H<Subscript>2</Subscript> enrichment from synthesis gas by <Emphasis Type="Italic">Desulfotomaculum</Emphasis><Emphasis Type="Italic">carboxydivorans</Emphasis> for potential applications in synthesis gas purification and biodesulfurization

Desulfotomaculum carboxydivorans, recently isolated from a full-scale anaerobic wastewater treatment facility, is a sulfate reducer capable of hydrogenogenic growth on carbon monoxide (CO). In the presence of sulfate, the hydrogen formed is used for sulfate reduction. The organism grows rapidly at 200 kPa CO, pH 7.0, and 55°C, with a generation time of 100 min, producing nearly equimolar amounts of H₂ and CO₂ from CO and H₂O. The high specific CO conversion rates, exceeding 0.8 mol CO (g protein)⁻¹ h⁻¹, makes this bacterium an interesting candidate for a biological alternative of the currently employed chemical catalytic water–gas shift reaction to purify synthesis gas (contains mainly H₂, CO, and CO₂). Furthermore, as D. carboxydivorans is capable of hydrogenotrophic sulfate reduction at partial CO pressures exceeding 100 kPa, it is also a good candidate for biodesulfurization processes using synthesis gas as electron donor at elevated temperatures, e.g., in biological flue gas desulfurization. Although high maximal specific sulfate reduction rates (32 mmol (g protein)⁻¹ h⁻¹) can be obtained, its sulfide tolerance is rather low and pH dependent, i.e., maximally 9 and 5 mM sulfide at pH 7.2 and pH 6.5, respectively.     

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.     

On-line estimation of O<Subscript>2</Subscript> production,CO<Subscript>2</Subscript> uptake,and growth kinetics of microalgal cultures in a gas-tight photobioreactor

Growth of the green algae Chlamydomonas reinhardtii and Chlorella sp. in batch cultures was investigated in a novel gas-tight photobioreactor, in which CO₂, H₂, and N₂ were titrated into the gas phase to control medium pH, dissolved oxygen partial pressure, and headspace pressure, respectively. The exit gas from the reactor was circulated through a loop of tubing and re-introduced into the culture. CO₂ uptake was estimated from the addition of CO₂ as acidic titrant and O₂ evolution was estimated from titration by H₂, which was used to reduce O₂ over a Pd catalyst. The photosynthetic quotient, PQ, was estimated as the ratio between O₂ evolution and CO₂ up-take rates. NH₄ ⁺, NO₂ ⁻, or NO₃ ⁻ was the final cell density limiting nutrient. Cultures of both algae were, in general, characterised by a nitrogen sufficient growth phase followed by a nitrogen depleted phase in which starch was the major product. The estimated PQ values were dependent on the level of oxidation of the nitrogen source. The PQ was 1 with NH₄ ⁺ as the nitrogen source and 1.3 when NO₃ ⁻ was the nitrogen source. In cultures grown on all nitrogen sources, the PQ value approached 1 when the nitrogen source was depleted and starch synthesis became dominant, to further increase towards 1.3 over a period of 3–4 days. This latter increase in PQ, which was indicative of production of reduced compounds like lipids, correlated with a simultaneous increase in the degree of reduction of the biomass. When using the titrations of CO₂ and H₂ into the reactor headspace to estimate the up-take of CO₂, the production of O₂, and the PQ, the rate of biomass production could be followed, the stoichiometrical composition of the produced algal biomass could be estimated, and different growth phases could be identified.     

The effect of sulfur compounds on H<Subscript>2</Subscript> evolution/consumption reactions,mediated by various hydrogenases,in the purple sulfur bacterium, <Emphasis Type="Italic">Thiocapsa roseopersicina</Emphasis>

The influence of reduced sulfur compounds (including stored S⁰) on H₂ evolution/consumption reactions in the purple sulfur bacterium, Thiocapsa roseopersicina BBS, was studied using mutants containing only one of the three known [NiFe] hydrogenase enzymes: Hox, Hup or Hyn. The observed effects depended on the kind of hydrogenase involved. The mutant harbouring Hox hydrogenase was able to use S₂O₃²⁻, SO₃²⁻, S²⁻ and S⁰ as electron donors for light-dependent H₂ production. Dark H₂ evolution from organic substrates via Hox hydrogenase was inhibited by S⁰. Under light conditions, endogenous H₂ uptake by Hox or Hup hydrogenases was suppressed by S compounds. СО₂-dependent H₂ uptake by Hox hydrogenase in the light required the additional presence of S compounds, unlike the Hup-mediated process. Dark H₂ consumption via Hyn hydrogenase was connected to utilization of S⁰ as an electron acceptor and resulted in the accumulation of H₂S. In wild type BBS, with high levels of stored S⁰, dark H₂ production from organic substrates was significantly lower, but H₂S accumulation significantly higher, than in the mutant GB1121(Hox⁺). There is a possibility that H₂ produced via Hox hydrogenase is consumed by Hyn hydrogenase to reduce S⁰.     

Methanol utilizing <Emphasis Type="Italic">Desulfotomaculum</Emphasis> species utilizes hydrogen in a methanol-fed sulfate-reducing bioreactor

A sulfate-reducing bacterium, strain WW1, was isolated from a thermophilic bioreactor operated at 65°C with methanol as sole energy source in the presence of sulfate. Growth of strain WW1 on methanol or acetate was inhibited at a sulfide concentration of 200 mg l⁻¹, while on H₂/CO₂, no apparent inhibition occurred up to a concentration of 500 mg l⁻¹. When strain WW1 was co-cultured under the same conditions with the methanol-utilizing, non-sulfate-reducing bacteria, Thermotoga lettingae and Moorella mulderi, both originating from the same bioreactor, growth and sulfide formation were observed up to 430 mg l⁻¹. These results indicated that in the co-cultures, a major part of the electron flow was directed from methanol via H₂/CO₂ to the reduction of sulfate to sulfide. Besides methanol, acetate, and hydrogen, strain WW1 was also able to use formate, malate, fumarate, propionate, succinate, butyrate, ethanol, propanol, butanol, isobutanol, with concomitant reduction of sulfate to sulfide. In the absence of sulfate, strain WW1 grew only on pyruvate and lactate. On the basis of 16S rRNA analysis, strain WW1 was most closely related to Desulfotomaculum thermocisternum and Desulfotomaculum australicum. However, physiological properties of strain WW1 differed in some aspects from those of the two related bacteria.     

Improved hydrogen photoproduction regulated by carbonylcyanide <Emphasis Type="Italic">m</Emphasis>-chlorophenylhrazone from marine green alga <Emphasis Type="Italic">Platymonas subcordiformis</Emphasis> grown in CO<Subscript>2</Subscript>-supplemented air bubble column bioreactor

To develop an integrated process of CO₂-fixation and H₂ photoproduction by marine green microalga Platymonas subcordiformis, the impact of algal cells grown in CO₂-supplemented air bubble column bioreactor was investigated on H₂ photoproduction regulated by carbonylcyanide m-chlorophenylhrazone. Highest cell growth (3.85 × 10⁶ cells ml⁻¹), starch content (0.25 ± 0.08 mg per 10⁶ cells) and hydrogen production (50 ± 3 ml l⁻¹) were achieved at 3% CO₂-supplemented culture, which are respectively 1.4, 2.1, 1.5-fold of the air-supplemented culture. Improved H₂ production correlated well with the increase in starch accumulation. In this process, the algal cells have been recycled for stable H₂ production of 40–50 ml l⁻¹ over five cycles.     

Decalactone Production by <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> under increased O<Subscript>2</Subscript> Transfer Rates

Yarrowia lipolytica converts methyl ricinoleate to γ-decalactone, a high-value fruity aroma compound. The highest amount of 3-hydroxy-γ-decalactone produced by the yeast (263 mg l^-1) occurred by increasing the k_La up to 120 h⁻¹ at atmospheric pressure; above it, its concentration decreased, suggesting a predominance of the activity of 3-hydroxyacyl-CoA dehydrogenase. Cultures were grown under high-pressure, i.e., under increased O₂ solubility, but, although growth was accelerated, γ-decalactone production decreased. However, by applying 0.5 MPa during growth and biotransformation gave increased concentrations of dec−2-en-4-olide and dec-3-en-4-olide (70 mg l⁻¹).     

Gas exchange and photosynthetic performance of the tropical tree <Emphasis Type="Italic">Acacia nigrescens</Emphasis> when grown in different CO<Subscript>2</Subscript> concentrations

The photosynthetic responses of the tropical tree species Acacia nigrescens Oliv. grown at different atmospheric CO₂ concentrations—from sub-ambient to super-ambient—have been studied. Light-saturated rates of net photosynthesis (A _sat) in A. nigrescens, measured after 120 days exposure, increased significantly from sub-ambient (196 μL L⁻¹) to current ambient (386 μL L⁻¹) CO₂ growth conditions but did not increase any further as [CO₂] became super-ambient (597 μL L⁻¹). Examination of photosynthetic CO₂ response curves, leaf nitrogen content, and leaf thickness showed that this acclimation was most likely caused by reduction in Rubisco activity and a shift towards ribulose-1,5-bisphosphate regeneration-limited photosynthesis, but not a consequence of changes in mesophyll conductance. Also, measurements of the maximum efficiency of PSII and the carotenoid to chlorophyll ratio of leaves indicated that it was unlikely that the pattern of A _sat seen was a consequence of growth [CO₂] induced stress. Many of the photosynthetic responses examined were not linear with respect to the concentration of CO₂ but could be explained by current models of photosynthesis.     

Kinetic limitations during the simultaneous removal of <Emphasis Type="Italic">p</Emphasis>-cresol and sulfide in a denitrifying process

The aim of this study was to evaluate the capacity of a denitrifying consortium to achieve the simultaneous removal of nitrate, sulfide and p-cresol and elucidate the rate-limiting steps in the mixotrophic process. Nitrite reduction appeared as the most evident rate-limiting step in the denitrifying respiratory process. The nitrite reduction rate achieved was up to 57 times lower than the nitrate reduction rate during the simultaneous removal of sulfide and p-cresol. Negligible accumulation of N₂O occurred in the denitrifying cultures corroborating that nitrite reduction was the main rate-limiting step of the respiratory process. A synergistic effect of nitrate and sulfide is proposed to explain the accumulation of nitrite. The study also points at the oxidation of S⁰ as another rate-limiting step in the denitrifying process. Different respiratory rates were achieved with the distinct electron donors provided (p-cresol and sulfide). The oxidation rate of p-cresol (q_CRES) was generally higher (up to 2.6-fold in terms of reducing equivalents) than the sulfide oxidation rate (q_S2−), except for the experiments performed at 100 mg S²⁻ L⁻¹ in which q_S2− was slightly (~1.4-fold in terms of reducing equivalents) higher than q_CRES. The present study provides kinetic information, which should be considered when designing and operating denitrifying reactors to treat industrial wastewaters containing large amounts of sulfurous, nitrogenous and phenolic contaminants such as those generated from petrochemical refineries.     

Biohydrogen production from carbon monoxide and water byRhodopseudomonas palustris P4

A reactor-scale hydrogen (H₂) productionvia the water-gas shift reaction of carbon monoxide (CO) and water was studied using the purple nonsulfur bacterium,Rhodopseudomonas palustris P4. The experiment was conducted in a two-step process: an aerobic/chemoheterotrophic cell growth step and a subsequent anaerobic H₂ production step. Important parameters investigated included the agitation speed, inlet CO concentration and gas retention time. P4 showed a stable H₂ production capability with a maximum activity of 41 mmol H₂ g cell⁻¹h⁻¹ during the continuous reactor operation of 400 h. The maximal volumetric H₂ production rate was estimated to be 41 mmol H₂ L¹h⁻¹, which was about nine-fold and fifteen-fold higher than the rates reported for the photosynthetic bacteriaRhodospirillum rubrum andRubrivivax gelatinosus, respectively. This is mainly attributed to the ability of P4 to grow to a high cell density with a high specific H₂ production activity. This study indicates that P4 has an outstanding potential for a continuous H₂ productionvia the water-gas shift reaction once a proper bioreactor system that provides a high rate of gas-liquid mass transfer is developed.     

Cross-talk between NMDA and GABA<Subscript>A</Subscript> receptors in cultured neurons of the rat inferior colliculus

Neuronal ion channels of different types often do not function independently but will inhibit or potentiate the activity of other types of channels, a process called cross-talk. The N-methyl-D-aspartate receptor (NMDA receptor) and the γ-aminobutyric acid type A receptor (GABA_A receptor) are important excitatory and inhibitory receptors in the central nervous system, respectively. Currently, cross-talk between the NMDA receptor and the GABA_A receptor, particularly in the central auditory system, is not well understood. In the present study, we investigated functional interactions between the NMDA receptor and the GABA_A receptor using whole-cell patch-clamp techniques in cultured neurons from the inferior colliculus, which is an important nucleus in the central auditory system. We found that the currents induced by aspartate at 100 μmol L⁻¹ were suppressed by the pre-perfusion of GABA at 100 μmol L⁻¹, indicating cross-inhibition of NMDA receptors by activation of GABA_A receptors. Moreover, we found that the currents induced by GABA at 100 μmol L⁻¹ (I _GABA) were not suppressed by the pre-perfusion of 100 μmol L⁻¹ aspartate, but those induced by GABA at 3 μmol L⁻¹ were suppressed, indicating concentration-dependent cross-inhibition of GABA_A receptors by activation of NMDA receptors. In addition, inhibition of IGABA by aspartate was not affected by blockade of voltage-dependent Ca²⁺ channels with CdCl₂ in a solution that contained Ca²⁺, however, CdCl₂ effectively attenuated the inhibition of I _GABA by aspartate when it was perfused in a solution that contained Ba²⁺ instead of Ca²⁺ or a solution that contained Ca²⁺ and 10 mmol L⁻¹ BAPTA, a membrane-permeable Ca²⁺ chelator, suggesting that this inhibition is mediated by Ca²⁺ influx through NMDA receptors, rather than voltage-dependent Ca²⁺ channels. Finally, KN-62, a potent inhibitor of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), reduced the inhibition of I _GABA by aspartate, indicating the involvement of CaMKII in this cross-inhibition. Our study demonstrates a functional interaction between NMDA and GABA_A receptors in the inferior colliculus of rats. The presence of cross-talk between these receptors suggests that the mechanisms underlying information processing in the central auditory system may be more complex than previously believed.     

Bio-hydrogen production from cellulose by sequential co-culture of cellulosic hydrogen bacteria of <Emphasis Type="Italic">Enterococcus gallinarum</Emphasis> G1 and <Emphasis Type="Italic">Ethanoigenens harbinense</Emphasis> B49

Microbial conversion of lignocellulose to hydrogen is a fascinating way to provide a renewable energy source. A mesophilic bacterium strain G1 that had high cellulose degradation and hydrogen production activity (2.38 mmol H₂ g⁻¹ cellulose) was isolated from rumen fluid and identified as the Enterococcus gallinarum. Hydrogen production from cellulose by using sequential co-cultures of a cellulosic-hydrolysis bacterium G1 and Ethanoigenens harbinense B49 was investigated. With an initial Avicel concentration of 5 g l^−l, the sequential co-culture with G1 and strain Ethanoigenens harbinense B49 produced H₂ yield approximately 2.97 mmol H₂ g⁻¹ cellulose for the co-culture system.     

Stomatal conductance and not stomatal density determines the long-term reduction in leaf transpiration of poplar in elevated CO<Subscript>2</Subscript>

Using a free-air CO₂ enrichment (FACE) experiment, poplar trees (Populus × euramericana clone I214) were exposed to either ambient or elevated [CO₂] from planting, for a 5-year period during canopy development, closure, coppice and re-growth. In each year, measurements were taken of stomatal density (SD, number mm⁻²) and stomatal index (SI, the proportion of epidermal cells forming stomata). In year 5, measurements were also taken of leaf stomatal conductance (g _s, μmol m⁻² s⁻¹), photosynthetic CO₂ fixation (A, mmol m⁻² s⁻¹), instantaneous water-use efficiency (A/E) and the ratio of intercellular to atmospheric CO₂ (C_i:C_a). Elevated [CO₂] caused reductions in SI in the first year, and in SD in the first 2 years, when the canopy was largely open. In following years, when the canopy had closed, elevated [CO₂] had no detectable effects on stomatal numbers or index. In contrast, even after 5 years of exposure to elevated [CO₂], g _s was reduced, A/E was stimulated, and C_i:C_a was reduced relative to ambient [CO₂]. These outcomes from the long-term realistic field conditions of this forest FACE experiment suggest that stomatal numbers (SD and SI) had no role in determining the improved instantaneous leaf-level efficiency of water use under elevated [CO₂]. We propose that altered cuticular development during canopy closure may partially explain the changing response of stomata to elevated [CO₂], although the mechanism for this remains obscure.     

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     

Oxidative coupling of a feruloyl-arabinoxylan trisaccharide (FAXX) in the walls of living maize cells requires endogenous hydrogen peroxide and is controlled by a low-M<Subscript>r</Subscript> apoplastic inhibitor

Feruloyl-polysaccharides can be oxidatively coupled in isolated cell walls by peroxidase plus exogenous H₂O₂ in vitro, but the extent to which similar reactions may occur in the apoplast in vivo was unclear. Numerous cellular factors potentially control feruloyl coupling in vivo, and their net controlling influence is not readily studied in vitro. Therefore, we have monitored apoplastic feruloyl coupling in cultured maize cells in vivo using a radiolabelled model substrate, 5-O-feruloyl-α-L-arabinofuranosyl-(1→3)-β-D-xylopyranosyl-(1→4)-D-xylose (FAXX). FAXX was expected to permeate the wall and to undergo reactions analogous to those normally exhibited by apoplastic feruloyl-polysaccharides in vivo. Little difference was found between the fates of [feruloyl−¹⁴C]FAXX and [pentosyl−³H]FAXX, indicating negligible apoplastic hydrolase or transferase activities. Very little radioactivity entered the protoplasm. Maize cells that had recently been washed in fresh medium were able to bind most of the FAXX (90%) in their cell walls, regardless of the age of the culture. During wall-binding, the [¹⁴C]feruloyl groups were converted to [¹⁴C]dehydrodiferulates and larger coupling products, as revealed by TLC after alkaline hydrolysis. As expected for an oxidative reaction, wall-binding was delayed by added anti-oxidants (ascorbate, ferulate, sinapate, chlorogenate or rutin). It was also completely inhibited by iodide, an H₂O₂-scavenger, indicating a role for peroxidase rather than oxidase. The observations indicate that oxidative coupling of feruloyl groups occurred within the cell wall, dependent on endogenous apoplastic H₂O₂ and wall-localised peroxidase, in vivo. Cells that had not recently been washed in fresh medium were much less able to bind FAXX, indicating the presence in the apoplast of an endogenous inhibitor of oxidative coupling. This inhibitor was of low M_r, was destroyed by heating, and remained in the aqueous phase (pH ≈3.5) when shaken with ethyl acetate. Its effectiveness was not altered by ascorbate oxidase. It is thus a small, heat-labile, hydrophilic inhibitor (not ascorbate) which we suggest plays a natural role in the control of wall cross-linking, and thus potentially in the control of cell growth.     

Influences of nitrogen load on the growth and photosynthetic responses of <Emphasis Type="Italic">Quercus serrata</Emphasis> seedlings to O<Subscript>3</Subscript>

The objectives of this study were to clarify the influences of nitrogen (N) load on the growth and photosynthetic responses of Quercus serrata seedlings to O₃ and to obtain basic data for evaluating the critical levels of O₃ for protecting Q. serrata forests in Japan. The effects of O₃ and/or N load on growth and photosynthetic activity of Q. serrata seedlings were investigated during the two growing seasons. Two-year-old seedlings were assigned to 12 experimental treatments, which were comprised of the combination of four gas treatments (charcoal-filtered air and three levels of O₃ at 1.0, 1.5 and 2.0 times ambient concentration) and three N treatments (0, 20 and 50 kg ha⁻¹ year⁻¹). During the second growing season, no significant interactive effects of O₃ and N load on the growth and net photosynthetic rate of the seedlings were detected. Threrfore, we concluded that N supply to the soil at ≤50 kg ha⁻¹ year⁻¹ does not significantly influence the growth and photosynthetic responses of Q. serrata seedlings to O₃. Based on the O₃ exposure-response relationships for the whole-plant growth of the seedlings, the critical level of O₃ for Q. serrata was estimated to be approximately 36 nmol mol⁻¹ as the average 15-h O₃ concentration during the one growing season.     

Integrated outdoor culture of two estuarine macroalgae as biofilters for dissolved nutrients from <Emphasis Type="Italic">Sparus auratus</Emphasis> waste waters

An integrated outdoor cultivation of two macroalgal species: Ulva rotundata (Chlorophyta) and Gracilariopsis longissima (Rhodophyta) was designed. The macroalgae were cultured in effluents from an intensive marine culture (growout phase) of gilthead seabream Sparus aurata. The biomass evolution of the algal tanks followed a logistic curve, where the approach to the maximum stocking density of seaweeds was governed by thalli self-shading, as nutrient limitation in the cultivation tank was unlikely. The maximum stocking density of the system was approximately 27.8 g U. rotundata L⁻¹ (16.7 Kg m⁻²) and 11.9 g G. longissima L⁻¹ (7.12 Kg m⁻²). Yield was more than 3 times higher in U. rotundata than in G. longissima. Overall, U. rotundata removed a greater percentage of phosphate (8.9%) and total dissolved inorganic nitrogen (54%) flowing into the algal tanks than G. longissima. The latter species biofiltered approximately 3.2% of phosphate and 17% of the total dissolved inorganic nitrogen input. However, mean nutrient uptake rates on wet weight basis were usually higher in G. longissima than in U. rotundata. The production of total oxidised nitrogen in the algal tanks, considered as being the nitrification rate occurring on the algal fronds by nitrifying bacteria, was less than half of the ammonium uptake by the macroalgae, suggesting that seaweeds competed efficiently for ammonia against the nitrifyers. The biofiltration during a diel cycle showed that mean phosphate biofiltration was lower than 4.5% in the two species whereas ammonium was biofiltered efficiently (up to 67%), especially in U. rotundata. The metal and heavy metal content in the algal tissue at the end of the monitoring period suggested no metal contamination of tissues so that both macroalgal species could be used in the food industry. The study reveals the value of ecological engineering techniques in reducing the dissolved nutrient content in effluents from the fish farm, with the prospect of a better management practises, based on integrated mariculture designs, being developed by the local farmers.     

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.     

Aquaporin expression in response to different water stress intensities and recovery in Richter-110 (<Emphasis Type="Italic">Vitis</Emphasis> sp.): relationship with ecophysiological status

Aquaporins seem essential for the regulation of plant water status and expenses. Richter-110 is a Vitis hybrid (Vitis berlandieri × rupestris) reputed to be strongly drought-tolerant. Three irrigation treatments were established in Richter-110 plants growing outdoors defined by the resulting maximum stomatal conductance (g _s), and ensuring water stress situations not severe enough as to stop photosynthesis and growth: well-watered plants (g _s about 250 mmol H₂O m⁻² s⁻¹), moderate water stress (g _s about 150 mmol H₂O m⁻² s⁻¹) and severe water stress (g _s about 50 mmol H₂O m⁻² s⁻¹). Plants under water stress were kept at constant water availability for 7 days to check for possible acclimation. Finally, plants were re-watered, and allowed to recover, for 3 days. Stomatal conductance, leaf water potential, xylem abscisic acid (ABA) content and root and stem hydraulic conductivity were determined. The relative amounts of expression of mRNA encoding seven putative aquaporins were determined in roots and leaves by RT-PCR. The decrease in stomatal conductance with moderate and severe water stress was associated with increasing ABA contents, but not with the leaf water potential and hydraulic conductivities, which remained unchanged during the entire experiment. Aquaporin gene expression varied depending on which aquaporin, water stress level and the plant organ. We suggest that aquaporin expression was responsive to water stress as part of the homeostasis, which resulted in constant leaf water potential and hydraulic conductivity.     

Influence of agitation and aeration on growth and antibiotic production by <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis>

The effect of agitation and aeration on the growth and antibiotic production by Xenorhabdus nematophila YL001 grown in batch cultures were investigated. Efficiency of aeration and agitation was evaluated through the oxygen mass transfer coefficient (K _L a). With increase in K _L a, the biomass and antibiotic activity increased. Activity units of antibiotic and dry cell weight were increased to 232 U ml⁻¹ and 19.58 g l⁻¹, respectively, productivity in cell and antibiotic was up more than 30% when K _L a increased from 115.9 h⁻¹ to 185.7 h⁻¹. During the exponential growth phase, DO concentration was zero, the oxygen supply was not sufficient. So, based on process analysis, a three-stage oxygen supply control strategy was used to improved the DO concentration above 30% by controlling the agitation speed and aeration rate. The dry cell weight and activity units of antibiotic were further increased to 24.22 g l⁻¹ and 249 U ml⁻¹, and were improved by 24.0% and 7.0%, compared with fermentation at a constant agitation speed and a constant aeration rate (300 rev min⁻¹, 2.5 l min⁻¹).