Maximum Photosynthetic Yield of Green Microalgae in Photobioreactors

The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 μmol photons m⁻² s⁻¹). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3–37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance. With this study, we demonstrated that the observed biomass yield on light in short light path bioreactors at high biomass densities decreases because maintenance requirements are relatively high at these conditions. All our experimental data for the two strains tested could be described by the physiological models of Pirt (New Phytol 102:3–37, 1986). Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate. A process with high biomass densities and high yields at high light intensities can only be obtained in short light path photobioreactors.     

Effect of aeration strategy on the metabolic flux of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> producing 1,3-propanediol in continuous cultures at different glycerol concentrations

The microbial production of 1,3-propaneidol (1,3-PD) by Klebsiella pneumoniae in continuous fermentation was investigated under low, medium and high glycerol concentrations in the absence and presence of oxygen. The production of 1,3-PD increased with increasing glycerol concentrations, reaching a maximum (266 mmol l⁻¹) under high glycerol concentration (760 mmol l⁻¹) with air sparging at 0.04 vvm. The yield of 1,3-PD, however, decreased gradually with increasing glycerol concentrations, with the highest yield (0.52 mol mol⁻¹) obtained for low glycerol concentration (270 mmol l⁻¹) under anaerobic condition. Enzyme activity assays showed that the specific activity of glycerol dehydratase was highest (0.04 U mg⁻¹) for culture sparged with 0.04 vvm air under high glycerol concentration. The specific activities of glycerol dehydrogenase and 1,3-propanediol oxidoreductase were also improved for all glycerol concentrations and in the presence of oxygen, implying that the dha operon was not repressed under microaerobic conditions. Analysis of metabolic fluxes showed that more carbon flux was shifted to the oxidative pathway with increasing glycerol concentrations, resulting in a reduced flux to 1,3-PD formation. However, the increases in carbon fluxes were not evenly distributed among the oxidative branches of the pathway. Furthermore, ethanol and acetic acid levels were slightly increased whereas 2,3-butanediol and lactic levels were greatly enhanced.     

Phenol biodegradation by the thermoacidophilic archaeon <Emphasis Type="Italic">Sulfolobus solfataricus</Emphasis> 98/2 in a fed-batch bioreactor

Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l⁻¹) and phenol (94 mg l⁻¹) at a constant dissolved oxygen concentration of 1.5 mg l⁻¹. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs (phenol < 365 mg l⁻¹), specific growth rate (μ_X) was 0.034 ± 0.001 h⁻¹, specific phenol degradation rate (q_P) was 57.5 ± 2 mg g⁻¹ h⁻¹, biomass yield (Y_X/P) was 52.2 ± 1.1 g mol⁻¹, and oxygen yield factor ( \textY_{\textX/\textO 2} ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol⁻¹. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO₂ (65%). Molar phenol oxidation constant ( \textY_{\textO 2 /\textP} ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO₂ conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol⁻¹. Respiratory quotient was about 0.84 mol mol⁻¹, very close to theoretical value (0.87 mol mol⁻¹). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments.     

Comparison of different mixed cultures for bio-hydrogen production from ground wheat starch by combined dark and light fermentation

Composition of the mixed culture was varied in combined dark-light fermentation of wheat powder starch in order to improve hydrogen gas formation rate and yield. Heat-treated anaerobic sludge and pure culture of Clostridium beijerinckii (DSMZ 791 ^T ) were combined with two different light fermentation bacteria of Rhodobacter sphaeroides (RS-NRRL and RS-RV) in order to select a more suitable mixture resulting in high hydrogen yield and formation rate. A combination of the anaerobic sludge and RS-NRRL yielded the highest cumulative hydrogen (CHF = 140 ml), the highest yield (0.36 mol H₂ mol⁻¹ glucose) and specific hydrogen formation rate (2.5 ml H₂ g⁻¹ biomass h⁻¹). During dark fermentation (70 h) hydrogen was produced simultaneously by the dark and light fermentation bacteria using glucose from hydrolyzed starch. However, only light fermentation bacteria produced hydrogen from VFA’s derived from dark fermentation after a long adaptation period.     

Using light as a lure is an efficient predatory strategy in <Emphasis Type="Italic">Arachnocampa flava,</Emphasis> an Australian glowworm

Trap-building, sit-and-wait predators such as spiders, flies and antlions tend to have low standard metabolic rates (SMRs) but potentially high metabolic costs of trap construction. Members of the genus Arachnocampa (glowworms) use an unusual predatory strategy: larvae bioluminesce to lure positively phototropic insects into their adhesive webs. We investigated the metabolic costs associated with bioluminescence and web maintenance in larval Arachnocampa flava. The mean rate of CO₂ production ([(V)\dot] \dot{V}CO₂) during continuous bioluminescence was 4.38 μl h⁻¹ ± 0.78 (SEM). The mean [(V)\dot] \dot{V}CO₂ of inactive, non-bioluminescing larvae was 3.49 ± 0.35 μl h⁻¹. The mean [(V)\dot] \dot{V}CO₂ during web maintenance when not bioluminescencing was 8.95 ± 1.78 μl h⁻¹, a value significantly lower than that measured during trap construction by other predatory arthropods. These results indicate that bioluminescence itself is not energetically expensive, in accordance with our prediction that a high cost of bioluminescence would render the Arachnocampa sit-and-lure predatory strategy inefficient. In laboratory experiments, both elevated feeding rates and daily web removal caused an increase in bioluminescent output. Thus, larvae increase their investment in light output when food is plentiful or when stressed through having to rebuild their webs. As light production is efficient and the cost of web maintenance is relatively low, the energetic returns associated with continuing to glow may outweigh the costs of continuing to attract prey.     

Effect of sucrose,light, and carbon dioxide on plantain micropropagation in temporary immersion bioreactors

In vitro physiology and carbon metabolism can be affected by the sink–source relationship. The effect of different sucrose concentrations (10, 30, and 50 g L⁻¹), light intensities (80 and 150 μmol m⁻² s⁻¹), and CO₂ levels (375 and 1,200 μmol mol⁻¹) were tested during plantain micropropagation in temporary immersion bioreactors. Activities of pyruvate kinase, phosphoenol pyruvate carboxylase, and the photosynthesis rate were recorded. From the morphological and practical point of view, the best results were obtained when plants were cultured with 30 g L⁻¹ sucrose, 80 μmol m⁻² s⁻¹ light intensity, and 1,200 μmol mol⁻¹ CO₂ concentration. This treatment improved leaf and root development, reduced respiration during in vitro culture, and increased starch level at the end of the hardening phase. In addition to that, the number of competent plants was increased from 80.0% to 91.0% at the end of the in vitro phase and the survival percentage from 95.71% to 99.80% during ex vitro hardening.     

Effects of dilution stress on the functioning of a saline Mediterranean stream

The effects of seasonality and dilution stress on the functioning of Rambla Salada, a hypersaline Mediterranean stream in SE Spain, were evaluated. The stream is subject to diffuse freshwater inputs from the drainage of intensively irrigated agriculture in the catchment and periodic losses of water through an irrigation channel. Metabolic rates and the biomass of primary producers and consumers were estimated over a 2-year period. During the first year several dilution events occurred, while during the second year the salinity recovery reached predisturbance levels. Functional indicators were compared in the disturbance and recovery salinity periods. Primary production and respiration rates in the Rambla Salada ranged between 0.07–21.05 and 0.19–17.39 g O₂ m⁻² day⁻¹, respectively. The mean values for these variables were 7.35 and 5.48 g O₂ m⁻² day⁻¹, respectively. Mean net daily metabolism rate was 1.87 ± 0.52 g O₂ m⁻² day⁻¹ and mean production/respiration ratio was 2.48 ± 1.1, reflecting autotrophic metabolism. The metabolic rates showed the typical seasonal pattern of Mediterranean open canopy streams. Therefore, gross primary production (GPP) and ecosystem respiration (ER) registered maximum values in summer, intermediate values in spring and autumn and minimum values in winter. The metabolic rates and biomass of consumers were greater in the disturbance period than in the recovery period. However, they did not show significant differences between periods due to their important dependence on seasonal cycle. Seasonality accounted for much of the temporal variability in GPP and ER (76% and 83% in the multiregression models, respectively). Light availability seems to be the most important factor for GPP and ER in the Rambla Salada. Autotrophic biomass responded more to variations in discharge and conductivity than to seasonal variations. In fact, it was severely affected by freshwater inputs after which the epipelic biomass decreased significantly and Cladophora glomerata proliferated rapidly. Epipelic algal biomass was the most sensitive parameter to dilution disturbance. Handling editor: Luigi Naselli-Flores     

Effects of light intensity and nitrogen starvation on growth, total fatty acids and arachidonic acid in the green microalga Parietochloris incisa

The effects of light and nitrogen deficiency on biomass, fatty acid content and composition were studied in Parietochloris incisa, the unicellular freshwater chlorophyte accumulating very high amounts of arachidonic-acid-rich triacylglycerols. P. incisa cultures grown on complete nutrient medium and under high light (400 μmol photons m^{− 2} s⁻¹) showed the highest rate of growth in comparison to medium (200 μmol photons m⁻² s⁻¹) and low (35 μmol photons m⁻² s⁻¹) light intensity. Cultures grown under high light (on complete BG-11 medium) attained higher volumetric contents of total fatty acids and arachidonic acid due to greater increase in biomass. Nitrogen starvation brought about a strong increase in the arachidonic acid proportion of total fatty acids. Thus, adjustments to cultivation conditions could serve as an efficient tool for manipulation of yield and relative content of arachidonic acid in P. incisa. The significance of the changes in lipid metabolism for adaptation of P. incisa to high-light stress and nitrogen deficiency is also discussed.     

The metabolic responses and acid–base status after feeding, exhaustive exercise, and both feeding and exhaustive exercise in Chinese catfish (Silurus asotus Linnaeus)

Feeding and exhaustive exercise are known to elevate metabolism. However, acid–base status may be oppositely affected by the two processes. In this study, we first investigated the acid–base response of Chinese catfish to feeding (the meal size was about 8% of body mass) to test whether an alkaline tide (a metabolic alkalosis created by gastric HCl secretion after feeding) would occur. We then determined the combined effects of feeding and exhaustive exercise on excess post-exercise oxygen consumption and acid–base status to determine whether the alkaline tide induced by feeding protects against acid–base disturbance during exhaustive exercise and affects subsequent recovery. Arterial blood pH increased from 7.74 ± 0.02 before feeding to 7.88 ± 0.02 and plasma [HCO₃ ⁻]_pl increased from 5.42 ± 0.29 to 7.83 ± 0.37 mmol L⁻¹ 6 h after feeding, while feeding had no significant effect on P_\textCO2 P_{{{\text{CO}}_{2} }} . Exhaustive exercise led to a significant reduction in pH by 0.46 units and a reduction of [HCO₃ ⁻]_pl by ~3 mmol L⁻¹. Lactate concentrations in white muscle and plasma increased by 2.4 mmol L⁻¹ and 13.4 μmol g⁻¹, respectively. Fed fish had a higher pH and [HCO₃ ⁻]_pl than fasting fish at rest, and the reductions in pH (0.36 units) and [HCO₃ ⁻]_pl (~2 mmol L⁻¹) were thus lower after exhaustive exercise. However, the recovery of acid–base status and metabolites were similar in digesting and fasting fish. Overall, a significant alkaline tide was found in Chinese catfish after feeding. The alkaline tide elicited by feeding significantly prevented the decreases in pH and [HCO₃ ⁻]_pl immediately after exhaustive exercise, but recovery from exhaustive exercise was not affected by digestion.     

Acclimation of the summer annual species, Lolium temulentum, to CO2 enrichment

Lolium temulentum L. Ba 3081 was grown hydroponically in air (350 μmol mol⁻¹ CO₂) and elevated CO₂ (700 μmol mol⁻¹ CO₂) at two irradiances (150 and 500 μmol m⁻² s⁻¹) for 35 days at which point the plants were harvested. Elevated CO₂ did not modify relative growth rate or biomass at either irradiance. Foliar carbon-to-nitrogen ratios were decreased at elevated CO₂ and plants had a greater number of shorter tillers, particularly at the lower growth irradiance. Both light-limited and light-saturated rates of photosynthesis were stimulated. The amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) protein was increased at elevated CO₂, but maximum extractable Rubisco activities were not significantly increased. A pronounced decrease in the Rubisco activation state was found with CO₂ enrichment, particularly at the higher growth irradiance. Elevated-CO₂-induced changes in leaf carbohydrate composition were small in comparison to those caused by changes in irradiance. No CO₂-dependent effects on fructan biosynthesis were observed. Leaf respiration rates were increased by 68% in plants grown with CO₂ enrichment and low light. We conclude that high CO₂ will only result in increased biomass if total light input favourably increases the photosynthesis-to-respiration ratio. At low irradiances, biomass is more limited by increased rates of respiration than by CO₂-induced enhancement of photosynthesis. Received: 23 February 1999 / Accepted: 15 June 1999     

Growth and physiological activity in <Emphasis Type="Italic">Larix kaempferi</Emphasis> seedlings inoculated with ectomycorrhizae as affected by soil acidification

To evaluate the effect of ectomycorrhizal colonization on growth and physiological activity of Larix kaempferi seedlings grown under soil acidification, we grew L. kaempferi seedlings with three types of ectomycorrhizae for 180 days in acidified brown forest soil derived from granite. The soil had been treated with an acid solution (0 (control), 10, 30, 60, and 90 mmol H⁺ kg⁻¹). The water-soluble concentrations of Ca, Mg, K, Al, and Mn increased with increasing amounts of H⁺ added to the soil. Ectomycorrhizal development significantly increased in soil treated with 10 and 30 mmol H⁺ kg⁻¹ but was significantly reduced in soil treated with 60 and 90 mmol H⁺ kg⁻¹. The concentrations of Al and Mn in needles or roots increased with increasing H⁺ added to the soil. The total N in seedlings significantly increased with increasing H⁺ in soil and colonization with ectomycorrhiza. The maximum net photosynthetic rate at light and CO₂ saturation (P _max) was greater in soil treated with 10 mmol H⁺ kg⁻¹ than in controls, and was less is soils treated with greater than with 30 mmol H⁺ kg⁻¹, especially with 60 and 90 mmol H⁺ kg⁻¹. However, colonization with ectomycorrhiza significantly reduced the concentration of Al and Mn in needles or roots and increased the values of P _max and total dry mass (TDM). The relative TDM of L. kaempferi seedlings was approximately 40% at a (BC, base cation)/Al ratio of 1.0. However, ectomycorrhizal seedlings had a 100–120% greater TDM at a BC/Al ratio of 1.0 than non-ectomycorrhizal seedlings, even though the acid treatment reduced their overall growth.     

Acid–base regulation in the plainfin midshipman (Porichthys notatus): an aglomerular marine teleost

The plainfin midshipman (Porichthys notatus) possesses an aglomerular kidney and like other marine teleosts, secretes base into the intestine to aid water absorption. Each of these features could potentially influence acid–base regulation during respiratory acidosis either by facilitating or constraining HCO₃ ⁻ accumulation, respectively. Thus, in the present study, we evaluated the capacity of P. notatus to regulate blood acid–base status during exposure to increasing levels of hypercapnia (nominally 1–5% CO₂). Fish exhibited a well-developed ability to increase plasma HCO₃ ⁻ levels with values of 39.8 ± 2.8 mmol l⁻¹ being achieved at the most severe stage of hypercapnic exposure (arterial blood PCO₂ = 21.9 ± 1.7 mmHg). Consequently, blood pH, while lowered by 0.15 units (pH = 7.63 ± 0.06) during the final step of hypercapnia, was regulated far above values predicted by chemical buffering (predicted pH = 7.0). The accumulation of plasma HCO₃ ⁻ during hypercapnia was associated with marked increases in branchial net acid excretion (J _NETH⁺) owing exclusively to increases in the titratable alkalinity component; total ammonia excretion was actually reduced during hypercapnia. The increase in J _NETH⁺ was accompanied by increases in branchial carbonic anhydrase (CA) enzymatic activity (2.8×) and CA protein levels (1.6×); branchial Na⁺/K⁺-ATPase activity was unaffected. Rectal fluids sampled from control fish contained on average HCO₃ ⁻ concentrations of 92.2 ± 4.8 mmol l⁻¹. At the highest level of hypercapnia, rectal fluid HCO₃ ⁻ levels were increased significantly to 141.8 ± 7.4 mmol l⁻¹ but returned to control levels during post-hypercapnia recovery (96.0 ± 13.2 mmol l⁻¹). Thus, the impressive accumulation of plasma HCO₃ ⁻ to compensate for hypercapnic acidosis occurred against a backdrop of increasing intestinal HCO₃ ⁻ excretion. Based on in vitro measurements of intestinal base secretion in Ussing chambers, it would appear that P. notatus did not respond by minimizing base loss during hypercapnia; the increases in base flux across the intestinal epithelium in response to alterations in serosal HCO₃ ⁻ concentration were similar in preparations obtained from control or hypercapnic fish. Fish returned to normocapnia developed profound metabolic alkalosis owing to unusually slow clearance of the accumulated plasma HCO₃ ⁻. The apparent inability of P. notatus to effectively excrete HCO₃ ⁻ following hypercapnia may reflect its aglomerular (i.e., non-filtering) kidney coupled with the normally low rates of urine production in marine teleosts.     

Modeling growth and photosynthetic response in <Emphasis Type="Italic">Arthrospira platensis</Emphasis> as function of light intensity and glucose concentration using factorial design

Combined effect of light intensity and glucose concentration on Arthrospira platensis growth and photosynthetic response was evaluated using a 3² factorial design. This design was carried out with light levels of 50, 100, and 150 μmol photons m⁻² s⁻¹ and glucose concentrations of 0.5, 1.5, and 2.5 g L⁻¹. Results from the response surface methodology were that the highest level of light intensity and glucose concentration improved biomass (1.33 g L⁻¹), maximum specific growth rate (0.49 day⁻¹), and net photosynthetic rate (139.89 μmol O₂ mg Chl⁻¹ h⁻¹). Furthermore, the interaction of both factors showed that at low light, glucose had a low effect on maximum biomass and maximal net photosynthetic rate. However, at the highest light levels, the effect of glucose was more sensitive and the increase of glucose concentration increased the levels of all responses. The rates of the instantaneous relative growth, net photosynthesis, and dark respiration of growth cultures showed two different phases in mixotrophic condition. The first was distinguished by the preponderance of the photoautotrophic mode; the second was based mainly on photoheterotrophy.     

Eco-physiological responses of nitrogen-fixing cyanobacteria to light

The eco-physiological responses of three nitrogen-fixing cyanobacteria (N-fixing cyanobacteria), Aphanizomenon gracile, Anabaena minderi, and Ana. torques-reginae, to light were assessed under nutrient saturation. The N-fixing cyanobacteria were isolated into monocultures from a natural bloom in a shallow colored lake and their growth irradiance parameters and pigment composition were assessed. The different ecological traits related to light use (μ_max, α, I _k) suggest that these N-fixing cyanobacteria are well adapted to low light conditions at sufficient nutrients, yet interspecific differences were observed. Aphanizomenon gracile and Anabaena minderi had high relative growth rates at low irradiances (ca. 70% of those in high light), low half saturation constant for light-limited growth (I _k < 9.09 μmol photon m⁻² s⁻¹) and high efficiency (α < 0.11 day⁻¹ μmol photon⁻¹ m² s). Conversely, Ana. torques-reginae showed poorer light competitiveness: low relative growth rates at low irradiances (ca. 40% of those in high light), low α (0.009 day⁻¹ μmol photon⁻¹ m² s) and higher I _k (35.5 μmol photon m⁻² s⁻¹). Final densities in Aphanizomenon gracile and Anabaena minderi reached bloom densities at irradiances above 30 μmol photon m⁻² s⁻¹ with different hierarchy depending on irradiance, whereas Ana. torques-reginae never achieved bloom densities. All species had very low densities at irradiances ≤17 μmol photon m⁻² s⁻¹, thus no N-fixing blooms would be expected at these irradiances. Also, under prolonged darkness and at lowest irradiance (0 and 3 μmol photon m⁻² s⁻¹) akinetes were degraded, suggesting that in ecosystems with permanently dark sediments, the prevalence of N-fixing cyanobacteria should not be favored. All species displayed peaks of phycocyanin, but no phycoeritrin, probably due to the prevailing red light in the ecosystem from which they were isolated.     

Fast cyclic electron transport around photosystem I in leaves under far-red light: a proton-uncoupled pathway?

Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 μmol quanta m⁻² s⁻¹. The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in redox equilibrium with K _e = 35 (ΔE _m = 90 mV). PS II ETR was based on O₂ evolution. CET [(PS I ETR) − (PS II ETR)] increased to 50–70 μmol e⁻ m⁻² s⁻¹ when linear electron transport (LET) under FRL was limited to 5 μmol e⁻ m⁻² s⁻¹ in a gas phase containing 20–40 μmol CO₂ mol⁻¹ and 20 μmol O₂ mol⁻¹. Under these conditions, pulse-saturated fluorescence yield F _m was non-photochemically quenched; however, F _m was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd → (FNR) → Cyt c_n → Cyt b_h → Cyt b_l → Rieske FeS → Cyt f → PC → P700 →→ Fd. CET is activated when PQH₂ oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e⁻ acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy dissipation under stress conditions.     

Performance assessment of malolactic fermenting bacteria Oenococcus oeni and Lactobacillus brevis in continuous culture

The growth performance of malolactic fermenting bacteria Oenococcus oeni NCIMB 11648 and Lactobacillus brevis X₂ was assessed in continuous culture. O. oeni grew at a dilution rate range of 0.007 to 0.052 h⁻¹ in a mixture of 5:6 (g l⁻¹) of glucose/fructose at an optimal pH of 4.5, and L. brevis X₂ grew at 0.010 to 0.089 h⁻¹ in 10 g l⁻¹ glucose at an optimal pH of 5.5 in a simple and safe medium. The cell dry weight, substrate uptake and product formation were monitored, as well as growth kinetics, yield parameters and fermentation balances were also evaluated under pH control conditions. A comparison of growth characteristics of two strains was made, and this showed significantly different performance. O. oeni has lower maximum specific growth rate (μ_max=0.073 h⁻¹), lower maximum cell productivity (Q _x ^max=17.6 mg cell l⁻¹ h⁻¹), lower maximum biomass yield (Y _x/s ^max=7.93 g cell mol⁻¹ sugar) and higher maintenance coefficient (m _s=0.45 mmol⁻¹ sugar g⁻¹ cell h⁻¹) as compared with L. brevis X₂ (μ_max=0.110 h⁻¹; Q _x ^max=93.2 g⁻¹ cell mol⁻¹ glucose; Y _x/s ^max=22.3 g cell mol⁻¹ glucose; m _s=0.21 mmol⁻¹ glucose g⁻¹ cell h⁻¹). These data suggest a possible more productive strategy for their combined use in maturation of cider and wine.     

Enzymatic synthesis of farnesyl laurate in organic solvent: initial water activity, kinetics mechanism, optimization of continuous operation using packed bed reactor and mass transfer studies

The influence of water activity and water content was investigated with farnesyl laurate synthesis catalyzed by Lipozyme RM IM. Lipozyme RM IM activity depended strongly on initial water activity value. The best results were achieved for a reaction medium with an initial water activity of 0.11 since it gives the best conversion value of 96.80%. The rate constants obtained in the kinetics study using Ping-Pong-Bi-Bi and Ordered-Bi-Bi mechanisms with dead-end complex inhibition of lauric acid were compared. The corresponding parameters were found to obey the Ordered-Bi-Bi mechanism with dead-end complex inhibition of lauric acid. Kinetic parameters were calculated based on this model as follows: V _max = 5.80 mmol l⁻¹ min⁻¹ g enzyme⁻¹, K _m,A = 0.70 mmol l⁻¹ g enzyme⁻¹, K _m,B = 115.48 mmol l⁻¹ g enzyme⁻¹, K _i = 11.25 mmol l⁻¹ g enzyme⁻¹. The optimum conditions for the esterification of farnesol with lauric acid in a continuous packed bed reactor were found as the following: 18.18 cm packed bed height and 0.9 ml/min substrate flow rate. The optimum molar conversion of lauric acid to farnesyl laurate was 98.07±0.82%. The effect of mass transfer in the packed bed reactor has also been studied using two models for cases of reaction limited and mass transfer limited. A very good agreement between the mass transfer limited model and the experimental data obtained indicating that the esterification in a packed bed reactor was mass transfer limited.     

Utilization of <Emphasis Type="Italic">Anabaena</Emphasis> sp. in CO<Subscript>2</Subscript> removal processes

This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO₂ fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate assayed, resulting to 0.5 g_bio l⁻¹ day⁻¹ and 0.2 g_eps l⁻¹ day⁻¹, and the CO₂ fixation rate measured was 1.0 gCO₂ l⁻¹ day⁻¹. The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m⁻² s⁻¹, its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration, the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s⁻¹, demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO₂ into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO₂ l⁻¹ day⁻¹ outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation of photobioreactors using this strain.     

Effect of temperature on <Emphasis Type="SmallCaps">d</Emphasis>-arabitol production from lactose by <Emphasis Type="Italic">Kluyveromyces lactis</Emphasis>

d-Arabitol production from lactose by Kluyveromyces lactis NBRC 1903 has been studied by following the time courses of concentrations of cell mass, lactose, d-arabitol, ethanol, and glycerol at different temperatures. It was found that temperature is a key factor in d-arabitol production. Within temperatures ranging from 25 to 39°C, the highest d-arabitol concentration of 99.2 mmol l⁻¹ was obtained from 555 mmol l⁻¹ of lactose after 120 h of batch cultivation at 37°C. The yield of d-arabitol production on cell mass growth increased drastically at temperatures higher than 35°C, and the yield reached 1.07 at 39°C. Increasing the cell mass concentration two-fold after 24 h of culture growth at 37°C, the d-arabitol concentration further increased to 168 mmol l⁻¹. According to the distribution of the metabolic products, metabolic changes related to growth phase were also discussed. The stationary-phase K. lactis cells in the batch culture that is started with exposing the precultured inoculum to high osmotic stress, high oxidative stress, and high heat stress are found to be preferable for d-arabitol production.     

The role of platelet ice microalgae in seeding phytoplankton blooms in Terra Nova Bay (Ross Sea,Antarctica): a mesocosm experiment

The aim of this study was to assess the role of platelet ice microalgal communities in seeding pelagic blooms. Nutrient dynamics, microalgal biomass, photosynthetic parameters, cell densities and species succession were studied in two mesocosm experiments, designed to simulate the transition of microalgal communities from platelet ice habitat to pelagic conditions. The microalgal assemblages were dominated by diatoms, 70% of which were benthic species such as Amphiprora kufferathii, Nitzschia stellata, and Berkeleya adeliensis. Photoacclimation of benthic species was inadequate also at relatively low irradiances. Exceptional growth capacity at different light levels was observed for pelagic species such as Fragilariopsis cylindrus and Chaetoceros spp. which may be important in seeding blooms at ice breakup. Fragilariopsis cylindrus showed high growth rates both at 65 and 10% of incident light and in nutrient replete as well as in nutrient depleted conditions. Five days after inoculation, phytoplankton biomass increased and nutrient concentrations decreased in both light conditions. Nutrient uptake rates were up to 9.10 μmol L⁻¹ d⁻¹ of TIN in the high light tank and 6.18 μmol L⁻¹ d⁻¹ in the low light tank and nutrient depletion in the high light tank occurred 3 days prior to depletion in the low light tank. At nutrient depletion, biomass concentrations were similar in both tanks, 30 and 34 μg Chla L⁻¹. This article belongs to a special topic: Five articles on Sea-ice communities in Terra Nova Bay (Ross Sea), coordinated by L. Guglielmo and V. Saggiomo, appear in this issue of Polar Biology. The studies were conducted in the frame of the National Program of Research in Antarctica (PNRA) of Italy.