Aerobic scope for activity in age 0 year Atlantic cod Gadus morhua

Key components of swimming metabolism: standard metabolism (R_s), active metabolism (R_a) and absolute aerobic scope for activity (R_a–R_s) were determined for small age 0 year Atlantic cod Gadus morhua. Gadus morhua juveniles grew from 0·50 to 2·89 g wet body mass (M_WB) over the experimental period of 100 days, and growth rates (G) ranged from 1·4 to 2·9% day^?1, which decreased with increasing size. Metabolic rates were recorded by measuring changes in oxygen consumption over time at different activity levels using modified Brett‐type respirometers designed to accommodate the small size and short swimming endurance of small fishes. Power performance relationships were established between oxygen consumption and swimming speed measurements were repeated for individual fish as each fish grew. Mass‐specific standard metabolic rates () were calculated from the power performance relationships by extrapolating to zero swimming speed and decreased from 7·00 to 5·77 μmol O₂ g^?1 h^?1, mass‐specific active metabolic rates () were calculated from extrapolation to maximum swimming speed (U_max) and decreased from 26·18 to 14·35 μmol O₂ g^?1 h^?1 and mass‐specific absolute scope for activity was calculated as the difference between active and standard metabolism () and decreased from 26·18 to 14·35 μmol O₂ g^?1 h^?1 as M_WB increased. Small fish with low R_s had bigger aerobic scopes but, as expected, R_s was higher in smaller fish than larger fish. The measurements and results from this study are unique as R_s, R_a and absolute aerobic scopes have not been previously determined for small age 0 year G. morhua.     

Tree size frequency distributions, plant density, age and community disturbance

We show that explicit mathematical and biological relationships exist among the scaling exponents and the allometric constants (α and β, respectively) of log–log linear tree‐community size frequency distributions, plant density N_T, and minimum, maximum and average stem diameters (D_min, D_max, and , respectively). As individuals grow in size and D_max increases, N_T is predicted to decrease as reflected by a decrease in the numerical value of α and an increase in the value of β. Our derivations further show that N_T decreases as increases even if D_min or D_max remain unchanged. Because D_max and the age of the largest individuals in a community are correlated, albeit weakly, we argue that the interdependent relationships among the numerical values of α, β, N_T, and shed light on the extent to which communities have experienced recent global disturbance. These predicted relationships receive strong statistical support using two large datasets spanning a broad spectrum of tree‐dominated communities.     

Bioenergetics of juvenile whitespotted bamboo shark Chiloscyllium plagiosum [Anonymous (Bennett)]

This study establishes the bioenergetics budget of juvenile whitespotted bamboo shark Chiloscyllium plagiosum by estimating the standard metabolic rate (R_S), measuring the effect of body size and temperature on the R_S, and identifying the specific dynamic action (R_SDA) magnitude and duration of that action in juvenile whitespotted bamboo sharks. The mean ±s .d . (R_S) of six fish (500–620 g) measured in a circular closed respirometry system was 30·21 ± 5·68 mg O₂ kg^?1 h^?1 at 18° C and 70·38 ± 14·81 mg O₂ kg^?1 h^?1 at 28° C, respectively. There were no significant differences in R_S between day and night at either 18 or 28° C (t‐test, P > 0·05). The mean ±s .d . Q₁₀ for 18–28° C was 2·32 ± 0·06 (n = 6). The amount of oxygen consumed per hour changed predictably with body mass (M; 295–750 g) following the relationship: (n = 40, r²= 0·92, P < 0·05). The mean magnitude of R_SDA was 95·28 ± 17·55 mg O₂ kg^?1 h^?1. The amount of gross ingested energy (E_I) expended as R_SDA ranged from 6·32 to 12·78% with a mean ±s .d . of 8·01 ± 0·03%. The duration of the R_SDA effect was 122 h. The energy content of juvenile whitespotted bamboo shark, squid and faeces determined by bomb calorimeter were 19·51, 20·3 and 18·62 kJ g dry mass^?1. A mean bioenergetic budget for juvenile whitespotted bamboo sharks fed with squid at 18° C was 100C = 29·5G + 31·9R_S+ 28·2R_SDA+ 6·7F + 2·1E + 1·6U, where C = consumption, G = growth, F = egestion, E = excretion and U = unaccounted energy.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Size‐dependent effects of daily thermal fluctuations on the growth and size heterogeneity of Nile tilapia Oreochromis niloticus

The growth of Nile tilapia Oreochromis niloticus (0·02–20·00 g) was measured when fed to excess during the hours of light, following their exposure to five thermal regimes fluctuating around the thermal optimum for growth (T_opt = 30° C) over the diel cycle of day (light, L) and night (dark, N), i.e. 27° C(L):33° C(N), 28·5° C(L):31·5° C(N), 30° C(L):30° C(N), 31·5° C(L):28·5° C(N) and 33° C(L):27° C(N) (two replicates per treatment, six weeks' rearing, growth measurements at weekly intervals). A model constructed with a stepwise multiple‐regression analysis accounted for 87·4% of the variation of the specific growth rate (G, % M day^?1) from the variations of wet mass (M), the extent of the thermal fluctuation (F_T) and their interactions, i.e. log₁₀G = 1·7686 ? 0·2136 log₁₀M + 0·0806 [log ₁₀M× log ₁₀ (1 + F_T)] ? 0·0394 [log₁₀M× log ₁₀ (1 + F_T)]². Based on this model, the thermal fluctuation that produces the fastest growth ( ,°C) decreases in a curvilinear way, from 5·1° C at 20 mg to c. 0·7° C at 20 g. Thermal regimes that produce the slowest growth also produce the highest size heterogeneity. Functional hypotheses behind the size‐dependent effects of thermal fluctuations are discussed, together with their implications in natural habitats and aquaculture systems with in different contexts of food availability.     

Critical oxygen tension increases during digestion in the perch Perca fluviatilis

Oxygen uptake () and critical oxygen tension (P_crit) were measured in resting perch Perca fluviatilis that were either fasting or digesting. Digestion caused to double (from 61 to 117 mg O₂ kg^?1h^?1) and was associated with a rise in P_crit (from 3·4 to 4·9 kPa), showing that the animal's digestive state must be considered when assessing the effect of hypoxia in natural conditions, and when defining optimal oxygen conditions in aquaculture.     

Leupeptins Produced by the Marine Alteromonas sp. B-10–31

Endo-1,4-β-D-mannanase (1,4-β-D-mannanohydrolase, EC 3.2.1.78) was purified from viscera of a mud snail, Pomacea insularus (de Ordigny). The purified enzyme gave a single protein band in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight of the purified enzyme was estimated to be 44,000. The amino-terminal sequence was H· Gly-X-Leu-Arg-Arg-Gln-Gly-Thr-Asn-Ile-Val-Asp-Ser-His-Gly-His-Lys-Val-Phe-Leu-Ser-Gly-Ala-Asn-Thr-Ala-Trp-Val-Ala-Tyr-Gly-Tyr-Asp-. The enzyme was stable from pH about 5.0 to about 10.5 and had its maximum activity at pH about 5.5. The purified enzyme produced M2, M3, M4,and M5 from β-1,4-mannan. Enzyme activity was greatly inhibited by Ag⁺, Hg²⁺, Cu²⁺, and dithiothreitol at 1 mM concentration. In addition, N-bromosuccinimide completely inhibited the enzyme activity.     

Antitumor Activities and Immunochemical Properties of the Cell-wall Polysaccharides from Aureobasidium pullulans

Delipidated cell walls from Aureobasidium pullulans were fractionated systematically.

The cell surface heteropolysaccharide contains D-mannose, D-galactose, D-glucose, and D-glucuronic acid (ratio, 8.5:3.9:1.0:1.0). It consists of a backbone of (1→6)-α-linked D-mannose residues, some of which are substituted at O-3 with single or β-(1→6)-linked D-galactofuranosyl side chains, some terminated with a D-glucuronic acid residue, and also with single residues of D-glucopyranose, D-galactopyranose, and D-mannopyranose.

This glucurono-gluco-galactomannan interacted with antiserum against Elsinoe leucospila, which also reacted with its galactomannan, indicating that both polysaccharides contain a common epitope, i.e., at least terminal β-galactofuranosyl groups and also possibly internal β-(1→6)-linked galactofuranose residues.

It was further separated by DEAE-Sephacel column chromatography to gluco-galactomannan and glucurono-gluco-galactomannan.

The alkali-extracted β-D-glucan was purified by DEAE-cellulose chromatography to afford two antitumor-active (1→3)-β-D-glucans. One of the glucans (M_r, 1–2 × 10⁵) was a O-6-branched (1→3)-β-D-glucan with a single β-D-glucosyl residue, d.b., 1/7, and the other (M_r, 3.5–4.5 × 10⁵) had similar branched structure, but having d.b., 1/5. Side chains of both glucans contain small proportions of β-(1→6)-and β-(1→4)-D-glucosidic linkages.     

Some observations on the ecology and the population dynamics of Merluccius angustimanus in the South Gulf ofCalifornia*

A population of Merluccius angustimanus Garman has been discovered in the south-east Gulf of California, where it is found at 80–120 m in the south of its range (Mazatlan to Altata) and down to 500 m at the northern end of its range (Isla San Pedro Nolasco, north of Guaymas). Studies of the otoliths and catch curves of M. angustimanus show that it lives up to seven years, and may reach 39 cm long (one fish) although it does not usually exceed 32 cm. Using the notation of Beverton & Holt (1959) the following parameters were estimated: L_∞= 32.7 cm, K= 0.35, t_∞= 0.016, t_∞= 7years, L_m= 22.0 cm, M for 3–7 years of age = 0.79, M for 2–3 years of age = 0.79-0.89. The von Bertalanffy equation for M. angustimanus was: and was shown to give a reasonably close fit to the real growth curve.     

Ontogenetic Changes of Photosynthetic and Dark Respiration Rates in Relation to Nitrogen Content in Individual Leaves of Field Crops

Ontogenetic changes of rates of photon-saturated photosynthesis (P _sat) and dark respiration (R _D) of individual leaves were examined in relation to nitrogen content (Nc) in rice, winter wheat, maize, soybean, field bean, tomato, potato, and beet. P _sat was positively correlated with Nc as follows: P _sat = CfNc + P _sat0, where Cf and P _sat0 are coefficients. The value of Cf was high in maize, medium in rice and soybean, and low in field bean, potato, tomato, and beet, of which difference was not explained by ribulose-1,5-bisphoshate carboxylase/oxygenase (RuBPCO) content. R _D was explained by P _sat and/or Nc, however, two models must be applied according to plant species. R _D related linearly with P _sat and Nc in maize, field bean, and potato as follows: R _D = a P _sat + b, or R _D = aNc + b, where a, a, b and b are coefficients. In other species, the R _D/P _sat ratio increased exponentially with the decrease of Nc as follows: R _D/P _sat = a exp(b Nc), where a and b are coefficients. Therefore, R _D in these crops was expressed as follows: In(R _D) = ln(a P _sat) + b Nc, indicating that R _D in these crops was regulated by both P _sat and Nc.     

Dependence of laser light scattering of DNA on NaCl concentration

We show that the persistence length a of DNA, derived from total intensity laser light scattering of linear Col E₁ DNA and corrected for excluded-volume effects, varies from about 68 nm in 0.005M NaCl to about 40 nm in 0.2M NaCl, leveling off to a constant value (about 27 nm) at high NaCl (1–4M) concentration. These observations do not agree with current views on the effect of electrostatic charge and ionic conditions on DNA dimensions. The apparent diffusion constant D_app, determined from laser light scattering autocorrelation as a function of scattering vector q, at NaCl concentrations 0.005–4M, correctly yields the translational diffusion coefficient D_t at low values of q and scales with molecular dimensions rather than segment length at high values of q; thus, D_app/D_t yields a universal curve when plotted against q²R, where R_g is the radius of the gyration. The sedimentation coefficients s at 0.1 and 0.2M NaCl concentration closely agree with the well-tested empirical relations, and a combination of s, D_t, and the appropriate density increments yield correct molar masses over the whole salt concentration range. Approximate constancy of D_tR_g indicates limited draining in translational flow. We present some observations and thoughts on the regimes in which a dependence of the correlation decay times on q³ rather than q² applies. We conclude that quasielastic laser light scattering discloses little information about dynamics of internal motion of DNA chains.     

Comparison of growth and condition indices of juvenile flatfish in differentcoastal nursery grounds

Coastal and estuarine ecosystems in the eastern channel and southern bight of the North Sea provide nursery habitats for juvenile fishes. We examined the age 0-group juveniles of three flatfish speciesSolea solea, Limanda limanda and Pleuronectes platessa, collected in five nursery areas with different characteristics (three sites located near small estuaries and two affected by important inputs of industrial effluents), to evaluate habitat influence on their growth and condition. We measured a biochemical index (RNA:DNA ratio), a morphometric index (Fultons K condition index), plus a recent growth index (marginal otolith increment width) on each individual (about 3months old), collected during surveys in autumn 1999. The three indices displayed few significant differences among the five nursery sites and different patterns for each species. We suggest that the investigated nursery areas provide habitats of equivalent quality for the age 0-group juvenile flatfishes in spite of different anthropogenic disturbances. On the other hand, this study focuses on the importance of using different biological indicators to assess habitat quality and environmental stressors in coastal areas.     

Energetics of chemolithoautotrophy in the hydrothermal system of Vulcano Island, southern Italy

The hydrothermal system at Vulcano, Aeolian Islands (Italy), is home to a wide variety of thermophilic, chemolithoautotrophic archaea and bacteria. As observed in laboratory growth studies, these organisms may use an array of terminal electron acceptors (TEAs), including O₂, , Fe(III), , elemental sulphur and CO₂; electron donors include H₂, , Fe²⁺, H₂S and CH₄. Concentrations of inorganic aqueous species and gases were measured in 10 hydrothermal fluids from seeps, wells and vents on Vulcano. These data were combined with standard Gibbs free energies () to calculate overall Gibbs free energies (ΔG_r) of 90 redox reactions that involve 16 inorganic N‐, S‐, C‐, Fe‐, H‐ and O‐bearing compounds. It is shown that oxidation reactions with O₂ as the TEA release significantly more energy (normalized per electron transferred) than most anaerobic oxidation reactions, but the energy yield is comparable or even higher for several reactions in which , or Fe(III) serves as the TEA. For example, the oxidation of CH₄ to CO₂ coupled to the reduction of Fe(III) in magnetite to Fe²⁺ releases between 94 and 123 kJ/mol e^?, depending on the site. By comparison, the aerobic oxidation of H₂ or reduced inorganic N‐, S‐, C‐ and Fe‐bearing compounds generally yields between 70 and 100 kJ/mol e^?. It is further shown that the energy yield from the reduction of elemental sulphur to H₂S is relatively low (8–19 kJ/mol e^?) despite being a very common metabolism among thermophiles. In addition, for many of the 90 reactions evaluated at each of the 10 sites, values of ΔG_r tend to cluster with differences < 20 kJ/mol e^?. However, large differences in ΔG_r (up to ～ 60 kJ/mol e^?) are observed in Fe redox reactions, due largely to considerable variations in Fe²⁺, H⁺ and H₂ concentrations. In fact, at the sites investigated, most variations in ΔG_r arise from differences in composition and not in temperature.     

The parabolic pattern of animal growth: determination of equation parameters and their temperature dependencies

1. Parabolic (power) growth is characteristic of many aquatic poikilothermic animals for certain stages of their development. The parabolic pattern describing growth in weight (or length) under constant ambient conditions can be expressed in the following general form: where Y is growth rate (or specific growth rate), X is animal size, and Ω and τ are coefficients. The constancy of ambient conditions is of cardinal importance in determining τ. The problem of maintaining a constant level of nutrition can be reliably solved only by the presence of food in excess of demand. Data satisfying these requirements have demonstrated that τ does not depend on factors such as temperature, and can be assumed to be independent of ambient conditions. In the growth rate-weight equation, τ ranges between 0.5 and 0.85 for animals representing a variety of taxonomic groups. 2. The coefficient Ω. is affected by ambient conditions (e. g. temperature, amount of food). Its value reflects the ‘level’ of the growth rate-size relationship under given conditions. For a specific time period, Ω can be computed from the following formula: where X₁ and X₂ are the animal sizes (weights, lengths) at time t₁ and t₂, the beginning and end of the time period. The calculated value of Ω corresponds to the average intensity of the ambient factor (F) affecting the growth during the period between the two observations. If the values of the Ω are calculated for wide range of the factor, the relationship between the Ω. and F, Ω=f(F), can be determined. The function can be then incorporated into the parabolic equation of growth, as 3. Dependence of the development rate (1/D, where D is time interval needed to complete a given stage) on temperature (T), and dependence of Ω on T, are both described by sigmoid-shape curves. The broad intermediate part of these curves, a range to which animals are adapted in nature, can be approximated by straight line functions. For two groups, pan-size sockeye salmon (Oncorhynchus nerka) and different species of chironomid larvae, it was shown that an equation combining parabolic growth and linear temperature patterns describes accurately the variability observed in growth rates under experimental and natural conditions.     

Light scattering and viscosity study of heat aggregation of insulin

Aggregation behavior and hydrodynamic parameters of insulin have been determined from static and dynamic light scattering experiments and intrinsic viscosity measurements carried out at pH 4.0, 7.5, and 9.0 in the temperature range 20–40°C in aqueous solutions. The protein aggregated extensively at elevated temperatures in the acidic solutions. Intermolecular interactions were found to be attractive and to increase with temperature. The measured intrinsic viscosity [η], diffusion coefficient D₀, molecular weight M, and radius of gyration R_g exhibited the universal behavior: M[η] = (2.4 ± 02) × 10⁻²⁷ (R_e,η/R_e,D)³(D_0η/T)⁻³ and (D₀√n)₋₁ ≃ (√6 πη₀ζβ/k_BT) [1 + 0.201)(v/β³)√n], where n is the number of segments in the polypeptide. The effective hydrodynamic radii deduced from [η], (R_e, η) and the same deduced from D₀, (R_e,D) showed a constant ratio, (R_e,η/R_e,D = 1.1 ± 0.1). R_e,D/R_g = ξ was found to be (0.76 ± 0.07). From the known solvent viscosity η₀, the segment length β was deduced to be (10 ± 1) Å. The excluded volume was deduced to be (5 Å)³ regardless of pH. The Flory-Huggins interaction parameter was found to be χ = 0.45 ± 0.04, independent of pH and temperature. © 1998 John Wiley & Sons, Inc. Biopoly 45: 1–8, 1998     

Biological traits and life table of the exotic Harmonia axyridis compared with Hippodamia variegata,and Adalia bipunctata (Col., Coccinellidae)

Abstract: As part of an environmental risk assessment study of exotic natural enemies used in inundative biological control, life‐history characteristics of Harmonia axyridis (Pallas), Hippodamia variegata (Goeze) and Adalia bipunctata (L.) (Col., Coccinellidae) were quantified under laboratory conditions at 25°C on Myzus persicae (Sulzer) as prey. Comparative studies showed significant differences among pre‐adult development times: H. axyridis developed slower ( = 19.8 days) than H. variegata ( = 18.1 days) and A. bipunctata ( = 18.4 days). Differences were also evident in the duration of egg, larval and pupal stages. No measurable differences among the three species were found for fecundity, oviposition rate and adult longevity. Harmonia axyridis exhibited the longest pre‐oviposition ( = 7.4 days) and interoviposition ( = 3.6 days) periods and the shortest oviposition period ( = 13.7 days). The Bieri model was used to describe age‐specific fecundity for the three species of coccinellids. The intrinsic rate of increase (r_m), net reproductive rate (R₀) and mean generation time (T) were higher for H. variegata (r_m = 0.114, R₀ = 52.75, T = 41.88 days) than for H. axyridis (r_m = 0.089, R₀ = 26.27, T = 38.81 days) or A. bipunctata (r_m = 0.081, R₀ = 18.49, T = 40.06 days). Our findings show that the biological traits of H. axyridis do not seem to be factors that may contribute to the invasiveness of this coccinellid.     

On the Fermenting Ability of Sand Cultures of Acetone-Butanol Organisms Stored for Long Years

β-N-Acetyl-D-hexosaminidase was isolated from the mid-gut gland of Patinopecten yessoensis. The enzyme was purifted by making an acetone-dried preparation of the mid-gut gland, extracting with 50 mM citrate-phosphate buffer (pH 4.0) (about 13% of the extracted proteins was β-N-acetyl-D-hexosaminidase), ammonium sulfate fractionation, and column chromatographies on CM-Sepharose and DEAE-Sepharose. The purifted β-N-acetyl-D-hexosaminidase was homogeneous on SDS–PAGE, and sufficiently free from other exo-type glycosidases. The molecular weight was 56,000 by SDS–PAGE. The enzyme hydrolyzed both p-nitrophenyl β-N-acetyl-D-glucosaminide and p-nitrophenyl β-N-acetyl-D-galactosaminide. For p-nitrophenyl β-N-acetyl-D-glucosaminide, the pH optimum was 3.7, the optimum temperature was 45°C, and the K_m was 0.24 mM. For p-nitrophenyl β-N-acetyl-D-galactosaminide, these were pH 3.4, 45°C, and 0.15 mM, respectively. The enzyme liberated non-reducing terminal β-Iinked N-acetyl-D-glucosamine or N-acetyl-D-galactosamine from various 2-aminopyridyl derivatives of oligosaccharides of N-glycan or glycolipid type except of G_M2-tetrasaccharide. As the enzyme was stable around pH 3.5–5.5, it may be useful for long time reactions around the optimum pH.     

The effect of temperature on the respiration rate of meiofauna

Summary The effect of temperature on respiration rate has been established, using Cartesian divers, for the meiofaunal sabellid polychaeteManayunkia aestuarina, the free-living nematodeSphaerolaimus hirsutus and the harpacticoid copepodTachidius discipes from a mudflat in the Lynher estuary, Cornwall, U.K. Over the temperature range normally experienced in the field, i.e. 5–20° C the size-compensated respiration rate (R _c) was related to the temperature (T) in °C by the equation Log₁₀ R _c=-0.635+0.0339T forManayunkia, Log₁₀ R _c=0.180+0.0069T forSphaerolaimus and Log₁₀ R _c=-0.428+0.0337T forTachidius, being equivalent toQ ₁₀ values of 2.19, 1.17 and 2.17 respectively. In order to derive the temperature response forManayunkia a relationship was first established between respiration rate and body size: Log₁₀ R=0.05+0.75 Log₁₀ V whereR=respiration in nl·O₂·ind^-1·h^-1 andV=body volume in nl.TheQ ₁₀ values are compared with values for other species derived from the literature. From these limited data a dichotomy emerges: species with aQ ₁₀2 which apparently feed on diatoms and bacteria, the abundance of which are subject to large short term variability, and species withQ ₁₀1 apparently dependent on more stable food sources.     

Secretory expression and enzymatic characterization of recombinant Agarivorans albus β-agarase in Escherichia coli

Agarase catalyzes the hydrolysis of agar, which is primarily used as a medium for microbiology, various food additives, and new biomass materials. In this study, we described the expression of the synthetic gene encoding β-agarase from Agarivorans albus (Aaβ-agarase) in Escherichia coli. The synthetic β-agarase gene was designed based on the biased codons of E. coli to optimize its expression and extracellular secretion in an active, soluble form. The synthesized agarase gene, including its signal sequence, was cloned into the pET-26 expression vector, and the pET-Aaβ-agarase plasmid was introduced into E. coli BL21-Star (DE3) cells. The E. coli transformants were cultured for high-yield secretion of recombinant Aaβ-agarase in Luria-Bertani broth containing 0.6?mM isopropyl β-D-1-thiogalactopyranoside for 9?h at 37°C. The expressed recombinant Aaβ-agarase was purified by ammonium sulfate precipitation and diethylaminoethyl-sepharose column chromatography, yielding ～10?mg/L Aaβ-agarase. The purified recombinant Aaβ-agarase exhibited optimal activity at pH 7 and 40°C, and its activity was strongly inhibited by Cu²⁺, Mn²⁺, Zn²⁺, and Al³⁺ ions. Furthermore, the K_M and k_cat values for purified Aaβ-agarase were ～0.02?mM and ～45/s, respectively. These kinetic values were up to approximately 15–100-fold lower than the K_M values reported for other agarases and approximately 7–30-fold higher than the k_cat/K_M values reported for other agarases, indicating that recombinant Aaβ-agarase exhibited good substrate-binding ability and high catalytic efficiency. These results demonstrated that the E. coli expression system was capable of producing recombinant Aaβ-agarase in an active form, at a high yield, and with attributes useful in the relevant industries.     

Growth simulation ofHansenula polymorpha

Summary Using the model presented in part I, the measured time and spacial variations of process variables were simulated with satisfactory accuracy. Especially the experimentally found minima of the longitudinal dissolved oxygen concentration profiles in the substrate limiting growth range, which are caused by the transition from oxygen transfer limited to substrate limited growth along the tower, can be simulated with great accuracy.Symbols L length - M mass - T time - K temperature - M_M mole mass - a Specific gas/liquid interfacial area with regard to the liquid volume in the tower (L^–1) - DS_R Substrate feed rate (ML^–3T^–1) - K_O Saturation constant of Monod kinetics with regard to oxygen (ML^–3) - K_S Saturation constant of Monod kinetics with regard to the substrate (ML^–3) - K_ST Constant - K_L Mass transfer coefficient (LT^–1) - k_La Volumetric mass transfer coefficient (T^–1) - k_La^E Volumetric mass transfer coefficient at the entrance (T^–1) - k_La Volumetric mass transfer coefficient at large distances from the entrance (T^–1) - k_La ₀ Volumetric mass transfer coefficient in the absence of substrate (ethanol) (T^–1) - L_R Gas-liquid layer height in the tower (L) - L_R Height of the loop (L) - - O_B Dissolved oxygen concentration in the loop liquid (ML^–3) - O_F Dissolved oxygen concentration in the tower liquid (ML^–3) - O _F ^* Saturation value of O_F (ML^–3) - OTR Oxygen transfer rate (ML^–3T^–1) - P Pressure - Oxygen transfer rate (ML^–3T) - S_B Substrate concentration in the loop liquid (ML^–3) - S_D Substrate concentration at which k_La=2 k_La ₀ (ML^–3) - S_F Substrate concentration in the tower liquid (ML^–3) - T Absolute temperature - t Time (T) - u_Go Superficial gas velocity in the tower - V_R Reactor volume (L³) - V_G Volumetric gas flow rate in the tower (L³T^–1) - V_B Volumetric liquid flow rate in the loop (L³T^–1) - V_F Volumetric liquid flow rate in the tower (L³T^–3) - V_u Liquid recycling rate (L³T^–1) - X_B Biomass concentration in the loop liquid (ML^–3) - X_F Biomass concentration in the tower liquid (ML^–3) - x Longitudinal coordinate in the tower (L) - x^* Longitudinal coordinate in the loop (L) - x_OG O₂ mole fraction in the gas phase - Y_X/O Yield coefficient of biomass with regard to oxygen - Y_X/S Yield coefficient of biomass with regard to substrate - z=x/L_R Dimensionless longitudinal coordinate in the tower - z^*=x^*/L_B Dimensionless longitudinal coordinate in the loop - Constant (L_R is the distance from the aerator on which k_L a is space dependent) - Liquid recirculation ratio - _G Mean relative gas holdup in the tower - _exp Experimentally determined (T^–1) - _max Maximum specific growth rate (T^–1) - _F Liquid density (ML^–3) - A At the exit - E At the inlet