Growth Rateof Research Articles

The effect of CaCl2 on growth rate, wood decay and oxalic acid accumulation in Serpula lacrymans and related brown-rot fungi

AbstractThe dry rot fungus,Serpula lacrymans, is one of the most destructive copper-tolerant fungi causing timber decay in buildings in temperate regions. Calcium and oxalic acid have been shown to play important roles in the mechanism of wood decay. The effect of calcium on growth and decay was evaluated for 12 strains ofS. lacrymansand compared to five brown-rot fungi. This was done by treating copper citrate (CC)-treated Southern yellow pine (SYP) wood with a CaCl2solution and estimating the decay rate and amount of soluble oxalic acid in an ASTM soil block test. Decay byS. lacrymanswas found to be significantly inhibited by treatment with CaCl2in the presence of copper. In addition, calcium showed no effect on two strains ofS. lacrymansand oneSerpula himantioidesstrain in non-copper-treated SYP wood blocks. The growth rate ofS. lacrymanswas not affected on malt extract agar containing CaCl2. In summary, a marked decrease was observed in the decay capacity ofS. lacrymansin pine treated with CC+CaCl2. The amount of soluble oxalic acid was measured in CC-treated blocks and blocks also treated with CaCl2. Of the comparative brown-rot fungi, bothAntrodia vaillantii(TFFH 294) andPostia placenta(Mad 698) displayed notable wood decay despite CaCl2treatment, while the remaining strains were inhibited.

Correlated Noises in a Prey–Predator Ecosystem

We investigate a Volterra ecosystem driven by correlated noises. Thefluctuation in the death rate of the predator induces an increase ofpopulation density of the predators. The fluctuation in the growth rateof the prey, however, leads the predators to decay. It is reported thatthe predators undergo sensitivity to a random environment, whereas thepreys exhibit a surprising endurance to the same stochastic factor. Thepredators are of better stability under strong correlation of noises.

Inhibition of Malignant Tumor Cells Growing in vitro by Chemical Method Through Increasing Intercellular Communication

目的 通过增加肿瘤细胞膜的渗透性来提高细胞通讯能力,观察对原代瘤细胞的抑制作用.方法使用甘油增加细胞膜的渗透性,用MTT法测定不同浓度的甘油对32例原代肿瘤细胞的抑制作用.结果MTT法显示2%甘油组肿瘤细胞抑制率为(40.19±30.63)%,1%甘油组的抑制率(30.23±27.58)%,两组间抑制率有显著性差异(P＜0.01).结论化学法提高细胞间的通讯对原代瘤细胞有明显的抑制作用。

A Bioeconomic Analysis of a Shellfishery: The Effects of Recruitment and Habitat in a Metapopulation Model

This paper presents a bioeconomic model wherefishing effort exerted has multiple impacts onthe recruitment process of a sedentaryshellfish population. Recognizing thatsedentary populations generally possessmetapopulation characteristics at therecruitment stage, we show that fishing effortexerted not only influences the recruitmentprocess indirectly by limiting the number ofadults that spawn, but also directly byaffecting the habitat in which shellfish larvaerecruit. Depending on the recruitmentcharacteristics, fishing can have negative andpositive direct and indirect effects on therecruitment process. Next, a positive directeffect that fishing can have on the growth rateof the shellfish population if space to recruitto is limited is studied. Generalcharacteristics of sustainable fishing areanalyzed for the case that recruitment occursimmediately once spawning has occurred as wellas for the case that recruitment takes placeover a longer period of time. Conditions areidentified under which shellfishing should beencouraged in order to facilitate therecruitment process of juveniles. The paperends by analyzing how fishing alters theoptimal sustainable solution when itcontributes to habitat destruction.

二酸化炭素施用がＳｏｎｅｒｉｌａ ｐｉｃｔａの生育，開花および光合成に及ぼす影響について

The effects of CO2enrichment on growth rate and flowering were investigated inSonerila picta, a Melastomataceae species. The plant height, leaf number, branch spread and root growth increased under 1200 and 2100 ppm CO2compared with those in ambient CO2 (340-450 ppm) . Flowering was advanced by 7d and number of florets per plant increased by 70% under 1200 and 2100 ppm CO2. The increase in florets under CO2enrichment may be related to increased number of mature branches and increased flowering percentage of the flower buds that differentiated on the branches. The CO2enrichment is useful to improve the growth rate and flower quality ofS. picta.

Closed-loop feedback of MHD instabilities on DIII-D†

A system of coils, sensors and amplifiers has been installed on the DIII-Dtokamak to study the physics of feedback stabilization of low-frequency MHDmodes such as the resistive wall mode (RWM). Experiments are being performedto assess the effectiveness of this minimal system and benchmark thepredictions of theoretical models and codes. In the last campaign theexperiments had been extended to a regime where the RWM threshold is loweredby a fast ramp of the plasma current. In these experiments the onset time ofthe RWM is very reproducible. With this system, the onset of the RWM had beendelayed by up to 100 ms without degrading the plasma performance. The growth rateof the mode increases proportional to the length of the delay, suggesting that theplasma is evolving towards a more unstable configuration. The present resultshave suggested directions for improving the feedback system, including bettersensors and improved feedback algorithms.

Kinetics of 110mAg, 60Co, 137Cs and 54Mn bioaccumulation from water and depuration by the crustacean Daphnia magna

As part of a research program on the transfer withinfreshwater ecosystems of the radionuclides present inthe weakly radioactive liquid effluents from nuclearpower stations, this article presents an assessment ofthe dynamics of zooplankton contamination from water.The experiments were carried out on young pre-adultdaphnids, placed at a density of 250 individualsL-1, in 0.45 μm filtered river water. Inorder to maintain the radionuclide contamination at ahigh level and to limit alterations in the chemicalcharacteristics of the medium, the water was reneweddaily. The dynamics of contamination were described bya one (137Cs) or a two compartmental model(110mAg, 60Co and 54Mn), taking intoaccount the fluctuations of the radionuclideconcentration in the water, as well as the growth rateof the daphnids. The contamination levels weredescribed by the steady state value of theconcentration factor, which was 2870 mL g-1 wetweight, 320 mL g-1 wet weight, 265 mL g-1wet weight and 30 mL g-1 wet weight, for110mAg, 54Mn, 60Co and 137Cs,respectively. During the depuration phase,radioactivity decrease in daphnids was a very fastphenomenon indicating that radionuclide adsorption tothe surface was the major process involved in thecontamination of daphnids. The two correspondinghalf-lives of the depuration kinetics were 10 min and7 d, 20 min and 1 d and 3 hr and 1.5 d for60Co, 110mAg and 54Mn, respectively.The loss of 137Cs was characterised by a singlehalf-life of 0.3 d.

Cultivation of the hyperthermophilic archaeonSulfolobus solfataricus in low-salt media

Two low-salt complex media, bactopeptone and desalted yeast extract, were used for high density cultivation of the hyperthermophilic archaeonSulfolobus solfataricus (DSM 1617). Bactopeptone, which has low mineral ion content among various complex media, was good for cell growth in batch cultures; the maximal cell density in bactopeptone was comparable to that in yeast extract. Howver, cell growth was rather poor when bactopeptone was added by the fed-batch procedure. Since several vitamins are deficient in bactopeptone, the effect of vitamins on cell growth was examined. Among the vitamins tested, pyridoxine was found to improve the growth rate ofS. solfataricus. To reduce the growth inhibition caused by mineral ions, yeast extract was dialyzed against distilled water and then fed-batch cultures were carried out using a feed medium containing desalted yeast extract. Although the concentrations of mineral ions in yeast extract were significantly lowered by the dialysis procedure, fed-batch cultivation with desalted yeast extract was unsatisfactory. To examine whether low molecular weight solutes in yeast extract are crucial for cell growth, we investigated the effect of trehalose, a most abundant compatible solute in yeast extract, on the growth pattern. Cell densities were increased and the length of the lag phase was markedly shortened by the presence of trehalose, indicating that trehalose plays an important role in the growth ofS. solfataricus.

On the stability of vertical double-diffusive interfaces. Part 3. Cylindrical interface

This is the final part of a three-part study of the stability of vertically oriented double-diffusive interfaces having an imposed vertical stable temperature gradient. In this study, flow is forced within a fluid of infinite extent by a prescribed excess of compositionally buoyant material within a circular cylindrical interface. Compositional diffusivity is ignored while thermal diffusivity and viscosity are finite. The instability of the interface is determined by quantifying the exponential growth rate of a harmonic deflection of infinitesimal amplitude. Attention is focused on the zonal wavenumber of the fastest growing mode.The interface is found to be unstable for some wavenumber for all values of the Prandtl number and interface radius. The zonal wavenumber of the fastest growing mode increases roughly linearly with interface radius, except for small values of the Prandtl number (<0.065). For small and moderate values of the radius, the preferred mode is either axisymmetric or has zonal wavenumber of 1, representing a helical instability. The growth rate of the fastest-growing mode is largest for interfaces having radii of from 2 to 3 salt-finger lengths.

A model experimental gel-surface for the growth of bacteria on foods

A method is presented for the growth of bacteria on the surfaces of gels as a model of the changes that occur on food surfaces, and is demonstrated forSalmonella typhimurium. The method is based on a gel cassette, which consists of a frame holding a layer of gel, in this case gelatin, formed between two PVC windows. After formation of a sterile gel, one of the PVC windows is removed to expose the gel surface for inoculation. Using this technique, the effect of sucrose and sodium chloride on the growth rate ofS. typhimuriumgrowing as surface colonies was compared with that of immersed colonies and planktonic cells in broth and was found to follow the order: broth>immersed colonies>surface colonies. The maximum numbers of cells decreased with increasing sucrose concentration and this decrease was more marked for surface colonies than for immersed colonies or planktonic cells. These results indicate that predictions of the growth rate of bacteria on food surfaces may be erroneous where these predictions are based on data collected in broth.

On the origin of the ‘surface current’ in turbulent free-surface flows

In this study, the interaction with a free surface of an initially axisymmetric jet issuing beneath and parallel to the surface was examined. The purpose was to determine the origin of the ‘surface current’ – the large outward velocity which exists in a thin layer adjacent to the surface. Using the equations of mean motion, it is shown that near the surface, outward acceleration results from the balance between a positive contribution from the lateral Reynolds-stress gradients and a negative contribution from the lateral pressure gradient. The local pressure field near the free surface is shown to be largely determined by the local Reynolds-stress field. Combining these results shows that the lateral acceleration which results in the surface current is related to the Reynolds-stress anisotropy near the surface. The results indicate that there should be roughly a three-fold increase in the lateral growth rate of the jet near the free surface and a similar increase in the outward velocity, when compared to a deep jet. Comparison to available experimental data showed that the maximum outward velocity was consistent with the theory, and that the lateral scale of the surface-current layer was roughly double that of the deep jet, slightly smaller than expected. The near-surface stress anisotropy was shown to be related to the interaction of vorticity with the free surface. This indicates that the results of this study are consistent with earlier explanations of the surface current in terms of vortex/free-surface interaction.

Mixing and reaction in curved liquid shear layers

The concentration field of mixing layers subject to stabilizing and destabilizing streamwise curvature was investigated at post-mixing-transition conditions. A set of operating conditions was implemented, identical to those at which straight layers were previously investigated in the same facility, in order to compare the effects of hydrodynamic instabilities upon scalar mixing. Quantitative imaging of planar laser-induced fluorescence was used for (i) passive scalar measurements, and (ii) chemical product measurements. Similar to the straight mixing layer, the results for the curved layers show that beyond the mixing transition the layer continues to evolve, and undergoes a small change in its scalar structure. At conditions just past the mixing transition both stable and unstable layers have average mixed-fluid compositions which are uniform across the layer, and average chemical product concentration profiles which are symmetric. At more fully developed conditions, the scalar field evolved: the average mixed-fluid concentration developed a small lateral variation, while the chemical product concentration profiles became asymmetric. Similar to the straight layer, the mixture-fraction PDF is believed to be of the tilted type for the most fully developed layer examined, with the marching PDF being a poor representation. Consistent with previous investigations, the growth rate of the unstable layer was found to be higher than that of straight or stable layers. The most important result is that the measured mixing efficiency of all the layers (curved and straight) was found to be the same: both the total mixed-fluid composition, and the volume fraction of mixed fluid were the same for all unstable, stable, and straight layers. The amount of mixed fluid (and of chemical product formed) was larger for the unstable layer, but always in a fixed proportion to the layer's thickness. The lack of increase in the mixing efficiency for the unstable layer is surprising, given that previous hydrodynamic measurements had shown enhanced turbulent transport for the unstable case. Thus, for all liquid shear layers studied, the rate of scalar mixing appears to be directly proportional to the entrainment rate (which essentially determines the layer's growth rate), and not to any hydrodynamic measures.

Seiridium papillatum, a New Species (Mitosporic Fungus) Described on Stems of Eucalypts in Australia

A second species of Seiridium is described on Eucalyptus spp. in Australia as S. papillatum sp. nov. It is distinguished from the known species of the genus by its short papillate conidium appendages and large, ellipsoid to sub-cylindrical, striate, 5- (4–7-) septate conidia. A key to S. papillatum and closely related Seiridium species is provided and morphological differences are discussed. Colony morphology and growth rate of S. papillatum at different temperatures are compared with those of S. eucalypti and a Seiridium isolate from Callitris.

Flooding tolerance: a reinterpretation of Crawford's metabolic theory

SynopsisThe flooding tolerance strategy of three tropical gallery forest species,Sebastiana klotzchyana, Hymenaea courbarilvar.stilbocarpaandChorisia speciosawas studied. Data from the flood-intolerantSchyzolobium parahybahave been included for comparison.In the case ofS. klotzchyanaflooding induced an acceleration of glycolysis, with ethanol as the sole end product of anaerobic metabolism. Oxygen diffusion to the root system was not detectable.The results obtained forH. courbarilandC. speciosashow a compromise between metabolic and morpho-anatomical adaptations to enable them to occupy seasonally flooded areas. In both species, at the onset of the stress, the roots stop producing high amounts of ethanol and lactate. diverting part of the pyruvate produced to malate. The amount of pyruvate converted into malate is determined by the amount of oxygen diffused from the aerial part to the roots. This is used to oxidise pyruvate through Krebs' cycle and the excess is converted to malate. ATP production in the root system is predominantly aerobic and therefore not linked to malate production.The low level of acceleration of the fermentative pathway, coupled with the lack of oxygen diffusion to the root system, resulted in a significant decrease in the growth rate ofS. parahyba.

Interactions between two species of marine diatoms: Effects on their individual copper tolerance

The purpose of this study was to examine the effect of the interaction of two species of marine diatoms,Skeletonema costatum (Cleve) Greville andNitzschia thermalis (Ehrenberg) Auerswald, on their individual copper tolerances. The two species, obtained from stock cultures in 1989, were grown together at three copper concentrations (1, 4 and 5 × 10−7 M added total copper). In the unialgal cultures that were used as controls, the two species grew as predicted from their tolerance tests. However, in mixed cultures,N. thermalis was the only species that exhibited growth, regardless of the copper concentration in the medium. Growth retardation ofS. costatum in the presence ofN. thermalis was attributed to an inhibitory exudate. The effect of the exudate appeared to have been temporary, as demonstrated by the extended lag phase and subsequent satisfactory exponential growth rate ofS. costatum. It is suggested that the exudate degraded within a period of 5 d (=lag phase) because exponential growth rate was resumed. It thus appears that the interaction between the two diatom species is more important in determining the survival ofS. costatum than its individual copper tolerance. This is not the case forN. thermalis. Such interactions would be unaccounted for in single-species toxicity tests. On the other hand, if they are known, prediction of how a community that includes these two species would respond to copper additions becomes possible.

Glycine betaine and proline are the principal compatible solutes ofStaphylococcus aureus

The foodborne pathogenStaphylococcus aureus is distinguished by its ability to grow within environments of extremely high osmolarity (e.g., foods with low water activity values). In the present study, we examined the accumulation of intracellular organic solutes withinS. aureus strain ATCC 12600 when cells were grown in a complex medium containing high concentrations of NaCl. Consistent with previous reports [Measures JC (1975) Nature 257:398–400; Koujima I, et al. (1978) Appl Environ Microbiol 35:467–470; and Anderson CB, Witter LD (1982) Appl Environ Microbiol 43:1501–1503], intracellular proline was found to accumulate to high concentrations. However, NMR spectroscopy of cell extracts revealed glycine betaine to be the predominant intracellular organic solute accumulated within cells grown at high osmolarity. In additional experiments, we examined the growth rate ofS. aureus in a defined medium of high osmolarity and found it to be stimulated significantly by the presence of either exogenous proline or glycine betaine. Highest growth rates were obtained when the defined medium was supplemented with glycine betaine.

Compressible mixing layer - Linear theory and direct simulation

Results from linear stability analysis are presented for a wide variety of mixing layers, including low-speed layers with variable density and high Mach number mixing layers. The linear amplification predicts correctly the experimentally observed trends in growth rate that are due to velocity ratio, density ratio, and Mach number, provided that the spatial theory is used and the mean flow is a computed solution of the compressible boundary-layer equations. It is found that three-dimensional modes are dominant in the high-speed mixing layer above a convective Mach number of 0.6, and a simple relationship is proposed that approximately describes the orientation of these waves. Direct numerical simulations of the compressible Navier-Stokes equations are used to show the reduced growth rate that is due to increasing Mach number. From consideration of the compressible vorticity equation, it is found that the dominant physics controlling the nonlinear roll-up of vortices in the high-speed mixing layer is contained in an elementary form in the linear eigenfunctions. It is concluded that the linear theory can be very useful for investigating the physics of free shear layers and predicting the growth rate of the developed plane mixing layer

Sporotrichum thermophile Growth, Cellulose Degradation, and Cellulase Activity

The activity of components of the extracellular cellulase system of the thermophilic fungus Sporotrichum thermophile showed appreciable differences between strains; beta-glucosidase (EC 3.2.1.21) was the most variable component. Although its endoglucanase (EC 3.2.1.4) and exoglucanase (EC 3.2.1.91) activities were markedly lower, S. thermophile degraded cellulose faster than Trichoderma reesei. The production of beta-glucosidase lagged behind that of endoglucanase and exoglucanase. The latter activities were produced during active growth. When growth was inhibited by cycloheximide treatment, the hydrolysis of cellulose was lower than in the control in spite of the presence of both endoglucanase and exoglucanase activities in the culture medium. Degradation of cellulose was a growth-associated process, with cellulase preparations hydrolyzing cellulose only to a limited extent. The growth rate and cell density of S. thermophile were similar in media containing cellulose or glucose. A distinctive feature of fungal development in media incorporating cellulose or lactose (inducers of cellulase activity) was the rapid differentiation of reproductive units and autolysis of hyphal cells to liberate propagules which were capable of renewing growth immediately.

Comparative Morphology and Behaviour of A1 and A2 Isolates of Phytophthora cinnamomi

Studies of morphology, physiological behaviour and pathogenicity indicated that some significant differences existed between isolates of the A1 and A2 compatibility types of Phytophthora cinnamomi from native plant communities in Australia. The majority of A1 isolates produced zoosporangia more rapidly and in greater numbers than A2 isolates, and zoosporangia were produced evenly on mycelial discs of A1 isolates whereas they occurred mostly at the perimeter of similar discs in the case of A2 isolates. Chlamydospores were produced more rapidly by A1 than A2 isolates, and in the former tended to be of an even size and were frequently single, whereas in A2 isolates the size was extremely variable and production was usually in clusters. Both compatibility types showed similar temperature-growth optima, but the mean growth rate of A1 isolates, over the range 15-30°C, was less than that of A2 isolates. Both types responded similarly to high temperature treatments and to a range of osmotic potentials and both showed similar pathogenicity to lupin and Pinus radiata seedlings. While both compatibility types showed similar reactions to a number of inhibitors, the growth of A2 isolates was inhibited more by rose bengal and pyronin G than that of A1 isolates. Thus, although significant differences were recorded, there was a general similarity of behaviour of isolates of both compatibility types and there were no striking differences from the recorded behaviour of the fungus in other countries.

Nitrogen nutrition inAtriplex hastata L.

The investigation was carried out in order to ascertain whyAtriplex hastata, previously recorded as a nitrophilous plant, can colonise fly ash which has a low nitrogen content.Sinapis arvensis, a weed which does not grow on fly ash, was selected as a control plant. Solution-culture experiments showed that the two species differed in their responses to high and low levels of nitrogen, the growth rate ofS. arvensis being much more severely affected by low levels of 0 to 50 ppm.A. hastata was found to make very efficient use of its nitrogen supply. Both species grew better with nitrate than with ammonium nitrogen. InA. hastata, uptake of nitrogen was not influenced by pH when only nitrate was present. Where both nitrate and ammonium were available, nitrate was absorbed preferentially at low pH and ammonium at high pH. Some properties of fly ash which render it a suitable medium for growth ofA. hastata are discussed.