) Peterfi (= Ochromonas malhamensis Pringsheim) (ca. 8 μm) feeding on phytoplankton, including the cyanobacteria Synechococcus sp. (ca. 2 μm) and Microcystis viridis (A. Brown) Lemmermann (ca. 6 μm) and the green alga Chlorella pyrenoidosa Chick (ca. 13 μm), were investigated in laboratory experiments involving the following treatments: (1) light without added algal prey (autotrophy), (2) light with added algal prey (mixotrophy), and (3) dark with added algal prey (phagotrophy). There were significantly higher cell numbers under mixotrophic and phagotrophic growth than under autotrophic growth. With phytoplankton as food, growth rates under both mixotrophy and phagotrophy were about two or three times higher than those under autotrophy, indicating that the algal diets were readily able to support the population growth of P. malhamensis. There were no significant differences in growth rate between mixotrophic and phagotrophic cultures during exponential growth. The ingestion rate of P. malhamensis with algal prey was also similar under both continuous light and dark. Poterioochromonas malhamensis ingested on average 0.27 M. viridis cells·flagellate^{− 1} ·h^{− 1} and 0.18 C. pyrenoidosa cells·flagellate^{− 1} ·h^{− 1} in continuous light and 0.25 M. viridis cells·flagellate^{− 1} ·h^{− 1} and 0.18 C. pyrenoidosa cells·flagellate^{− 1} ·h^{− 1} in continuous dark during exponential growth. The results showed that light had no effect on the growth and ingestion rates of P. malhamensis for phagotrophy during exponential growth. However, phagotrophic populations of P. malhamensis were incapable of growth in continuous darkness for longer than 5 days. Populations of P. malhamensis showed no increase when prey was added again after 4 days in continuous darkness, indicating that light is necessary for sustained phagotrophic growth of P. malhamensis. The study suggests that P. malhamensis, which has strong tolerance for light, is light dependent for phagotrophy.     

Influence of the concentrations of d-xylose and yeast extract on ethanol production by Pachysolen tannophilus

To determine the most favorable conditions for the production of ethanol by Pachysolen tannophilus, this yeast was grown in batch cultures with various initial concentrations of two of the constituents of the culture medium: d-xylose (s_o), ranging from 1 g·l⁻¹ to 200 g·l⁻¹, and yeast extract (l_o), ranging from 0 g·l⁻¹ to 8 g·l⁻¹. The most favorable conditions proved to be initial concentrations of S_o=25 g·l⁻¹ and l_o=4 g·l⁻¹, which gave a maximum specific growth rate of 0.26 h⁻¹, biomass productivity of 0.023 g·l⁻¹·h⁻¹, overall biomass yield of 0.094 g·g⁻¹, specific xylose-uptake rate (q_s) of 0.3 g·g⁻¹·h⁻¹ (for t=50 h), specific ethanol-production rate (q_E) of 0.065 g·g⁻¹·h⁻¹ and overall ethanol yield of 0.34 g·g⁻¹; q_s values decreased after the exponential growth phase while q_E remained practically constant.     

Does midazolam inhibit the development of acute tolerance to the analgesic effect of alfentanil?

Alfentanil-midazolam analgesic interactions were studied in rats with continuous infusions or bolus injections of the drugs. Analgesia was determined by measuring the threshold of motor response to noxious pressure. The continous constant-rate infusion of alfentanil demonstrated that after an initial peak, the analgesia profoundly declined due to the development of acute tolerance. When alfentanil (250 μg·kg⁻¹·h⁻¹) was given together with midazolam (3 mg·kg⁻¹·h⁻¹), the decline in the analgesic effect of alfentanil was attenuated. Following the 4 h period of the constant-rate (250 μg·kg⁻¹·h⁻¹) infusion of alfentanil, when acute tolerance was already developed, midazolam (3 mg·kg⁻¹) given as a bolus injection enhanced the alfentanil-induced anesthesia. At the same time, when alfentanil was given as a bolus injection (30 μg·kg⁻¹) with or without midazolam (3 mg·kg⁻¹) also by bolus injection, no changes were seen to indicate an enhancement of the analgesic effect of alfentanil by midazolam. The results suggest that midazolam attenuates the development of acute tolerance to the analgesic effect of alfentanil.     

Evaluation of methanogenic kinetics in an anaerobic fluidized bed reactor (AFBR)

A kinetic study of the methanogenic phase was carried out on a pilot lab scale anaerobic fluidized bed reactor (AFBR) in batch mode. An examination of the effect of initial acetate concentration, bed expansion and bed segregation is presented.Experimental data observed for the acetate removal against time were adjusted to a zero-order kinetic equation, over the chemical oxygen demand (COD) range studied (1430–5340 mg litre⁻¹), independently of the bed expansion (11–37%). The kinetic constant was calculated using robust regression analysis. The zero-order kinetic constant, K₀ was between 1180–1380 mg COD litre⁻¹ h⁻¹ on the fixed bed volume basis, and the maximum specific substrate utilization rate, k, was between 145–198 mg COD g VS⁻¹ h⁻¹.The kinetic behaviour was found to be different throughout the reactor, on the fixed bed volume basis and the activity at the bottom of the bed was lower than the activity in the upper region. However, on an attached volatile solids basis, the activity at the bottom level was the greatest.     

Prodigiosin formation by Serratia marcescens in a chemostat

In a study of the control of metabolite formation, prodigiosin production by Serratia marcescens was used as a model. Specific production rates of prodigiosin formation were determined using batch culture technique. Sucrose as carbon source and NH₄NO₃ as nitrogen source resulted in a specific production rate of 0.476 mg prodigiosin (g cell dry weight)⁻¹ h⁻¹. Prodigiosin formation and productivity was inversely correlated to growth rate when the bacterium was grown under carbon limitation on a defined medium in a chemostat culture. The maximum specific growth rate (μ_max) was 0.54 h⁻¹ and prodigiosin was formed in amounts over 1 mg l⁻¹ up to a growth rate (μ) of 0.3 h⁻¹ at steady state conditions. At a dilution rate of 0.1 h⁻¹ growth at steady state with carbon and phosphate limitation supported prodigiosin formation giving a similar specific yield [1.17 mg prodigiosin (g cell dry weight)⁻¹ and 0.94 mg g⁻¹, respectively], however, cells grown with nitrogen limitation [(NH₄)₂SO₄] did not form prodigiosin. Productivity in batch culture was 1.33 mg l⁻¹ h⁻¹ as compared to 0.57 mg l⁻¹ h⁻¹ in the chemostat.     

Zooplankton and bacteria contribution to phosphorus and nitrogen internal cycling in a tropical and eutrophic reservoir: Pampulha Lake,Brazil

Nutrient regeneration and respiration rates of natural zooplankton from a tropical reservoir were experimentally measured. Excretion rates of ammonia (E_a), orthophosphate (E_p) and community respiration rates (R) were estimated considering the variations in the concentrations of ammonia, orthophosphate and dissolved oxygen between control and experimental units. The ranges obtained for these rates from the 2 h assays were E_a = 1.95–4.95 μg N-NH₄ · mg · DW⁻¹ · h⁻¹; E_p = 0.12–0.76 μg P-PO₄ mg DW⁻¹ · h⁻¹. Respiratory rates were quite constant (R = 0.01–0.02 mg O₂ · mg DW⁻¹ · h⁻¹). The uptake of nutrients due to bacteria can affect the experimental determination of excretion rates of zooplankton. Orthophosphate release increased from 0.28 to 0.82 μg P-PO₄ · mg DW⁻¹ · h⁻¹ when bacterial activity was depleted by antibiotic addition in experimental vessels (Exp IV). This demonstrates that free living bacteria are able to consume promptly most phosphorus excreted by zooplankton. Ammonia excretion rates were lower in experimental units containing antibiotics. Lower excretion rates were also obtained with longer exposure times and higher biomass levels in the experimental units. Finally, this study also showed that zooplankton excretion can affect significantly turn over rates of total phosphorus in Pampulha Reservoir. In some periods, specially during the dry season when zooplankton biomass was very high, phosphorus release by zooplankton, during one single day, can be as high as 40% of the total phosphorus content in lake water (Turn over time = 2.5 days).     

Guanosine diphosphate binding,metabolism and regulation of follitropin-sensitive adenylate cyclase activity in Sertoli cell membranes

Nucleotides such as GTP and GDP appear to be involved in signal transduction via G protein modulation of adenylate cyclase activity. Studies on direct binding of [³H]GDP to membranes prepared from cultured immature rat Sertoli cells indicated that this process was reversible, approached steady state within 10 min, had a K_a of 4.5 ·10⁶M⁻¹ and was specific for guanine nucleotides. The non-hydrolyzable analog, guanosine 5′-O-[3-thio]triphosphate (GPPP[S]), was most effective as an inhibitor of [³H]GDP binding (ED₅₀ = 4.8·10⁻⁸M), whereas guanosine 5′-O-[2-thio]diphosphate (Gpp[S]) was less potent (ED₅₀ = 3.4·10⁻⁷M). Release of bound GDP was enhanced by follitropin (FSH) in the presence of Gppp[S], although not by FSH alone. Sertoli cell membranes possess guanine nucleotide hydrolase activity, where 95% of added nucleotide was rapidly degraded to guanosine. Binding kinetics were significantly influenced by nucleotide metabolism, which was prevented by controlling the Mg²⁺ concentration with EDTA and including App[NH]p to reduce nonspecific hydrolysis. Kinetic studies indicated that Gpp[S] inhibited (P < 0.05) Gppp[S]-stimulated adenylate cyclase activity (K_i = 1.8·10⁻⁷M), whereas basal activity remained unaffected. Addition of Gpp[S] to pre-activated enzyme (FSH plus GTP) resulted in a time-dependent decay of adenylate cyclase activity with a K_off value of 6 ± 1·min⁻¹. Using a two-stage pre-inculbation technique, adenylate cyclase activity was demonstrated to be sensitive to the nucleotide bound. When FSH was included, catalytic activity was not altered by the order of pre-incubation with the nucleotides. This suggested that the exchange of bound Gpp[S] for Gppp[S] was enhance by FSH. Activation and attenuation of FSH-sensitive adenylate cyclase activity is dependent on a nucleotide exchange mechanism which is driven by (1) the higher affinity of G for GTP than GDP, (2) enhanced release of GD when FSH is present and (3) GTP hydrolysis coupled to rapid metabolism of guanine nucleotides.     

The study of renin–angiotensin–aldosterone in experimental diabetes mellitus

It is generally accepted that hypertension and other vascular pathologies increase in diabetes mellitus (DM) patients as a result of the renin–angiotensin–aldosterone (RAA) system. In this study, changes in the renin‐angiotensin‐aldosterone (RAA) system level was determined in Streptozotocin (STZ)‐injected rats. A total of 46 female Wistar albino rats (180–220 g body weight) was utilized in these experiments. STZ was given intraperitoneally to induce diabetes in rats. Streptozotocin (60 mg kg⁻¹ body weight) was dissolved in 0·1 m citrate–‐phosphate buffer (pH 4–5). The non‐diabetic rats were injected with sterilized buffer alone to act as a control group. Blood glucose levels were 398±8·2 mg dl⁻¹, 488±11·75 mg dl⁻¹ and 658±29·6 mg dl⁻¹ at days 3, 12 and 30 respectively. The level of plasma renin activity (PRA) was measured as 7·69±1·07 ng ml⁻¹ h⁻¹; 1·82±0·22 ng ml⁻¹ h⁻¹ and 0·67±0·12 ng ml⁻¹ h⁻¹ at days 3, 12 and 30, respectively. These values showed that the PRA levels are decreased with increased time period. Serum angiotensin converting enzyme (ACE, E.C. 3.4.15.1) levels were increased at days 12 and 30 (p<0·05 and p<0·005), whereas serum aldosterone levels were increased at days 3 and 12 (p<0·05). The level of urea and creatinine increased at days 12 and 30 (p<0·05 and p<0·005, respectively) when compared to the control group. The data from these experiments indicate that the PRA level decreased whereas ACE activity level increased in diabetic rats compared with the control. Aldosterone levels increased at the first stage of the experiment, but then decreased by the end of the experiment as a result of changes in renin and ACE levels. Copyright © 1999 John Wiley & Sons, Ltd.     

Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis

The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l⁻¹) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 μmol s⁻¹ m⁻² at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s⁻¹ m⁻²), with fish capturing up to 5 prey larva⁻¹ h⁻¹. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s⁻¹ m⁻²) exceeding 100 prey larva⁻¹ h⁻¹. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s⁻¹ m⁻², remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva⁻¹ h⁻¹) that was independent of larval age.     

Effects of dehydration and low temperatures on the oxidation of high-potential cytochrome c by photosynthetic reaction centers in Ectothiorhodospira shaposhnikovii

Effects of temperature and dehydration on the efficiency of electron transfer from membrane-bound high-potential cytochromes c_h to the reaction-center bacteriochlorophyll (P-890) in Ectothiorhodospira shaposhnikovii have been studied. A kinetic analysis of the cytochrome oxidation suggests that there are at least two conformational states of the c_h-P-890 complex, of which only one allows photoinduced electron transfer from cytochrome to P-890⁺. Lowering the temperature of dehydration leads to a change in the proportion of the populations in the two conformations. The observed 2-fold deceleration of cytochrome oxidation can be related only to the diminution of the amount of photoactive cytochromes per reaction center. The rate constant for the transfer of an electron from cytochrome c_h to bacteriochlorophyll is 2.8 · 10⁵ s⁻¹ and is independent of temperature and dehydration (as estimated within the accuracy of the experiments). The effects produced by low temperature and dehydration are completely reversible. The thermodynamic parameters of the transition of the cytochrome from the nontransfer to electron-transfer conformation were estimated. For room temperature (+ 20°C) in chromatophore preparations, ΔG = −5.4 kJ · M⁻¹, ΔH = 60 kJ · M⁻¹, ΔS = 0.22 kJ · M⁻¹ · K⁻¹. For Triton X-100 subchromatophore preparations, the absolute values of the above parameters are significantly lower: ΔG = −2.8 kJ · M⁻¹, ΔH = 18 kJ · M⁻¹, and ΔS = 0.075 kJ · M⁻¹ · K⁻¹. To a larger extent, the above parameters are diminished for chromatophore preparations in an 80% glycerol solution: ΔG = −1.7 kJ · M⁻¹, ΔH = 6 kJ · M⁻¹, ΔS = 0.025 kJ · M⁻¹ · K⁻¹. The data suggest the hydrophobic character of the forces that maintain the P-890-c_h complex in the electron-transfer conformation. The results obtained suggest that electron tunneling within the complex cannot occur until a specific conformational configuration of the complex is formed. The efficiency of cytochrome c_h oxidation is determined by the temperature, the degree of dehydration and the environmental conditions, whereas the transfer of an electron itself in the electron-transfer configuration is essentially independent of temperature and hydration.     

Primary production of phytoplankton in Lake Valencia (Venezuela)

Lake Valencia is heavily polluted by waste water of domestic, agricultural and industrial origin. The high organic load may have produced important changes in the limnological properties. Cyanobacteria dominated in numbers and biomass (over 90% throughout the year). Chlorophyll-a content averaged 37.7 + 15 μg · 1⁻¹. Maximum concentrations of 50–80 μg · 1⁻¹ were found near the inflows affected by organically polluted affluents. There has been a 50% reduction in the euphotic zone in only 13 years. The maximum rate of gross photosynthesis per hour at light saturation was determined within the uppermost 1-meter layer. The highest value was 16,290 mg O₂ · m⁻³ · h⁻¹. Lake Valencia is among the most productive lakes in the world, with areal net photosynthesis averaging 7.5 g C · m⁻² · d⁻¹.     

Enhanced production of peroxidase in continuous culture of Arthromyces ramosus by selective bleeding of mycelium

A new method of continuous culture with selective bleeding of mycelia using 9-mesh screen was developed to improve the production rate of peroxidase (POD) by Arthromyces ramosus. At the dilution rate of 0.05 h⁻¹ with the mycelium leakage rate of 60%, a high production rate (average value was 1.67 U·ml⁻¹·h⁻¹) was maintained for over 100 h: the rate was 3.2 times that in a glucose-fed batch culture. At the same dilution rate, the volumetric and specific production rates of POD in the continuous culture without the screen were lower than those in the first continuous culture and decreased gradually in the later phase of the culture. In the continuous culture with low mycelium leakage rate of 1.6%, the POD production rate was not improved further, although the mycelial concentration (43 g·l⁻¹) increased 2.9 times. It is suggested that the high agitation rate required to meet the oxygen demand is unfavorable for the POD production.     

Continuous ethanol production by yeast immobilized on to channeled alumina beads

Vertical and near-horizontal (15° angle) packed-bed columns were compared for continuous ethanol fermentation using an alcohol- and glucose-tolerant Saccharomyces cerevisiae strain immobilized on to channeled alumina beads (5·0 × 10⁹ cells g⁻¹ beads). Spaces between beads (1·0–6·5 mm) and angle (15°) of near-horizontal reactor columns (with six ports in each) efficiently removed CO₂ and increased ethanol productivity. Malt-glucose-yeast-extract broth containing 16·7% glucose at 35°C fed at a dilution rate of 3· h⁻¹ to thw two horizontal columns (in series) yielded maximum ethanol productivity of 40·0 g liter⁻¹ h⁻¹. Feedstock flow rate and other factors (temperature, pH, nutrients, and glucose levels) affected productivities. The immobilized-cell system showed operational stability for >3 months without plugging, and could be stored for at least one year with no loss of bioreactor performance. Scanning electron micrographs of the beads revealed large numbers of yeast-cells attached on to internal and external surfaces of beads.     

The gills as an important uptake route for the essential nutrient iron in freshwater rainbow trout Oncorhynchus mykiss

Short-term (3h) acquisition of iron (16 nmol ⁵⁹FeCl₃ l⁻¹) from oxic, alkaline fresh water was assessed in rainbow trout Oncorhynchus mykiss in the presence or absence of a range of iron chelators, all of which had differing binding affinities for ferric iron [100 μmol l⁻¹ of desferrioxamine (DFO), Log₁₀K₁ 32·5; citric acid Log₁₀K₁ 11·9; nitrilotriacetic acid (NTA) Log₁₀K₁ 15·9, CP20 and CP94 (Log₁₀K₁ > 30), as well as humic acid (HA), Log₁₀K₁ 5·04, 5 mg l⁻¹]. In the absence of chelators (control conditions) O. mykiss acquired iron from the water under laboratory lights (wavelength range of the lights 440–650 nm, peak intensity 548–626 nm) via the gill. In these conditions iron uptake onto the gill had a maximum transport capacity (J_max) of 11·2 pmol Fe g⁻¹ h⁻¹ (gill organ mass) and a K_m of 21·3 nmol Fe l⁻¹ h⁻¹. Furthermore, there were two components to iron accumulation into the carcass of these fish, a slow rate of aqueous iron uptake at low concentrations (6–24 nmol Fe l⁻¹), followed by a faster rate of uptake at higher iron concentrations (48–96 nmol Fe l⁻¹), suggesting that the rate-limiting step of iron uptake at low iron concentrations is the apical entry step. O. mykiss also acquired iron in the presence of HA, although the majority of the other chelators prevented iron uptake. Ultraviolet light (354 nm) treatment of Fe-DFO increased iron bioavailability. Results suggest that rainbow trout are able to access either the predicted very low concentrations (picomolar) of ferrous iron present in fresh water or the ferric oxide complexes present in oxic environments. The iron uptake rate measured (0·75 pmol g⁻¹ h⁻¹) would be sufficient to provide a substantial proportion (c. 85%) of the daily iron requirements of growing salmonid fry.