Marine Microalgal Strains Research Articles

Evaluation of selected tropical marine microalgal cultures for use in biophotovoltaic platforms

In this study, the bioelectrical power generation potential of four tropical marine microalgal strains native to Malaysia was investigated using BPV platforms. Chlorella UMACC 258 produced the highest power density (0.108 mW m−2), followed by Halamphora subtropica UMACC 370 (0.090 mW m−2), Synechococcus UMACC 371 (0.065 mW m−2) and Parachlorella UMACC 245 (0.017 mW m−2). The chlorophyll-a (chl-a) content was examined to have a linear positive relationship with the power density (p < 0.05). The photosynthetic performance of strains was studied using the pulse-amplitude modulation (PAM) fluorometer; parameters measured include the following: maximum quantum efficiency (Fv/Fm), alpha (α), maximum relative electron transport rate (rETRmax), photo-adaptive index (Ek) and non-photochemical quenching (NPQ). The Fv/Fm values of all strains, except Synechococcus UMACC 371, ranged between 0.37 and 0.50 during exponential and stationary growth phases, suggesting their general health during those periods. The low Fv/Fm value of Synechococcus UMACC 371 was possibly caused by the presence of background fluorescence from phycobilisomes or phycobiliproteins. Electrochemical studies via cyclic voltammetry (CV) suggest the presence of electrochemically active proteins on the cellular surface of strains on the carbon anode of the BPV platform, while morphological studies via field emission scanning electron microscope (FESEM) imaging verify the biocompatibility of the biofilms on the carbon anode.Key points• Maximum power output of 0.108 mW m−2 is recorded by Chlorella UMACC 258• There is a positive correlation between chl-a content and power output• Proven biocompatibility between biofilms and carbon anode sans exogenous mediators

Bacterial exudates as growth‐promoting agents for the cultivation of commercially relevant marine microalgal strains

AbstractIn laboratory and industrial cultivation of marine microalgae, it is customary to enrich cultures with macronutrients (N, P), chelated trace metals, and vitamins at ~104× concentrations found in nature to obtain high culture densities. Other naturally occurring growth‐promoting compounds found in local seawater are not enriched and remain at environmental concentrations. Microalgae may thus be deprived of the mutualistic contributions of co‐occurring microorganisms with which they have evolved complex chemical relationships. In the present study, we assess the direct (mixed bacteria–microalgae cultivation) and indirect (exposure to exudates only, without physical contact) effects of 10 bacterial strains on the growth of five marine microalgal strains used as feeds in marine aquaculture hatcheries. Bacterial strains were selected based upon previously reported growth‐promoting characteristics in plants or microalgae, or known release of probiotics. Our experiments demonstrate superior stimulation of microalgal growth by bacterial exudates, and without the presence of the bacteria that produced these exudates. However, response to bacterial exudate enrichment was dependent upon the microalgae strain and bacterial pairing. Exudates fromBacillus,Mesorhizobium, andPhaeobacterstrains were most effective, with 22%–69% increases in microalgal specific growth rate. Such findings indicate that bacterial exudates accelerate rate‐limiting processes governing nutrient acquisition, assimilation, or anabolism, and possibly algal release of exopolymeric substances. Maximal cell density, however, remained constrained by macronutrient limitation. Scaled‐up trials in an oyster hatchery confirmed the practical benefit of bacterial exudate culture medium enrichment and demonstrated the suitability of exudate‐enriched microalgae to feed hatchery‐reared bay scallops. This work presents a promising strategy to improve microalgal culture media formulations using bacterial exudate components as growth promoters, and is the first such study to identify specific pairings with relevance for aquaculture production.

Marine microalgae for outdoor biomass production-A laboratory study simulating seasonal light and temperature for the west coast of Sweden.

At Nordic latitudes, year-round outdoor cultivation of microalgae is debatable due to seasonal variations in productivity. Shall the same species/strains be used throughout the year, or shall seasonal-adapted ones be used? To elucidate this, a laboratory study was performed where two out of 167 marine microalgal strains were selected for intended cultivation at the west coast of Sweden. The two local strains belong to Nannochloropsis granulata (Ng) and Skeletonema marinoi (Sm142). They were cultivated in photobioreactors and compared in conditions simulating variations in light and temperature of a year divided into three growth seasons (spring, summer and winter). The strains grew similarly well in summer (and also in spring), but Ng produced more biomass (0.225 vs. 0.066 g DW L-1 day-1 ) which was more energy rich (25.0 vs. 16.6MJ kg-1 DW). In winter, Sm142 grew faster and produced more biomass (0.017 vs. 0.007 g DW L-1 day-1 ), having similar energy to the other seasons. The higher energy of the Ng biomass is attributed to a higher lipid content (40 vs. 16% in summer). The biomass of both strains was richest in proteins (65%) in spring. In all seasons, Sm142 was more effective in removing phosphorus from the cultivation medium (6.58 vs. 4.14 mg L-1 day-1 in summer), whereas Ng was more effective in removing nitrogen only in summer (55.0 vs. 30.8mg L-1 day-1 ). Our results suggest that, depending on the purpose, either the same or different local species can be cultivated, and are relevant when designing outdoor studies.

Effect of pluronic block polymers and N-acetylcysteine culture media additives on growth rate and fatty acid composition of six marine microalgae species

The efficiency of microalgal biomass production is a determining factor for the economic competitiveness of microalgae-based industries. N-acetylcysteine (NAC) and pluronic block polymers are two compounds of interest as novel culture media constituents because of their respective protective properties against oxidative stress and shear-stress-induced cell damage. Here we quantify the effect of NAC and two pluronic (F127 and F68) culture media additives upon the culture productivity of six marine microalgal species of relevance to the aquaculture industry (four diatoms-Chaetoceros calcitrans, Chaetoceros muelleri, Skeletonema costatum, and Thalassiosira pseudonana; two haptophytes-Tisochrysis lutea and Pavlova salina). Algal culture performance in response to the addition of NAC and pluronic, singly or combined, is dosage- and species-dependent. Combined NAC and pluronic F127 algal culture media additives resulted in specific growth rate increases of 38%, 16%, and 24% for C. calcitrans, C. muelleri, and P. salina, respectively. Enhanced culture productivity for strains belonging to the genus Chaetoceros was paired with an ~27% increase in stationary-phase cell density. For some of the species examined, culture media enrichments with NAC and pluronic resulted in increased omega-3-fatty acid content of the algal biomass. Larval development (i.e., growth and survival) of the Pacific oyster (Crassostrea gigas) was not changed when fed a mixture of microalgae grown in NAC- and F127-supplemented culture medium. Based upon these results, we propose that culture media enrichment with NAC and pluronic F127 is an effective and easily adopted approach to increase algal productivity and enhance the nutritional quality of marine microalgal strains commonly cultured for live-feed applications in aquaculture.Key points• Single and combined NAC and pluronic F127 culture media supplementation significantly enhanced the productivity of Chaetoceros calcitrans and Chaetoceros muelleri cultures.• Culture media enrichments with NAC and F127 can increase omega-3-fatty acid content of algal biomass.• Microalgae grown in NAC- and pluronic F127-supplemented culture media are suitable for live-feed applications.

Improvement of carotenoid extraction from a recently isolated, robust microalga, Tetraselmis sp. CTP4 (chlorophyta).

In recent years, there has been increasing consumer interest in carotenoids, particularly of marine sustainable origin with applications in the food, cosmeceutical, nutritional supplement and pharmaceutical industries. For instance, microalgae belonging to the genus Tetraselmis are known for their biotechnologically relevant carotenoid profile. The recently isolated marine microalgal strain Tetraselmissp. CTP4 is a fast-growing, robust industrial strain, which has successfully been produced in 100-m3 photobioreactors. However, there are no reports on total carotenoid contents from this strain belonging to T. striata/convolutae clade. Although there are several reports on extraction methods targeting chlorophytes, extraction depends on the strength of cell coverings, solvent polarity and the nature of the targeted carotenoids. Therefore, this article evaluates different extraction methods targeting Tetraselmissp. CTP4, a strain known to contain a mechanically resistant theca. Here, we propose a factorial experimental design to compare extraction of total carotenoids from wet and freeze-dried microalgal biomass using four different solvents (acetone, ethanol, methanol or tetrahydrofuran) in combination with two types of mechanical cell disruption (glass beads or dispersion). The extraction efficiency of the methods was assessed by pigment contents and profiles present in the extracts. Extraction of wet biomass by means of glass bead-assisted cell disruption using tetrahydrofuran yielded the highest amounts of lutein and β-carotene (622 ± 40 and 618 ± 32µgg-1DW, respectively). Although acetone was slightly less efficient than tetrahydrofuran, it is preferable due to its lower costs and toxicity.

The Strategies for the Production of Biodiesel through Eco-Friendly Microalgal Systems

The fast depleting energy sources and other environmental concerns, like carbon emissions, have led the scientific community on a race against time to find an ecofriendly, sustainable and renewable source of energy. Biofuels obtained from domestic used materials cannot practically satisfy the existing demand for an industrial fuel. Biodiesel is mono-alkyl esters of vegetable oils or animal fats. The major advantage of biodiesel is that it can be used directly into existing engines without any modifications. One of the potential sources for renewable biodiesel production which can effectively supply biodiesel for international and industrial demand is microalgae. Besides production of biofuels microalgae have been seen as a potential source for a number of areas including pharmaceuticals, nutrition and aquaculture. This review discusses on the different aspects, challenges and current scenario in the biodiesel production from microalgae. Cultivation of a high yielding marine microalgal strain in a very economical and well scrutinised open raceway pond could prove to be the key to future of energy sector. Various lipid enhancement methods and proposed culture methods are also discussed. On an industrial perspective, a well-engineered and continuously monitored open raceway pond for cultivation of marine micro algae seems to be a promising economically viable method for production of biofuel.

Screening of trace metal elements for pollution tolerance of freshwater and marine microalgal strains: Overview and perspectives

Microalgae represent a putative solution to decontaminate metal polluted aquatic sites (phycoremediation). Seven different freshwater and seawater microalgal strains (Nannochloropsis sp., Dunaliella sp., Phaeodactylum sp., Chlorella sp., Isochrysis sp., Euglena sp. and Chlorogonium sp.) were exposed to five metals (Cu, Zn, As (III), Fe and Ni) at three concentrations each, simulating highly polluted sites. The experiment was conducted for a week; the survival ability of each strain and the photosynthetic pigments content (chlorophyll a, b and carotenoids) were evaluated, together with the Optical Density of each culture, pH, growth rate and biomass. Results highlighted different resistance patterns towards metals characterizing each algal strain, and the tolerance of all the microalgal strains towards arsenite. For the first time, the metal resistance pattern of Chlorogonium sp. was evaluated. Finally, our Euglena sp. and Dunaliella sp. strains were considered among the most promising organisms for phycoremediation of freshwater and seawater polluted sites respectively.

3D Printing of Functional Microalgal Silk Structures for Environmental Applications.

Silk protein-based hydrogel materials suitable for hosting living microalgae due to the biocompatibility and ambient conditions gelation were developed. The silk was selected due to its robust mechanical properties, safe and compatible utility, green sourcing, and versatile materials formation. Through a series of assessments the mechanics and gelation kinetics of the hydrogel materials were optimized for three-dimensional (3D) printing. Silk hydrogel structures containing a marine microalgal strain, Platymonas sp. were printed and these structures supported cell proliferation for at least 4 weeks and consistent photosynthetic activity for more than 90 days, the limits of the study time frame. This long-term cell viability and function suggest that these systems may be suitable for a broad range of applications, such as oxygen replenishment and carbon dioxide reduction toward a green, healthier indoor environment.

Development of a culture protocol for Rhodomonas sp. Hf-1 strain through laboratory trials

Rhodomonas sp. Hf-1 is a marine microalgal strain with a high nutritional value. In order to produce this microalga effectively and inexpensively in a hatchery, its production protocol was reexamined through several culture trials. Firstly, it was found that the Hf-1 strain required nitrogen, phosphorus, iron, manganese and vitamin B12. The optimal nitrogen source was urea. Based on these results, a new medium, MU–SW, was formulated from agricultural fertilizers. Secondly, MU–SW medium was verified at production scale, in which satisfactory growth of the Hf-1 strain was obtained. The cell density reached approximately 3.0 × 106 cells ml−1, and five harvest cycles at 4-day intervals could be achieved. The high unsaturated fatty acid content of the harvested cells fluctuated in the following ranges: C18:2n-6, 19.8–25.2%; C18:3n-6, 8.7–15.2%; C20:4n-6, 2.0–4.6%; C20:5n-3, 8.2–11.3% and C22:6n-3, 5.6–7.3%. This study provides the baseline conditions for introducing the Hf-1 strain into an aquaculture food chain.

Mass harvesting of marine microalgae using different techniques

The marine species microalgae are an attractive source of feedstock for biofuel production and other bio-products such as omega-3 fatty acids and aquaculture feeds. The prevailing main nutrients in seawater environment for their growth are believed to be more economical than freshwater in terms of their cultivation system which may lead to low cost for upstream processing. Hence, marine microalgae provide attractive potential to be further explored. However, harvesting process of microalgae is known to be too costly because of their dilute nature that accounts for 20–30% of the overall production costs rendering using microalgae as the raw material not economically feasible. Currently the various harvesting methods including centrifugation, flocculation, flotation, filtration and magnetic separation had been applied to harvest marine species. For instance, harvesting by electrolytic means that require less energy to harvest marine species compared to the freshwater species. This can potentially help to reduce the challenges related to the exploitation of microalgae biomass. However, different techniques have their own advantages and drawbacks, whereas their cost and energy requirement vary accordingly depending on the selection of marine microalgal strains, equipment used and/or the choice of harvesting aid (flocculants, surfactant). Thus far, no single technique may still be proposed. Therefore, this paper aims to provide further details of each method used focusing only for marine species of microalgae with their respective advantages and disadvantages.

Lipid accumulation and CO2 utilization of two marine oil-rich microalgal strains in response to CO2 aeration

Biological CO2 sequestration by microalgae is a promising and environmentally friendly technology applied to sequester CO2. The characteristics of neutral lipid accumulation by two marine oil-rich microalgal strains, namely, Isochrysis galbana and Nannochloropsis sp., through CO2 enrichment cultivation were investigated in this study. The optimum culture conditions of the two microalgal strains are 10% CO2 and f medium. The maximum biomass productivity, total lipid content, maximum lipid productivity, carbon content, and CO2 fixation ability of the two microalgal strains were obtained. The corresponding parameters of the two strains were as follows: ((142.42±4.58) g/(m2·d), (149.92±1.80) g/(m2·d)), ((39.95±0.77)%, (37.91±0.58)%), ((84.47±1.56) g/(m2·d), (89.90±1.98) g/(m2·d)), ((45.98±1.75)%, (46.88±2.01)%), and ((33.74±1.65) g/(m2·d), (34.08±1.32) g/(m2·d)). Results indicated that the two marine microalgal strains with high CO2 fixation ability are potential strains for marine biodiesel development coupled with CO2 emission reduction.

Bioprospecting North Atlantic microalgae with fast growth and high polyunsaturated fatty acid (PUFA) content for microalgae-based technologies

Microalgae are considered to be an important and sustainable alternative to fish oil as a source for the polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Due to their health benefits, there is an increasing interest in the commercial application of these fatty acids (FA) to health and dietary products, and to aquaculture feeds. However, FA from microalgae are still expensive to produce compared to fish or plant oils. With only a few microalgal strains being cultivated on a large scale for commercial PUFA production, prospecting for new, robust and fast-growing strains with increased PUFA content is essential in order to reduce production costs. Microalgae from northern high latitudes, exposed to cold temperatures, may be especially promising candidates as previous studies have shown increasing unsaturation of FA in response to decreasing growth temperatures in different microalgae, most likely to maintain membrane fluidity and function. We have designed a screening pipeline, targeting a focused search and selection for marine microalgal strains from extreme North Atlantic locations with high robustness and biomass production, and increased levels of EPA and DHA. The pipeline includes a rational sampling plan, isolation and cultivation of clonal strains, followed by a batch growth experiment designed to obtain information on robustness, growth characteristics, and the FA content of selected isolates during both nutrient replete exponential cultivation and nutrient limited stationary cultivation. A number of clonal cultures (N=149) have been established, and twenty of these strains have been screened for growth and FA content and composition. Among those strains, three showed growth rates ≥0.7d−1 at temperatures of 15°C or below, and high amounts of EPA (>3% DW), suggesting their potential as candidates for large scale production.

Cultivation study of the marine microalga Picochlorum oculatum and outdoor deployment in a novel bioreactor for high-density production of algal cell mass

Microalgae are considered a promising source of renewable diesel and jet fuel. Currently, large-scale microalgae cultivations are performed in open ponds because of their low capital and operating costs, but they generally suffer from low cell mass yield and high risk of contamination. A novel, cost-effective, and modular horizontal bioreactor (HBR) for algae cultivation was developed, as described in the present study. The HBR was designed to keep costs low and was engineered to minimize water and energy use while enhancing CO2 and nutrient uptake. The selected marine microalgal strain, Picochlorum oculatum (Nannochloris oculata), has shown potential for biofuel production. A series of controlled indoor growth experiments was first performed to identify the appropriate P. oculatum growth conditions before demonstrating the HBR performance. Supplying CO2 continuously or by pH-control (pulsed) did not affect culture progression. Growth on urea and nitrate yielded comparable results, while ammonium was less effective. Varying inoculum size from 10% to 15% or 20% had no significant effect on lag time and final cell concentration and comparable growth was measured in the 7–8 pH range. The 150-L HBR's performance was successfully demonstrated outdoors by growing P. oculatum at the identified growth conditions selected to reduce operating costs (pH-controlled CO2, pH 7.5, 10% inoculum, and nitrate). High-density growth was achieved without any contamination issues in outdoor HBR cultivations over 68 days in central Florida during two consecutive growth cycles.

Effects of microalgal polyunsaturated fatty acid oil on body weight and lipid accumulation in the liver of C57BL/6 mice fed a high fat diet.

Dietary polyunsaturated fatty acids (PUFAs), which are abundant in marine fish oils, have recently received global attention for their prominent anti-obesogenic effects. Among PUFAs, eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), which are n-3 long-chain PUFAs widely referred to as omega-3 oils, were reported to prevent the development of obesity in rodents and humans. In the present study, we evaluated the anti-obesity effects of microalgal oil on high-fat induced obese C57BL/6 mice, compared with commercial omega-3 fish oil and vegetable corn oil. Microalgal oil is an inherent mixture of several PUFAs, including EPA, DHA and other fatty acids produced from a marine microalgal strain of Thraustochytriidae sp. derived mutant. It was found to contain more PUFAs (>80%) and more omega-3 oils than commercial omega-3 fish oil (PUFAs >31%) and corn oil (PUFAs 59%). All three types of oils induced weight loss in high-fat-induced obese mice, with the loss induced by microalgal oil being most significant at 9 weeks (10% reduction). However, the oils tested did not improve blood lipid levels, although microalgal oil showed an apparent inhibitory effect on lipid accumulation in the liver. These findings may be attributed to the higher PUFA content, including omega-3 oils of microalgal oil than other oils. Collectively, these findings suggest that microalgal oil, derived from Thraustochytriidae sp. derived mutant, is a prominent candidate for replacement of omega-3 fish oils based on its apparent anti-obesity effect in vivo.

Unlocking nature's treasure-chest: screening for oleaginous algae.

Micro-algae synthesize high levels of lipids, carbohydrates and proteins photoautotrophically, thus attracting considerable interest for the biotechnological production of fuels, environmental remediation, functional foods and nutraceuticals. Currently, only a few micro-algae species are grown commercially at large-scale, primarily for “health-foods” and pigments. For a range of potential products (fuel to pharma), high lipid productivity strains are required to mitigate the economic costs of mass culture. Here we present a screen concentrating on marine micro-algal strains, which if suitable for scale-up would minimise competition with agriculture for water. Mass-Spectrophotometric analysis (MS) of nitrogen (N) and carbon (C) was subsequently validated by measurement of total fatty acids (TFA) by Gas-Chromatography (GC). This identified a rapid and accurate screening strategy based on elemental analysis. The screen identified Nannochloropsis oceanica CCAP 849/10 and a marine isolate of Chlorella vulgaris CCAP 211/21A as the best lipid producers. Analysis of C, N, protein, carbohydrate and Fatty Acid (FA) composition identified a suite of strains for further biotechnological applications e.g. Dunaliella polymorpha CCAP 19/14, significantly the most productive for carbohydrates, and Cyclotella cryptica CCAP 1070/2, with utility for EPA production and N-assimilation.

PhytoREF: a reference database of the plastidial 16S rRNA gene of photosynthetic eukaryotes with curated taxonomy.

Photosynthetic eukaryotes have a critical role as the main producers in most ecosystems of the biosphere. The ongoing environmental metabarcoding revolution opens the perspective for holistic ecosystems biological studies of these organisms, in particular the unicellular microalgae that often lack distinctive morphological characters and have complex life cycles. To interpret environmental sequences, metabarcoding necessarily relies on taxonomically curated databases containing reference sequences of the targeted gene (or barcode) from identified organisms. To date, no such reference framework exists for photosynthetic eukaryotes. In this study, we built the PhytoREF database that contains 6490 plastidial 16S rDNA reference sequences that originate from a large diversity of eukaryotes representing all known major photosynthetic lineages. We compiled 3333 amplicon sequences available from public databases and 879 sequences extracted from plastidial genomes, and generated 411 novel sequences from cultured marine microalgal strains belonging to different eukaryotic lineages. A total of 1867 environmental Sanger 16S rDNA sequences were also included in the database. Stringent quality filtering and a phylogeny-based taxonomic classification were applied for each 16S rDNA sequence. The database mainly focuses on marine microalgae, but sequences from land plants (representing half of the PhytoREF sequences) and freshwater taxa were also included to broaden the applicability of PhytoREF to different aquatic and terrestrial habitats. PhytoREF, accessible via a web interface (http://phytoref.fr), is a new resource in molecular ecology to foster the discovery, assessment and monitoring of the diversity of photosynthetic eukaryotes using high-throughput sequencing.

Characterization of Amphora sp., a newly isolated diatom wild strain, potentially usable for biodiesel production.

Microalgae as feedstock for biofuel production have attracted serious consideration as an important sustainable source of energy. For biodiesel production with microalgae, a series of consecutive processes should be performed as selection of adequate microalgal strains, mass culture, cell harvesting, oil extraction and transesterification. The aim of this study was to investigate the growth and lipid accumulation of a new isolated marine microalgal strain by optimizing culture medium composition and applying different stressful culture conditions. Microalga CTM 20023 was isolated from the evaporating salt-ponds at Sfax, Tunisia, using serial-dilution technique from enriched cultures. Phylogenetic analysis based on SSU rDNA and rbcL-3P sequences attributed this isolate to a new species of the Amphora genus. This wild strain possesses rapid gravity sedimentation of 2.91 m h(-1), suitable for an easy and low-cost biomass harvest. The optimization of the composition of the culture medium through statistical experimental designs improved the specific growth rate of Amphora sp. from 0.149 to 0.262 day(-1) and increased its 15-day culture biomass production from 465 to 2200 mg L(-1) (dw) and its lipid content from 140 to 370 mg g(-1) (dw). Highest biomass productivity of 178 mg L(-1) day(-1) was achieved at the 10th day of culture. Highest lipid content of 530 mg g(-1) (dw) was obtained under phosphorus starvation and 64.34% of these lipids were saturated fatty acids. A first growth stage, in optimized condition, would thus offer the maximum productivity for an algal biomass feed stream, followed by second stressful stage for lipid accumulation, thus suitable for biodiesel production.

Influence of growth phase and nutrient source on fatty acid composition of Isochrysis galbana CCMP 1324 in a batch photoreactor

The marine microalgal strain Isochrysis galbana CCMP 1324 was cultured in Walne medium to examine the changes in lipid bodies and fatty acid composition, with special emphasis on different iron, nitrogen, and phosphorus sources associated changes in the growth kinetic parameters and fatty acid composition. All the experiments were performed at 20 °C, with the culture medium at pH 9.0, a specific rate of air supply of 1.0 vv −1 m −1 and a continuous illumination of 68 μEm −2 s −1. Lipid bodies in I. galbana CCMP 1324 were observed at different growth phase in Walne medium by light and transmission electron microscopy. Lipid granules from 0.4 to 2.0 μm were observed from exponential growth stage to stationary stage. The I. galbana CCMP 1324 had the highest contents of saturated and monounsaturated fatty acids (SFA + MUFA) as well as polyunsaturated fatty acids (PUFA) in the early stationary phase. The n-3/n-6 value reached a maximal value of 4.9 in the late stationary phase. The Walne medium could be a good iron, nitrogen and phosphorus sources to culture I. galbana to maximize PUFA production and harvesting the biomass at stationary phase may enable better yields in lipid and PUFA composition. The ratio of SFA + MUFA to PUFA was highest in NH 4NO 3 modified Walne culture and minimal in Walne culture. The n-3 PUFA was predominant in Walne culture. A compromise between the docosahexaenoic acid (DHA) production and growth kinetics can be achieved by using NH 4NO 3 as N-source in modified Walne medium, which provides the greatest value of DHA production (15.6% of total fatty acids) with the highest maximum specific growth rate (2.34 per day) even though the microalgal cell productivity (43.1 mg l −1 per day) is not the highly attained. The approaches presented in this study could be employed for the design of pilot or full-scale photoreactor for PUFA commercial productions by I. galbana CCMP 1324.

Evaluation of the sensitivity of marine microalgal strains to the heavy metals, Cu, As, Sb, Pb and Cd

The sensitivity of nine marine microalgal species (consisting of five divisions and seven genera) to the five heavy metals, Cu(II), As(V), Sb(III), Pb(II) and Cd(II) was studied by using a fluorometric growth-inhibition assay with 96-well microplates. The algal strains studied were Cylindrotheca sp. and the LPP group that respectively characterize aggregating and filamentous types, and Chlorococcum littorale, Chlorococcum sp., Isochrysis galbana, Tetraselmis tetrathele, Heterocapsa sp., Synechococcus sp. and Prasinococcus sp. for types that occur as single cells. A good linear relationship was observed between the chlorophyll a concentration and intensity of chlorophyll fluorescence (485-nm excitation filter and 645-nm emission filter) when the chlorophyll a concentration was within the range of 0.10–5.0 μg ml −1. A starting cell concentration of 0.10 or 0.25 μg Chl a ml −1 was therefore selected. In accordance with OECD 201 standard procedures, the IC 50 value (concentration of a metal producing 50% growth inhibition relative to the control) was determined 72 h after adding a heavy metal by using the biomass integral. The microplate toxicity test used in this study is considered to be applicable to diverse algae, not only enumerating species but also hardly enumerating ones.

Effects of salinity on cell growth and docosahexaenoic acid content of the heterotrophic marine microalga Crypthecodinium cohnii

The effects of salinity on cell growth and docosahexaenoic acid (DHA) content of three marine microalgal strains, Crythecodinium cohnii ATCC 30556, C. cohnii ATCC 50051 and C. cohnii RJH were investigated. The lag phases of the three strains increased with increasing salinity in Porphyridium medium. The specific growth rate of C. cohnii ATCC 30556 was the highest at 9 g L−1 NaCl while the other two strains had their highest specific growth rates at 5 g L−1 NaCl. The highest cell dry weight concentrations of 2.51 g L−1 and 1.56 g L−1 were achieved at 9 g L−1 NaCl for C. cohnii ATCC 30556 and ATCC 50051, respectively, while the highest dry weight concentration of 2.49 g L−1 was achieved at 5 g L−1 NaCl for C. cohnii RJH. The highest cell growth yield coefficient on glucose was 0.5 g g−1 for both C. cohnii ATCC 30556 and C. cohnii RJH and 0.45 g g−1 for C. cohnii ATCC 50051. All three strains responded to the change of salinity by modifying their cellular fatty acid compositions. At 9 g L−1 NaCl, C. cohnii ATCC 30556 had the highest total fatty acid content and DHA (C22:6) proportion. In contrast, C. cohnii ATCC 50051 and C. cohnii RJH had the highest DHA content at 5 g L−1 NaCl. C. cohnii ATCC 30556 and ATCC 50051 had the highest DHA yield (131.55 and 68.24 mg L−1 respectively) at 9 g L−1 NaCl while C. cohnii RJH had the highest DHA yield (128.83 mg L−1) at 5 g L−1 NaCl.