M.C. Cerón-García

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.

Simultaneous Effect of Temperature and Irradiance on Growth and Okadaic Acid Production from the Marine Dinoflagellate Prorocentrum belizeanum

Benthic marine dioflagellate microalgae belonging to the genus Prorocentrum are a major source of okadaic acid (OA), OA analogues and polyketides. However, dinoflagellates produce these valuable toxins and bioactives in tiny quantities, and they grow slowly compared to other commercially used microalgae. This hinders evaluation in possible large-scale applications. The careful selection of producer species is therefore crucial for success in a hypothetical scale-up of culture, as are appropriate environmental conditions for optimal growth. A clone of the marine toxic dinoflagellate P. belizeanum was studied in vitro to evaluate its capacities to grow and produce OA as an indicator of general polyketide toxin production under the simultaneous influence of temperature (T) and irradiance (I0). Three temperatures and four irradiance levels were tested (18, 25 and 28 °C; 20, 40, 80 and 120 µE·m−2·s−1), and the response variables measured were concentration of cells, maximum photochemical yield of photosystem II (PSII), pigments and OA. Experiments were conducted in T-flasks, since their parallelepipedal geometry proved ideal to ensure optically thin cultures, which are essential for reliable modeling of growth-irradiance curves. The net maximum specific growth rate (µm) was 0.204 day−1 at 25 °C and 40 µE·m−2·s−1. Photo-inhibition was observed at I0 > 40 μEm−2s−1, leading to culture death at 120 µE·m−2·s−1 and 28 °C. Cells at I0 ≥ 80 µE·m−2·s−1 were photoinhibited irrespective of the temperature assayed. A mechanistic model for µm-I0 curves and another empirical model for relating µm-T satisfactorily interpreted the growth kinetics obtained. ANOVA for responses of PSII maximum photochemical yield and pigment profile has demonstrated that P. belizeanum is extremely light sensitive. The pool of photoprotective pigments (diadinoxanthin and dinoxanthin) and peridinin was not able to regulate the excessive light-absorption at high I0-T. OA synthesis in cells was decoupled from optimal growth conditions, as OA overproduction was observed at high temperatures and when both temperature and irradiance were low. T-flask culture observations were consistent with preliminary assays outdoors.

Genetic algorithm for the medium optimization of the microalga Nannochloropsis gaditana cultured to aquaculture

A genetic algorithm has been used to optimize the composition of the culture medium for growing the microalga Nannochloropsis gaditana, based on the nutrients composition of the commercial medium ALGAL. This strategy was carried out through the implementation of 270 experiments spread over nine generations, which allowed achieving an eicosapentaenoic acid (EPA) productivity of 17.8 m gL(-1) d(-1) in a continuous culture of N. gaditana, with an increase of 23% compared to the commercial medium. The EPA yield on nitrogen and phosphorous, 0.042 and 1.146 g(EPA) g(s)(-1), respectively, were 40% and 5-fold higher, respectively, than the values obtained with the nitrogen-optimized ALGAL medium. This improvement was obtained with the medium G-8, which also allowed reducing the requirement of several nutrients such as P, Mo, Mn in 74%, 69% and 66%, respectively, as well as the thiamine content a 46%.

Stability of Carotenoids in Scenedesmus almeriensis Biomass and Extracts under Various Storage Conditions

Scenedesmus almeriensis biomass is a source of carotenoids, particularly lutein, and is considered to be promising as an alternative source to marigold. One key question concerning alternative sources of lutein is the loss of carotenoids that takes place between harvesting and processing, which in the case of marigold is frequently up to 50%. The work described here involved a study into the stability of the main carotenoids (lutein, violaxanthin, and beta-carotene), as well as other components, under different storage conditions. The experiments were carried out with biomass in three forms: frozen, freeze-dried, and spray-dried. The stability of extracts of Scenedesmus biomass in acetone and olive oil was also studied. The results show that the most important factor in retaining carotenoids is a low temperature. At -18 degrees C the loss of carotenoids was negligible after the storage period, regardless of the biomass form used (frozen, freeze-dried, or spray-dried). On the other hand, the carotenoid content and fatty acid profile was increasingly affected with increasing temperature. However, the protein content is unaffected by storage conditions.

Tetraselmis suecia and Tisochrysis lutea meal as dietary ingredients for gilthead sea bream (Sparus aurata L.) fry

In the present study, the nutritional value of Tetraselmis suecica and Tisochrysis lutea (previously known as Isochrysis aff galbana T-ISO strain) freeze-dried biomass for feeding Sparus aurata fry was evaluated. A total of 25,500 fry (3.7xa0mg body weight) were fed for 55xa0days on diets containing 5 and 10xa0% (w/w) Tetraselmis or Tisochrysis, as well as on a microalgae-free diet. Fish fed 5xa0% Tetraselmis showed higher growth performance, nutrient utilization, and survival values than fish fed Tisochrysis. The use of microalgae significantly decreased the body lipid content in fry fed the highest microalgae level. Fry fed Tisochrysis-supplemented diets increased the DHA content in muscle, and consequently the EPA/DHA ratio decreased significantly, whatever dietary level considered. In general, digestive protease activities were not adversely affected by dietary microalgae inclusion, although slight variations were observed during fish development. Microalgae utilization causes a positive effect on intestinal mucosa ultrastructure owing to an increase of total enterocyte absorption surface that was observed in fish fed microalgae-supplemented diets. Cluster analysis of data separated clearly fish fed Tisochrysis-supplemented diets from the rest of experimental groups. This study confirms that Tetraselmis freeze-dried biomass can be used as dietary ingredient in started feeds for S. aurata fry, although an inclusion level of 5xa0% is recommended.

Biofouling in photobioreactors for marine microalgae

Abstract The economic and/or energetic feasibility of processes based on using microalgae biomass requires an efficient cultivation system. In photobioreactors (PBRs), the adhesion of microalgae to the transparent PBR surfaces leads to biofouling and reduces the solar radiation penetrating the PBR. Light reduction within the PBR decreases biomass productivity and, therefore, the photosynthetic efficiency of the cultivation system. Additionally, PBR biofouling leads to a series of further undesirable events including changes in cell pigmentation, culture degradation, and contamination by invasive microorganisms; all of which can result in the cultivation process having to be stopped. Designing PBR surfaces with proper materials, functional groups or surface coatings, to prevent microalgal adhesion is essential for solving the biofouling problem. Such a significant advance in microalgal biotechnology would enable extended operational periods at high productivity and reduce maintenance costs. In this paper, we review the few systematic studies performed so far and applied the existing thermodynamic and colloidal theories for microbial biofouling formation in order to understand microalgal adhesion on PBR surfaces and the microalgae–microalgae cell interactions. Their relationship to the physicochemical properties of the solid PBR surface, the microalgae cell surfaces, and the ionic strength of the culture medium is discussed. The suitability and the applicability of such theories are reviewed. To this end, an example of biofouling formation on a commercial glass surface is presented for the marine microalgae Nannochloropsis gaditana. It highlights the adhesion dynamics and the inaccuracies of the process and the need for further refinement of previous theories so as to apply them to flowing systems, such as is the case for PBRs used to culture microalgae.

Long-term culture of the marine dinoflagellate microalga Amphidinium carterae in an indoor LED-lighted raceway photobioreactor: Production of carotenoids and fatty acids

The feasibility of the long-term (>170u202fdays) culture of a dinoflagellate microalga in a raceway photobioreactor is demonstrated for the first time. Amphidinium carterae was chosen for this study as it is producer of interesting high-value compounds. Repeated semicontinuous culture provided to be a robust operational mode. Different concentration levels of the f/2 medium nutrients (i.e. f/2×1-3) were assayed. The composition f/2×3 (N:Pu202f=u202f5), combined with a sinusoidal irradiance pattern (L/Du202f=u202f24:0) with a 570u202fµEu202fm-2u202fs-1 daily mean irradiance, maximized the biomass productivity (2.5u202fgu202fm-2u202fday-1) and production rate of the valuable carotenoid peridinin (19.4u202f±u202f1.35u202fmgu202fm-2u202fL-1 with nearly 1% of the biomass d.w.). Several carotenoids and polyunsaturated fatty acids were also present in significant percentages in the harvested biomass (EPA, 1.69u202f±u202f0.31% d.w.; DHA, 3.47u202f±u202f0.24% d.w.), which had an average P-molar formulate of C40.7O21.2H73.9N3.9S0.3P1.

Long-term preservation of concentrated Nannochloropsis gaditana cultures for use in aquaculture

The aim of this paper is to solve problems that may arise in microalgae cultivation facilities at a hatchery in such a way that its activities are not disrupted. Thus, the effect of storage conditions (time, initial biomass concentration, presence or absence of light, addition of preservatives and conservation atmospheres) on cell viability, evolution of sample concentration, contamination, fatty acid and pigment content for long-term preservation of Nannochloropsis gaditana biomass has been studied. The polyunsaturated fatty acid content was maintained and the eicosapentaenoic acid (EPA, 20:5n3) content was kept stable at 3.6xa0% (d.w.). The total pigments content was also preserved at 0.85xa0% (d.w.), what allowed maintaining the antioxidant activity of samples. The results show that samples preserved both as concentrated inocula ready to run a photobioreactor, at an initial biomass (N. gaditana) concentration of 5xa0g L−1, and as pastes to be used as live food if any incident happens in a hatchery, at 150xa0g L−1, can be stored for up to 4xa0months at 4xa0°C under nitrogen or air atmosphere of conservation maintaining the cell viability and the sample concentration stable and at low incident irradiance (35xa0μmol photons m−2 s−1). This allows the photosynthetic activity of cells to be preserved in the case of samples at 5xa0g L−1. The bacterial load was kept at low level by the regular addition of preservative agents.

Microalgae as a potential ingredient for partial fish meal replacement in aquafeeds: nutrient stability under different storage conditions

Aquaculture provides half of the fish for human consumption, and the trend is on a significant rise over the coming decades. However, the soaring price of traditional ingredients used in aquafeeds is becoming prohibitive, especially in the case of capture fishery derivatives. Therefore, new alternative ingredients and additives are required in order to substitute fish meal and fish oil in aquaculture feeds. Microalgae are a reliable alternative to these as they are potential stabilizing agents against nutrient oxidation. In the present study, three experimental aquafeeds were elaborated with 15% microalgae biomass (Isochrysis galbana, Nannochloropsis gaditana, and Scenedesmus almeriensis); these were then stored under different temperature and light conditions for 15xa0months in order to analyze the stability of proteins, lipids, fatty acids, and carotenoids. The antioxidant activity of the natural pigments present in microalgae allowed frozen microalgae-based aquafeeds to maintain stable quality over 9xa0months of storage. Nannochloropsis- and Isochrysis-supplemented feeds had higher eicosapentaenoic and docosahexaenoic acid contents than the microalgae-free control feed. However, longer storage times led to a drop in protein and carotenoid levels.

Maximizing carotenoid extraction from microalgae used as food additives and determined by liquid chromatography (HPLC)

Microalgae are an interesting source of natural pigments that have valuable applications. However, further research is necessary to develop processes that allow us to achieve high levels of carotenoid recovery while avoiding degradation. This work presents a comprehensive study on the recovery of carotenoids from several microalgae genera, optimizing carotenoid extraction using alkaline saponification at various temperatures and KOH concentrations. Results show that I. galbana requires a temperature of 60u202f°C and <10% KOH, N. gaditana and K. veneficum require 60u202f°C and no saponification, P. reticulatum requires 40u202f°C and 10% KOH, T. suecica and H. pluvialis require 25u202f°C and 40% KOH while C. sp. and S. almeriensis require 80u202f°C and 40% KOH. The influence of the solvent on carotenoid recovery was also studied. In general terms, an ethanol:hexane:water (77:17:6u202fv/v/v) mixture results in good yields.