Isochrysis Strains Research Articles

Lipid dynamics and nutritional value of the estuarine strain Isochrysis galbana VLP grown from hypo to hyper salinity

Novel nutritional/functional applications of Isochrysis strains are mostly based on their diversified lipid classes. The content of these lipids is modulated by different factors, among which salinity has been comparatively understudied. Since managing salinity is key for optimal microalgae outdoor mass production and most studied Isochrysis strains are marine, the lipid response to nearly extreme hypo and hyper salinity in a new estuarine strain is here described. Total lipids in exponentially grown Isochrysis galbana VLP gradually decreased from 334 ± 36.6 mg g-1 at a salinity of 5 psu to 164.3 ± 24.4 mg g-1 at 50 psu. Present is the first report on lipid class (LC) remodeling in response to salinity in any Isochrysis strain. Two main storage lipids, steryl esters (SE) and triacylglycerol (TAG), underwent the fastest absolute decrease as salinity increased during both active and halted growth in the estuarine strain I. galbana VLP. Alkenones also decreased with salinity although less markedly. Among photosynthetic lipids, galactolipids were more affected by salinity than the anionic lipids. Salinity had minor influence on the relative sterol and betaine lipid proportions. Salinity explained more of total LC variation (34.6%) than culture stage (30.3%), whereas the opposite occurred with fatty acid (FA) variation. The main FA affected by salinity were 20:5n-3, 18:3n-3, 18:5n-3 and 18:2n-6. Nutritional value of I. galbana VLP from 5 psu exponential cultures was 1.5-fold to 2-fold higher than under all other conditions. Isochrysis production in low salinity waters can be a sustainable procedure compatible with its optimized nutritional value.

Screening of Isochrysis strains for simultaneous production of docosahexaenoic acid and fucoxanthin

Microalgae are capable of synthesizing a wide range of value-added compounds such as docosahexaenoic acid (DHA) and fucoxanthin. In the present study, the potential for simultaneous production of DHA and fucoxanthin by the marine alga Isochrysis was investigated via strain screening and culture optimization. A comparative analysis of sixteen Isochrysis strains revealed that CCMP1324 was superior with regard to growth and production of DHA and fucoxanthin. In response to various nutritional and environmental cues, CCMP1324 accumulated DHA and fucoxanthin in a coordinated and growth-dependent manner, which reached ~17.1 and 14.1 mg g−1, respectively. A semi-continuous culture strategy leading to high productivities of DHA (9.05 mg L−1 day−1) and fucoxanthin (7.96 mg L−1 day−1) was developed. Taken together, our study represents a pioneering work studying the accumulation coordination between DHA and fucoxanthin in Isochrysis. These findings provide valuable insights into future exploration for the integrated production of high-value compounds.

Screening of Isochrysis Strains and Utilization of a Two-Stage Outdoor Cultivation Strategy for Algal Biomass and Lipid Production.

Isochrysis is a genus of marine algae without cell wall and capable of accumulating lipids. In this study, the lipid production potential of Isochrysis was assessed by comparing 15 Isochrysis strains with respect to their growth rate, lipid production, and fatty acid profiles. Three best strains were selected (lipid productivity, 103.0~121.7mgL-1day-1) and their lipid-producing capacities were further examined under different controlled parameters, e.g., growth phase, medium nutrient, and light intensity in laboratory cultures. Furthermore, the three Isochrysis strains were monitored in outdoor panel photobioreactors with various initial cell densities and optical paths, and the strain CS177 demonstrated the superior potential for outdoor cultivation. A two-stage semi-continuous strategy for CS177 was subsequently developed, where high productivities of biomass (1.1gL-1day-1) and lipid (0.35gL-1day-1) were achieved. This is a comprehensive study to evaluate the lipid-producing capability of Isochrysis strains under both indoor and outdoor conditions. Results of the present work lay a solid foundation for the physiological and biochemical responses of Isochrysis to various conditions, shedding light on the future utilization of this cell wall-lacking marine alga for biofuel production.

Physiological and Biochemical Changes Reveal Differential Patterns of Docosahexaenoic Acid Partitioning in Two Marine Algal Strains of Isochrysis.

The marine microalgae Isochrysis are a good producer of natural docosahexaenoic acid (DHA). To better understand the patterns of DHA accumulation and distribution, two Isochrysis strains, CL153180 and CCMP462, were evaluated in this study. In a batch culture, CL153180 showed a decline in DHA content while CCMP462 exhibited a progressive increase during the late growth period when nitrogen was almost exhausted. In response to nitrogen deficiency (ND), both strains showed a considerable increase in neutral lipids (NL) at the expense of glycolipids (GL) but had little variation in phospholipids (PL). In CL153180, the DHA percentage of NL decreased gradually upon ND, while that in CCMP462 increased progressively to 21.4% after 4 days of ND, which is around 5-fold higher than CL153180. Accordingly, in contrast to CL153180 that stored DHA predominantly in GL, CCMP462 accumulated DHA mainly in NL in late days of ND. Taken together, we proposed a working model for the differential DHA partitioning patterns between two Isochrysis strains: for CCMP462, the degradation of GL released free fatty acids including DHA, which was incorporated into NL upon ND; whereas for CL153180, the released DHA from GL might not be incorporated into NL, and, consequently, might be subject to β-oxidation for degradation.

Screening and characterization of Isochrysis strains and optimization of culture conditions for docosahexaenoic acid production

Isochrysis is a genus of marine unicellular microalgae that produces docosahexaenoic acid (DHA, C22:6), a very long chain polyunsaturated fatty acid (PUFA) of significant health and nutritional value. Mass cultivation of Isochrysis for DHA production for human consumption has not been established due to disappointing low DHA productivity obtained from commonly used Isochrysis strains. In this study, 19 natural Isochrysis strains were screened for DHA yields and the results showed that the cellular DHA content ranged from 6.8 to 17.0 % of total fatty acids with the highest DHA content occurring in the exponential growth phase. Isochrysis galbana #153180 exhibited the greatest DHA production potential and was selected for further investigation. The effects of different light intensities, forms, and concentrations of nitrogen, phosphorus, and salinity on growth and DHA production of I. galbana #153180 were studied in a bubble column photobioreactor (PBR). Under favorable culture conditions, I. galbana #153180 contained DHA up to 17.5 % of total fatty acids or 1.7 % of cell dry weight. I. galbana #153180 was further tested in outdoor flat-plate PBRs varying in light path length, starting cell density (SCD), and culture mode (batch versus semicontinuous). When optimized, record high biomass and DHA productivity of I. galbana #153180 of 0.72 g L(-1) day(-1) and 13.6 mg L(-1) day(-1), or 26.4 g m(-2) day(-1) and 547.7 mg m(-2) day(-1), respectively, were obtained, suggesting that I. galbana #153180 may be a desirable strain for commercial production of DHA.

Reproductive performance, survival and development of nauplii and copepodites, sex ratio and adult life expectancy of the harpacticoid copepod, Euterpina acutifrons, fed different microalgal diets

A series of laboratory experiments were conducted on the harpacticoid copepod, Euterpina acutifrons, to assess the influence of 10 different microalgal diets (four monoalgal and six mixed algal diets) on several parameters related to its productivity in culture. The four monoalgal diets were the Tahitian strain of Isochrysis sp. (T-Iso), Pavlova salina (Pav), Tetraselmis chuii (Tet) and the diatom Chaetoceros muelleri (Chaet), the five binary diets were T-Iso+Tet, Pav+Tet, T-Iso+Pav, Tet+Chaet and Pav+Chaet, while the tri-algal diet was T-Iso+Tet+Pav. All diets were fed to copepods at 1500 μ gC L−1 and in the case of binary or trialgal diets, carbon concentration was divided equally between the two or three algae offered. Among monoalgal diets, the diatom Chaet was excellent for E. acutifrons. Out of the 10 diets tested, the binary diet Tet+Chaet, which contained the diatom Chaet, was the best for naupliar production of single pair E. acutifrons (19.5±1.7 nauplii female−1 day−1), significantly (P 0.05). Similarly, in the group naupliar production trial (50 adult E. acutifrons per replicate), Tet+Chaet produced a significantly higher number of nauplii (405.8±18.6 nauplii day−1) than the other treatments (P<0.05). Tet+Chaet further supported the highest naupliar survival (82.0±2.8%) and copepodite survival (89.0±2.8%), while the mono-algal diet Chaet produced the second highest naupliar (76.7±2.6%) and copepodite survival (83.5±2.6%). In contrast, Pav produced the lowest overall survival at the naupliar stage (30.0±2.9%), significantly lower than all other treatments (P<0.05). While development from newly hatched nauplii to copepodites was not significantly affected by diets, mean development time from nauplius to adult was significantly different among treatments. Mean development time from hatching (naupliar I stage; NI) to the adult stage was the fastest with Tet+Chaet and Chaet (6.8±0.0 days for both treatments), which was significantly faster than that of Pav, T-Iso Pav+Tet and T-Iso+Pav+Te treatment (P<0.05). E. acutifrons sex ratio was significantly affected by diets, and always skewed in favour of males. Feeding on Pav resulted in the lowest proportion of females (23.7±1.2%), significantly lower than for six of the other treatments (P<0.05). Adult females had longer average life expectancy than males for all treatments, and were the longest when fed Tet+Chaet (9.5±0.4 days), which was more than twice as long as the shortest lifespan recorded for the Pav treatment (4.2±0.6 days) (P<0.05). In summary, among 10 diets tested, the binary diet Tet+Chaet appeared to support the highest culture productivity of E. acutifrons while the diatom Chaet also performed well as a monoalgal diet.

Egg production, egg hatching success and population increase of the tropical paracalanid copepod, Bestiolina similis (Calanoida: Paracalanidae) fed different microalgal diets

A series of experiments was conducted to evaluate the suitability of ten microalgal diets, including 4 monoalgal, 5 binary and 1 tri-algal diet, for the culture of the tropical paracalanid copepod Bestiolina similis. The four monoalgal diets were the Tahitian strain of Isochrysis sp. (T-Iso), Pavlova 50 (Pav), Tetraselmis chuii (Tet) and the diatom Chaetoceros muelleri (Chaet), the 5 binary diets were Tet + T-Iso, Tet + Pav, T-Iso + Pav, Chaet + Tet and Chaet + Pav while the tri-algal diet was T-Iso + Tet + Pav. After feeding B. similis with 10 algal diets for 3 days, 24 h egg production rate (EPR, eggs female − 1 day − 1 ) was obtained for each diet treatment by averaging the egg output of 6 individual females (replaced daily) for 4 consecutive days. The tri-algal diet T-Iso + Tet + Pav produced the highest EPR (44.1 eggs female − 1 day − 1 ), which was significantly higher than any other diets tested ( p < 0.05). Highest 48 h and 96 h egg hatching rates (EHR) were also found from the eggs produced by B. similis fed with T-Iso + Tet + Pav (48 and 96 h EHR = 91.0% and 96.3% respectively) and significant differences in 48 h EHR were detected for 5 out of the 9 other diets tested, while for 96 h EHR, only for 2 diets. Population increase was determined over a 12 day culture period for 10 initial B. similis adults (7 females and 3 males) and the result showed that the tri-algal diet T-Iso + Tet + Pav produced significantly higher population number by the end of 12 days than any of the mono-algal or binary diets tested ( p < 0.05). When all developmental stages were included (including eggs), the tri-algal diet produced a population increase from 10 to 887 over the 12 days. The binary diet Tet + T-Iso was the second most productive diet, providing a total population increase from 10 to 541, which was significantly higher than the rest of the diets, except that of Pav + T-Iso (479), T-Iso (334) and Chaet + Pav (285) ( p > 0.05). Based on the current results, it is suggested that among the diets tested, the tri-algal diet of T-Iso + Tet + Pav was the best for the culture of B. similis.

Effects of microalgal diets on the growth and survival of larvae and post-larvae of the basket cockle, Clinocardiumnuttallii

The nutritional value of four microalgal species: Chaetoceros muelleri, Pavlova lutheri, Tahitian strain of Isochrysis sp. (TISO), and Thalassiosira pseudonana in single- and bi-species diets was evaluated for larvae and post-larvae of the basket cockle, Clinocardium nuttallii. Larval shell growth and metamorphic rate were found to be the greatest with both single- and mixed-species diets comprising TISO. For the post-larvae, however, optimal shell growth was observed in both single- and mixed-species diets containing Chaetoceros muelleri. In another feeding experiment, the microalga Tetraselmis suecica was tested singly and in combination with TISO. Results showed that the food value of Tetraselmis suecica alone was poor for both larvae and post-larvae. In contrast, the mixed-species diet of Tetraselmis suecica and TISO resulted in significantly improved larval and post-larval growth, similar to the respective best (control) diets as identified in the first experiment. It is concluded that, for the hatchery production of Clinocardium nuttallii seed, a single-species diet of TISO is the best for the larvae and a single-species diet of Chaetoceros muelleri is the best for the post-larvae. A nutritional transition period during which both the microalgal species may be required, is also suggested for the hatchery production of basket cockle seed.

The effects of temperature and salinity on population growth and egg hatching success of the tropical calanoid copepod, Acartia sinjiensis

The tropical calanoid copepod, Acartia sinjiensis, has good potential for mass culture as a live feed for tropical reef fish larvae. This study was carried out to investigate the effects of temperature and salinity on population growth and egg hatching rates of A. sinjiensis. At a salinity of 30±1 psu, temperature effects on population growth of A. sinjiensis was determined after 8 day culture at eight temperatures of 10, 15, 20, 25, 28, 30, 34 and 38 °C. Adopting similar experimental protocols, effects of salinity on population growth of A. sinjiensis were investigated under nine salinities of 10, 15, 20, 25, 30, 35, 40, 45 and 50 psu, with culture temperature set at 30±1 °C. In addition to population growth experiments, egg hatching rates (%) after 48 h of incubation at various temperature and salinity conditions were also examined. For all experiments, five replicates were set up for each treatment. A. sinjiensis were fed an identical binary algal diet of Tetraselmis chuii and the Tahitian strain of Isochrysis sp. (T-ISO), photoperiod was maintained at 12 L:12D.The results showed that temperature had significant effects on both population growth and egg hatching rates. Population growth at 30 °C (with an initial number of 10 adults/replicate, final mean population reached 677.2±136.6) was significantly higher (p<0.001) than the other temperature treatments except that of 25 °C and 28 °C treatments. The egg hatching rate did not differ significantly (p<0.05) when incubated at temperature 25, 30 and 34 °C although the highest hatching rate was recorded at 34 °C (96.3±2.2%). Salinity also had significant effects on both population growth and egg hatching rates. The highest population growth (final mean population: 669.0±111.3) and egg hatching rate (98.0±1.4%) both occurred at salinity of 30 psu. Population growth at 30 psu was significantly higher (p<0.001) than all other treatments except that of 25 and 35 psu, while there was no significant difference (p<0.05) between egg hatch rates at all salinity levels tested.The results of this study suggest that for maximum population growth and egg hatching success, A. sinjiensis should be cultured at 30 °C with a salinity of 30 psu.

The effects of algal diets on population growth and egg hatching success of the tropical calanoid copepod, Acartia sinjiensis

As natural diets of fish larvae, a number of calanoid copepod species are being investigated for use as live prey in aquaculture hatcheries. One of these, the tropical calanoid copepod, Acartia sinjiensis, has good potential as a live feed for tropical reef fish larvae. However, the rearing techniques for A. sinjiensis require further development to improve productivity. This study was carried out to investigate the population growth and egg hatching success of A. sinjiensis when fed a range of mono-and binary algal diets, including algae in the form of frozen paste.For the population growth experiment, the final A. sinjiensis population, including eggs, nauplii, copepodites and adults, was determined after feeding eight algal diets (two frozen algae, four live monoalgal and two live binary algal diets) for 8 days at temperature 28±1 °C; salinity 34±1 psu and photoperiod 12 L:12 D. Five replicates, with an initial 12 adult A. sinjiensis per replicate, were set up for each treatment. In a separate experiment, effects of diets on egg hatching success were examined after 48 h incubation of eggs produced by A. sinjiensis fed the same eight diets.The results showed that diet significantly affected both population growth and hatching success of A. sinjiensis. Of the diets tested, the binary algal diets were more successful than monoalgal diets, while the frozen algae had little dietary value. The highest population growth was recorded on A. sinjiensis fed a binary diet of Tetraselmis chuii and the Tahitian strain of Isochrysis sp. (T-ISO) (final population: 1091±80), which was significantly higher (P<0.001) than all other diets tested except for the other binary diet of Nannochloropsis sp. and T-ISO (final population: 897±123). Diet also had a significant effect (P<0.001) on egg hatching rate, though the highest hatch rate was recorded with eggs produced by A. sinjiensis fed binary diet Nannochloropsis sp. and T-ISO (88.1±2.1%), this was not significantly different from that of eggs produced by A. sinjiensis fed either T-ISO alone (88.0±1.7%) or the binary algal diet of T. chuii and T-ISO (76.4±7.1%). The results of this study suggest that among the diets tested, a combination of live T. chuii and T-ISO was the best for the culture of A. sinjiensis.

Differences in strains of Isochrysis of importance to mariculture

Algal strains identified as Isochrysis are used widely in commerical mariculture and in rearing marine invertebrates for research purposes. Isochrysis isolates are from several geographic locations, and their relationships to each other are not known. Research reports of Isochrysis growth characteristics, biochemical composition, and nutritional value to invertebrates suggest that a number of these strains differ in terms of their taxonomy and fundamental biology; their practical use as mariculture feeds differs as well. In this note, we discuss origins of some of these strains, describe differences between these from our own and others' research, and recommend that researchers be cognizant of the cultural history of their Isochrysis strains because differences between them will affect their use as mariculture feeds.

FOOD AND FEEDING STRATEGIES IN CULTURE OF LARVAL AND EARLY JUVENILE PURPLE‐HINGE ROCK SCALLOPS, Hinnites multirugosus (GALE)

AbstractThe 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.

COMPARATIVE GROWTH OF Isochrysis galbana PARKE AND Isochrysis aff. galbana, CLONE T‐ISO AT POUR TEMPERATURES AND THREE LIGHT INTENSITIES

AbstractThe 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.

THE EFFECT OF FEED DENSITY ON THE GROWTH OF JUVENILE Mercenaria campechiensis, THE SOUTHERN HARD CLAM1

ABSTRACTA Tahitian strain of Isochrysis sp. was grown in outdoors continuous culture and fed to juvenile Mercenaria campechiensis at five different cell densities: 5times105, 1times105, 5times104, and 1times104 cells/ml; these correspond to inflow algal protein concentrations of 56.01, 11.34, 5.15, and 1.28 μg‐at particulate protein nitrogen (PPN) per liter, respectively. A control group received only 1 μ‐filtered seawater. An additional control consisted of an identical experimental setup receiving 5times104 cells/ml, without animals. Each treatment went to duplicate populations of 100 animals of 0.1 g each. Each population had a whole wet weight of 10.0 g. The total flow rate to each population was 120ml/ min.The filtered seawater, algal culture, and effluent from each shellfish population was sampled daily. All samples were analyzed for nitrite, nitrate, ammonia, urea, dissolved free amino acids, soluble protein, total dissolved nitrogen, and particulate protein.The control treatment of 1 μ‐filtered seawater gave no growth. The most concentrated treatment (56.01 μg‐at PPN/1) gave good growth. However, better growth was obtained at concentrations of 5.75 and 11.34 μg‐at PPN/1. At the flow rates and population weights used, 56.01 μg‐at PPN/1 is too concentrated, resulting in poorer growth. The lease dense treatment (1times104 cells/ml or 1.28 μg‐at PPN/1) resulted in the poorest growth (other than the control). Under the experimental conditions used, this cell density apparently represents a suboptimum ration size.The effect of feed density on the growth of juvenile M. campechiensis is discussed in terms of traditional models of growth as a function of ingested ration.