Cultures Of Phaeodactylum Tricornutum Research Articles

Antibacterial and antifungal activity of zinc oxide nanoparticles produced by Phaeodactylum tricornutum culture supernatants and their potential application to extend the shelf life of sweet cherry (Prunus avium L.)

In the current work, zinc oxide nanoparticles (ZnONPs) synthesized by the cell-free supernatant of Phaeodactylum tricornutum cultures were first examined for their physicochemical and antimicrobial proprieties. They were then applied as spray coating on the surface of fresh sweet cherries to evaluate their efficacy on quality maintenance of the fruit over 10 days of storage at 25 °C. Synthesized nanoparticles showed a large-scale inhibitory effect against Escherichia coli (ATCC 25922), Staphylococcus aureus MRSA (ATCC 43300) and Candida albicans (ATCC 14053) with minimum inhibitory concentrations (MIC) ranged between 0.078 and 0.156 mg/mL. Furthermore, ZnONPs at 100–1000 mg/L effectively inhibited mycelia growth of Mucor heimalis, a causative agent of Mucor rot in sweet cherries. The results also indicated that ZnONPs significantly delayed the changes of visual and biochemical attributes of the fruit. Compared to untreated control, coated cherries with ZnONP at a concentration of 500 mg/L showed very small change in moisture and total sugar content. Therefore, all coated fruits exhibited less decay rates. In addition, spray coating with ZnONPs had a positive effect on maintaining suitable amounts of ascorbic acid (29.74 mg/100 g FW), polyphenols (579.2 μg/g FW) and flavonoids in the fruits (1991.87 μg/g FW). Data from this study showed 5.11% and 11.63%, increase in flavonoid content and antioxidant activity in the fruits coated with 500 mg/L ZnONPs, respectively, at the end of storage. These data together suggest that green ZnONPs-based coating is one of the safest and effective ways to preserve commercial fruits for prolonged storage.

Use of crude glycerol for mixotrophic culture of Phaeodactylum tricornutum

Crude glycerol is a waste stream from biodiesel production, which has previously been shown to be useable for mixotrophic cultivation of microalgae; however, at high concentrations the presence of contaminants may limit culture growth. In this study two previously identified methods of contaminant removal from crude glycerol were trialled for use in mixotrophic culture of Phaeodactylum tricornutum. Neither crude glycerol without contaminant removal, nor crude glycerol which has had contaminants removed through calcium precipitation, lead to culture growth of P. tricornutum. However, pH adjusted crude glycerol gave comparable cell densities (6.03 ± 0.24 × 106 cells ml−1 compared to 5.66 ± 0.15 × 106 cells ml−1), growth rates (3.25 ± 0.26 days compared to 2.85 ± 0.21 days) and fatty acid profiles compared to reagent grade glycerol. There were alterations in the carbon partitioning of the microalgae, in addition to changes in cell widths. Cell widths increasing when harvested at stationary phase, compared to reagent grade glycerol (4.88 compared to 4.28 μm), while chlorophyll (11.38 compared to 6.25 %DW) and carbohydrate contents decreased (17.29 compared to 14.15 %DW respectively). As a result, it can be concluded that this method of contaminant removal meant that crude glycerol may be successfully used for culture of P. tricornutum, which may reduce the costs of microalgal culture, depending upon the end use.

Evaluation of microalgae concentrates as partial fishmeal replacements for hybrid striped bass Morone sp.

Processed microalgae concentrates recently have been considered potentially viable alternatives to partially replace fishmeal (FM) and fish oil in aquafeeds. Two feeding trials were conducted to evaluate incremental replacement of FM and soy protein concentrate (SPC) with different types of microalgae in the diet of hybrid striped bass. Microalgae evaluated in feeding trial 1 included dried products from monocultures of Phaeodactylum tricornutum and Nanochloropsis salina, as well as mixed cultures of those two species. Several preparations of Chlorella sp. lipid extracted by various means as well as bluegreen algae biomass (BGAB) also were evaluated. In feeding trial 2, the microalgae products supporting most efficient fish performance in feeding trial 1 were reassessed along with mixed cultures of Phaeodactylum tricornutum and Nanochloropsis salina as well as BGAB. Two additional mixed cultures of Nanochloropsis salina with Amphora sp. or Cylindrotheca sp. also were evaluated. Algae products were substituted to replace either 10, 15 or 20% of protein provided equally from menhaden FM and SPC in the Reference diet. All diets were isonitrogenous (40% crude protein) and isocaloric (3.3 kcal digestible energy g−1), and each were fed to triplicate groups of juvenile fish with average initial weights (+SEM) of 15.1 ± 0.6 g and 21.4 ± 1.3 g/fish in feeding trials 1 and 2, respectively for 7 weeks.Weight gain and feed efficiency ratio (FER) of hybrid striped bass were high (>330% of initial weight and 0.79) but significantly (P < 0.05) affected by diet in trial 1 with no mortality. Fish fed the Reference diet and the one containing BGAB had the greatest but similar weight gain. Substitution of the other algae meals significantly reduced weight gain by 8.2 to 14.7% compared to the Reference diet. Most diets containing algae meal yielded similar FER as the Reference diet except for those containing solvent-extracted Chlorella sp. (both 10% and 20% substitution), Phaeodactylum tricornutum (10%), and Phaeodactylum tricornutum × Nanochloropsis salina (10% and 20%), in which FER was significantly reduced by 5.8 to 8.1%. Whole-body proximate composition and protein retention efficiency values revealed no significant differences among diets. In feeding trial 2, the various diets with algae products substituted at 10 or 15% of dietary protein did not significantly affect growth performance or whole-body composition of hybrid striped bass compared to the Reference diet. In conclusion, replacement of up to 15% crude protein in the Reference diet with BGAB, the Phaeodactylum tricornutum and Nanochloropsis salina mixture, as well as mixtures of Nanochloropsis salina with Amphora sp. or Cylindrothecatheca sp.was possible without affecting growth performance or body composition of hybrid striped bass.

Dynamics of the Bacterial Community Associated with Phaeodactylum tricornutum Cultures

The pennate diatom Phaeodactylum tricornutum is a model organism able to synthesize industrially-relevant molecules. Commercial-scale cultivation currently requires large monocultures, prone to bio-contamination. However, little is known about the identity of the invading organisms. To reduce the complexity of natural systems, we systematically investigated the microbiome of non-axenic P. tricornutum cultures from a culture collection in reproducible experiments. The results revealed a dynamic bacterial community that developed differently in “complete” and “minimal” media conditions. In complete media, we observed an accelerated “culture crash”, indicating a more stable culture in minimal media. The identification of only four bacterial families as major players within the microbiome suggests specific roles depending on environmental conditions. From our results we propose a network of putative interactions between P. tricornutum and these main bacterial factions. We demonstrate that, even with rather sparse data, a mathematical model can be reconstructed that qualitatively reproduces the observed population dynamics, thus indicating that our hypotheses regarding the molecular interactions are in agreement with experimental data. Whereas the model in its current state is only qualitative, we argue that it serves as a starting point to develop quantitative and predictive mathematical models, which may guide experimental efforts to synthetically construct and monitor stable communities required for robust upscaling strategies.

Defense related decadienal elicits membrane lipid remodeling in the diatom Phaeodactylum tricornutum.

Diatoms rapidly release extracellular oxylipins (oxygenated lipids) including polyunsaturated aldehydes in response to herbivory and other stresses. Oxylipins have several defense-related activities including inhibition of reproduction in herbivores and signaling to distant diatoms. Physiological changes in diatoms exposed to varying levels of oxylipins are only beginning to be understood. In this study, Phaeodactylum tricornutum cultures were treated with sublethal concentrations of the polyunsaturated aldehyde trans,trans-2,4-decadienal (DD) to assess effects on lipid composition and membrane permeability. In cells treated with DD for 3 hr, all measured saturated and unsaturated fatty acids significantly decreased (0.46–0.69 fold of levels in solvent control cells) except for 18:2 (decreased but not significantly). The decrease was greater in the polyunsaturated fatty acid pool than the saturated and monounsaturated fatty acid pool. Analysis of lipid classes revealed increased abundances of phosphatidylethanolamine and phosphatidylcholine at 3 and 6 hr. Concomitantly, these and other membrane lipids exhibited increased saturated and monounsaturated acyl chains content relative to polyunsaturated acyl chains compared to control cells. Evidence of decreased plasma membrane permeability in DD treated cells was obtained, based on reduced uptake of two of three dyes relative to control cells. Additionally, cells pre-conditioned with a sublethal DD dose for 3 hr then treated with a lethal DD dose for 2 hr exhibited greater membrane integrity than solvent pre-conditioned control cells that were similarly treated. Taken together, the data are supportive of the hypothesis that membrane remodeling induced by sublethal DD is a key element in the development of cellular resistance in diatoms to varying and potentially toxic levels of polyunsaturated aldehydes in environments impacted by herbivory or other stresses.

Effects of outdoor cultures on the growth and lipid production of Phaeodactylum tricornutum using closed photobioreactors.

One of the principal challenges for large scale production of microalgae is the high costs of biomass production. Aiming for minimize this problem, microalgal biodiesel production should focus on outdoors cultures, using available solar light and allowing lower energy cost process. Testing species that proved to be common and easy to culture may be a good approach in this process. The present work reports indoor-outdoor cultures of Phaeodactylum tricornutum using different bioreactors types, using cell growth, biochemical composition, and the profiles of the fatty acids produced as the parameters to test the optimization processes. The results show that the use of outdoor cultures is a good choice to obtain P. tricornutum biomass with a good potential for biodiesel production. The microalgae produced reached better growth efficiency, major lipid content and showed an increment in the percentage of saturated fatty acids (required on the biodiesel production) respect indoor cultures. These results are important to show the relevance of using outdoor cultures as a way to improve the efficiency and the energetic balance of the biodiesel production with P. tricornutum algae.

Iodine balance, growth and biochemical composition of three marine microalgae cultured under various inorganic iodine concentrations

Marine phytoplankton have been found to be involved in the biogeochemical cycle of iodine in the ocean. However, the role of iodine in the metabolism of marine microalgae has hardly been studied and whether iodine is an element required for growth is not known. In this study, three species of marine microalgae were grown in batch cultures at various concentrations of iodide (I−) or iodate (IO3 −) in order to evaluate their effect on growth rate and biochemical composition. Changes in inorganic iodine concentrations in the culture medium were also determined. Growth rate was not affected by external inorganic iodine concentration in cultures of Dunaliella salina and Tisochrysis lutea. In cultures of Phaeodactylum tricornutum, growth was inhibited at 2500 µM IO3 −. No clear effects of I− or IO3 − were observed on biochemical composition, except for the particulate iodine content of the microalgae, which increased with increasing dissolved iodine concentration. Results of dissolved inorganic iodine measurements indicated that IO3 − was reduced to I− during the exponential growth phase of microalgae cultures, under both natural and higher IO3 − concentrations. Iodine balance calculations showed that the amount of disappeared IO3 − was higher than the amount of I− produced in several cultures and that this discrepancy could not be explained by the formation of particulate iodine. I incorporation rates into biomass were low compared to I− production rates. We conclude that although iodine is clearly taken up from the external medium and it is transformed by microalgae, it seems unlikely that it is an element required for growth or that it plays an essential role in microalgal metabolism.

An efficient screening method for the isolation of heterotrophic bacteria influencing growth of diatoms under photoautotrophic conditions

Interactions between photoautotrophic diatoms and heterotrophic bacteria are important for the biogeochemical C-cycle in the oceans. Additionally, biofilms formed by diatoms and bacteria are the initiating step of biofouling processes, which causes high costs in shipping. Despite this ecological and economical importance, the knowledge about biochemical and molecular mechanisms underlying these interkingdom interactions is relatively small. For analyzing these mechanisms, laboratory model systems are required. In this study, an efficient screening method for isolating bacteria influencing photoautotrophic diatom growth was established. First, diatom cultures of Phaeodactylum tricornutum and Thalassiosira pseudonana were made axenic by applying β-lactam antibiotics. Second, a non-invasive method for measuring growth of multiple parallel diatom cultures by chlorophyll fluorescence was established. This method allowed semi-quantitative chlorophyll determination of cultures with up to 3μg (chlorophyll) ml−1. Axenic diatom cultures were then used for enriching bacteria and led to the isolation of 24 strains influencing growth of both diatom strains in various ways. For example, Rheinheimera sp. strain Tn16 inhibited growth of T. pseudonana, while it stimulated growth and cell aggregation of P. tricornutum. Thus, this screening method is appropriate for isolating heterotrophic bacteria showing different interactions with different diatom species ranging from synergistic to antagonistic. In consecutive applications, this method will be useful to screen for bacterial mutants with altered phenotypes regarding the influence on diatom growth.

Growth kinetics and fucoxanthin production of Phaeodactylum tricornutum and Isochrysis galbana cultures at different light and agitation conditions

Fucoxanthin is a carotenoid that exerts multiple beneficial effects on human health. However, reports comparing microalgae culture conditions and their effect on growth and fucoxanthin production are still limited. Isochrysis galbana and Phaeodactylum tricornutum cultures in different light (62.0, 25.9, 13.5, or 9.1 μmol photons m-2 s-1), mixing conditions (1 vvm aeration or 130 rpm agitation), and media compositions (F/2 and Conway medium) were studied for comparison of cellular growth and fucoxanthin production on F/2 medium. I. galbana showed a better adaptation to tested culture conditions in comparison with P. tricornutum, reaching 2.15 × 107 ± 4.07 × 106 cells mL-1 and a specific growth rate (μ) of 1.12 ± 0.05 day-1 under aerated conditions and 62.0 μmol photons m-2 s-1 light intensity. Fucoxanthin concentration was about 25 % higher in P. tricornutum cultures under 13.5 μmol photons m-2 s-1 light intensity and aerated conditions, but the highest fucoxanthin total production was higher in I. galbana, where 3.32 mg can be obtained from 1 L batch cultures at the 16th day under these conditions. Moreover, higher cell densities (~32.41 %), fucoxanthin concentration (~42.46 %), and total production (~50.68 %) were observed in I. galbana cultures grown in Conway medium, if compared with cultures grown in F/2 medium. The results show that the best growth conditions did not result in the best fucoxanthin production for either microalgae, implying that there is not a direct relationship between cellular growth and fucoxanthin production. Moreover, the results suggest that I. galbana cultures on Conway medium are strong candidates for fucoxanthin production, where 1.2 to 15 times higher fucoxanthin concentration are observed in comparison to macroalgal sources.

Mixotrophic growth of Phaeodactylum tricornutum on fructose and glycerol in fed-batch and semi-continuous modes

Mixotrophic cultures of Phaeodactylum tricornutum were carried out in bubble columns using fructose and glycerol in indoor fed-batch and semi-continuous modes. In the fed-batch cultures, different nutrient-addition strategies, combined with stepwise increments in the light intensity, were assayed. It was found that glycerol promoted significantly higher biomass productivity than fructose. A glycerol-induced photoinhibition that arrested the growth of P. tricornutun was also observed. As this was considered a limitation as regards transferring the fed-batch mode to outdoor conditions, this information was used to culture P. tricornutum in semi-continuous mode. Similar glycerol-induced photoinhibition was not observed in these cultures, even at highest dilution rates. Although the highest biomass (1.5 g L(-1) d(-1)) and EPA (40 mg L(-1) d(-1)) productivities found in the semi-continuous cultures were lower than those obtained photoautotrophically in outdoor photobioreactors, the findings showed that semi-continuous mode was an excellent candidate for transferring mixotrophic culture to an outdoor setting.

Photoacclimation of Phaeodactylum tricornutum (Bacillariophyceae) cultures grown outdoors in photobioreactors and open ponds

The acclimation to high light of Phaeodactylum tricornutum cultures grown outdoors both in an open pond and in tubular photobioreactors (PBRs) was studied by means of chlorophyll fluorescence, pigment analysis and growth. Cultures grown in PBRs (5-cm tube diameter) at two biomass concentrations (0.3 and 0.6 g l−1) were compared with a culture grown in a 10-cm deep open pond (0.3 g l−1). Therefore, the performance of the cultures was compared on the basis of both the same biomass concentration and areal density. Cultures grown at 0.3 g l−1 in PBRs experienced the highest light stress, which resulted in dramatic changes in both chlorophyll fluorescence and photosynthesis parameters, and in low areal productivity. In this culture, the Fv/Fm ratio was 0.5 in the morning and dropped to about 0.1 within 1 h of exposure to bright sunlight. Similar behaviour was observed with the measurements of rETR, and the initial slope (αETR) of the photosynthesis curve, while the saturation irradiance parameter (Ik) increased about four-fold compared to the morning value. These changes were accompanied by a higher induction of the diadinoxanthin-cycle pigments, evidenced by an increasing ratio of diatoxanthin to diadinoxanthin during the day (up to 104% at 1400 h), and a higher value of non-photochemical quenching (NPQ) that rose to up to 1.2 in the high stress culture. The culture grown in the open pond at the same biomass concentration (0.3 g l−1) did not show sizeable changes either in pigments or in chlorophyll fluorescence parameters. Denser cultures in PBRs (0.6 g l−1) showed less dramatic changes in the photochemical parameters. Changes in the areal productivity of the cultures correlated well with changes in the photochemical parameters. Areal productivity was about 27% higher in the open pond than in PBRs when cultivated at the same concentration of 0.3 g l−1.

Characterization of low molecular weight dissolved organic nitrogen by liquid chromatography‐electrospray ionization‐mass spectrometry

Low molecular weight (LMW; &lt;1 kDa) dissolved organic nitrogen (DON) is the dominant DON fraction in marine systems. However, existing methods for DON characterization exclude this fraction through size exclusion or destruction during sample hydrolysis. In this study, we developed a method for the extraction and analysis of LMW peptides in saline waters. The procedure involves a solid phase extraction (SPE) preconcentration step using a polystyrene‐divinylbenzene sorbent, then elution and detection by liquid chromatographyelectrospray ionization‐mass spectrometry (LC/ESI/MS). The procedure was tested with 1‐L water samples containing peptides (10 ng L−1) ranging from 188.2‐1946.0 Da. The analytes were characterized using “top‐down” sequencing to confirm their structure, and the method was then successfully applied to saline water samples extracted from a mono‐algal culture of Phaeodactylum tricornutum. This enabled a number of unknown analytes to be partially sequenced (complete sequencing should be possible using additional MSn scans and larger sample volumes). The method allows for the detection of peptides at the ng L−1 level and further preconcentration is possible. The SPE step allowed determination of peptides from saline water, a matrix incompatible with direct LC/MS analysis. The method can, therefore, be used in DON characterization studies.

Changes in growth, chlorophyll fluorescence and fatty acid composition with culture age in batch cultures of Phaeodactylum tricornutum and Chaetoceros muelleri (Bacillariophyceae)

In this study, we investigated changes with culture age in growth rate, ΦPSIIe-max (the maximal effective quantum yield of PSII,=Fv/Fm), the photosynthetic parameters α, rETRmax and Ik, fatty acid composition and macromolecular content (via IR spectroscopy) in batch cultures of Phaeodactylum tricornutum and Chaetoceros muelleri. ΦPSIIe-max, and the initial slope of the photosynthesis vs. light curve (α) in the two diatoms exhibited almost the same pattern of variation over the experimental period, first increasing slightly to a maximum value, then decreasing with increasing culture age. There was also a significant decrease, with increasing culture age, in the parameters rETRmax and Ik in both diatoms. FT-IR spectra of P. tricornutum and C. muelleri all showed changes over the growth period. The bands attributed to lipids (C-H stretching between 3000 cm-1 and 2800 cm-1 along with the ester C=O 1740 cm-1) in both diatoms showed the same tendency, increasing with increasing culture age over the entire growth period, consistent with the onset of major nutrient (P) limitation. Changes with culture age were also found in the fatty acid composition. P. tricornutum showed a marked increase in the levels of 16:1 n-7 and 18:1 n-9 and a marked decrease in the levels of 16:3 n-4 and 20:5 n-3 with increasing culture age. There was a slight variation in the fatty acid composition of C. muelleri related to culture age, with the largest increase shown by 16:0 and the largest decrease by 16:3 n-4.

The cultivation of Phaeodactylum tricornutum in crossed gradients of temperature and light

Phaeodactylum tricornutum BOHLIN, is one of the most important species in the algal biotests. The cultivation of this species in the crossed gradients evaluated the dependence of the growth rates and morphology on particular combinations of environmental factors (temperature, light). The main advantage of this method is the simplicity and quickness of obtaining data from different conditions. The results of the cultivation of Phaeodactylum tricornutum, in the crossed gradients, showed that maximal growth rates occurred at temperatures between 15 and 23 °C and at irradiance between 15 and 125 μmol.m -2 , s -1 ). There were not observed differences in morphology of the alga cultivated at different combinations of growth conditions. The conversion curves were calculated for three cultures of Phaeodactylum tricornutum (two old cultures and one young one) and for four different ways of measurements of optical density at 750 nm (in immunological plates, culture wells, Petri dishes and 20 ml cultivation flasks).

Modeling of eicosapentaenoic acid (EPA) production from Phaeodactylum tricornutum cultures in tubular photobioreactors. Effects of dilution rate, tube diameter, and solar irradiance

Modeling of eicosapentaenoic acid (EPA) production from Phaeodactylum tricornutum cultures in tubular photobioreactors. Effects of dilution rate, tube diameter, and solar irradiance

Modeling of eicosapentaenoic acid (EPA) production from Phaeodactylum tricornutum cultures in tubular photobioreactors. Effects of dilution rate, tube diameter, and solar irradiance.

A model for the prediction of eicosapentaenoic acid (EPA) productivity from Phaeodactylum tricornutum cultures that takes into account the existence of photolimitation and photoinhibition of growth under outdoor conditions is presented. The effects of the external irradiance on the culture surface, the average irradiance inside the culture, and the light regime at which the cells are exposed on pigments and EPA content are studied. The chlorophyll content decreases exponentially with the average irradiance, whereas the carotenoids content increases linearly with the external irradiance due to a higher extension of photoinhibition. A decrease in the fatty acid content of the biomass with irradiance on reactor surface is observed when photoinhibition becomes relevant. The average irradiance within the culture mainly influenced the fatty acid profile of the biomass. As the average irradiance becomes higher, percentages of saturated and monounsaturated fatty acids decrease, increasing the portion of EPA. By taking into account the different relationships among pigment and EPA content with the irradiance, the variation in EPA productivity over the year can be simulated as a function of average and external irradiance. For the two photobioreactors employed the maximum EPA productivity is attained in spring and fall (30 mg L(-1) day(-1) for tube diameter 0. 06 m and 50 mg L(-1) day(-1) for tube diameter 0.03 m). In winter, the biomass productivity is limited by low light availability although the EPA content is maximum. In summer, the biomass productivity is higher although the EPA content diminished by photoinhibition; the higher the dilution rate, the lower the minimum. Thus, the conditions that increase the biomass productivity and the polyunsaturated fatty acids content are in opposition, the optimum being reached by operating under photolimitation with high growth rates in order to produce a high proportion of polyunsaturated fatty acids.

Scanning and transmission electron microscopical evidence of the capacity of diatoms to penetrate the alveolo-capillary barrier in drowning.

The diagnostic value of diatom analysis for drowning is considered to be one of the most controversial arguments in forensic medicine. However, the theoretical assumption of the method, i.e. the capacity of diatoms to penetrate the alveolo-capillary barrier during drowning, has never been addressed. Using scanning (SEM) and transmission electron microscopy (TEM), we have investigated the interaction of a natural population of diatoms and an unialgal culture of Phaeodactylum tricornutum (PT) with the alveolo-capillary barrier in an experimental model of drowning. The SEM analysis allowed the identification of several diatom species along the whole airways and their close interaction with the alveolar wall, but was poorly informative about the effective penetration of diatoms into pulmonary vessels. The TEM analysis was more informative and allowed a precise identification of the PT cells in alveolar spaces and to detect their phagocytosis by alveolar macrophages. PT penetrated into the pulmonary vessels through the thinnest portions of the alveolo-capillary barrier and through the interstitial spaces and were identified in pulmonary capillaries and venules. The morphological demonstration of the capacity of diatoms to penetrate the alveolo-capillary barrier is a step forward in assessing the potentiality, reliability and limitations of diatom analysis on a new basis as a tool for the diagnosis of drowning.

Investigation of three wastewaters entering Izmit Bay (Turkey) by means of batch and chemostat culture algal bioassays

The bay of Ízmit is the focus of much of Turkey's industrial development and three of the most important of the wastes discharged into its surface waters have been studied as a necessary step in minimising their environmental impact. Gas chromatography/mass spectrometry of the extracted wastes revealed the presence of organic xenobiotics listed as priority pollutants. Nevertheless, measurements of cell populations, chlorophyll fluorescence and the consumption of nutrients demonstrated that most of the wastes stimulated the growth of both batch and chemostat cultures of Phaeodactylum tricornutum (Bohlin). Experiments showed the growth of the cultures to be phosphate limited and it appears that the major effect of the wastes was due to their excessive loading of phosphate.

Productivity analysis of outdoor chemostat culture in tubular air-lift photobioreactors

Net productivity and biomass night losses in outdoor chemostat cultures ofPhaeodactylum tricornutum were analyzed in two tubular airlift photobioreactors at different dilution rates, photobioreactor surface/volume ratios and incident solar irradiance. In addition, an approximate model for the estimation of light profile and average irradiance inside outdoor tubular photobioreactors was proposed. In both photobioreactors, biomass productivity increased with dilution rate and daily incident solar radiation except at the highest incident solar irradiances and dilution rates, when photoinhibition effect was observed in the middle of the day. Variation of estimated average irradiance vs mean incident irradiance showed two effects: first, the outdoor cultures are adapted to average irradiance, and second, simultaneous photolimitation and photoinhibition took place at all assayed culture conditions, the extent of this phenomena being a function of the (incident)1 irradiance and light regime inside the culture. Productivity ranged between 0.50 and 2.04 g L−1 d−1 in the tubular photobioreactor with the lower surface/volume ratio (S/V = 77.5 m−1) and between 1.08 and 2.76 g L−1 d−1 in the other (S/V = 122.0 m−1). The optimum dilution rate was 0.040 h−1 in both reactors. Night-time biomass losses were a function of the average irradiance inside the culture, being lower in TPB0.03 than TPB0.06, due to a better light regime in the first. In both photobioreactors, biomass night losses strongly decreased when the photoinhibition effect was pronounced. However, net biomass productivity also decreased due to lower biomass generation during the day. Thus, optimum culture conditions were obtained when photolimitation and photoinhibition were balanced.

Optimal Renewal Rate and Nutrient Concentration for the Production of the Marine Microalga Phaeodactylum tricornutum in Semicontinuous Cultures

A factorial experiment comprising six nutrient concentrations and six renewal rates was set to optimize semicontinuous cultures of Phaeodactylum tricornutum. Maximal cell density, 85 x 10(sup6) cells ml(sup-1), was obtained with 8 and 16 mmol of N per liter and a renewal rate of 10%. Protein stabilized at about 60% of the organic fraction for nitrogen-sufficient cultures. Both lipids and carbohydrates were stored as energetic reserves.