Search

Polyunsaturated long-chain alkenones are a unique class of lipids biosynthesized in significant quantities (up to 20% of cell carbon) by several algae including the industrially grown marine microalgae Isochrysis. Alkenone structures are characterized by a long linear carbon chain (35–40 carbons) with one to four trans double bonds and terminating in a methyl or ethyl ketone. Alkenones were extracted and isolated from commercially obtained Isochrysis biomass and then subjected to cross-metathesis (CM) with methyl acrylate or acrylic acid using the Hoveyda–Grubbs metathesis initiator. Within 1 h at room temperature alkenones were consumed; however, complete fragmentation (i.e., conversion to the smallest subunits by double bond cleavage) required up to 16 h. Analysis of the reaction mixture by gas chromatography and comprehensive two-dimensional gas chromatography revealed a predictable product mixture consisting primarily of long-chain (mostly C17) acids (or methyl esters from CM with methyl acrylate) and diacids (or diesters), along with smaller amounts (~5%) of the honey bee “queen substance” (E)-9-oxo-decenoic acid. Together, these compounds comprise a diverse mixture of valuable chemicals that includes surfactants, monomers, and an agriculturally relevant bee pheromone.

There is a shortage of established chronic toxicity test methods for assessing the toxicity of contaminants to tropical marine organisms. The authors tested the suitability of the tropical microalga Isochrysis galbana for use in routine ecotoxicology and assessed the effects of 72-h exposures to copper (Cu, a reference toxicant), aluminium (Al), gallium (Ga), and molybdenum (Mo), key metals of alumina refinery discharge, on the growth of I. galbana at 3 temperatures: 24 °C, 28 °C, and 31 °C. The sensitivity of both I. galbana and the test method was validated by the response to Cu exposure, with 10% and 50% effect concentrations (EC10 and EC50) of 2.5 μg/L and 18 μg/L, respectively. The EC10 and EC50 values for total Al at 28 °C were 640 μg/L and 3045 μg/L, respectively. The toxicity of both Cu and Al at 24 °C and 31 °C was similar to that at 28 °C. There was no measurable toxicity from dissolved Ga exposures of up to 6000 μg/L or exposures to dissolved Mo of up to 9500 μg/L. Solubility limits at 28 °C for the dissolved fractions (10 kDa) of Al, Ga, and Mo were approximately 650 μg/L Al,7000 μg/L Ga, and6000 μg/L Mo. In test solutions containing650 μg/L total Al, dissolved and precipitated forms of Al were present, with precipitated Al becoming more dominant as total Al increased. The test method proved suitable for routine ecotoxicology, with I. galbana showing sensitivity to Cu but Al, Ga, and Mo exhibiting little to no toxicity to this species.

SUMMARY The nitrogenous resource used to promote algal growth has cost implications for mass culture processes. The present study therefore aimed to determine the effect of different nitrogenous resources (nitrate, ammonium and urea) on various performance parameters (growth, final cell yield, pigmentation, lipid yield and cellular and sub-cellular characteristics) in Isochrysis galbana. Growth rate was unaffected by nitrogenous resource, but the final cellular yield in the nitrate and urea treatments far exceeded that evident in the ammonium treatments. The reduced cell yield in ammonium treatments and the earlier onset of the stationary phase was brought about by nitrogenstarvation due to an increase in pH and resultant ammonia volatilization. This starvation initiated an early onset of lipid accumulation, chlorophyll depletion and an increase in the carotenoid to chlorophyll ratio relative to the other nitrogen (N) source treatments. Hence, in spite of being potentially the preferred source of N by algae (due to its reduced state), ammonium-nitrogen is undesirable for mass culture. The performance parameters of Isochrysis grown in urea (an organic N source) and nitrate (an inorganic N source) were similar, but lipid accrued earlier in cells grown in medium supplemented with urea. This is advantageous for lipid acquisition for the production of biodiesel since it would reduce the duration of photobioreactor runs. Urea is easily available and considerably cheaper than all the other N sources tested and is thus recommended as the nitrogenous resource for large-scale culture of I. galbana for biodiesel production.

Summary Lipid accumulation has been investigated in numerous microalgal species to assess their potential with respect to biodiesel production. The present work determines the effect of nitrogen stress on physiological and ultrastructural changes in Isochrysis galbana U4. This study is unique in showing the correlations between growth, lipid production, pigmentation and ultrastructural changes in Isochrysis cells undergoing nitrogen starvation. The continuation of algal growth after the complete depletion of external nitrogen was shown to be supported by internal nitrogen stores, possibly in the pyrenoid. Cell growth ceased and lipid accumulation was initiated after the internal store of nitrogen had become exhausted. The depletion of intracellular nitrogen reservoirs to critical thresholds initiated the onset of the stationary phase, a decline in chlorophyll content and the initiation of lipid and carotenoid accumulation. The most notable ultrastructural changes, upon nitrogen stress, were the accumulation of plastidial and cytoplasmic lipid bodies and the dismantling of the chloroplast. The size of the pyrenoid when external nitrogen became depleted was found to decrease significantly, up to four-fold. This was attributed to the remobilization of nitrogen from Rubisco. The level of expression of heterochromatin was found to increase when cells were nitrogen starved. This is thought to favor long-term dormancy in this species because aging cells have been noted to recover rapidly when returned to conditions favorable for growth. The observations of this study are consistent with the hypothesis that the responses of Isochrysis cells to nitrogen starvation are regulated by the internal reserves of nitrogen, and the depletion of these reserves is an important trigger for lipid accumulation in this species. The findings of this study also indicate that Isochrysis galbana U4 is a promising candidate for biodiesel lipid production.

The goal of this study was to investigate the time response of two major carbon (C) reserves, respectively neutral lipids (NL) and total carbohydrate (TC), in the Haptophyte Isochrysis sp. growing in nitrogen (N)-sufficient or N-starved conditions and under light:dark (L:D) cycles. Experiments were carried out in a cyclostat culture system that allowed the following of the dynamics of the main cell compounds at both hourly and daily time scales. Under N-sufficient conditions, the L:D cycles cause the population to be synchronized, with most of the cells dividing at the beginning of the dark period. The C-specific growth rate was maximal around midday and negative during the dark period due to respiration processes. NL and TC both accumulated during the day and consumed during the night. We showed that NL and TC are highly dynamic compounds, as more than three quarters of NL and TC accumulated during the light period were consumed during the dark period. In contrast to NL, phospholipid and glycolipid to C ratios remained quite stable during the light/dark cycles. The major effect of N starvation on the NL and TC dynamics was to uncouple their diel variations from the L:D cycle, in two different ways depending on their respective role during short-term acclimation. Whereas the TC per cell ratio increased rapidly to reach a stable value in response to N starvation, NL per cell continued to oscillate, but with a pattern out of phase with the L:D cycle.

This study assessed the nutritional value of four species of microalgae for larval sandfish, Holothuria scabra (Echinodermata: Holothuroidea). Two-day-old larvae were fed either a single diatom (Chaetoceros muelleri, Chaetoceros calcitrans), flagellate (Isochrysis aff. galbana (T-ISO), Pavlova salina), or a ternary microalgal diet (TMD) comprised of 40% C. muelleri, 40% T-ISO, and 20% P. salina for 12 d. On Days 4, 6, and 8 length of larvae fed either C. muelleri, C. calcitrans, or the TMD was significantly greater than in T-ISO and P. salina fed larvae as well as the unfed control larvae. T-ISO fed larvae had a significantly greater length compared to unfed larvae on Days 4, 6, and 8; however, larvae fed P. salina had a significantly greater length compared to unfed larvae on Days 6 and 8 only. Survival of larvae fed either C. muelleri or the TMD was significantly better than the flagellate fed and unfed larvae on Days 4, 8, and 12. There was no significant difference between survival of unfed larvae and larvae fed either T-ISO or P. salina during the 12-d larval culture period. On Day 12, larvae fed either a diatom or the TMD developed in excess of 84% competent doliolariae. Larvae fed C. muelleri had a significantly higher percentage competent doliolariae than larvae from all other treatments except the TMD. Neither larvae fed either T-ISO or P. salina nor unfed larvae developed any competent doliolariae. In conclusion, this study showed C. muelleri to be the most effective of the four microalgae tested as a single microalgal diet for larval H. scabra and, as such, C. muelleri will be used as a reference diet in future studies.

Biomass and lipid productivity, lipid content, and quantitative and qualitative lipid composition are critical parameters in selecting microalgal species for commercial scale-up production. This study compares lipid content and composition, and lipid and biomass productivity during logarithmic, late logarithmic, and stationary phase of Nannochloropsis sp., Isochrysis sp., Tetraselmis sp., and Rhodomonas sp. grown in L1-, f/2-, and K-medium. Of the tested species, Tetraselmis sp. exhibited a lipid productivity of 3.9-4.8 g m(-2) day(-1) in any media type, with comparable lipid productivity by Nannochloropsis sp. and Isochrysis sp. when grown in L1-medium. The dry biomass productivity of Tetraselmis sp. (33.1-45.0 g m(-2) day(-1)) exceeded that of the other species by a factor 2-10. Of the organisms studied, Tetraselmis sp. had the best dry biomass and/or lipid production profile in large-scale cultures. The present study provides a practical benchmark, which allows comparison of microalgal production systems with different footprints, as well as terrestrial systems.

The growth of a temperate and a tropical strain of Isochrysis was studied at four temperatures and three light intensity levels. All algal cultures were grown in an enriched artificial seawater medium under constant illumination and were bubbled with air enriched with 0.1% CO2. Culture density (cells/ml) was measured periodically during exponential growth. Average growth rates for each combination of temperature and light intensity are presented as doublings/day. Observations of growth under the various culture conditions indicate that T-ISO (tropical strain) grows rapidly over a much broader range of temperatures than does I. galbana. Variations in growth at different light intensity levels suggest that the optimum light level increases as a function of temperature for T-ISO and that the growth of I. galbana is inhibited by high levels of light (1500 μW/cm2). The relative value of both strains as food for larval and juvenile oysters and the advantages and limitations of large scale culture are discussed.

Feeding experiments using commonly-cultured algae were conducted with purple-hinge rock scallops, Hinnites multirugosus Gale, to suggest the application of these algae to hatchery culture of scallops. The uptake of finely divided particulate matter was also studied to ascertain the possible importance of detritus as a supplemental food for the rock scallop. A 1:1:1 mixture by culture volume of Tahitian Isochrysis, Tetraselmis suecica, and Dunaliella salina appeared to be superior as a diet for juvenile rock scallops. Significant growth also occurred in juvenile rock scallops fed T-Isochrysis, T. suecica, Isochrysis galbana, and Rhodomonas sp. Gymnodinium splendens, Monochrysis lutheri, and Dunaliella salina fed alone were poor foods for juvenile rock scallops. Finely divided particulate matter as radiolabeled abalone fecal matter was utilized as food. Significant radioactivity appeared in DNA, RNA, lipid, protein, carbohydrate, and free-reducing substances after one week providing evidence that particulate matter was incorporated into juvenile rock scallop metabolic pathways.

Spawning, larval rearing, and settlement of Mytilus californianus were performed over a one-year period at the University of California, Bodega Marine Laboratory in northern California. A combination of shell scraping followed by a 30 to 60 min immersion in 30 or 60 mM hydrogen peroxide was the most successful spawning stimulus tested. Larvae fed a diet of Isochrysis galbana grew significantly faster than did larvae fed Dunaliella sp. Larval growth rate was significantly more rapid at 20°C than at either 14 or 17°C and no significant differences in mortality rates between these three temperatures were detected. At 17 and 20°C, larvae fed a diet of 80 Isochrysis cells/μ1 daily grew significantly faster than those fed 20 Isochrysis cells/μ1 daily. Mortality of pedi-veligers was high, but survivors settled and metamorphosed on byssal threads cut from adult M. californianus. Plantigrades had a mean growth rate of 7.8 μm/day between days 15 and 33 following settlement. In this study, a temperature of 20°C, a diet of Isochrysis galbana of at least 80 cells/μ1 daily, and a settlement substrate of byssal threads were the most successful conditions for artificial spat production of this potentially valuable bivalve mollusc.

The purple-hinge rock scallop is receiving increasing interest as a candidate for commercial mariculture. Hatchery culture of juveniles is prerequisite since natural recruitment of juveniles is variable and not dependable as a source of stock. Success in carrying larvae through metamorphosis has been limited. Critical to larval culture is a sound understanding of optimal food and feeding strategies. Growth and survival were examined in early larvae fed six algal diets at four separate concentrations. The data clearly illustrate the superiority of both Isochrysis galbana and a Tahitian (T) strain of Isochrysis. Feed concentrations of 1 × 105 cells/ml were found to be optimal for these species of Isochrysis. An I. galbana diet supported 80% survival through metamorphosis. The other algae examined included Mono-chrysis lutheri, Rhodomonas sp., Carteria pallida, and a 1:1:1 mixture of Rhodomonas, Monochrysis, and Isochrysis. All these diets supported 5–6% survival, and the growth was only slightly better than starvation controls. A similar study was done with early juveniles (1 mm dia). The diets included: I. galbana, M. lutheri, Thalassiosira pseudonana (3H), T-Isochrysis sp., and Phaedactylum tricornutum. As with the larvae, superior growth and survival occurred with diets of both species of Isochrysis. Cell concentrations between 1 × 105 and 2 × 105 cells/ml were optimal. The other diets supported minimal growth. In the feeding runs of both larvae and early juveniles, cell densities in excess of 5 × 105 cells/ml were detrimental.

Studies on spawning and larval culture in the purple-hinge rock scallop (Hinnites multirugosus) are described together with information on growth of juveniles and adults. Gravid individuals were collected from field populations throughout most of the year. These produced viable eggs when induced to spawn in the laboratory. Larval development appeared normal over the range 8–18°C (optimal for culture, 14–18°C). Acceptable growth and survival were achieved on a mixed diet of Isochrysis, Monochrysis, Tetraselmis and Skeletonema. Metamorphosis began in larvae 200 μm in shell diameter (age, 3 weeks). Most rapidly growing post-larvae reached 1.8 mm at two months (15–18°C). Pre-cementing juveniles held in cages in Mission Bay, San Diego, averaged approximately 8 mm/mo during summer (18–22°C) and half that rate throughout the rest of the year (13–18°C). Individuals 1.5 to 3.0 cm in October, 1975, reached shell diameters of 5.0 to 7.5 cm one year later.

1. Dreissena polymorpha is an extraordinarily successful invasive species that shows high recruitment of small juvenile mussels on established mussel banks. Such juvenile settlement on, and overgrowth of, large adult mussels; however, leads to competition with adults, and often at high densities and low-food concentrations. 2. The concept of food thresholds for zero growth has been a powerful approach to explaining size-related exploitative competition in different zooplankton species. We applied it to investigate whether food threshold concentrations for zero growth (C 0 ) differ between juvenile and adult zebra mussels. 3. By determining body mass growth at various concentrations of a diet mixture (Nannochloropsis limnetica and Isochrysis aff. galbana) we demonstrate that the threshold food concentration for growth of juvenile mussels (C 0 = 0.08 mg C L -1 ) is substantially lower than that for adults (C 0 = 0.36 mg C L -1 ). 4. This indicates that, at low food availability, juvenile zebra mussels are competitively superior to their larger conspecifics. Within zebra mussel banks plankton food is substantially depleted and so the observed mechanism might ensure juvenile success and therefore the regeneration of mussel banks in nature.

This study reports the potential contribution of organic bases to the alkalinity of seawater samples. The con- centration of organic bases in these samples was inferred from the difference between the measured alkalinity and that calculated from a knowledge of pH and concentrations of the various inorganic acid-bases species such as total carbon, total boron, and so on. Significant concentrations of such organic bases were measured in cul- tures of the marine microalgae Rhodomonas sp. (800 µmol kg -1 ) and Isochrysis aff. Galbana (400 µmol kg -1 ), as well as in three marine environments (northern gulf of California, Mexico; San Quintin Bay, B.C., Mexico; and San Diego Bay). These three sites are characterized by significant biological activity and restricted mixing, and the organic bases were found at concentrations greater than 50 µmol kg -1 in each of these three locations.

To investigate whether particles are ingested or merely trapped in the house of the appendicularian Oikopleura dioica, we developed a real-time quantitative polymerase chain reaction (qPCR) assay and applied it in a controlled study where O. dioica was fed three types of algae at different concentrations. At particle concentrations ranging from 100 to 10,000 cells mL 21 , highest ingestion efficiencies (75–96%) were observed with the smallest algal species (Isochrysis sp.) compared to the larger cryptophyte Rhinomonas sp. (2–87%) and a similar sized but spiny diatom, Chaetoceros calcitrans (4–65%). When prey were mixed, the presence of C. calcitrans inhibited ingestion of Rhinomonas sp. but not the smaller Isochrysis sp., suggesting that C. calcitrans clogged the inlet filter and mechanically hindered ingestion of larger algae. O. dioica is adapted to feed on smaller particles at low (nonbloom) concentrations and may thus be subjected to bottom-up regulation by larger spiny or colonial prey that typically dominate late-stage phytoplankton blooms.

Phytoplankton over-blooming and consequent die-off is one of the major contributory factors for ammonia and chemical oxygen demand (COD) loadings. In this work, electrolysis technology was applied to determine its ability to remove ammonia and total chemical oxygen demand (TCOD) in both laboratory-scale batch and continuous systems. Under an initially set voltage of 5 V, a constant current of 0.1 A was applied and different retention times were used for ammonia-removal experiments. Results showed that these conditions are not satisfactory in removing TCOD loadings contributed by algal cells. However, a retention time of 35.7 min was sufficient to remove 100% ammonia from algal-uncontaminated waters. Ammonia removals in waters containing Chlorella spp and Isochrysis spp were 87 and 68%, respectively, after 140 min of electrolysis. Energy consumption for ammonia removal in algal-free water was 50 W mg−1 of ammonia. For waters containing Chlorella spp and Isochrysis spp energy consumptions were 67 and 85 W mg−1 of ammonia, respectively. Interestingly, the applied mild electrolysis condition was just sufficient to control excess algal blooming and ammonia without increasing the dissolved COD and chlorine in shrimp grow-out ponds. This minimizes operating costs due the process requiring less energy. Furthermore, it was also found that electrolysis does not lower alkalinity. Copyright © 2005 Society of Chemical Industry

The lipid profile of seven species of unicellular eukaryotic microalgae grown under controlled conditions was studied with emphasis on the hydrocarbons and the fatty acids as part of a search for oil-producing algae. Green, slow-growing colonies of Botryococcus braunii Kutz contained the highest lipid content of 45% based on the organic weight, with an increase to 55% under nitrogen deficiency and with no effect of sodium chloride stress. Ankistrodesmus sp. Thomas, Dunaliella spp., Isochrysis sp., Nannochloris sp. Thomas, and Nitzschia sp. Chapman contained an average of 25% lipids under nitrogen sufficient conditions. Nitrogen deficiency resulted in significant increase in the lipid content in all species but Dunaliella spp., which produced a higher content of carbohydrates. Significant low amounts of acyclic hydrocarbons were detected only in Botryococcus braunii Kutz and not in the other algae. The major hydrocarbon fractions in nitrogen deficient Botryococcus braunii Kutz, Dunaliella salina Thomas, Isochrysis spp. and Nannochloris sp. Thomas were cyclic and branched polyunsaturated components which were identified as various isoprenoid derivatives. The polar lipid composition of glycolipids and phospholipids of all species investigated was fairly typical of photosynthetic eukaryotic algae. Fatty acid composition was species specific, with changes occurring in the relative amounts of individual acids of cells cultivated under different conditions and growth phases. All species synthesized C14:0, C16.0, C18:1, C18:2 and C18:3 fatty acids; C 16:4 in Ankistrodesmus sp. Thomas; C18:4 and C 22.6 in Isochrysis sp.; C16:2, C16:3 and C20:5 in Nannochloris sp. Thomas; C16:2, C16:3 and C20:5 in Nitzschia sp. Chapman. Nitrogen deficiency and salt stress induced accumulation of C18:1 in all treated species and to a lesser extent in Botryococcus braunii Kutz. The low production of hydrocarbons under optimal growth conditions and the high production of hydrocarbons under limited growth conditions cannot support the notion that microalgae can be utilized as biosolar energy converters for the production of liquid fuel, but point to the availability of a variety of neutral and polar lipid products.

Inorganic carbon acquisition has been investigated in the marine haptophyte Isochrysis galbana. External carbonic anhydrase (CA) was present in air-grown (0.034% CO 2 ) cells but completely repressed in high (3%) CO 2 -grown cells. External CA was not inhibited by 1.0 mM acetazolamide. The capacity of cells to take up bicarbonate was examined by comparing the rate of photosynthetic O 2 evolution with the calculated rate of spontaneous CO 2 supply; at pH 8.2 the rates of O 2 evolution exceeded the CO 2 supply rate 14-fold, indicating that this alga was able to take up HCO 3 -. Monitoring CO 2 concentrations by mass spectrometry showed that suspensions of high CO 2 -grown cells caused a rapid drop in the extracellular CO 2 in the light and addition of bovine CA raised the CO 2 concentration by restoring the HCO 3 --CO 2 equilibrium, indicating that cells were maintaining the CO 2 in the medium below its equilibrium value during photosynthesis. A rapid increase in extracellular CO 2 concentration occurred on darkening the cells, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. Active CO 2 uptake was blocked by the photosynthetic electron transport inhibitor 3-(3',4'-dichlorphenyl)-1,1-dimethylurea, indicating that CO 2 transport was supported by photosynthetic reactions. These results demonstrate that this species has the capacity to take up HCO 3 - and CO 2 actively as sources of substrate for photosynthesis and that inorganic carbon transport is not repressed by growth on high CO 2 , although external CA expression is regulated by CO 2 concentration.

Isochrysis galbana, a marine prymnesiophyte microalga, is rich in long chain polyunsaturated fatty acids such as docosahexaenoic acid (C22:6n-3, Δ4,7,10,13,16,19). We used a polymerase chain reaction-based strategy to isolate a cDNA, designated IgASE1, encoding a polyunsaturated fatty acid-elongating activity from I. galbana. The coding region of 263 amino acids predicts a protein of 30 kDa that shares only limited homology to animal and fungal proteins with elongating activity. Functional analysis of IgASE1, by expression in Saccharomyces cerevisiae, was used to determine its activity and substrate specificity. Transformed yeast cells specifically elongated the C18-Δ9 polyunsaturated fatty acids, linoleic acid (C18:2n-6, Δ9,12) and α-linolenic acid (C18:3n-3, Δ9,12,15), to eicosadienoic acid (C20:2n-6, Δ11,14) and eicosatrienoic acid (C20:3n-3, Δ11,14,17), respectively. To our knowledge this is the first time such an elongating activity has been functionally characterised. The results also suggest that a major route for eicosapentaenoic acid (C20:5n-3, Δ5,8,11,14,17) and docosahexaenoic acid syntheses in I. galbana may involve a Δ8 desaturation pathway.

— The effects of four kinds of foods (Artemia nauplii, rotifer, and microalgae Chaetoceros gracilis and Isochrysis galbana) and four temperature regimes on survival and development of larval Lysmata wurdemanni, a marine ornamental shrimp, were determined. The larvae fed with Chaetoceros or Isochrysis only survived for a maximum of 17 d, before developing to zoea IV. The survivorship of the larvae fed with Artemia nauplii or rotifer from zoea II to post-larvae was 66.7% and 68.9%. respectively, without significant difference (P > 0.05). But larvae fed with Artemia nauplii grew significantly (P < 0.05) faster than those fed with rotifer. Larvae fed with Artemia nauplii reached postlarvae in 29–32 d, compared with 32–36 d in the rotifer treatment. Artemia nauplii are also suitable food for the postlarvae and juveniles of L. wurdemanni. The 30 postlarvae fed on Artemia nauplii all survived to reach sexual maturity in 50 to 70 d, growing from about 7 to 28 mm in total length. The effects of four temperature regimes on larval development of L. wurdemanni was also investigated. The duration (mean ± SD d) to the postlarvae at temperatures of 26 C (37.4 ± 5.4) and of 26–30 C daily (40.2 ± 5.8) was significantly (P < 0.05) longer than that at 28.5 C (29.3 ± 4.8) and at 27–29 C daily (28.7 ± 3.5).

Knowledge of tolerance to cryoprotectants is important in determining viability after biological freezing of algae. Six taxonomically divers marine microalgae were evaluated for their tolerance to the widely used cryoprotectants dimethyl sulfoxide (DMSO) and methanol. Tetraselmis chuii Butcher survived exposure to 30% (v/v) DMSO and 25% methanol for periods of up to 4 h. All other species were more sensitive to high concentrations of these cryoprotectants. DMSO was lethal at 25% after a 15-min exposure of Rhodomonas baltica Karsten, Isochrysis aff. galbana (strain T-ISO) Parke, and Nannochloropsis gaditana Lubian

The effects of irradiance on the biochemical composition of the prymnesiophyte microalga, Isochrysis sp. (Parke; clone T-ISO), a popular species for mariculture, were examined. Cultures were grown under a 12:12 h light: dark (L:D) regime at five irradiances ranging from 50 to 1000 μE·m 2·s−1 and harvested at late-logarithmic phase for analysis of biochemical composition. Gross composition varied aver the range of irradiances. The highest levels of protein were present in cells from cultures grown at 100 and 250 μE·m 3·s1, and minimum levels of carbohydrate and lipid occurred at 50 μE·m−2·s−1. Because the cell dry weight was reduced at lower irradiances, different trends were evident when results were expressed as percentage of dry weights. Protein percentages were highest at Wand 100 μE·m−2·s−1 and carbohydrate at 100 μE·m−2·s−1. The composition of amino acids did not differ over the range of irradiances. Glutamate and aspartate were always present in high proportions (9.0–13.5%); histidine. methionine, tryptophan, cystine, and hydroxy-proline were minor constituents (0.0–2.6%). Glucose was the predominant sugar in all cultures, ranging from 23.0% (50 μE·m−2·s−1) to 45.0% (100 μE·m−2·s−1) of total polysaccharide. No correlation was found between the proportion of any of the sugars and irradiance. The proportions of the lipid class components and fatty acids showed little change with irradiance. The main fatty acids were 14:0, 16:0, 16:1(n-7), 18:1(n-9), 18:3(n-3). 18:4(n-3), 18:5(n-3), and 22:6(n-3). Proportions of 22: 6(n-3) increased, whereas l8:3(n-3). 18:3(n-6). and 18:4(n-3) decreased, with increasing irradiance. Pigment concentrations were highest in cultures grown at 50 μE·m−2·s−1, except for fucoxanthin and diadinoxanthin (100 μE·m−2·s−1). The concentrations of accessory pigments correlated with chlorophyll a, which decreased in concentration with increasing irradiance. On the basts of biochemical composition, an irradiance of 100 μE·m−1·s−1 (12:12 h L:D cycle)for the culture of Isochrysis sp. (clone T-ISO) may provide optimal nutritional value for maricultured animals, although feeding trials are now necessary to substantiate this.

Preset larval Mercenaria mercenaria were exposed to nominal concentrations of 1 (control) to 495 μg Cu/L in artificial seawater and monitored for mortality, activity, development, and metamorphosis in sealed 30-mm plastic petri plates containing 1.5 ml of artificial seawater or toxicant solution. The plastic petri plates sorbed only about 2.6 μg/L at any dose and allowed direct observation of larval clams under a light microscope for a period of two weeks; control survivorship was in excess of 60% at 400 h. The dose-response curve for mortality for clams exposed to copper and fed Isochrysis galbana was characterized by survival similar to or better than controls at doses of 5 and 14 μg Cu/L, while doses of 7 and ≥29 μg Cu/L exhibited mortality greater than controls. Values of lowest concentration at which 50% of the organisms died (LC50) were 62.4, 21.2, and 11.7 μg Cu/L, and the lowest observed adverse effect concentration values of 57, 29, and 29 μg Cu/L were determined at 48, 96, and 192 h, respectively. In contrast, activity, as judged by swimming, exhibited a typical exponentially decreasing response at these same concentrations. Experiments on the uptake of dissolved copper by I. galbana confirmed literature reports that these algae concentrate copper. Ingesting copper-containing algae was demonstrated to be a source of copper toxicity for larval clams.

Cultures of Isochrysis galbana Parks and Phaeodactylum tricornutum Bohlin were grown in iron-limited chemostats. With increasing iron deficiency, photosynthetic rate per cell and assimilation number decreased. The pattern of photosynthesis was also altered; in Fe deficient cells the proportion of 14C fixed in glycine and serine decreased with an accompanying increase into alanine after 3 min assimilation. Although there was no significant effect of Fe deficiency on the proportion of 14C incorporated into total amino acids and amides, the percentage of total 14C fixed in protein increased with increasing Fe deficiency. Cellular levels of chlorophyll a, carotenoids, cytochromes and protein also decreased with increasing Fe deficiency. However, the reduction in chlorophyll a/cell was not as great as that of cytochrorne f1 and Fe deficient cells therefore showed a marked increase in chlorophyll a:cytochrorne f1 ratio.

SUMMARY The growth rates of 3 species of phytoplankton were found to be dependent on the vitamin B12 concentrations in the media. In batch cultures, the vitamin B12 half-saturation constants and standard errors were 0.39 ± 0.042 μμg/ml for Thalassiosira pseudonana (clone 3H), 1.69 ± 0.24 μμg/ml for Isochrysis galbana, and 2.77 ± 1.65 μμg/ml for Monochrysis lutheri. A chemostat was used to grow T. pseudonana with vitamin B12 as the controlling factor. In the chemostat the yield and standard deviation, 102 ± 21 × 104 cells/μμg vitamin B12, was the same as in the batch culture, 126 ± 13 ± 104 cells/μμg. The chemostat half-saturation constant, 0.26 ± 0.068 μμg/ml vitamin B12, and maximum growth rate were in agreement with those obtained in batch cultures. Vitamin concentrations for maximum growth, rates were greater than those calculated necessary from yield data to give observed population densities similar to those in natural waters. In the sea the effect of vitamin B12 concentration on growth rates may be complicated by low concentrations of other nutrients or the presence of inhibitors.

The marine diatom Navicula incerta Hustedt and the haptophyte Isochrysis galbana Parke, both accustomed to grow on nitrate, were tested for their adaptive capacity for growth in axenic culture on 0.025–2.0 mM l-, d-, and dl-isomers of phenylalanine and tyrosine as sole nitrogen sources. The diatom showed immediate and excellent growth (superior to nitrate) on l-phenylalanine and l-tyrosine but required prolonged periods of adaptation before growing on the d-isomers, which growth was considerably slower. Isochrysis showed good growth on l-phenylalanine after short adaptation, fair growth on low but poor growth on high concentrations of l-tyrosine and no growth on the d-isomers of both amino acids. The racemate (dl-mixture) of each amino acid produced growth responses, from both algae, inferior to those of the corresponding l-isomer, indicating competitive inhibition from the d-isomer in the presence of equal amounts of its counterpart. Increasing tyrosine concentration was beneficial to growth of Navicula but markedly inhibitory or toxic to that of Isochrysis. Phenylalanine concentration appeared to benefit growth of both algae. Ecological considerations suggest that N. incerta may be habituated to utilize both aromatic amino acids in its native milieu.

Large numbers of penaeid shrimp were reared to postlarvae from eggs spawned in the laboratory. Rearing containers were four 1,040-liter tanks and one 1,890-liter tank. Temperature affected the rate of development through the larval stages. In water of 30 ppt (parts per thousand) salinity, the average time required for larvae of brown shrimp to reach first postlarval stage was 17 days at 24 C, 12.5 days at 28 C, and 11 days at 32 C. Survival of nauplii was best at 24 C, and as the shrimp became protozoeae and myses, survival usually increased with an incease in temperature. Larvae did not survive at salinities above 35 ppt or below 27 ppt. Algae tested for shrimp food were: Cyclotella nana, Isochrysis galbana, Skeletonema costatum, Thalassiosira sp., and a mixture of all four types. Isochrysis appeared to be the least suitable food, and the mixed algae and Thalassiosira probably were the best.

Extraccllular carbohydrate production during the growth of bacteria-free cultures of tho marine flagellates Isochrysis g,albana, Monochrysis lutheri, Prynanesium parvum, Dunaliella euchlora, Pyraminomonas sp., Rhodomonas (?) sp., and Chlamydomonas sp. was followed by the N-ethyl carbazole method. Carbohydrate production did not parallel cell numbers during exponential growth of any of these organisms; maximum concentrations during this phase wcrc under 3 mg/L. Carbohydrates accumulated in all stationary cultures (having 106--10’ cells/ml), to the greatest extent in Prymnesium cultures, which attained 123 mg/L. Isochrysis and Monochrysis produced 25 and 16 mg/L, respectively, while the others had under 10 mg/L even when cell disintegration was evident. Aging cultures (not all bacteria-free) of 4 diatoms, 2 dinoflagellates, 2 additional green algae, and a cyanophyte were assayed. Concentrations ranged from 1.5 to 60 mg/L. This suggests that the organisms studied contribute significant, free carbohydrates only during late bloom conditions, when algae are abundant and under physiological circumstances resembling stationary or declining culture.