A mathematical model of the effects of light on the eclosion rhythm of the fruit flydrosophila pseudoobscura

A mathematical formulation useful in characterizing the effects of light on the pupal eclosion rhythm of the fruit flyDrosophila pseudoobscura is presented. It is based upon the premise that the underlying pacemaker oscillator behaves in a manner analogous to a customized version of a phase-locked loop circuit. Theoretical analyses supplemented with numerical simulations reveal that this phase-locked loop approach yields a concise mathematical characterization which is quite comprehensive in its scope, yet surprisingly accurate in the detail with which it can be used to successfully predict observed experimental results.     

The temporal ‘structure’ and function of the insect photoperiodic clock: a tribute to Colin S. Pittendrigh

In 1936, Erwin Bünning suggested that photoperiodic time measurement was a function of the circadian system. Colin Pittendrigh became an ardent supporter of Bünning's hypothesis, drawing parallels between photoperiodism and his own group's investigations of adult eclosion rhythmicity in the fruit fly Drosophila pseudoobscura. They developed several more modern versions of Bünning's general hypothesis based on the entrainment of circadian oscillations to the light cycle, including ‘external coincidence’, which is a derivation of Bünning's original model, and ‘internal coincidence’, which relied upon seasonal changes in the mutual phase relationship of oscillators within a multi‐oscillator circadian system. This review considers the experimental evidence for the central role of the circadian system in photoperiodic timing and, in some species, for both external and internal coincidence. Pittendrigh, however, pursued the idea of internal coincidence further with his analysis of the pacemaker–slave organization of eclosion rhythmicity in D. pseudoobscura and proposed a similar theoretical model for photoperiodism comprising a group of slave oscillators driven by a light‐sensitive pacemaker. In this model, the phase relationships of the slaves to the pacemaker were affected by (i) the relative periods of the pacemaker and slave(s); (ii) the strength(s) of the coupling between the two; and (iii) the dampening coefficients of the various slaves. Manipulation of these variables showed that the slaves adopted different internal phase relationships (both to each other and to the pacemaker) under the influence of changes in daily photophase, the period of the Zeitgeber and phase shifts of the entraining light cycle.     

Changes in in vivo fluorescence quenching in rye and barley as a function of reduced PSII light harvesting antenna size

The relationship between the size of the light harvesting antenna to photosystem II (LHCII) and quenching of non-photochemical and dark level fluorescence was studied in wild-type rye (Secale cereale L. cv. Musketeer) and barley (Hordeum vulgare L. cv. Gunilla) as well as in the barley chlorophyll b-less chlorina F2 mutant (H. vulgare L. cv. Dornaria, chlorina-F2). Exposure for 10 min to an irradiance of 500 μmol m^?2 s^?1 resulted in a strong (0.71–0.73) non-photochemical (q_s) quenching of the fluorescence yield in wild-type (WT) material, while the barley chlorina F2-mutant was quenched to 75% of this level. Relaxation of q_s in darkness revealed a fast initial decay, related to relaxation of the high-energy-state dependent (q_E) part of q_s. Etiolated seedlings of rye and barley exposed to intermittent light (IML) for 36 cycles of 2 min light and 118 min darkness had suppressed Chl b and LHCII-production in both WT rye and barley, while the barley chlorina F2-mutant became totally devoid of all LHCII-polypeptides. It was found that the levels of q_s and q_s were similar in control grown barley chlorina F2 and IML-grown WT rye and barley, but q_s was reduced by 30 to 35% and q_s by 50 to 65%, respectively, as compared to control-grown. WT plants. No significant q_s could be detected in IML-grown barley chlorina F2. It is clear, from these changes in in vivo fluorescence quenching in rye and barley that a significant level of q_s is detectable even in the absence of LHCII. Only when the proximal antennae are totally absent, does q_E completely disappear. We conclude that the presence of LHCII is not an absolute requirement for q_E-quenching and suggest that distal as well as proximal antenna may contribute to q_E in vivo.     

Inhibitory effect of dihydroxyacetone onGluconobacter oxydans: Kinetic aspects and expression by mathematical equations

Summary Microbial conversion of glycerol into dihydroxyacetone (DHA) byGluconobacter oxydans was subjected to inhibition by excess substrate. Comparison of cultures containing increasing initial DHA contents (0 to 100 g l^–1) demonstrated that DHA also inhibited this fermentation process. The first effect was on bacterial growth (cellular development stopped when DHA concentration reached 67 gl^–1), and then on oxidation of glycerol (DHA synthesis only occurred when the DHA concentration in the culture medium was lower than 85 g l^–1). Productivity, specific rates and, to a lesser extent, conversion yields decreased as initial concentrations of DHA increased. The changes in the specific parameters according to increasing initial DHA contents were described by general equations. These formulae satisfactorily express the concave aspect of the curves and the reduction in biological activity when the cells were in contact with DHA concentrations of up to 96 g l^–1.Abbreviations X, S, P biomass, substrate, product concentrations - r _x,r _s,r _p rates of growth, consumption and production - ,q _s,q _p specific rates of growth, glycerol consumption and DHA production - Y _x/s, Y_p/s conversion yields of substrate into biomass and product - K _s constant of affinity of cells to the substrate - K _ip product inhibition constant - P _m threshold concentration of DHA in substrate     

Theory of emotional stress and mental illness

A theoretical study of emotion in human beings yields results which are potentially useful in a practical way. Two variables are used—the total amount of healthy emotionr and the total amount of emotional stresss. A stabilizing factor in the value ofr is the interrelationship between it ands. Differential equations forr ands are readily solved simultaneously with the use of the Laplace transform. Onset of emotional illness is signaled in a feasible way by development of a relationship between the parameters which causess to increase indefinitely with the passage of time. Among the potentially useful conclusions which arise from this relationship is that the presence of psychosomatic disease protects against emotional illness.     

Adult eclosion rhythm of the Indian meal moth Plodia interpunctella: response to various thermocycles with different means and amplitudes

In addition to photoperiod, thermoperiod (or thermocycle) might be an important Zeitgeber for entraining the circadian oscillator controlling adult eclosion rhythm in the Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae). This is confirmed by exposing larvae receiving diapause‐preventing treatments to various thermocycles with different means and amplitudes of temperature. The thermocycles investigated in the present study are TC 8 : 16 h, TC 12 : 12 h, TC 16 : 8 h and TC 20 : 4 h, where T and C represent thermophase (30 °C) and cryophase (20 °C), respectively. For all thermocycles, the peak of adult eclosion rhythm occurs at around the mid‐thermophase. This indicates that the larvae use both ‘temperature‐rise’ and ‘temperature‐fall’ signals to adjust the eclosion phase in each thermocycle. The absence (DD) or presence (LL) of light affects this time‐keeping system slightly under the given thermocycle. The rhythmic adult eclosion noted after exposure of larvae to 30 °C DD for 14 days is recorded in the thermocycles (TC 12 : 12 h, DD; mean temperature = 25 °C) with different amplitudes of 27.5/22.5 °C, 26.5/23.5 °C and 25.5/24.5 °C. The peak in adult eclosion advances in time as the amplitude of the temperature cycle decreases. In the temperature cycle of 25.5/24.5 °C, a peak occurs at the end of the cryophase, 2 h before the temperature‐rise. The adult eclosion rhythm is also observed under various thermocycles (TC 12 : 12 h, DD) consisting of different temperature levels (30 to 20 °C) with different amplitudes. It is found that the temporal position of the peak advances significantly when the amplitude of the thermocycle becomes lower.     

The kinetics of protein-protein recognition

We examine a simple kinetic model for association that incorporates the basic features of protein-protein recognition within the rigid body approximation, that is, when no large conformation change occurs. Association starts with random collision at the rate k_coll predicted by the Einstein-Smoluchowski equation. This creates an encounter pair that can evolve into a stable complex if and only if the two molecules are correctly oriented and positioned, which has a probability p_r. In the absence of long-range interactions, the bimolecular rate of association is p_r k_coll. Long-range electrostatic interactions affect both k_coll and p_r. The collision rate is multiplied by q_t, a factor larger than 1 when the molecules carry net charges of opposite sign as coulombic attraction makes collisions more frequent, and less than 1 in the opposite case. The probability p_r is multiplied by a factor q_r that represents the steering effect of electric dipoles, which preorient the molecules before they collide. The model is applied to experimental data obtained by Schreiber and Fersht (Nat. Struct. Biol. 3:427–431, 1996) on the kinetics of barnase-barstar association. When long-range electrostatic interactions are fully screened or mutated away, q_tq_r ≈1, and the observed rate of productive collision is p_r k_coll ≈10⁵ M⁻¹ · s⁻¹. Under these conditions, p_r ≈1.5 · 10⁻⁵ is determined by geometric constraints corresponding to a loss of rotational freedom. Its value is compatible with computer docking simulations and implies a rotational entropy loss ΔS_rot ≈ 22 e.u. in the transition state. At low ionic strength, long-range electrostatic interactions accelerate barnase-barstar association by a factor q_tq_rof up to 10⁵ as favorable charge-charge and charge-dipole interactions work together to make it much faster than free diffusion would allow. Proteins 28:153–161, 1997. © 1997 Wiley-Liss Inc.     

Eclosion hormone activity in developing embryos of the silkworm, Bombyx mori

The ultimate timing of hatching in the silkworm, Bombyx mori, is controlled by a circadian oscillator. The presence of eclosion hormone in developing embryos of the silkworm is demonstrated. Eclosion hormone activity first becomes detectable in embryos which have developed almost to the stage of the differentiation of the neuroendocrine system. Hormonal activity increases sharply to a maximum level 1 day before hatching and falls by about a half in the newly hatched larvae. Eclosion hormone was partially purified from the pharate first-instar larvae and approx, a 2100-fold purification was achieved. The molecular weight of the embryo eclosion hormone is estimated to be 7000 ～ 9000 Daltons by gel-filtration on Sephadex G-50 (superfine). The role of eclosion hormone on hatching behaviour of the silkworm, Bombyx mori, is discussed.     

Development of projections between areas of the nervous system

A theory of projections in the nervous system (such as the retino-tectal projection) is proposed. Components of axonal growth cones and target tissue interact and cooperate, within the area of contact, to generate a guiding parameter, in the simplest case a guiding substance of distributionp. The components which are involved in this production are assumed to have graded distributions with respect to position in the projecting and target area, respectively. The distributionp thus produced guides the growth cone in the direction of maximal slope until the minimal value ofp is reached. In this way, each growth cone can be guided to a position on the target tissue which depends on the origin of the fiber in such a manner that a projection results. Adhesive forces could but need not be involved in the guiding mechanism. The slope ofp may interfere with an intracellular pattern forming mechanism within the growth cone, determining the polarity of activation (as modelled previously on the basis of autocatalysis and lateral inhibition) and thus the direction of growth. For the generation of a distribution ofp leading to a reliable projection, simple graded distributions in the projecting and target area suffice, involving one or two components in each dimension. Their effect on the generation ofp may be activatory as well as inhibitory. Exponential gradients give rise to particularly simple mapping functions. The following is an example of this general type of model: Growth cones as well as target tissue contribute to the production of a guiding substance. For each dimension, there is, in the target tissue, an exponentially graded component exerting (directly or indirectly) two functions: it actively produces guiding substancep and it interacts, in an inhibitory fashion, with the production ofp by a component of the growth cone (which is, in turn, graded with respect to position of origin in the projecting area). While the theory is proposed as a fair approximation of the primary events in neural projections, superimposed regulatory effects can also be incorporated. These include fiber-fiber interactions, mechanisms smoothing out unequal density distributions of axon terminals and effects of time of arrival of fibers on the projection, which have been proposed previously as primary mechanisms generating projections. A further extension of the model is to assume that crude and more refined positional specificity is determined in a combinatorial fashion, allowing the possibility of interchanges and transformations of parameters.     

An eclosion timing mechanism in the mosquito Anopheles gambiae

The circadian control of adult emergence was studied in Anopheles gambiae. In contrast to the situation reported for other mosquitoes, the timing of adult eclosion can be modified by the light regime. Comparison of the timing of pupal—adult ecdysis in groups of individuals pupating at the same time and then kept either in 12 h light alternating with 12 h dark (LD 12:12) or constant light, at temperatures from 22 to 34·5°C, showed that the timing can be modified by the light regime. In LD, eclosion due to take place during the middle and later part of the light phase was delayed, giving a peak near light-off; the maximum delay was of the order of 4–5 h at both 22 and 34·5°C. This effect appears to be mediated by a temperature-compensated timing mechanism. Experiments with different light regimes indicated that the time cue is a previous change from light to dark. When this was given to late fourth stage larvae it affected the timing of adult eclosion without affecting the time of pupation.     

Design and use of a simulation model to evaluate germplasm for antibiotic resistance to the greenhouse whitefly (Trialeurodes vaporariorum) and the sweetpotato whitefly (Bemisia tabaci)

SARAH (Software for theAssessment of antibioticResistance toAleyrodidae inHost plants) is a deterministic simulation model of whitefly population growth based on whitefly life-history components determined on individual plants. The life-history components recorded were oviposition rate, adult survival, pre-adult survival, developmental period, and sex ratio. The simulation model serves as a tool to combine these components and to obtain a single criterion for (antibiotic) resistance. The criterion used was the decrease in simulated intrinsic population growth rate, r _s , relative the r _s value determined on a susceptible control genotype. This model-based evaluation method was tested using the greenhouse whitefly,Trialeurodes vaporariorum Westwood, on tomato and the sweetpotato whitefly,Bemisia tabaci Gennadius, on tomato, eggplant, collard, and pepper. To study its consistency over time, the evaluation method was repeated six times forT. vaporariorum on a susceptible and a resistant tomato cultivar. Simulated intrinsic population growth rate was more consistent in indicating resistance than any of the individual life-history components. Of tenL. hirsutum accessions tested for resistance toT. vaporariorum, three exhibited r _s values that were significantly lower than those for the susceptible control. In addition, on these tenL. hirsutum accessions, a significant positive correlation was observed between r _s and sex ratio (# females/# males). Four host plant species (tomato, collard, eggplant, and pepper) were evaluated for resistance toB. tabaci. All life-history components and r _s values varied among host species, while a negative r _s value was observed forB. tabaci on pepper. A high correlation was found between results from a sensitivity analysis of SARAH and results from a sensitivity analysis of a validated whitefly population simulation model by Yanoet al. (1989a). Significant correlations were found for the relationships between oviposition rate, adult survival, or pre-adult survival and r _s , indicating that none of these life-history components can be omitted from the test procedure. This model-based evaluation method offers a standardized way to quantify levels of antibiotic resistance to whiteflies and will enhance efficiency in breeding programs.     

Influence of light and food on the circadian clock in liver of rainbow trout,Oncorhynchus mykiss

Several reports support the existence of multiple peripheral oscillators in fish, which may be able to modulate the rhythmic functions developed by those tissues hosting them. Thus, a circadian oscillator has been proposed to be located within fish liver. In this vertebrate group, the role played by the circadian system in regulating metabolic processes in liver is mostly unknown. We, therefore investigated the liver of rainbow trout (Oncorhynchus mykiss) as a potential element participating in the regulation of circadian rhythms in fish by hosting a functional circadian oscillator. The presence and expression pattern of main components of the circadian molecular machinery (clock1a, bmal1, per1 and rev-erbβ-like) were assessed. Furthermore, the role of environmental cues such as light and food, and their interaction in order to modulate the circadian oscillator was also assessed by exposing animals to constant conditions (absence of light for 48 h, and/or a 4 days fasting period). Our results demonstrate the existence of a functional circadian oscillator within trout liver, as demonstrated by significant rhythms of all clock genes assessed, independently of the environmental conditions studied. In addition, the daily profile of mRNA abundance of clock genes is influenced by both light (mainly clock1a and per1) and food (rev-erbβ-like), which is indicative of an interaction between both synchronizers. Our results point to rev-erbβ-like as possible mediator between the influence of light and food on the circadian oscillator within trout liver, since its daily profile is influenced by both light and food, thus affecting that of bmal1.     

Modelling of alcohol fermentation in a tubular reactor with high biomass recycle

Fermentation in tubular recycle reactors with high biomass concentrations is a way to boost productivity in alcohol production. A computer model has been developed to investigate the potential as well as to establish the limits of this process from a chemical engineering point of view. The model takes into account the kinetics of the reaction, the nonideality of flow and the segregation in the bioreactor. In accordance with literature, it is shown that tubular reactors with biomass recycle can improve productivity of alcohol fermentation substantially.With the help of the computer based reactor model it was also possible to estimate the detrimental effects of cell damage due to pumping. These effects are shown to play a major role, if the biomass separation is performed by filtration units which need high flow rates, e.g. tangential flow filters.List of Symbols Bo d Bodenstein number - c kg/m³ concentration of any component - CPFR continuous plug flow reactor - CSTR continuous stirred tank reactor - d _h m hydraulic diameter - D _eff m²/s dispersion coefficient - f residence time distribution function - K _s kg/m³ monod constant for biomass production - K _s kg/m³ monod constant for alcohol production - p kg/m³ product concentration - P _i kg/m³ lower inhibition limit concentration for biomass production - p _i kg/m³ lower inhibition limit concentration for alcohol production - p _m kg/m³ maximum inhibition limit concentration for biomass production - p _m kg/m³ maximum inhibition limit concentration for alcohol production - q _p h^–1 specific production rate - q _p,max h^–1 maximum specific production rate for alcohol production - q _s h^–1 specific substrate consumption rate - Q _L m _gas ³ /m³h specific gas rate - r _p , r _s , r _x kg/(m³ · h) reaction rate for ethanol production substrate consumption and cell growth, respectively - S _F kg/m³ substrate concentration in feed stream - s kg/m³ substrate concentration - t h time - x kg/m³ biomass concentration - x _max kg/m³ maximum biomass concentration for biomass production - Y _p/s yield coefficient - h^–1 specific growth rate - _max h^–1 maximum specific growth rate - dimensionless time (t/) - h mean residence time - _s glucose conversion     

LIGHT‐INDUCED RESPONSES OF OXYGEN PHOTOREDUCTION,REACTIVE OXYGEN SPECIES PRODUCTION AND SCAVENGING IN TWO DIATOM SPECIES1

Diatoms are frequently exposed to high light (HL) levels, which can result in photoinhibition and damage to PSII. Many microalgae can photoreduce oxygen using the Mehler reaction driven by PSI, which could protect PSII. The ability of Nitzschia epithemioides Grunow and Thalassiosira pseudonana Hasle et Heimdal grown at 50 and 300 μmol photons · m^?2 · s^?1 to photoreduce oxygen was examined by mass spectrometric measurements of ¹⁸O₂. Both species exhibited significant rates of oxygen photoreduction at saturating light levels, with cells grown in HL exhibiting higher rates. HL‐grown T. pseudonana had maximum rates of oxygen photoreduction five times greater than N. epithemoides, with 49% of electrons transported through PSII being used to reduce oxygen. Exposure to excess light (1,000 μmol photons · m^?2 · s^?1) produced similar decreases in the operating quantum efficiency of PSII (F_q′/F_m′) of low light (LL)‐ and HL‐grown N. epithemoides, whereas HL‐grown T. pseudonana exhibited much smaller decreases in F_q′/F_m′ than LL‐grown cells. HL‐grown T. pseudonana and N. epithemioides exhibited greater superoxide and hydrogen peroxide production, higher activities (in T. pseudonana) of superoxide dismutase (SOD) and ascorbate peroxidase (APX), and increased expression of three SOD‐ and one APX‐encoding genes after 60 min of excess light compared to LL‐grown cells. These responses provide a mechanism that contributes to the photoprotection of PSII against photodamage.     

The relative glucose uptake abilities of non-Saccharomyces yeasts play a role in their coexistence with Saccharomyces cerevisiae in mixed cultures

The growth and glucose uptake of single cultures of the wine-related yeasts Kluyveromyces thermotolerans, Torulaspora delbrueckii, and Saccharomyces cerevisiae were investigated. The yeasts had different specific glucose uptake rates (q _s) that depended on the residual glucose concentration and the oxygen availability. In mixed cultures, the q _s values of the yeasts were not subject to any interaction effects over a wide range of glucose concentrations. Our results strongly indicate that the relative glucose uptake abilities of both non-Saccharomyces yeasts, i.e. the q _s(non-Saccharomyces)/q _s(S. cerevisiae) ratios, regulated their abilities to compete for space in mixed cultures with S. cerevisiae, which, in turn, regulated their early deaths. This hypothesis enabled us to explain why K. thermotolerans was less able than T. delbrueckii to coexist with S. cerevisiae in mixed cultures. Furthermore, it enabled us to explain why oxygen increased the abilities of K. thermotolerans and T. delbrueckii to coexist with S. cerevisiae in the mixed cultures.     

From where are insects recruited? A new model to interpret catches of attractive traps

Abstract 1 Two new concepts describing the origin of insects caught in an attractive trap are presented. 2 Male European pine sawflies Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae) were marked and released from 50, 100, 200, 400 and 800 m in the four cardinal directions around a centrally placed pheromone trap. 3 Based on linear regression of transformed data, we calculated the seasonal sampling range (r_s) as 1040 m. 4 We estimated the previously defined ‘effective sampling area’ (α) at 4.9 ha, assuming that the insects are evenly distributed around the trap and that they are attracted from a circular area around it. This is the area from which all insects originate if the trap is 100% effective within the area but captures nothing outside of it. The effective sampling area reveals nothing about the origin of the insects caught. We defined the Cumulative Proportional Catch (CPC) that gives the proportion of the trap catch that originates from an area within a distance r from the trap. At r = r_s CPC = 1, and in our study 50% of the captured insects originated up to 450 m from the trap. Thus, for the trap used in this study, a relatively large proportion of the catch originates some distance from the trap. 5 We also defined the Catch Concentration (CC), which is the ratio of the radius of the effective sampling area (r_α) to r_s. For our data, CC = 0.12, which is intermediate to high compared to the few other studies that we have extracted information from. If r_α is considerably lower than r_s, then only a small proportion of the insects caught originate from close proximity to the trap. When r_α is close to r_s, the catch adequately mirrors the population within most of its sampling range. 6 By using these two new concepts, we will better understand why monitoring traps mirror the local population in some cases but not in others. This will help in designing more reliable monitoring programmes.     

Specific light uptake rates can enhance astaxanthin productivity in <Emphasis Type="Italic">Haematococcus lacustris</Emphasis>

Lumostatic operation was applied for efficient astaxanthin production in autotrophic Haematococcus lacustris cultures using 0.4-L bubble column photobioreactors. The lumostatic operation in this study was performed with three different specific light uptake rates (q _e) based on cell concentration, cell projection area, and fresh weight as one-, two- and three-dimensional characteristics values, respectively. The q _e value from the cell concentration (q _e1D) obtained was 13.5 × 10^?8 μE cell^?1 s^?1, and the maximum astaxanthin concentration was increased to 150 % compared to that of a control with constant light intensity. The other optimum q _e values by cell projection area (q _e2D) and fresh weight (q _e3D) were determined to be 195 μE m^?2 s^?1 and 10.5 μE g^?1 s^?1 for astaxanthin production, respectively. The maximum astaxanthin production from the lumostatic cultures using the parameters controlled by cell projection area (2D) and fresh weight (3D) also increased by 36 and 22 % over that of the controls, respectively. When comparing the optimal q _e values among the three different types, the lumostatic cultures using q _e based on fresh weight showed the highest astaxanthin productivity (22.8 mg L^?1 day^?1), which was a higher level than previously reported. The lumostatic operations reported here demonstrated that more efficient and effective astaxanthin production was obtained by H. lacustris than providing a constant light intensity, regardless of which parameter is used to calculate the specific light uptake rate.     

Polymorphic and autoreactive H-2-specific monoclonal antibody isolated after injections of syngeneic sendai virus-coated lymphocytes

An H-2-specific monoclonal antibody (mAb Q-1) was obtained from B10.Q (H-2 ^q) mice injected with syngeneic Sendai virus-coated cells. The IgM monoclonal antibody recognizes the public determinant H-2.25 shared by H-2 ^k (K ^k) and H-2 ^r haplotypes and cross-reacts with H-2^d, H-2^s, H-2^p, and H-2^q cells, the latter being the haplotype of the challenged B-cell donor. The binding of mAb Q-1 to H-2^d, H-2^s, H-2^q, and H-2^p cells was lower than to H-2^k and H-2^r and of decreasing affinity but could be clearly distinguished from the negative reactions with H-2^b and H-2^f cells. MAb Q-1 distinguishes between Sendai virus-coated and uncoated lymphocytes only cells with low-affinity binding. On virus-coated or infected (H-2^p, H-2^q, H-2^d, H-2^s) cells lysis was stronger than on normal lymphocytes. We interpret the enhanced lysis of Sendai virus-positive cells by mAb Q-1 to be due to recognition of a modified exposure of public H-2 determinants induced by Sendai virus.On leave from The Institute of Immunology and Experimental Therapy, Wroclaw, Poland     

Modeling two-oscillator circadian systems entrained by two environmental cycles

Several experimental studies have altered the phase relationship between photic and non-photic environmental, 24 h cycles (zeitgebers) in order to assess their role in the synchronization of circadian rhythms. To assist in the interpretation of the complex activity patterns that emerge from these "conflicting zeitgeber" protocols, we present computer simulations of coupled circadian oscillators forced by two independent zeitgebers. This circadian system configuration was first employed by Pittendrigh and Bruce (1959), to model their studies of the light and temperature entrainment of the eclosion oscillator in Drosophila. Whereas most of the recent experiments have restricted conflicting zeitgeber experiments to two experimental conditions, by comparing circadian oscillator phases under two distinct phase relationships between zeitgebers (usually 0 and 12 h), Pittendrigh and Bruce compared eclosion phase under 12 distinct phase relationships, spanning the 24 h interval. Our simulations using non-linear differential equations replicated complex non-linear phenomena, such as "phase jumps" and sudden switches in zeitgeber preferences, which had previously been difficult to interpret. Our simulations reveal that these phenomena generally arise when inter-oscillator coupling is high in relation to the zeitgeber strength. Manipulations in the structural symmetry of the model indicated that these results can be expected to apply to a wide range of system configurations. Finally, our studies recommend the use of the complete protocol employed by Pittendrigh and Bruce, because different system configurations can generate similar results when a "conflicting zeitgeber experiment" incorporates only two phase relationships between zeitgebers.     

Enhanced catalase synthesis by a novel combined system of photocatalytic reactor and fermentor

A novel combined system of a photocatalytic reactor, with UV and titanium dioxide as photocatalyst, and a fermentor with Bacillus sp. F26 as catalase producer was developed. Production of catalase was enhanced by 14% to 18.5 U ml⁻¹ without affecting cell growth.Nomenclature q_s: specific glucose consumption rate; μ: specific growth rate; q_p: specific CAT production rate