Production of eicosapentaenoic acid (EPA) in Monodus subterraneus grown in a helical tubular photobioreactor as affected by cell density and light intensity

The effect of cell density (1–4.5 g L^-1) and light intensity (44 and 82 mol m^-2 s^-1) on fatty acid composition andeicosapentaenoic acid (EPA, 20:5 3) production was studied ina semi-continuous culture of Monodus subterraneus grown in a helicaltubular photobioreactor (`Biocoil') under laboratory conditions. Under lowlight, the highest proportion of EPA (31.5% of total fatty acids) and EPAcontent (3.5% of dry weight), biomass productivity (1.3 g L^-124 h^-1) and EPA productivity (44 mg L^-1 24 h^-1)occurred at optimal cell density of about 1.7 g L^-1. Cell densityhad no effect on the total fatty acid (TFA) content and was maintained atca. 11% of dry weight. Under high light, the highest proportion ofEPA to fatty acids (31.8%), the total fatty acids content (13.4%) andEPA content (4.3% of dry weight) occurred at cell density of about 3.4gL^-1. But the highest biomass productivity (1.7 g L^-124 h^-1) and EPA productivity (56 mg L^-1 24 h^-1) wereobtained at a cell density of 1.6 and 2.6g L^-1, respectively. Ourresults suggest that manipulating the cell density and light intensity canmodify the composition of fatty acid and production of eicosapentaenoicacid (EPA) in M. subterraneus.     

Optimization of eicosapentaenoic acid production byPhaeodactylum tricornutumin the flat panel airlift (FPA) reactor

Biomass and eicosapentaenoic acid (EPA) productivities were investigated in a flat panel airlift loop reactor ideally mixed by static mixers. Growth with ammonium, urea and nitrate as nitrogen source were performed at different aeration rates. Cultures grew on ammonium but the decay of pH strongly inhibited biomass increase. On urea biomass productivity reached 2.35 g L^–1d^–1at an aeration rate of 0.66 vvm (24 h light per day, 1000 mol photon m^–2s^–1). Aeration rates between 0.33 vvm and 0.66 vvm and maximal productivities on urea were linearly dependent. Productivity on nitrate never exceeded 1.37 g L^–1d^–1. In the range of maximum productivity photosynthesis efficiency of 10.6% was reached at low irradiance (250 mol photon m^–2s^–1). Photosynthesis efficiency decreased to 4.8% at 1000 mol photon m^–2s^–1. At these high irradiances the flat panel airlift reactor showed a 35% higher volume productivity than the bubble column. At continuous culture conditions the influence of CO₂concentration in the supply air was tested. Highest productivities were reached at 1.25% (v/v) CO₂where the continuous culture yielded 1.04 g L^–1d^–1(16 h light per day, 1000 mol photon m^–2s^–1). The average EPA content amounted to 5.0% of cell dry weight, that resulted in EPA productivities of 52 mg L^–1d^–1(continuous culture, 16 h light per day) or 118 mg L^–1d^–1(batch culture, 24 h light per day).     

Effects of nitrogen source and concentration on growth rate and fatty acid composition of Ellipsoidion sp. (Eustigmatophyta)

In order to study the effects of different nitrogen source and concentrationon the growth rate and fatty acid composition, a marine microalga Ellipsoidion sp. with a high content of eicosapentaenoic acid (EPA) wascultured in media with different nitrogen sources and concentrations.During the pre-logarithmic phase, the alga grew faster with ammoniumas N source than with nitrate, but the reverse applied during thepost-logarithmic phase. The alga grew poorly in N-free mediumor medium with urea as the sole N source. In the same growth phase,ammonium medium resulted in higher yield of total lipid, but the EPA yielddid not differ significantly different from that using nitrate medium. Themaximum growth rate occurred in medium containing 1.28 mmolL^-1 sodium nitrate, while maximum EPA and total lipid contents werereached at 1.92 mmol L^-1, when EPA accounted for 27.9% totalfatty acids. The growth rate kept stable when NH₄Cl ranged from0.64 to 2.56 mmol L^-1, and the maximum content of total lipidand EPA occurred in the medium with 2.56 mmol L^-1NH₄Cl. The EPA content was higher in the pre- thanpost-logarithmic phase, though the total lipid content was lower. Thehighest EPA content expressed as percent total fatty acid was 27.9% innitrate medium and and 39.0% in ammonium medium.     

Effect of cell density and irradiance on growth,proximate composition and eicosapentaenoic acid production ofPhaeodactylum tricornutum grown in a tubular photobioreactor

Growth and eicosapentaenoic acid (EPA) productivity of the diatomPhaeodactylum tricornutum grown semicontinuously in a helical tubular photobioreactor were examined under a range of irradiances (approximately 56 to 1712 µmol photons m^-2 s^-1) and cell densities (3 × 10⁶ to 18 × 10⁶ cells mL^-1). Self shading sets the upper limit of operational maximum cell density. Higher irradiance increases this upper limit and also increase the growth rate. Biomass productivity and EPA productivity were enhanced at those cell densities which support the fastest growth rate irrespective of irradiance. The cell protein content increased with increasing irradiance and the carbohydrate and lipid content increased with increasing cell density. EPA productivity was greatest at the highest irradiance. This study shows that biomass productivity and EPA productivity can be maximised by optimising cell density and irradiance, as well as by addition of CO₂.Author for correspondence     

Linear growth in microbial cultures limited by accumulated substrate

Summary The linear growth phase in cultures limited by intracellular (conservative) substrate is represented by a flat exponential curve. Within the range of experimental errors, the presented model fits well the data from both batch and continuous cultures ofEscherichia coli, whose growth is limited in that way.List of symbols D dilution rate, h^–1 - K_S saturation constant, g.L^–1 - S concentration of the limiting substrate, g.L^–1 - S_i concentration of the limiting substrate accumulated in the cells, g.g^–1 - S_o initial concentration of the limiting substrate, g.L^–1 - t time of cultivation, h - t₁ time of exhaustion of the limiting substrate from medium, h - t_o beginning of exponential phase, h - X biomass concentration, g.L^–1 - X₁ biomass concentration at the time of exhaustion of the limiting substrate from the medium, g.L^–1 - X_o biomass concn. at the beginning of exponential phase, g.L^–1 - biomass concn. at steady-state, g.L^–1 - Y growth yield coefficient (biomass/substrate) - specific growth rate, h^–1 - _m maximum specific growth rate, h^–1     

Modelling growth responses of soil nitrifiers to additions of ammonium sulphate and ammonium chloride

Summary Following the addition of 0–75 mole N g^–1 as ammonium chloride or ammonium sulphate to a sandy loam soil the nitrate formed was measured daily for a period of 15–17 days. The nitrate produced as a function of time was described using the Monod equation for microbial growth. An optimisation technique is described for obtaining, from the nitrification time course data, the maximum specific growth rate, the affinity constantant and an index limited by the concentration of ammonium in soil solution. Additions of more than 7.3 moles N g^–1 soil as ammonium chloride were found to inhibit nitrification. The inhibition was interpreted as being caused by osmotic pressure or by chloride ion. A similar effect was not found with ammonium sulphate, because the salt concentration in the soil solution was restricted by the precipitation of calcium sulphate. The model developed was capable of accounting for nitrate production in the soil under non-steady state conditions of substrate concentrations and nitrifier biomass.     

Optimization of biomass and fatty acid productivity of Scenedesmus obliquus as a promising microalga for biodiesel production

Nowadays, microalgae are discussed as a promising feedstock for biodiesel production. The present study examines the possibility of enhancement of fatty acid productivity of Scenedesmus obliquus by modifications of the culture medium composition. The effect of different concentrations of sodium bicarbonate, salinity, potassium nitrate, glycerol and sugarcane molasses on the enhancement of biomass and esterified fatty acids production was studied. NaHCO₃ caused an increase in the biomass productivity at low concentrations (0.5 g L^?1), while negatively affected fatty acid productivity at all tested concentrations. Increase of salinity enhanced both biomass and fatty acid productivity. The optimum NaCl concentration and sea water ratio were 0.94 g L^?1 and 25 % which resulted in 56 and 39 % increase in fatty acid productivity, respectively. Nitrogen deficiency showed increase in fatty acid content by 54 % over control but fatty acid productivity was decreased as a result of growth inhibition. Nitrogen-free cultures and cultures treated with ?50 % concentrations of KNO₃ showed 96 and 42 % decrease in EFA productivity, respectively, as compared with the control. Addition of 0.05 and 0.1 M of glycerol increased the biomass productivity by 6 and 5 %, respectively but showed no significant effect on fatty acid productivity as a result of decrease in fatty acid content. Finally, usage of sugarcane molasses stimulated both biomass and fatty acid content. The increase in fatty acid productivity was 32, 65 and 73 % above the control level at 1, 3 and 5 g L^?1 of sugarcane molasses, respectively.     

Heterotrophic production of Chlorella sp. TISTR 8990—biomass growth and composition under various production conditions

The green microalga Chlorella sp. TISTR 8990 was grown heterotrophically in the dark using various concentrations of a basal glucose medium with a carbon‐to‐nitrogen mass ratio of 29:1. The final biomass concentration and the rate of growth were highest in the fivefold concentrated basal glucose medium (25 g L^?1 glucose, 2.5 g L^?1 KNO₃) in batch operations. Improving oxygen transfer in the culture by increasing the agitation rate and decreasing the culture volume in 500‐mL shake flasks improved growth and glucose utilization. A maximum biomass concentration of nearly 12 g L^?1 was obtained within 4 days at 300 rpm, 30°C, with a glucose utilization of nearly 76% in batch culture. The total fatty acid (TFA) content of the biomass and the TFA productivity were 102 mg g^?1 and 305 mg L^?1 day^?1, respectively. A repeated fed‐batch culture with four cycles of feeding with the fivefold concentrated medium in a 3‐L bioreactor was evaluated for biomass production. The total culture period was 11 days. A maximum biomass concentration of nearly 26 g L^?1 was obtained with a TFA productivity of 223 mg L^?1 day^?1. The final biomass contained (w/w) 13.5% lipids, 20.8% protein and 17.2% starch. Of the fatty acids produced, 52% (w/w) were saturated, 41% were monounsaturated and 7% were polyunsaturated (PUFA). A low content of PUFA in TFA feedstock is required for producing high quality biodiesel. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1589–1600, 2017     

Effects of initial population density (IPD) on growth and lipid composition of Nannochloropsis sp.

The microalga Nannochloropsis sp. was cultured under different initial population densities (IPDs) ranging from 0.11 to 9.09 g L^?1. The IPD affected the biomass and lipid accumulation significantly. The algal cultured with higher IPD resulted higher biomass concentration (up to 13.07 g L^?1) in 10 days growth. The biomass productivity with 0.98 g L^?1 IPD was 0.75 g L^?1 d^?1 which was higher than that of other IPDs. For IPDs ranging from 0.11 to 0.98 g L^?1, with the increase of IPD, the biomass productivity increased, while for IPD over 0.98 g L^?1, the biomass productivity decreased. Lipid content of the algal culture started with 0.11 g L^?1 IPD reached to 42 % of dry weight. But with the increase of IPD, the lipid content decreased. Lipid composition was analyzed using thin layer chromatography coupled with flame ionization detection (TLC/FID). Seven lipid classes were identified and quantified. The main reserve lipid, triacylglyceride (TAG), accumulated under all different IPD conditions. However, with the increasing IPD values, TAG content decreased from 59.1 to 23.5 % of the total lipids. Based on these results, to obtain the maximal biomass productivity and lipid productivity of Nannochloropsis sp. in mass cultivation systems, it is necessary to select an appropriate IPD.     

Mixotrophic culture of Chlorella pyrenoidosa with olive-mill wastewater as the nutrient medium

With olive-mill wastewater (`alpechín') as the nutrient medium, theinfluence of specific rate of aeration and initial alpechín concentrationhave been analysed in cultures of Chlorella pyrenoidosa, exposed bothto continuous and intermittent illumination (12/12 h light/dark cycles). The stirring rate in the bioreactor, as well as pH and temperature werefixed previously at 180 rpm, 6.5 and 30 ^°C, respectively. Themaximum specific growth rate (_m) and biomass productivity(b) were determined as kinetic parameters. The chlorophyll, protein andcarbohydrate contents were evaluated, as well as the fatty-acid compositionof the lipid fraction. The experimental conditions most conducive to abalanced biomass composition with regard to proteins and lipids were: initial alpechín concentration of 10% (v/v), continuous illumination,and aeration rate of 1 L (litre cell suspension)^-1 min^-1. Under these conditions, the highest values of _m and b wereclose to 0.04 h^-1 and 1.4 10^-3 g L^-1 h^-1, respectively.     

Investigation of biomass concentration,lipid production,and cellulose content in Chlorella vulgaris cultures using response surface methodology

The microalgae Chlorella vulgaris produce lipids that after extraction from cells can be converted into biodiesel. However, these lipids cannot be efficiently extracted from cells due to the presence of the microalgae cell wall, which acts as a barrier for lipid removal when traditional extraction methods are employed. Therefore, a microalgae system with high lipid productivity and thinner cell walls could be more suitable for lipid production from microalgae. This study addresses the effect of culture conditions, specifically carbon dioxide and sodium nitrate concentrations, on biomass concentration and the ratio of lipid productivity/cellulose content. Optimization of culture conditions was done by response surface methodology. The empirical model for biomass concentration (R² = 96.0%) led to a predicted maximum of 1123.2 mg dw L^?1 when carbon dioxide and sodium nitrate concentrations were 2.33% (v/v) and 5.77 mM, respectively. For lipid productivity/cellulose content ratio (R² = 95.2%) the maximum predicted value was 0.46 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 when carbon dioxide concentration was 4.02% (v/v) and sodium nitrate concentration was 3.21 mM. A common optimum point for both variables (biomass concentration and lipid productivity/cellulose content ratio) was also found, predicting a biomass concentration of 1119.7 mg dw L^?1 and lipid productivity/cellulose content ratio of 0.44 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 for culture conditions of 3.77% (v/v) carbon dioxide and 4.01 mM sodium nitrate. The models were experimentally validated and results supported their accuracy. This study shows that it is possible to improve lipid productivity/cellulose content by manipulation of culture conditions, which may be applicable to any scale of bioreactors. Biotechnol. Bioeng. 2013; 110: 2114–2122. © 2013 Wiley Periodicals, Inc.     

Effect of nitrate on lipid production by T. suecica, M. contortum, and C. minutissima

Microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Nitrate is a good nitrogen source for many microalgae and affects biomass and lipid yields of microalgae. In this study, the effect of nitrate on cell growth and lipid production and composition in Monoraphidium contortum, Tetraselmis suecica, and Chlorella minutissima was investigated. Nitrate affected the production of biomass and the production and composition of lipids of the three microalgae tested. Increasing the nitrate concentration in the culture medium resulted in increased biomass production and higher biomass productivity. Furthermore, increasing the nitrate concentration resulted in a reduction in lipid content and productivity in M. contortum; however, the opposite effect was observed in T. suecica and C. minutissima cultures. C. minutissima and M. contortum lipids contain high levels of oleic acid, with values ranging from 26 to 45.7% and 36.4 to 40.1%, respectively. The data suggest that because of its high lipid productivity (13.79 mg L^?1 d^?1) and high oleic acid productivity (3.78 mg L^?1 d^?1), Chlorella minutissima is a potential candidate for the production of high quality biodiesel.     

Modeling of the pyruvate production with<Emphasis Type="Italic"> Escherichia coli</Emphasis> in a fed-batch bioreactor

A family of 10 competing, unstructured models has been developed to model cell growth, substrate consumption, and product formation of the pyruvate producing strain Escherichia coli YYC202 ldhA::Kan strain used in fed-batch processes. The strain is completely blocked in its ability to convert pyruvate into acetyl-CoA or acetate (using glucose as the carbon source) resulting in an acetate auxotrophy during growth in glucose minimal medium. Parameter estimation was carried out using data from fed-batch fermentation performed at constant glucose feed rates of q_VG=10 mL h^–1. Acetate was fed according to the previously developed feeding strategy. While the model identification was realized by least-square fit, the model discrimination was based on the model selection criterion (MSC). The validation of model parameters was performed applying data from two different fed-batch experiments with glucose feed rate q_VG=20 and 30 mL h^–1, respectively. Consequently, the most suitable model was identified that reflected the pyruvate and biomass curves adequately by considering a pyruvate inhibited growth (Jerusalimsky approach) and pyruvate inhibited product formation (described by modified Luedeking–Piret/Levenspiel term).List of symbols c_A acetate concentration (g L^–1) - c_A,0 acetate concentration in the feed (g L^–1) - c_G glucose concentration (g L^–1) - c_G,0 glucose concentration in the feed (g L^–1) - c_P pyruvate concentration (g L^–1) - c_P,max critical pyruvate concentration above which reaction cannot proceed (g L^–1) - c_X biomass concentration (g L^–1) - K_I inhibition constant for pyruvate production (g L^–1) - K_I^A inhibition constant for biomass growth on acetate (g L^–1) - K_P saturation constant for pyruvate production (g L^–1) - K_P inhibition constant of Jerusalimsky (g L^–1) - K_S^A Monod growth constant for acetate (g L^–1) - K_S^G Monod growth constant for glucose (g L^–1) - m_A maintenance coefficient for growth on acetate (g g^–1 h^–1) - m_G maintenance coefficient for growth on glucose (g g^–1 h^–1) - n constant of extended Monod kinetics (Levenspiel) (–) - q_V volumetric flow rate (L h^–1) - q_VA volumetric flow rate of acetate (L h^–1) - q_VG volumetric flow rate of glucose (L h^–1) - r_A specific rate of acetate consumption (g g^–1 h^–1) - r_G specific rate of glucose consumption (g g^–1 h^–1) - r_P specific rate of pyruvate production (g g^–1 h^–1) - r_P,max maximum specific rate of pyruvate production (g g^–1 h^–1) - t time (h) - V reaction (broth) volume (L) - Y_P/G yield coefficient pyruvate from glucose (g g^–1) - Y_X/A yield coefficient biomass from acetate (g g^–1) - Y_X/A,max maximum yield coefficient biomass from acetate (g g^–1) - Y_X/G yield coefficient biomass from glucose (g g^–1) - Y_X/G,max maximum yield coefficient biomass from glucose (g g^–1) - growth associated product formation coefficient (g g^–1) - non-growth associated product formation coefficient (g g^–1 h^–1) - specific growth rate (h^–1) - _max maximum specific growth rate (h^–1)     

Production and recovery of recombinant protease inhibitor α1-antitrypsin

Human α₁-antitrypsin (AAT) was produced in the recombinant yeast Saccharomyces cerevisiae ATCC 20699 grown in batch and fed-batch culture. The final biomass concentration and antitrypsin concentration attained were 55 g·L⁻¹ and 1.23 g·L⁻¹, respectively, in the fed-batch. The maximum productivities of biomass and antitrypsin were 1.6 and > 0.04 g L⁻¹h⁻¹, respectively, or substantially greater than the highest productivity values reported in the past. For recovering the antitrypsin, the cell slurry was concentrated 4-fold (231 g·L⁻¹ biomass, 122 min of processing) by cross-flow microfiltration and the cells were disrupted by bead milling (3 passes of 3 min total retention time). The cell homogenate was treated with aluminum chloride or PBS (pH 7) to aid separation of the cell debris by flocculation and sedimentation. The clarified cell homogenate was subjected to ammonium sulfate fractionation to precipitate the recombinant antitrypsin. The AAT precipitated at 45–75% saturation of ammonium sulfate, depending on the age of the homogenate. The crude AAT in the homogenate degraded at room temperature (25°C), with a zero order deactivation rate of 1.815 × 10⁻³ ± 3.43 × 10⁻⁴ g AAT L⁻¹h⁻¹.     

Pilot-plant-scale outdoor mixotrophic cultures of Phaeodactylum tricornutum using glycerol in vertical bubble column and airlift photobioreactors: studies in fed-batch mode

Pilot-scale (0.19 m column diameter, 2 m tall, and 60 L working volume) outdoor vertical bubble column (BC) and airlift photobioreactors (a split-cylinder (SC) and a draft-tube airlift device (DT)) were compared for fed-batch mixotrophic culture of the microalga Phaeodactylum tricornutum UTEX 640. The cultures were started photoautotrophically until the onset of a quasi-steady-state biomass concentration of 3.4 g L(-)(1). After this, the cultures were supplemented with organic nutrient (glycerol 0.1 M) and a reduced nitrogen source, resulting in an immediate growth rate boost, which was repeated with successive additions of nutrients in all three photobioreactors. During this period the biomass productivity was enhanced compared to photoautotrophic cultures in the three reactors, although differences were found among them. These could be attributed to the different hydrodynamic behavior influencing the transport phenomena inside the cultures. A 25.4 g L(-)(1) maximum biomass concentration was attained in the SC. Further additions of nutrients did not promote any more growth. The consumption of glycerol was quantitative in the first additions but slowed at high biomass concentration, suggesting that a minimum amount of light is needed to sustain growth. No significant effect of the supplied organic nutrient on carotenoids and chlorophylls content was observed, although it had a profound effect on the fatty acid composition. Eicosapentaenoic acid (EPA) content was increased up to 3% (DW) in mixotrophic growth, giving a productivity of 56 mg L(-)(1) d(-)(1), a significant increase compared to the photoautotrophic control, which yielded a maximum EPA content of 1.9% (DW) and a productivity of 18 mg L(-)(1) d(-)(1). The maximum biomass and EPA volumetric yields obtained in this work are comparable with those reported for commercial photoautotrophic monoculture of large quantities of P. tricornutum in closed continuous-run tubular loop bioreactors with tubes that are typically less than 0.08 m in diameter. When the comparison is established in terms of productivities based on the land area occupied, the vertical airlift and bubble-column bioreactors are extraordinarily more productive.     

Outdoor pilot-scale production of Botryococcus braunii in panel reactors

In this paper, the outdoor production of Botryococcus braunii in pilot-scale panel reactors (0.4?m³) is studied under uncontrolled conditions at a location close to the Atacama Desert (Chile). Discontinuous experiments were performed on different dates to determine the feasibility of the culture and the influence of environmental conditions on the system yield. Data showed that solar radiation is a major parameter in determining system yield, the average irradiance inside the culture determining both the growth rate and biomass productivity. A maximum specific growth rate of 0.09?day^?1 and biomass productivity of 0.02?g?L^?1?day^?1 (dry weight) were measured in discontinuous mode, at an average irradiance of 60?μE?m^?2?s^?1. With respect to lipids, a productivity of 2.5?mg?L^?1?day^?1 was obtained under favourable growth conditions; no accumulation of lipids at the stationary phase was observed. To confirm this behaviour, a semicontinuous culture was performed at 0.04?day^?1 in a larger reactor (1?m³). In this experiment, the biomass concentration and productivity was 0.3?g?L^?1 and 0.015?g?L^?1?day^?1, respectively. The lipid content and productivity was 15.6% and 2.4?mg?L^?1?day^?1, respectively, the mean average irradiance inside the reactor being 60?μmol photons?m^?2?s^?1. The light path of the reactor determines the light availability, thus determining also the biomass concentration and productivity of the reactor once the dilution rate is fixed. Experimentally, biomass productivity of 0.015?g?L^?1?day^?1 was determined for a light path of 0.15?m, but this can be increased by more than three times for a light path of 0.1?m. These data confirm that this alga can be produced outdoors in a secure form, the culture yield improving when optimal conditions are applied, the data reported here establishing the starting point for the development of the process.     

Glycerol increases growth,protein production and alters the fatty acids profile of Spirulina (Arthrospira) sp LEB 18

Most of the crude glycerol produced globally is generated by biodiesel production, which makes this byproduct an environmental responsibility of the biofuel industries. Among the forms of this compound in use, microalgae cultivation is a promising alternative that may generate a reduction in crude glycerol treatment costs via using it as an organic, carbon-rich substrate in culture media. In this work, the influence of different concentrations of glycerol in the culture medium, the composition of fatty acids and proteins in Spirulina sp. LEB 18 biomass and their effect on its growth were investigated. The fatty acid profile of the biomass was altered, showing a 20% increase in the unsaturated concentration and a 60% reduction in the saturated concentration in the culture supplemented with 0.05 mol L⁻¹ of glycerol compared to those in the control. The addition of the substrate stimulated an increase in its cellular concentration (3.00 g L⁻¹, 0.05 mol L⁻¹), productivity (0.72 g L⁻¹ d⁻¹, 0.05 mol L⁻¹) and its protein production (69.78% w w⁻¹, 0.05 mol L⁻¹).     

Environmental effects on growth and biochemical composition ofNitzschia inconspicua Grunow

The effects of nitrate and silicate levels, and carbon source on growth, biochemical composition and fatty acid composition ofNitzschia inconspicua were investigated using batch cultures. Within the range of silicate levels supplied (8.8–176 M), no marked variations in growth trend, biochemical composition or fatty acid composition were shown. Biomass at stationary phase, ranging from 64–66 mg ash-free dry weight (AFDW) L^–1, and specific growth rate () based on chlorophylla (0.41–0.50 d^–1) of the cultures grown within 0.3–3.0 mM NaNO₃ were not significantly different. Cultures supplemented with glucose (0.1 % w/v), acetate (0.1 % w/v) or 5% CO₂ attained higher biomass (85, 85, 97 mg AFDW L^–1) than the control which was grown in synthetic seawater and agitated by magnetic stirring. Cells grown at <3.0 mM NaNO₃ contained higher carbohydrate contents (14.8–21.5% AFDW) than those grown at 3.0 mM (4.0% AFDW). Lipid content increased at the expense of proteins in cells aerated with 5% CO₂. The dominant fatty acids, 16:0 and 16:1, ranged from 35.7–45.0% and 36.4–45.4% total fatty acids (TFA), respectively, while the relative proportions of 20:4 (n-6) and 20:5 (n-3) ranged from 1.7–5.4% and 3.4–5.9% TFA respectively. Cultures aerated with 5% CO₂ attained the highest biomass (97 mg AFDW L^–1) and yield of 20:5 (n-3) (0.34 mg L^–1).     

Optimization of the microbial synthesis of dihydroxyacetone from glycerol with <Emphasis Type="Italic">Gluconobacter oxydans</Emphasis>

An optimized repeated-fed-batch fermentation process for the synthesis of dihydroxyacetone (DHA) from glycerol utilizing Gluconobacter oxydans is presented. Cleaning, sterilization, and inoculation procedures could be reduced significantly compared to the conventional fed-batch process. A stringent requirement was that the product concentration was kept below a critical threshold level at all times in order to avoid irreversible product inhibition of the cells. On the basis of experimentally validated model calculations, a threshold value of about 60 kg m^-3 DHA was obtained. The innovative bioreactor system consisted of a stirred tank reactor combined with a packed trickle-bed column. In the packed column, active cells could be retained by in situ immobilization on a hydrophilized Ralu-ring carrier material. Within 17 days, the productivity of the process could be increased by 75% to about 2.8 kg m^-3 h^-1. However, it was observed that the maximum achievable productivity had not been reached yet.Abbreviations K _O Monod half saturation constant of dissolved oxygen (kg m^-3) - K _S Monod half saturation constant of substrate glycerol (kg m^-3) - O Dissolved oxygen concentration (kg m^-3) - P Product concentration (kg m^-3) - P _crit Critical product concentration constant (kg m^-3) - S Substrate concentration (kg m^-3) - t Time (s) - X Biomass concentration (dry weight) (kg m^-3) - Y _P/S Yield coefficient of product from substrate - Y _X/S Yield coefficient of biomass from substrate - Growth dependent specific production rate constant (kg m^-3) - Growth independent specific production rate constant (s^-1) - Specific growth rate (s^-1) - _max Maximum specific growth rate constant (s^-1)     

Mixotrophic cultivation of <Emphasis Type="Italic">Platymonas subcordiformis</Emphasis>

The effects of glucose concentration and irradiance on mixotrophiccultivation of Platymonas subcordiformis were investigated in flaskcultures. The optimal glucose concentration was 24 g L^-1, andirradiance was 95 mol photon m^-2 s^-1. Based on theoptimization of culture conditions and a modified SK(IA) medium, themaximum biomass was 3.68 g L^-1 after 14 days, which was about6 times that in autotrophic culture, and the specific growth rate reached0.62 d^-1, twice that in autotrophic culture. Using the optimalconditions established in flasks, mixotrophic culture in a 5.0-Lphotobioreactor was achieved, and the yield after 8 days was 3.30 gL^-1.