Effects of environmental factors on basidiospore germination of ammonia fungi <Emphasis Type="Italic">Coprinopsis</Emphasis> spp. collected from different geographical areas

Effects of pH, NH₄-N, and temperature on basidiospore germination in Coprinopsis austrophlyctidospora from New Zealand, C. phlyctidospora from Japan, C. aff. rugosobispora from Canada, and C. echinospora from Canada were investigated. The Coprinopsis spp. required the presence of ammonium-nitrogen under weak alkaline to neutral conditions for germination, regardless of their different areas of occurrence. The former two species had a wider concentration of NH₄Cl solution and pH range for germination in comparison to the latter two species. The optimum concentration of NH₄Cl solution for the germination was 0.01 M in C. austrophlyctidospora and 0.1 M in the other three species. The pH optimum for germination in the former two species was 8.0 whereas that for germination in the latter two species was 8.0–8.5. The temperature range (5.0–40.0°C) for the former two species was wider than that (5–30°C) for the latter two species. Temperature optima for the germination in the former two species, C. aff. rugosobispora and C. echinospora, were 30, 20–25 and 15°C, respectively. The germination abilities of these Coprinopsis species in a wide range of temperatures are relevant to their natural temperature regime, showing their potential ability to propagate in tropical to subarctic regions.     

Isolation and characterization of a <Emphasis Type="Italic">Mastigocladus</Emphasis> species capable of growth,N<Subscript>2</Subscript>-fixation and N-assimilation at elevated temperature

A Mastigocladus species was isolated from the hot spring of Jakrem (Meghalaya) India. Uptake and utilization of nitrate, nitrite, ammonium and amino acids (glutamine, asparagine, arginine, alanine) were studied in this cyanobacterium grown at different temperatures (25°C, 45°C). There was 2–3 fold increase in the heterocyst formation and nitrogenase activity in N-free medium at higher temperature (45°C). Growth and uptake and assimilation of various nitrogen sources were also 2–3 fold higher at 45°C indicating that it is a thermophile. The extent of induction and repression of nitrate uptake by NO₃ ⁻ and NH₄ ⁺, respectively, differed from that of nitrite. It appeared that Mastigocladus had two independent nitrate/nitrite transport systems. Nitrate reductase and nitrite reductase activitiy was not NO₃ ⁻-inducible and ammonium or amino acids caused only partial repression. Presence of various amino acids in the media partially repressed glutamine synthetase activity. Ammonium (methylammonium) and amino acid uptake showed a biphasic pattern, was energy-dependent and the induction of uptake required de novo protein synthesis. Ammonium transport was substrate (NH₄ ⁺)-repressible, while the amino acid uptake was substrate inducible. When grown at 25°C, the cyanobacterium formed maximum akinetes that remained viable upto 5 years under dry conditions.     

Germination responses of <Emphasis Type="Italic">Erica andevalensis</Emphasis> to different chemical and physical treatments

Erica andevalensis Cabezudo & Rivera is a threatened edaphic endemic species of Andalusia (SW Spain). Under natural conditions, the plants produce a very large number of small seeds (0.3–0.4 mm) but very few seedlings survive. Different treatments (high temperature, cold pre-treatment, nitrogen salts, and gibberellic acid applications) were tested to assess germination patterns in different populations and to determinate the most favorable conditions for germination. Gibberellic acid was provided in five different concentrations from 0 to 400 ppm GA₃, while nitrogen was applied as 10 mM of either KNO₃ or NH₄NO₃. The effect of pH on germination was also tested. The species always showed a low germination rate (6.50–22%) that was not stimulated either by 1 or 4 months in dry cold pre-treatment, nitrogen application, acid pH medium, or by high temperature (80°C for 10 min); although gibberellic acid application (100–400 ppm) significantly enhanced germination. The highest percentage of germination (41.6%) was achieved with a mean germination time to start germination (t ₀) of 7.6 ± 0.54 days when the seeds were subjected to 400 ppm gibberellic acid treatment. The population origin did not have a significant effect on germination percentage.     

The Influence of Water Activity and Temperature on Germination,Growth and Sporulation of <Emphasis Type="Italic">Stachybotrys chartarum</Emphasis> Strains

The objectives were to determine the influence of water activity (a_w, 0.997–0.92) and temperature (10–37°C) and their interactions on conidial germination, mycelial growth and sporulation of two strains of Stachybotrys chartarum in vitro on a potato dextrose medium. Studies were carried out by modifying the medium with glycerol and either spread plating with conidia to evaluate germination and germ tube extension or centrally inoculating treatment media for measuring mycelial growth rates and harvesting whole colonies for determining sporulation. Overall, germination of conidia was significantly influenced by a_w and temperature and was fastest at 0.997–0.98 a_w between 15 and 30°C with complete germination within 24 h. Germ tube extension was found to be most rapid at similar a_w levels and 25–30°C. Mycelial growth rates of both strains were optimal at 0.997 a_w between 25 and 30°C, with very little growth at 37°C. Sporulation was optimum at 30°C at 0.997 a_w. However, under drier conditions, this was optimum at 25°C. This shows that there are differences in the ranges of a_w x temperature for germination and growth and for sporulation. This may help in understanding the role of this fungal species in damp buildings and conditions under which immune-compromised patients may be at risk when exposed to such contaminants in the indoor air environment.     

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing <Emphasis Type="Italic">Xenopus</Emphasis> oocytes to Solutions Containing NH<Subscript>3</Subscript>/NH<Subscript>4</Subscript><Superscript>+</Superscript>

Others have shown that exposing oocytes to high levels of (10–20 mM) causes a paradoxical fall in intracellular pH (pH_i), whereas low levels (e.g., 0.5 mM) cause little pH_i change. Here we monitored pH_i and extracellular surface pH (pH_S) while exposing oocytes to 5 or 0.5 mM NH₃/NH₄ ⁺. We confirm that 5 mM causes a paradoxical pH_i fall (−ΔpH_i ≅ 0.2), but also observe an abrupt pH_S fall (−ΔpH_S ≅ 0.2)—indicative of NH₃ influx—followed by a slow decay. Reducing [NH₃/NH₄ ⁺] to 0.5 mM minimizes pH_i changes but maintains pH_S changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates −ΔpH_S at both levels. During removal of 0.5 or 5 mM NH₃/NH₄ ⁺, failure of pH_S to markedly overshoot bulk extracellular pH implies little NH₃ efflux and, thus, little free cytosolic NH₃/NH₄ ⁺. A new analysis of the effects of NH₃ vs. NH₄ ⁺ fluxes on pH_S and pH_i indicates that (a) NH₃ rather than NH₄ ⁺ fluxes dominate pH_i and pH_S changes and (b) oocytes dispose of most incoming NH₃. NMR studies of oocytes exposed to ¹⁵N-labeled show no significant formation of glutamine but substantial accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pH_i and pH_S demonstrate that NH₃ flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances the flux of a gas across a biological membrane.

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Reactive oxygen species,ABA and nitric oxide interactions on the germination of warm-season C<Subscript>4</Subscript>-grasses

Hydrogen peroxide (H₂O₂) as a source of reactive oxygen species (ROS) significantly stimulated germination of switchgrass (Panicum virgatum L.) seeds with an optimal concentration of 20 mM at both 25 and 35°C. For non-dormant switchgrass seeds exhibiting different levels of germination, treatment with H₂O₂ resulted in rapid germination (<3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H₂O₂ elicited simultaneous growth of the root and shoot system, resulting in more uniform seedling development. Seeds of big bluestem (Andropogon gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash] also responded positively to H₂O₂ treatment, indicating the universality of the effect of H₂O₂ on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor, diphenyleneiodonium (DPI) at 20 μM retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase activity in seeds. H₂O₂ reversed the inhibitory effects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition of root elongation. Treatment with H₂O₂ appeared to enhance endogenous production of nitric oxide, and a scavenger of nitric oxide abolished the peroxide-responsive stimulation of switchgrass seed germination. The activities and levels of several proteins changed earlier in seeds imbibed on H₂O₂ as compared to seeds maintained on water or on ABA. These data demonstrate that seed germination of warm-season grasses is significantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS and NO in this system.     

Combination of elevated CO<Subscript>2</Subscript> concentration and elevated temperature and elevated temperature only promote photosynthesis of <Emphasis Type="Italic">Quercus mongolica</Emphasis> seedlings

One-year-old oak (Quercus mongolica Fisch.) seedlings were grown in growth chambers for 30 days to investigate the effects of the combination of elevated CO₂ concentration ([CO₂], 700 μmol/mol) and temperature (ambient T + 4°C) and only elevated temperature (ambient T +4°C) on leaf gas exchange, chlorophyll a fluorescence, and chlorophyll content. In the growth chambers, natural conditions of the Maoershan mountain regions of Heilongjiang Province (45–46°N, 127–128°E) of China for the average growth season were simulated. The results showed that the maximum net photosynthetic rate (P _Nmax) was ≈ 1.64 times greater at elevated temperature than at ambient temperature. The irradiance saturation point (I _s), apparent quantum yield (AQY), maximum photosystem II efficiency (F _v/F _m), and chlorophyll content significantly increased, while irradiance compensation point (I _c) was not affected by elevated temperature. The combination of elevated [CO₂] and temperature also significantly increased P _Nmax by approximately 34% but much lower than that under elevated temperature only. In the case of factor combination, dark respiration (R _d), I _c, F _v/F _m, and total chlorophyll content increased significantly, while I _s and AQY were not affected. Moreover, under elevated [CO₂] and temperature, R _d and I _c, F _v/F _m were significantly higher than under elevated temperature only. The results indicated that the combination of elevated [CO₂] and temperature expected in connection with the further global climate change may affect carbon storage of the coenotype of Q. mongolica in this region of China. This text was submitted by the authors in English.     

Kinetics of CO conversion into H<Subscript>2</Subscript> by <Emphasis Type="Italic">Carboxydothermus hydrogenoformans</Emphasis>

The objective of this study was to improve the biological water–gas shift reaction for producing hydrogen (H₂) by conversion of carbon monoxide (CO) using an anaerobic thermophilic pure strain, Carboxydothermus hydrogenoformans. Specific hydrogen production rates and yields were investigated at initial biomass densities varying from 5 to 20 mg volatile suspended solid (VSS) L⁻¹. Results showed that the gas–liquid mass transfer limits the CO conversion rate at high biomass concentrations. At 100-rpm agitation and at CO partial pressure of 1 atm, the optimal substrate/biomass ratio must exceed 5 mol CO g⁻¹ biomass VSS in order to avoid gas–liquid substrate transfer limitation. An average H₂ yield of 94 ± 3% and a specific hydrogen production rate of ca. 3 mol g⁻¹ VSS day⁻¹ were obtained at initial biomass densities between 5 and 8 mg VSS⁻¹. In addition, CO bioconversion kinetics was assessed at CO partial pressure from 0.16 to 2 atm, corresponding to a dissolved CO concentration at 70°C from 0.09 to 1.1 mM. Specific bioactivity was maximal at 3.5 mol CO g⁻¹ VSS day⁻¹ for a dissolved CO concentration of 0.55 mM in the culture. This optimal concentration is higher than with most other hydrogenogenic carboxydotrophic species.     

Light and growth temperature alter carbon isotope discrimination and estimated bundle sheath leakiness in C<Subscript>4</Subscript> grasses and dicots

We combined measurements of short-term (during gas exchange) and long-term (from plant dry matter) carbon isotope discrimination to estimate CO₂ leakiness from bundle sheath cells in six C₄ species (three grasses and three dicots) as a function of leaf insertion level, growth temperature and short-term irradiance. The two methods for determining leakiness yielded similar results (P > 0.05) for all species except Setaria macrostachya, which may be explained by the leaf of this species not being accommodating to gas exchange. Leaf insertion level had no effect on leakiness. At the highest growth temperature (36°C) leakiness was lower than at the two lower growth temperatures (16°C and 26°C), between which no differences in leakiness were apparent. Higher irradiance decreased leakiness in three species, while it had no significant effect on the others (there was an opposite trend in two species). The inverse response to increasing irradiance was most marked in the two NAD-ME dicots (both Amaranthus species), which both showed almost 50% leakiness at low light (300 μmol quanta m⁻² s⁻¹) compared to about 30% at high light (1,600 μmol quanta m⁻² s⁻¹). NADP-ME subtype grasses had lower leakiness than NAD-ME dicots. Although there were exceptions, particularly in the effect of irradiance on leakiness in Sorghum and Boerhavia, we conclude that conditions favourable to C₄ photosynthesis (high temperature and high light) lead to a reduction in leakiness.     

The germination characteristics of <Emphasis Type="Italic">Scrophularia marilandica</Emphasis> L. (Scrophulariaceae) seeds

Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA₃ and KNO₃). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO_3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10⁻⁴ M GA₃ caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.     

Effect of nitrogen forms on growth,cell composition and N<Subscript>2</Subscript> fixation of <Emphasis Type="Italic">Cylindrospermopsis raciborskii</Emphasis> in phosphorus-limited chemostat cultures

The aim of this research was to test whether NH₄ ⁺ and NO₃ ⁻ affect the growth, P demand, cell composition and N₂ fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l⁻¹ PO₄-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l⁻¹ NH₄-N, 4,000 μg l⁻¹ NO₃-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH₄ ⁺ and NO₃ ⁻ supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N₂-grown culture was significantly lower. The maximum specific growth rate of N₂-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the P and energy requirement for heterocyte formation, nitrogenase synthesis and N₂ fixation. N₂ fixation was partially inhibited by NO₃ ⁻ and completely inhibited by NH₄ ⁺. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH₄ ⁺ or NO₃ ⁻ is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies. Handling editor: Luigi Naselli-Flores     

The peroxidase activity of cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>6</Subscript><Emphasis Type="Italic">f</Emphasis> complex from spinach chloroplasts

The cytochrome b ₆ f (Cyt b ₆ f) complex, which functions as a plastoquinol-plastocyanin oxidoreductase and mediates the linear electron flow between photosystem II (PSII) and photosystem I (PSI) and the cyclic electron flow around PSI, was isolated from spinach (Spinacia oleracea L.) chloroplasts using n-octyl-β-D-glucopyranoside (β-OG). The preparation was also able to catalyze the peroxidase-like reaction in the presence of hydrogen peroxide (H₂O₂) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and temperature 35°C. The apparent Michaelis constant (K _m) values for H₂O₂ and guaiacol were 50 mM and 2 mM, respectively. The bimolecular rate constant (k _obs) was about 26 M⁻¹ s⁻¹ and the turnover number (K _cat) was about 60 min⁻¹ (20 mM guaiacol, 100 mM sodium phosphate, pH 3.6, 25°C, [H₂O₂]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c.     

Photosynthetic responses of apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) to photosynthetic photon flux density,leaf temperature,and CO<Subscript>2</Subscript> concentration

Two cultivars (Katy and Erhuacao) of apricot (Prunus armeniaca L.) were evaluated under open-field and solar-heated greenhouse conditions in northwest China, to determine the effect of photosynthetic photon flux density (PPFD), leaf temperature, and CO₂ concentration on the net photosynthetic rate (P _N). In greenhouse, Katy registered 28.3 μmol m⁻² s⁻¹ for compensation irradiance and 823 μmol m⁻² s⁻¹ for saturation irradiance, which were 73 and 117 % of those required by Erhuacao, respectively. The optimum temperatures for cvs. Katy and Erhuacao were 25 and 35 °C in open-field and 22 and 30 °C in greenhouse, respectively. At optimal temperatures, P _N of the field-grown Katy was 16.5 μmol m⁻² s⁻¹, 21 % less than for a greenhouse-grown apricot. Both cultivars responded positively to CO₂ concentrations below the CO₂ saturation concentration, whereas Katy exhibited greater P _N (18 %) and higher carboxylation efficiency (91 %) than Erhuacao at optimal CO₂ concentration. Both cultivars exhibited greater photosynthesis in solar-heated greenhouses than in open-field, but Katy performed better than Erhuacao under greenhouse conditions.     

Functional response and life history parameters of <Emphasis Type="Italic">Apanteles taragamae</Emphasis>, a larval parasitoid of <Emphasis Type="Italic">Maruca vitrata</Emphasis>

The legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) is a serious pest of cowpea in West-Africa. The parasitoid Apanteles taragamae Viereck (Hymenoptera: Braconidae) that originates from Taiwan is a potential candidate for biological control of M. vitrata. We investigated under laboratory conditions the functional response of the parasitoid by offering each experienced female 10, 20, 30 and 40 larvae of M. vitrata. We studied the influence of different host larval ages on the development, longevity, sex ratio, lifetime fecundity and parasitization rate of the wasp. In a comparative study, we also investigated the life history of A. taragamae and M. vitrata at different temperatures in the range of 20–30°C. The parasitoid successfully parasitized two- and three-day-old host larvae (first and second instars). Younger larvae (one-day-old) were parasitized to a lesser extent, and only males developed in them. Older larvae were not parasitized, partly because of defensive host behaviour. The success of parasitization was positively correlated with the density of two-day-old M. vitrata larvae. Parasitoid developmental time and longevity decreased with increasing temperature. The intrinsic rate of population increase (r _m ) exhibited an optimum curve with a maximum at 24–28°C. For the host M. vitrata, r _m was maximal at temperatures of 26–30°C. The data are discussed in the context of the potential of A. taragamae for biological control of M. vitrata.     

Characterization of enzymes involved in the ethanol production of <Emphasis Type="Italic">Moorella</Emphasis> sp. HUC22-1

Since the thermophilic bacterium Moorella sp. HUC22-1 produces 120 mM acetate and 5.2 mM ethanol from H₂–CO₂, several candidate genes, which were predicted to code for three alcohol dehydrogenases (AdhA, B, C) and one acetaldehyde dehydrogenase (Aldh), were cloned from HUC22-1. The cloned genes were subcloned into a His-tagged expression vector and expressed in Escherichia coli. Recombinant AdhA and B were both dependent on NADP(H) but independent of NAD(H), and their reduction activities from aldehyde to alcohol were higher than their oxidation activities. In contrast with AdhA and B, no activity of AdhC was observed in either reaction. On the other hand, Aldh was active toward both NADP(H) and NAD(H). The enzyme activity of Aldh was directed toward the thioester cleavage and the thioester condensation. When 50 μg of AdhA and 50 μg Aldh were added to the buffer solution (pH 8.0) containing NADPH, NADH and acetyl-CoA at 60°C, 1.6 mM ethanol was produced from 3 mM acetyl-CoA after 90 min. Expression analysis of the mRNAs revealed that the expression level of aldh was threefold higher in the H₂–CO₂ culture than that in the fructose culture, but levels of adhA, B and C were decreased.     

Dynamics of reductive TCE dechlorination in two distinct H<Subscript>2</Subscript> supply scenarios and at various temperatures

Anaerobic microbial dechlorination of trichloroethene (TCE) by a mixed, Dehalococcoides containing culture was investigated at different temperatures (4–60 °C) using propionate and lactate as a slow- and fast-releasing hydrogen (H₂) source, respectively. Distinct temperature-dependent dynamics of substrate fermentation and H₂ levels could explain observed patterns of dechlorination. While varying the temperature caused changes in rate, the overall pattern of dechlorination was characteristic of the supplied electron donor. Feeding cultures with a rapidly fermentable substrate such as lactate generally resulted in high H₂ concentrations and fast and complete dechlorination accompanied by rapid methanogenesis. In contrast, low H₂ release rates resulting from fermentation of propionate were associated with 2 to 3−fold longer time frames necessary for complete dechlorination at intermediate temperatures (15–30 °C). A lag-phase prior to dechlorination of cis-dichloroethene (cDCE), together with a characteristic build-up of H₂ and methane, was consistently observed at slow H₂ supply. At temperatures of 10 °C and lower, the system remained in this lag phase and no dechlorination past cDCE was observed within the experimental time frame. However, when lactate was the substrate, complete dechlorination of TCE occurred within 74 days at 10 °C, accompanied by methane production. The choice of fermentable substrate decisively influenced the rate and degree of dechlorination at an electron donor/TCE ratio as high as 666:1. Temperature-dependent H₂ levels resulting from fermentation of different substrates could be satisfactorily explained through thermodynamic calculations of the Gibbs free energy yield assuming a constant metabolic energy threshold of −20 kJ/(mol reaction).     

Cross-mating experiments with geographically different populations of <Emphasis Type="Italic">Amblyomma cajennense</Emphasis> (Acari: Ixodidae)

The effect of temperature on the development and fecundity of Sancassania polyphyllae fed on tissues of Polyphylla fullo larvae was studied at 15, 20, 25, 30, and 35 ± 1°C and 65 ± 10% RH in a dark incubator. Mean developmental period of immature stages decreased significantly with increasing temperatures from 15 to 30°C. Developmental periods at 30–35°C were not significantly different. The estimated lower developmental thresholds of the various immature stages ranged between 10.1 and 11.5°C. The thermal constant for the egg-to-female adult was 93.5 degree-days. The pre-oviposition, oviposition, and post-oviposition periods and female longevity were significantly longer at 15°C than at higher temperatures. Mean total and daily fecundity were the highest at 25°C, which were significantly different from those obtained at 15, 20 and 30°C. The net reproductive rate (R ₀) was the highest at 25°C (588.3 ♀/♀). The longest mean generation time (T ₀) occurred at 15°C (36 days) and the shortest occurred at 30°C (9.2 days). The highest intrinsic rate of increase (r _m) for S. polyphyllae was observed at 25 (0.61 ♀/♀/day) and 30°C (0.62 ♀/♀/day).     

Rise in CO<Subscript>2</Subscript> affects soil water transport through repellency

Several studies have shown improved soil stability under elevated atmospheric CO₂ caused by increased plant and microbial biomass. These studies have not quantified the mechanisms responsible for soil stabilisation or the effect on water relations. The objective of this study was to assess changes in water repellency under elevated CO₂. We hypothesised that increased plant biomass will drive an increase in water repellency, either directly or through secondary microbial processes. Barley plants were grown at ambient (360 ppm) and elevated (720 ppm) CO₂ concentrations in controlled chambers. Each plant was grown in a separate tube of 1.2 m length constructed from 22 mm depth × 47 mm width plastic conduit trunk and packed with sieved arable soil to 55% porosity. After 10 weeks growth the soil was dried at 40°C before measuring water sorptivity, ethanol sorptivity and repellency at many depths with a 0.14 mm radius microinfiltrometer. This provided a microscale measure of the capacity of soil to rewet after severe drying. At testing roots extended throughout the depth of the soil in the tube. The depth of the measurement had no effect on sorptivity or repellency. A rise in CO₂ resulted in a decrease in water sorptivity from 1.13 ± 0.06 (s.e) mm s^−1/2 to 1.00 ± 0.05 mm s^−1/2 (P < 0.05) and an increase in water repellency from 1.80 ± 0.09 to 2.07 ± 0.08 (P < 0.05). Ethanol sorptivity was not affected by CO₂ concentration, suggesting a similar pore structure. Repellency was therefore the primary cause of decreased water sorptivity. The implications will be both positive and negative, with repellency potentially increasing soil stability but also causing patchier wetting of the root-zone.     

Purification and properties of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis><Emphasis Type="Italic">S</Emphasis>-adenosylmethionine synthetase expressed in recombinant <Emphasis Type="Italic">Pichia pastoris</Emphasis>

An intracellular S-adenosylmethionine synthetase (SAM-s) was purified from the fermentation broth of Pichia pastoris GS115 by a sequence chromatography column. It was purified to apparent homogeneity by (NH₄)₂SO₄ fractionation (30–60%), anion exchange, hydrophobic interaction, anion exchange and gel filtration chromatography. HPLC showed the purity of purified SAM-s was 91.2%. The enzyme was purified up to 49.5-fold with a final yield of 20.3%. The molecular weight of the homogeneous enzyme was 43.6 KDa, as determined by electro-spray ionization mass spectrometry (ESI-MS). Its isoelectric point was approximately 4.7, indicating an acidic character. The optimum pH and temperature for the enzyme reaction were 8.5 and 35 °C, respectively. The enzyme was stable at pH 7.0–9.0 and was easy to inactivate in acid solution (pH ≤ 5.0). The temperature stability was up to 45 °C. Metal ions, such as, Mn²⁺ and K⁺ at the concentration of 5 mM had a slight activation effect on the enzyme activity and the Mg²⁺ activated the enzyme significantly. The enzyme activity was strongly inhibited by heavy metal ions (Cu²⁺ and Ag²⁺) and EDTA. The purified enzyme from the transformed Pichia pastoris synthesized S-adenosylmethionine (SAM) from ATP and l-methionine in vitro with a K _m of 120 and 330 μM and V _max of 8.1 and 23.2 μmol/mg/min for l-methionine and ATP, respectively.