Nucleolar changes in human phytohaemagglutinin-stimulated lymphocytes

Summary The nucleoli of lymphocytes from circulating peripheral blood and from phytohaemagglutinin (PHA)-stimulated cultures (from 2 h–96 h) were studied using a silver method, RNA-specific fluorescent staining, and electron microscopy of ultrathin sections. In peripheral blood about 75% of the lymphocytes have one ring-shaped nucleolus composed of a distinct fibrillar centre surrounded by a dense pars fibrillaris and little granular material; the remaining lymphocytes showing two or more small ring-shaped nucleoli. With PHA stimulation, the number of cells with several nucleoli increases first (from 2 h–12 h). Next, cells containing one or, at most, two large nucleoli with nucleolonema devoid of fibrillar centers are seen (from 4 h on). 34 h after PHA, nucleoli of the compact type containing one or more fibrillar centres appear and comprise about 60% of the cells after 72 h. The appearance of more than one nucleolus per cell shortly after PHA administration suggests an activation of additional nucleolar organizer regions (NOR), which fuse to form one or two large nucleoli with nucleolonema. These are then transformed into compact nucleoli. The fibrillar centers stain preferentially with silver. They contain nonchromosomal proteins and may serve as stores for nucleolar proteins. The fusion of activated NORs during the first cell cycle explains the relatively high frequency of satellite associations in first mitoses compared to later mitoses after stimulation.     

Growth of the Thermophilic Bacterium Geobacillus uralicus as a Function of Temperature and pH: An SCM-Based Kinetic Analysis

The synthetic chemostat model (SCM), originally developed to describe nonstationary growth under widely varying concentrations of the limiting substrate, was modified to account for the effects of nontrophic factors such as temperature and pH. The bacterium Geobacillus uralicus, isolated from an ultradeep well (4680 m), was grown at temperatures ranging from 40 to 75°C and at pH varying from 5 to 9. The biomass kinetics was reasonably well described by the SCM, including the phase of growth deceleration observed in the first hours after a change in the cultivation temperature. At an early stage of batch growth in a neutral or alkalescent medium, bacterial cells showed reversible attachment to the glass surface of the fermentation vessel. The temperature dependence of the maximum specific growth rate (_m) was fitted using the equation _m = Aexp(T)/{1 + expB[1 – C/(T + 273)]}, where A, , B, and C are constants. The maximum specific growth rate of 2.7 h^–1 (generation time, 15.4 min) was attained on a complex nutrient medium (peptone and yeast extract) at 66.5°C and pH 7.5. On a synthetic mineral medium with glucose, the specific growth rate declined to 1.2 h^–1, and the optimal temperature for growth decreased to 62.3°C.     

Adaptive networks using learning matrices

Summary The performance of the Learning Matrix (LM) is suitable for the design of adaptive networks of higher complexity. It has been published, how to connect a LM with a generator of patterns (binary or nonbinary) and a ring-counter to result in an automatic classification of the presented patterns. This paper describes, how to connect two LM's to form an Autonomous Learning Matrix Dipole (ALD) and how to organize it, so that it adapts itself to an environment according to a given evaluation scale. For this purpose, a third type of input (beside e and b), namely h seems to be useful. This h-input controls the rate of adaptation of the LM.Using such ALD's, one may design adaptive structures of even higher complexity, for example with an adaptive internal model.The principle of Learning Matrices has been explained in detail (see e.g. IEEE Transactions on Electronic Computers, Vol. EC-12, No. 6, December, 1963, pp. 846–862). Using such learning matrices (LM), one may build up adaptive networks with rather interesting functions. Perhaps they are interesting for the physiologist and psychologist as well as for the engineer. Let us first recall the most essential details of the LM's.

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Zusammenfassung Die Funktion der Lernmatrix (LM) erlaubt den Entwurf adaptiver Netzwerke höherer Komplexität. Es wurde an anderer Stelle schon beschrieben, wie eine LM (binär oder nichtbinär) mit einem Generator für Eigenschaftssätze und einem Ringzähler zusammengeschaltet werden kann, um eine selbsttätige Klassifikation der angebotenen Eigenschaftssätze zu bewirken. Im vorliegenden Aufsatz wird erklärt, wie zwei LM so zusammengeschaltet werden können, dacß sich ein Autonomer Lernmatrix-Dipol (ALD) ergibt, und wie dieser zu organisieren ist, daß er sich einer gegebenen Außenwelt nach Maßgabe einer vorgegebenen Werteskala anpaßt. Zu diesem Zweck erweist sich außer den bisher beschriebenen beiden Zugangen zur LM (nämlich e und b) ein dritter sehr zweckmäßig, nämlich h. Dieser h-Eingang beeinflußt die Lerngeschwindigkeit der LM.Unter Verwendung solcher ALD's kann man adaptive Strukturen noch höherer Komplexität aufbauen, beispielsweise solche mit adaptivem innerem Modell.

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Visiting Professor of Electrical Engineering Stanford University.     

Ethanol fermentation by flocculating yeast: Performance and stability dependence on a critical fermentation rate

Summary A system coupling fermentor and decantor permitted strong accumulation of yeast flocs that were homogeneously suspended in the reactional volume. At 100–190 g/l glucose feed practically total substrate conversion was attained. At 130 g/l glucose feed the highest productivity (18.4 g.l.h) and the highest ethanol yield (90.6%) were reached with biomass levels of 80–90 g/l. We observed that the stability of this system is limited when a critical fermentation rate (D.S_o) close to 39–40 g/l.h (with corresponding ethanol productivities of 19–20 g/l.h) is reached. Higher fermentation rates provoked de-flocculation and lost of biomass.Symbols D dilution rate (h^–1) - E ethanol (g/l) - S_r residual substrate (g/l) - S_o substrate in the feed (g/l) - X biomass (g/l) - ethanol yield (%) - DS_o fermentation rate (g/l.h) (for S_r0) - P_E ethanol productivity (g/l.h)     

Metabolic engineering for direct lactose utilization by Saccharomyces cerevisiae

A recombinant strain of Saccharomyces cerevisiae, secreting -galactosidase from Kluyveromyces lactis, grew efficiently with more than 60 g lactose l^–1. The growth rate (0.23 h^–1) in a cheese-whey medium was close to the highest reported hitherto for other recombinant S. cerevisiae strains that express intracellular -galactosidase and lactose-permease genes. The conditions for growth and -galactosidase secretion in this medium were optimized in a series of factorial experiments. Best results were obtained at 23 °C for 72 h. Since the recombinant strain produced less than 3% ethanol from the lactose, it was also assayed for the production of fructose 1,6-bisphosphate from cheese whey, and 0.06 g l^–1 h^–1 were obtained.     

Model aided design of repeated fed-batch penicillin fermentation

Structured models of antibiotic fermentation that quantify maturation and aging of product forming biomass are fitted to experimental data. Conditions of superiority of repeated fed batch cultivation are characterized on the basis of a performance criterion that includes penicillin productivity and costs of operation. Emphasis is placed on the relevance of such research to the model aided design of optimal cyclic operation.List of Symbols c IU/mg cost factor - D s^–1 dilution rate - J IU · cm^–3 · h^–1 net productivity - k _p IU · mg^–11 · h^–1 specific product formation rate - k _pm IU · mg^–1 · h^–1 maximum specific product formation rate - p IU/cm³ concentration of penicillin - T s final time of fermentation - t s fermentation time - X kg/m³ concentration of biomass dry weight - X ₁kg/m³ concentration of young, immature biomass - X ₂ kg/m³ concentration of mature product forming biomass - X _c kg/m³ biomass concentration of the end of growth phase - X _mkg/m³ maximum biomass concentration Greek Letters s^–1 specific maturation rate - s^–1 specific aging rate - s^–1 specific growth rate - _m s^–1 maximum specific growth rate - _p s^–1 specific growth rate during the product formation phase - s cycle time - % volume fraction of draw-off Abbreviations CC chemostat culture - RFBC repeated fed batch culture - RBC repeated batch culture     

Linear growth in microbial cultures limited by accumulated substrate

Summary The linear growth phase in cultures limited by intracellular (conservative) substrate is represented by a flat exponential curve. Within the range of experimental errors, the presented model fits well the data from both batch and continuous cultures ofEscherichia coli, whose growth is limited in that way.List of symbols D dilution rate, h^–1 - K_S saturation constant, g.L^–1 - S concentration of the limiting substrate, g.L^–1 - S_i concentration of the limiting substrate accumulated in the cells, g.g^–1 - S_o initial concentration of the limiting substrate, g.L^–1 - t time of cultivation, h - t₁ time of exhaustion of the limiting substrate from medium, h - t_o beginning of exponential phase, h - X biomass concentration, g.L^–1 - X₁ biomass concentration at the time of exhaustion of the limiting substrate from the medium, g.L^–1 - X_o biomass concn. at the beginning of exponential phase, g.L^–1 - biomass concn. at steady-state, g.L^–1 - Y growth yield coefficient (biomass/substrate) - specific growth rate, h^–1 - _m maximum specific growth rate, h^–1     

The economic production of anti-microbial factor from human promyelocytes in low serum containing medium under chemostat cultivation

It proves that a purifed Anti-Microbial Factor (AMF) from human promyelocytes has strong activity on Gram(–) and Gram(+) bacteria, showing 0.5 (g/ml) of Minimal Bacterical Concentration (MBC) on bothE. coli andS. aureus. For mass production of AMF, chemostat cultivation is recommended to accumulate cells out of the reactor since it is an intracellular protein and its system requires only 1% serum in the medium. Its production process proves to be closely growth-related. 1.7×10^–8 (g/viable cell/day) of maximum specific AMF production rate is estimated at 0.026 h^–1 of dilution rate, maintaining 6×10⁶ (viable cell/ml). Ca. 300 (mg/ml) of crude AMF can be obtained for 50 days of continuous cultivation under optimal conditions. The cell growth reaches relatively fast steady state.     

Abbau von 14C-, 3H- und 36Cl-markiertem γ-Hexachlorcyclohexan durch anaerobe Bodenmikroorganismen

Zusammenfassung Durch eine anaerobe Mischflora aus Ackerboden wurde -Hexachlorcyclohexan (-HCH) in 4–5 Tagen zu 90% abgebaut. Dabei erfolgte eine schnelle Abspaltung des Chlors in Form von Chloridionen und danach eine Freisetzung des C- und H-Anteiles in Form flüchtiger Verbindungen, in denen kein Chlor und auch kein CO₂ nachzuweisen war.Die Verwendung von ¹⁴C/³H- und ³⁶Cl/³H-doppelmarkiertem -HCH zeigte, daß die Cl- und H-Abspaltung nicht im Verhältnis von 1:1 erfolgte, sondern mehr Cl als H abgespalten wurde. Die flüchtigen Verbindungen enthielten andererseits höhere ¹⁴C- als ³H-Anteile. Gaschromatographische Untersuchungen zeigten ebenfalls eine rasche Verminderung des -HCH und die Bildung verschiedener Metabolite. Es wurde jedoch kein -Pentachlorcyclohexen nachgewiesen. Bei steigenden O₂-Gehalten in der Gasphase verminderte sich der -HCH-Abbau. Jedoch fanden auch noch bei 5% O₂ Chlorabspaltung und die Freisetzung flüchtiger Metabolite statt.-HCH wurde ebenfalls, jedoch langsamer, durch die anaerobe Mischflora abgebaut. Auch hier wurde Chlorid abgespalten, und es traten ebenfalls flüchtige Verbindungen auf, die kein Chlor enthielten.

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Degradation of ¹⁴C-, ³H- and ³⁶Cl-labelled -hexachlorocyclohexane by anaerobic soil microorganisms

Up to 90% of the -Hexachlorocyclohexane (-HCH) applied to an anaerobic mixed bacterial flora enriched from an arable soil were degraded within 4–5 days. Degradation resulted in a rapid release of chloride and in formation of chlorine-free volatile metabolites. CO₂ formation from the molecule was not detected.Investigations with ¹⁴C/³H- and ³⁶Cl/³H double-labelled -HCH indicated that the release of Cl and H did not occur in the ratio of 1:1. More Cl than H was split off. The volatile compounds contained more ¹⁴C than ³H. Gas chromatographic studies also showed the rapid decrease of -HCH and the formation of several metabolites. -Pentachlorocyclohexene was not detected. Increasing O₂-contents in the gas phase of cultures resulted in decreases of the compound's degradation. Release of chloride and of volatile metabolites were observed with O₂ contents in the gas phase up to 5%.-HCH was also, but more slowly as with -HCH, degraded by the anaerobic mixed flora. Chloride was released and volatile, chlorine-free metabolites were found.

     

An electron microscopic study of picoplanktonic organisms from a Small Lake

Picoplankton, both prokaryotic and eukaryotic, are distinguished from other aquatic organisms by their small size (0.1–2.0 m). Such organisms were recovered from waters of a small oligotrophic lake using screens, filters, and high-speed centrifugation. The majority of the picoplankton were unable to form visible colonies on common media. Cells examined in thin sections by electron microscopy showed that 60–75% of the cells had an average diameter after dehydration of 0.48–0.51 m. The maximum dimensions of the rest of the cells ranged from 0.56–1.81 m. Using details of ultrastructure, cells were classified as prokaryotic or eukaryotic. Phototrophs present included two cyanobacterial morphotypes (5–6%) and two eukaryotic algae (less than I%). The arrays of intracytoplasmic membranes in 18–20% of the cells were suggestive of methanotrophic rods and chemoautotrophs. Relatively few prosthecate bacteria were observed in the water column samples. The smallest cells (1–2%) contained magnetosomes, the presence of which were confirmed by x-ray spectroscopy. Iron was also detected in the envelopes of some rod shaped cells by the same technique. The study of in situ picoplankton populations using TEM coupled with other techniques may provide better understanding of picoplankton biomass.     

On the Nature of the Three-Phase Response of Scenedesmus quadricauda Populations to the Action of Imazalil Sulfate

Three-phase dose responses of biological systems of different levels of organization are often called paradoxical because the biological effects are clearly manifested under low- and high-intensity treatments, but are absent during moderate-strength treatments. In this work, we found anomalous changes in the cell number of a green alga Scenedesmus quadricauda (Turp.) Breb. grown in the presence of the fungicide imazalil sulfate. At low imazalil concentrations (2.5 × 10^–9–2.5 × 10^–6 M), the slow increase in the cell number as compared to an untreated culture was not related to cell death. As seen by the dynamics of the population structure and cell functional characteristics (photosynthesis, thermal stability of photosynthetic membranes, etc.), the decrease in the growth rate at low concentrations of imazalil (2–10 × 10^–9 M) was due to a long-term arrest of cell division in a fraction of the cell population rather than to a decrease in the rate of division. The absence of a toxic effect or even a slight stimulation of culture growth at moderate concentrations (0.05–1.25 × 10^–6 M) was due to the resumption of cell division after a temporal cessation. At these concentrations, imazalil induced cell stress and adaptive elevation of cell tolerance to the fungicide (acclimation). Cell death was observed only at a high fungicide content in the medium (6.25 × 10^–6 and higher). Thus, the three-phase (bimodal) dose response corresponds to two regimes (steady-states) of cell functioning which differ in cell sensitivity to external stimuli. The low-sensitivity state, which is characteristic of cells that have experienced stress, is likely to be the state known as hormesis.     

Growth rate and methane affinity of a turbidostatic and oxystatic continuous culture ofMethylococcus capsulatus (Bath)

Summary A turbidostatic and oxystatic fermentation system was used to study the growth kinetic ofMethylococcus capsulatus (Bath). Dissolved oxygen and methane concentrations were measured continuously with membrane inlet mass spectrometry. The specific growth rate was found to increase from 0.25 h^–1 to 0.37 h^–1 and the saturation constant for methane was found to decrease from 71 M to 1.3 M as the copper content of the medium was varied from a very low to a high value.     

Development of a structured model for biopolymer synthesis in the fungus Aureobasidium pullulans

Previous modelling of the pullulan fermentation is discussed and found to lack any mechanistic basis. It is concluded that predictive ability can only be conferred by a structured model with at least two compartments, based upon the best available knowledge of the physiology of the microorganism. Such a model is constructed and compared with experimental data.List of Symbols A (gdm^–3)(g/l) Ammonium ion concentration - B (gdm^–3)(g/l) Concentration of balanced growth compartment of biomass - G (gdm^–3)(g/l) Glucose concentration - k _A (gdm^–3)(g/l) Saturation constant for ammonium - k _G (gdm^–3)(g/l) Saturation constant for glucose - k _S (gdm^–3)(g/l) Saturation constant for sucrose - P (gdm^–3)(g/l) Pullulan concentration - Q Quality of biomass=U/(U+B) - r _G (gdm^–1h^–1)(g/l/h) Rate of removal of glucose from broth - r _GB (gdm^–3h^–1)(g/l/h) Rate of incorporation of glucose into balanced compartment - r _GB (gdm^–3h^–1)(g/l/h) Rate of utilisation of glucose for energy production and cell maintenance - r _GP (gdm^–3h^–1)(g/l/h) Rate of conversion of glucose to pullulan - r _GU (gdm^–3h^–1)(g/l/h) Rate of incorporation of glucose into unbalanced compartment - r _s (gdm^–3h^–1)(g/l/h) Rate of conversion of sucrose to glucose - S (gdm^–3)(g/l) Concentration of sucrose - U (gdm^–3)(g/l) Concentration of unbalanced growth compartment of biomass - X (gdm^–3)(g/l) Biomass concentration - Y _G/A Grams of glucose consumed per gram of ammonium consumed - Y _G/B Grams of glucose consumed per gram of balanced biomass produced - Y _G/U Grams of glucose consumed per gram of unbalanced biomass produced - Y _G/P Grams of glucose consumed per gram of pullulan produced - Rate constant for conversion of sucrose to glucose - Rate constant for uptake of glucose by the cells - Model parameter governing inhibition of sucrose conversion and glucose utilisation - Model parameter denoting fraction of glucose uptake devoted to cell maintenance and energy production - Model parameter governing apportionment of glucose between pseudo-growth and pullulan production This work was funded by the National Engineering Laboratory (NEL) through the Bioreactor Design Club. The authors would like to express their gratitude to the NEL for this generous support.     

Seasonal change in the proportion of bacterial and phytoplankton production along a salinity gradient in a shallow estuary

We intended to evaluate the relative contribution of primary production versus allochthonous carbon in the production of bacterial biomass in a mesotrophic estuary. Different spatial and temporal ranges were observed in the values of bacterioplankton biomass (31–273 g C l^–1) and production (0.1–16.0 g C l^–1 h^–1, 1.5–36.8 mg C m^–2 h^–1) as well as in phytoplankton abundance (50–1700 g C l^–1) and primary production (0.1–512.9 g C l^–1 h^–1, 1.5–512.9 mg C m^–2 h^–1). Bacterial specific growth rate (0.10–1.68 d^–1) during the year did not fluctuate as much as phytoplankton specific growth rate (0.02–0.74 d^–1). Along the salinity gradient and towards the inner estuary, bacterio- and phytoplankton biomass and production increased steadily both in the warm and cold seasons. The maximum geographical increase observed in these variables was 12 times more for the bacterial community and 8 times more for the phytoplankton community. The warm to cold season ratios of the biological variables varied geographically and according to these variables. The increase at the warm season achieved its maximum in the biomass production, particularly in the marine zone and at high tide (20 and 112 times higher in bacterial and phytoplankton production, respectively). The seasonal variation in specific growth rate was most noticeable in phytoplankton, with seasonal ratios of 3–26. The bacterial community of the marine zone responded positively – generating seasonal ratios of 1–13 in bacterial specific growth rate – to the strong warm season increment in phytoplankton growth rate in this zone. In the brackish water zone where even during the warm season allochthonous carbon accounted for 41% (on average) of the bacterial carbon demand, the seasonal ratio of bacterial specific growth rate varied from about 1 to 2. During the warm season, an average of 21% of the primary production was potentially sufficient to support the whole bacterial production. During the cold months, however, the total primary production would be either required or even insufficient to support bacterial production. The estuary turned then into a mostly heterotrophic system. However, the calculated annual production of biomass by bacterio- and phytoplankton in the whole ecosystem showed that auto- and heterotrophic production was balanced in this estuary.     

Kinetics of yeast growth and enzyme syntheses in a phosphate-limited continuous culture

Summary The effect of a deficiency of inorganic phosphate on the growth rate and on the invertase and phosphatase activities inSaccharomyces carlsbergensis was studied in a chemostat culture using a synthetic medium in which ethanol was the sole carbon source.The kinetic relationship between the growth rate and both the rates of phosphate uptake and the ethanol consumption agreed well with the threshold model but not the multicative model. The invertase activity of the yeast increased as the dilution rate decreased. As the phosphate concentration in the feed was reduced, the enzyme synthesis increased remarkably. Acid phosphatase activity was repressed completely above a critical molecular ratio, 0.015, of monopotassium phosphate to ethanol in the feed medium. As the phosphate concentration in the feed decreased, the maximum specific enzyme activity increased and the corresponding optimum dilution rate decreased. These experimental changes in enzyme synthesis were expressed mathematically using the modified operon models for enzyme regulation in terms of two fractions of limited inorganic phosphate; one which affects growth and the other which is incorporated in excess by the cells.Nomenclature A ethanol concentration in the culture (mM) - a, b, c, d exponents in the operon model - D dilution rate (h^–1) - E enzyme concentration in the culture (enzyme unit l^–1) - K_a, K_b, K_c, K_d, k equilibrium constants used in the operon model, see Toda (1976b) - o operator gene - P inorganic phosphate concentration in the culture (mM) - Pi limited inorganic phosphate concentration in the cells (mmole inorganic phosphate/g dry weight of cell) - Q specific enzyme activity, no units: (E/X)/(E/X)_max - Q_c, Q_d as defined in Eq. 12 - R repressor - r regulator gene - X cell concentration in the culture (dry cell weight l^–1) Greek Letters molecular ratio of inorganic phosphate to ethanol in the feed medium (mole/mole) - specific growth rate (h^–1) - A specific uptake rate of ethanol (mmole/g cell·h) - P specific uptake rate of inorganic phosphate (mmole/g cell·h) Suffix crit critical value - f feed - max maximum - min minimum - t total - 1, 2 number of species Superfix eff effective for cell growth - exc excess - str structural     

Determination of the overall volumetric mass transfer coefficient kLa,by a temperature dependent change of gas solubility

Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and k_La was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum k_La that can be measured by this method in a standard laboratory scale bioreactor is 145 h^–1 corresponding to a temperature change rate of 320°C h^–1.Nomenclature p Difference between p_G and p_L (% saturation) - T Ramp change of temperature (°C) - E Temperature-compensated output from the oxygen electrode (A) - E_u Uncompensated output from the oxygen electrode (A) - k_La Overall volumetric mass transfer coefficient (h^–1) - k_La_Tm Overall volumetric mass transfer coefficient at temperature T_m (h^–1) - P_G Dissolved oxygen activity in equilibrium with the gas phase (% saturation) - p_L Dissolved oxygen activity (% saturation) - p_Lm Dissolved oxygen activity at time t_m (% saturation) - t Time (h) - t_m Time of maximum p (h) - T Temperature (°C) - T_cal Calibration temperature of the oxygen electrode (°C) - T_m Final temperature after a temperature shift (°C) - T_n Temperature at time t_n     

Invertase and phosphatase of yeast in a phosphate-limited continuous culture

Summary Deficiency of inorganic phosphate caused the hyper production of invertase and the derepression of acid phosphatase in a continuous culture ofSaccharomyces carlsbergensis. The specific invertase activity was 40,000 enzyme units per g dry cell weight at a dilution rate lower than 0.05 h^–1 with a synthetic glucose medium of which the molecular ratio of KH₂PO₄ to glucose was less than 0.006. This activity is eight fold higher than in a batch growth and 1.5 fold as much as the highest enzyme activity observed so far in a glucose-limited continuous culture.For the hyper production of invertase, it is necessary to culture the yeast continuously by keeping the Nyholm's conservative inorganic phosphate concentration at less than 0.2 m mole per g dry weight cell. The derepression of acid phosphatase brought about by phosphate deficiency, was similar in both batch and continuous cultures.Nomenclature D dilution rate of continuous culture (h^–1) - E_i invertase concentration in culture (enzyme unit l^–1) - E_p acid phosphatase concentration in culture (enzyme unit l^–1) - P inorganic phosphate concentration in culture (mM) - S glucose concentration in culture (mM) - X cell concentration in culture (g dry weight cell l^–1) Greek Letter specific rate of growth (h^–1) Suffix f feed - 0 initial value     

Factors affecting the growth form of Aspergillus terreus NRRL 1960 in relation to itaconic acid fermentation

The effect of medium composition on the growth form of Aspergillus terreus NRRL 1960 in relation to itaconic acid fermentation has been studied. Four types of mycelial pellets were obtained under the conditions used and may be classified as (a) frayed and loose with 0.1–0.5 mm diameter (b) compact with 0.1–0.5 mm diameter (c) loose with 0.5–2.0 mm diameter and (d) compact with 0.5–2.0 mm diameter. Their respective maximum specific rates of formation and yields of itaconic acid, based on 100 g sucrose supplied, were (a) 1.25 mol mg^–1h^–1 and 55–59 g, (b) 0.27–0.43 mol mg^–1 h^–1 and 26–38 g, (c) 0.75–0.90 mol mg^–1 h^–1 and 45–51 g and (d) 0.12 mol mg^–1 h^–1 and 10 g. The presence of Ca²⁺, Zn²⁺ and Fe²⁺ in the basal medium at concentrations of 23.3 mg/100 ml, 0.01 mg/100 ml and 0.006 mg/100 ml respectively were found to be adequate and crucial in obtaining the desired outgrowth for both high production rates and consistent yields of itaconic acid. The further addition of either commercial plaster of Paris or analytical-reagent-grade CaSO₄, especially when activated by heating to 530°C and present in excess of solubility, results in small and frayed pellets, which lead to itaconic acid yields of 55–59 g acid/100 g sugar supplied.     

Effect of molybdenum on the efficiency of tetrathionate utilisation by chemostat cultures ofSulfolobus BC

Summary Continuous cultures ofSulfolobus BC oxidising tetrathionate were found not to be tetrathionate limited, but molybdenum limited. Incorporation of only 1.3M Na₂MoO₄ into the medium of autotrophically grown, continuous cultures ofSulfolobus BC oxidising 15mM tetrathionate at a dilution rate of 0.029h^–1 increased the steady state biomass from absorbance (660nm) 0.160 to 0.315. The biomass yield gave a corresponding increase from 5.93±0.84 to 11.52±0.68 g dry weight mol^–1 tetrathionate oxidised.     

Application of a membrane recycle bioreactor for continuous ethanol production

Summary A series of continuous fermentations were carried out with a production strain of the yeast Saccharomyces cerevisiae in a membrane bioreactor. A membrane separation module composed of ultrafiltration tubular membranes retained all biomass in a fermentation zone of the bioreactor and allowed continuous removal of fermentation products into a cell-free permeate. In a system with total (100%) cell recycle the impact of fermentation conditions [dilution rate (0.03–0.3 h^–1); substrate concentration in the feed (50–300 g·1^–1); biomass concentration (depending on the experimental conditions)] was studied on the behaviour of the immobilized cell population and on ethanol formation. Maximum ethanol productivity (15 g·1^–1·h^–1) was attained at an ethanol concentration of 81 g·1^–1. The highest demands of cells for maintenance energy were found at the maximum feed substrate concentration (300 g·1^–1) and at very low concentrations of cells in the broth.