Marine Microalgal Species Research Articles

Serum-Free Media Formulation Using Marine Microalgae Extracts and Growth Factor Cocktails for Madin-Darby Canine Kidney and Vero Cell Cultures.

The development of serum-free media (SFM) is critical to advance cell culture techniques used in viral vaccine production and address the ethical concerns and contamination risks associated with fetal bovine serum (FBS). This study evaluated the effects of marine microalgal extracts and growth factor cocktails on the activity of Madin-Darby canine kidney (MDCK) and Vero cells. Five marine microalgal species were used: Spirulina platensis (SP), Dunaliella salina (DS), Haematococcus pluvialis (HP), Nannochloropsis salina (NS), and Tetraselmis sp. (TS). DS and SP extracts significantly increased the proliferation rate of both MDCK and Vero cells. DS had a proliferation rate of 149.56% and 195.50% in MDCK and Vero cells, respectively, compared with that in serum-free medium (SFM). Notably, DS and SP extracts significantly increased superoxide dismutase (SOD) activity, which was 118.61% in MDCK cells and 130.08% in Vero cells for DS, and 108.72% in MDCK cells and 125.63% in Vero cells for SP, indicating a reduction in intracellular oxidative stress. Marine microalgal extracts, especially DS and SP, are feasible alternatives to FBS in cell culture as they promote cell proliferation, ensure safety, and supply essential nutrients while reducing oxidative stress.

Bicarbonate concentration influences carbon utilization rates and biochemical profiles of freshwater and marine microalgae.

Selecting the optimal microalgal strain for carbon capture and biomass production is crucial for ensuring the commercial viability of microalgae-based biorefinery processes. This study aimed to evaluate the impact of varying bicarbonate concentrations on the growth rates, inorganic carbon (IC) utilization, and biochemical composition of three freshwater and two marine microalgal species. Parachlorella kessleri, Vischeria cf. stellata, and Porphyridium purpureum achieved the highest carbon removal efficiency (>85%) and biomass production at 6gL-1 sodium bicarbonate (NaHCO3), while Phaeodactylum tricornutum showed optimal performance at 1gL-1 NaHCO3. The growth and carbon removal rate of Scenedesmus quadricauda increased with increasing NaHCO3 concentrations, although its highest carbon removal efficiency (∼70%) was lower than the other species. Varying NaHCO3 levels significantly impacted the biochemical composition of P. kessleri, S. quadricauda, and P. purpureum but did not affect the composition of the remaining species. The fatty acid profiles of the microalgae were dominated by C16 and C18 fatty acids, with P. purpureum and P. tricornutum yielding relatively high polyunsaturated fatty acid content ranging between 14% and 30%. Furthermore, bicarbonate concentration had a species-specific effect on the fatty acid and chlorophyll-a content. This study demonstrates the potential of bicarbonate as an effective IC source for microalgal cultivation, highlighting its ability to select microalgal species for various applications based on their carbon capture efficiency and biochemical composition.

A comprehensive review on versatile microalga Tetraselmis: Potentials applications in wastewater remediation and bulk chemical production

Microalgae are considered sustainable resources for the production of biofuel, feed, and bioactive compounds. Among various microalgal genera, the Tetraselmis genus, containing predominantly marine microalgal species with wide tolerance to salinity and temperature, has a high potential for large-scale commercialization. Until now, Tetraselmis sp. are exploited at smaller levels for aquaculture hatcheries and bivalve production. However, its prolific growth rate leads to promising areal productivity and energy-dense biomass, so it is considered a viable source of third-generation biofuel. Also, microbial pathogens and contaminants are not generally associated with Tetraselmis sp. in outdoor conditions due to faster growth as well as dominance in the culture. Numerous studies revealed that the metabolite compositions of Tetraselmis could be altered favorably by changing the growth conditions, taking advantage of its acclimatization or adaptation ability in different conditions. Furthermore, the biorefinery approach produces multiple fractions that can be successfully upgraded into various value-added products along with biofuel. Overall, Tetraselmis sp. could be considered a potential strain for further algal biorefinery development under the circular bioeconomy framework. In this aspect, this review discusses the recent advancements in the cultivation and harvesting of Tetraselmis sp. for wider application in different sectors. Furthermore, this review highlights the key challenges associated with large-scale cultivation, biomass harvesting, and commercial applications for Tetraselmis sp.

Distribution and Level of Bioactive Monoacylglycerols in 12 Marine Microalgal Species.

Microalgae are currently considered an attractive source of highly valuable metabolites potentially exploitable as anticancer agents, nutraceuticals and cosmeceuticals and for bioenergy purposes. Their ease of culturing and their high growth rates further promote their use as raw material for the production of specialty products. In the present paper, we focused our attention on specific glycerol-based lipid compounds, monoacylglycerols (MAGs), which displayed in our previous studies a selective cytotoxic activity against the haematological U-937 and the colon HCT-116 cancer cell lines. Here, we performed a quali/quantitative analysis of MAGs and total fatty acids (FAs) along with a profiling of the main lipid classes in a panel of 12 microalgal species, including diatoms and dinoflagellates. Our results highlight an inter- and intraspecific variability of MAG profile in the selected strains. Among them, Skeletonema marinoi (strain FE7) has emerged as the most promising source for possible biotechnological production of MAGs.

A Review of Cyclic Imines in Shellfish: Worldwide Occurrence, Toxicity and Assessment of the Risk to Consumers.

Cyclic imines are a class of lipophilic shellfish toxins comprising gymnodimines, spirolides, pinnatoxins, portimines, pteriatoxins, prorocentrolides, spiro-prorocentrimine, symbiomines and kabirimine. They are structurally diverse, but all share an imine moiety as part of a bicyclic ring system. These compounds are produced by marine microalgal species and are characterized by the rapid death that they induce when injected into mice. Cyclic imines have been detected in a range of shellfish species collected from all over the world, which raises the question as to whether they present a food safety risk. The European Food Safety Authority (EFSA) considers them to be an emerging food safety issue, and in this review, the risk posed by these toxins to shellfish consumers is assessed by collating all available occurrence and toxicity data. Except for pinnatoxins, the risk posed to human health by the cyclic imines appears low, although this is based on only a limited dataset. For pinnatoxins, two different health-based guidance values have been proposed at which the concentration should not be exceeded in shellfish (268 and 23 µg PnTX/kg shellfish flesh), with the discrepancy caused by the application of different uncertainty factors. Pinnatoxins have been recorded globally in multiple shellfish species at concentrations of up to 54 times higher than the lower guidance figure. Despite this observation, pinnatoxins have not been associated with recorded human illness, so it appears that the lower guidance value may be conservative. However, there is insufficient data to generate a more robust guidance value, so additional occurrence data and toxicity information are needed.

Biometric and fatty acid profile of the brine shrimp Artemia franciscana enriched with marine microalgal species belonging to prymnesiophytes and eustigmatophytes

Biometric and fatty acid profile of the brine shrimp Artemia franciscana enriched with marine microalgal species belonging to prymnesiophytes and eustigmatophytes

Production of Antioxidants and High Value Biomass from Nannochloropsis oculata: Effects of pH, Temperature and Light Period in Batch Photobioreactors

Nannochloropsis oculata is a marine microalgal species with a great potential as food or feed due to its high pigment, protein and eicosapentaenoic acid contents. However, for such an application to be realized on a large scale, a biorefinery approach is necessary due to the high cost of microalgal biomass production. For example, techno economic analyses have suggested the co-production of food or feed with antioxidants, which can be extracted and supplied separately to the market. The aim of this study was to investigate the effect of cultivation conditions on the antioxidant capacity of Nannochlosopsis oculata extracts, derived with ultrasound-assisted extraction at room temperature, as well as the proximate composition and fatty acid profile of the biomass. A fractional factorial approach was applied to examine the effects of temperature (20–35 °C), pH (6.5–9.5) and light period (24:0, 12:12). At the end of each run, biomass was collected, washed with 0.5M ammonium bicarbonate and freeze-dried. Antioxidant capacity as gallic acid equivalents as well as pigment content were measured in the ethanolic extracts. Optimal conditions were different for productivity and biomass composition. Interesting results regarding the effect of light period (LP) and pH require further investigation, whereas the effect of moisture on the extraction process was confounded with biomass composition. Finally, further data is provided regarding the relation between chlorophyll content and apparent phenolic content using the Folin–Ciocalteu assay, in agreement with our previous work.

Total Phenolic Content, Biomass Composition, and Antioxidant Activity of Selected Marine Microalgal Species with Potential as Aquaculture Feed.

There has been growing interest in microalgal biomolecules for health and cosmetics, as well as in the use of microalgae as aquaculture feed due to the need to replace fishmeal and fish oil with sustainable yet equally nutritious alternatives. Aim of this study is to evaluate the potential of five marine microalgal species, namely Chlorella minutissima, Dunaliella salina, Isochrysis galbana, Nannochloropsis oculata and Tisochrysis lutea, for the co-production of antioxidants and aquaculture feed. Batch cultivation was performed under saturating light intensity and continuous aeration. Freeze-dried biomass was extracted sequentially with water and methanol and evaluated for phenolic content and antioxidant activity, as well as proximate composition and fatty acid profile. Methanolic extracts of C. minutissima presented the highest phenolic content, measured with the Folin–Ciocalteu assay, and antioxidant activity. However, HPLC and LC-MS showed the presence of non-pigment compounds only in T. lutea. Total phenolic content and antioxidant activity were correlated to chlorophyll content. N. oculata and T. lutea were rich in eicosapentaenoic acid and docosahexaenoic acid, respectively, as well as in protein. In conclusion, N. oculata and T. lutea are suitable candidates for further optimization, while the data presented suggest that pigment effects on the Folin–Ciocalteu method require reconsideration.

Anti-biofouling functional surfaces for marine aquaculture

Aquaculture is a global-scale industry providing sustainable production of protein-rich foods required to feed the growing world population. Microalgae cultivation in aquaculture bioreactors can exude extracellular polymeric substances leading to biofouling of culture infrastructure and increased algal disease risk. A structure–behaviour relationship was developed by examining how the surface wettability of a range of functional nanocoatings impacts the extent of biofouling during exposure to continuous microalgae culture under normal hydrodynamic conditions. High-wetting (hydrophilic) surfaces were found to reduce biofouling better than water-repelling (hydrophobic) surfaces. Low toxicity in conjunction with antifouling behaviour was found for pulsed plasma poly(4-vinylpyridine) coated bioreactor surfaces (water contact angle = 38 ± 5°) towards the marine microalgal species Chaetoceros calcitrans, Chaetoceros mulleri, and Tisochrysis lutea (T-Iso), which are commonly grown as aquaculture food.

Comparative Response of Marine Microalgae to H2O2-Induced Oxidative Stress.

There have been growing interests in the biorefining of bioactive compounds from marine microalgae, including pigments, omega-3 fatty acids or antioxidants for use in the nutraceutical and cosmetic sectors. This study focused on the comparative responses of five marine microalgal species from different lineages, including the dinoflagellate Amphidinium carterae, chlorophyte Brachiomonas submarina, diatom Stauroneis sp., haptophyte Diacronema sp. and rhodophyte Rhodella violacea, to exposure during their batch growth to hydrogen peroxide (H2O2). A. carterae returned an enhanced signal with the DPPH assay (8.8µmol Trolox eq/g DW) when exposed to H2O2, which was associated with reduced pigment yields and increased proportions in saturated C16 and C18 fatty acids. B. submarina showed enhanced antioxidant response upon exposure to H2O2 with the DPPH assay (10µmol Trolox eq/g DW), a threefold decrease in lutein (from 2.3 to 0.8mg/g) but a twofold increase in chlorophyll b (up to 30.0mg/g). Stauroneis sp. showed a downward response for the antioxidant assays, but its pigment yields did not vary significantly from the control. Diacronema sp. showed reduced antioxidant response and fucoxanthin content (from 4.0 to 0.2mg/g) when exposed to 0.5mM H2O2. R. violacea exposed to H2O2 returned enhanced antioxidant activity and proportions of EPA but was not significantly impacted in terms of pigment content. Results indicate that H2O2 can be used to induce stress and initiate metabolic changes in microalgae. The responses were however species-specific, which would require further dosage optimisation to modulate the yields of specific metabolites in individual species.

Biodegradable, metal-chelating compounds as alternatives to EDTA for cultivation of marine microalgae

Iron (Fe) is an essential nutrient for microalgal metabolism. The low solubility of Fe in oxic aquatic environments can be a growth-limiting factor for phytoplankton. Synthetic chelating agents, such as ethylenediaminetetraacetic acid (EDTA), are used widely to maintain Fe in solution for microalgal cultivation. The non-biodegradable nature of EDTA, combined with sub-optimal bioavailability of Fe-EDTA complexes to microalgae, indicates opportunity to improve microalgal cultivation practices that amplify production efficiency and environmental compatibility. In the present study, the effects of four organic chelating ligands known to form readily bioavailable organic complexes with Fe in natural aquatic environments were investigated in relation to growth and biochemical composition of two marine microalgae grown as live feeds in shellfish hatcheries (Chaetoceros calcitrans and Tisochrysis lutea). Three saccharides, alginic acid (ALG), glucuronic acid (GLU), and dextran (DEX), as well as the siderophore desferrioxamine B (DFB), were compared to EDTA. Organic ligands characterized by weaker binding capacity for cationic metals (i.e., ALG, GLU, DEX) significantly improved microalgal growth and yields in laboratory-scale static batch cultures or bubbled photobioreactors. Maximal microalgal growth enhancement relative to the control (e.g., EDTA) was recorded for GLU, followed by ALG, with 20–35% increase in specific growth rate in the early stages of culture development of C. calcitrans and T. lutea. Substitution of EDTA with GLU resulted in a 27% increase in cellular omega 3-polyunsaturetd fatty acid content of C. calcitrans and doubled final cell yields. Enhanced microalgal culture performance is likely associated with increased intracellular Fe uptake efficiency combined with heterotrophic growth stimulated by the organic ligands. Based upon these results, we propose that replacement of EDTA with one of these organic metal-chelating ligands is an effective and easily implementable strategy to enhance the environmental compatibility of microalgal cultivation practices while also maximizing algal growth and enhancing the nutritional quality of marine microalgal species commonly cultured for live-feed applications in aquaculture.

A Recommendation for a Pre-Standardized Marine Microalgal Dry Weight Determination Protocol for Laboratory Scale Culture Using Ammonium Formate as a Washing Agent.

Simple SummaryMicroalgae are increasingly recognized as a source of valuable biomass with numerous health benefits. Cleaning of marine microalgal biomass is very crucial for microalgal studies as the salt on the microalgae cells will lead to overestimation of biomass determination. Incomplete washing of salt from microalgae could also interfere with the nutritional analyses. The biomass, especially dry weight, has been utilized for nutritional or compositional evaluation. Although standard methods of marine microalgal dry weight determination are available, these methods did not provide comprehensive details, and the parameters vary among themselves. Without a standard method, a comparison of results among previous studies can be misleading and unreliable. Therefore, the current study aimed to investigate and determine the ideal setting of several parameters in the marine microalgal dry weight determination for laboratory-scale culture. The present findings could assist in developing a standardized protocol to ensure a high quality of biomass for microalgal studies. Microalgal biomass is one of the crucial criteria in microalgal studies. Many reported methods, even the well-established protocol on microalgal dry weight (DW) determination, vary greatly, and reliable comparative assessment amongst published results could be problematic. This study aimed to determine the best condition of critical parameters in marine microalgal DW determination for laboratory-scale culture using four different marine microalgal species. These parameters included the washing process, grades of glass microfiber filter (GMF), GMF pretreatment conditions, washing agent (ammonium formate) concentrations, culture: washing agent ratios (v:v) and washing cycles. GMF grade GF/A with precombustion at 450 °C provided the most satisfactory DW and the highest ash-free dry weight (AFDW)/DW ratio. Furthermore, 0.05 M ammonium formate with 1:2 culture: washing agent ratio and a minimum of two washing cycles appeared to be the best settings of microalgal DW determination. The present treatment increased the AFDW/DW ratio of the four respective microalgae by a minimum of 19%. The findings of this study could serve as a pivotal reference in developing a standardized protocol of marine microalgal DW determination to obtain veracious and reliable marine microalgal DW.

Screening the biochemical composition of some marine microalgal species for feeding Cyclops abyssorum divergens

Recently, the use of microalgal bioproducts in aquaculture research has gotten consideration. The current study aims to screen the biochemical components of three microalgae: Nannochloropsis salina, Chlorella salina and Tetraselmis chuii for using in the feeding of Cyclops abyssorum divergens copepods that are suitable prey for the mouth gape of the cultured fish larvae. The effect of different initial densities of these algal cells used for copepods feeding was determined by estimation of proximate composition, polyunsaturated fatty acids (PUFAs), amino acids (AAs) and enzyme activities of copepods. N. salina showed high protein and lipid contents, while C. salina presented high carbohydrate content. C. salina and T. chuii presented high PUFAs, with proportions of 22.35 and 22.67%, respectively, and are considered as the source of n-3 fatty acids. Also, they had higher concentrations of total AAs (21.46 and 24.14 mg. g−1 dry wt., respectively). The experiment study showed that the C. salina diet at an initial concentration of 1 × 106 cells ml−1 resulted in a maximum increase of copepods population density (503.3%) and high protease and trypsin activities (42.65 and 31.80 U. mg−1 protein, respectively) in copepods. T. chuii diet at an initial concentration of 1 × 106 cells ml−1 resulted in a maximum protein, lipid, PUFAs and AAs contents of copepods. Therefore, C. abyssorum divergens copepods after 18 days feeding with an initial concentration of 1 × 106 C. salina or T. chuii cells ml−1 are the suitable candidate diets in larviculture because they achieved higher productivity and attained better nutritional composition of the copepods.

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.

Cultivation of Mixed Microalgae Using Municipal Wastewater: Biomass Productivity, Nutrient Removal, and Biochemical Content.

Background: Microalgal biotechnology has gained much attention previously. Monoculture algae cultivation has been carried out extensively in the last decades. However, although the mixed microalgae cultivation has some advantageous over pure cultures, there is still a lack of knowledge about the performance of mixed cultures.Objective: In this study, it has been tried to investigate all growth aspects of marine and freshwater microalgal species in a mixed culture and their biological effects on biomass growth and composition based on wastewater nutrient consumption.Material and Methods: Three algal species of Chlorella vulgaris, Scenedesmus obliquus, and Nannochloropsis sp. were cultivated in saline wastewater individually, then the effects of mixing the three strains on biomass productivity, nutrient removal efficiency, chlorophyll, carotenoid, and lipid content were investigated.Results: The obtained results revealed that the mixed culture of three strains showed the highest biomass productivity of 191 mg. L-1.d-1. Also, while there were no significant differences between the performance of mono and mixed culture of algal species in the removal efficiency of wastewater nutrients, the three-strain microalgal mixed culture showed the highest values of 3.5 mg.L-1.d-1 and 5.75 mg.L-1.d-1 in the removal rate of phosphate and nitrate, respectively. In terms of total chlorophyll and carotenoid per produced biomass, however, the mixed culture of three species showed the lowest values of 4.08 and 0.6 mg. g biomass-1, respectively.Conclusions: The finding proves the potential of attractive and economically feasible mixed microalgae cultivation for high percentage nutrient removal and microalgal biomass production.

Toxic marine microalgae and noxious blooms in the Mediterranean Sea: A contribution to the Global HAB Status Report

We review the spatial distribution of toxic marine microalgal species and the impacts of all types of harmful algal events (Harmful Algal Blooms, HABs) in the Mediterranean Sea (MS), including the Black Sea, the Sea of Marmara, coastal lagoons and transitional waters, based on two databases compiled in the Ocean Biogeographic Information System (OBIS). Eighty-four potentially toxic species have been detected in the MS (2,350 records), of which 16 described from these waters between 1860 and 2014 and a few suspected to have been introduced. More than half of these species (46) produce toxins that may affect human health, the remainders ichthyotoxic substances (29) or other types of toxins (9). Nevertheless, toxicity-related events are not frequent in the MS (308 records in 31 years), and mainly consist of impacts on aquaculture, caused by the dinoflagellates Dinophysis and Alexandrium, along with a few actual shellfish poisoning cases. Pseudo-nitzschia blooms are widespread, but domoic acid in shellfish rarely exceeds regulatory levels. Fish kills are probably less sporadic than reported, representing a problem at a few places along the southern MS coasts and in the Ebro River Delta. Since the last decade of the 20th century, blooms of the benthic dinoflagellates Ostreopsis cf. ovata have regularly occurred all along rocky shores of the MS, at times with human health problems caused by toxic aerosol. New records of Gambierdiscus and Fukuyoa, until now reported for the westernmost and easternmost MS coasts, raise concerns about the risk of ciguatera, a syndrome so far known only for subtropical and tropical areas. Recent discoveries are the dinoflagellates Vulcanodinium rugosum, responsible for the presence of pinnatoxins in French lagoons’ shellfish, and the azaspiracid-producers Azadinium spp. Mucilages and discolorations have a major impact on tourism in summer. Reports of toxic species and HABs have apparently increased in the MS over the last half century, which is likely related to the increased awareness and monitoring operations rather than to an actual increase of these phenomena. Indeed, while the case of Ostreopsis appears as a sudden upsurge rather than a trend, no actual increase of toxic or noxious events has so far emerged in intensively studied areas, such as the French and Spanish coasts or the Adriatic Sea. Moreover, some cases of decrease are reported, e.g., for Alexandrium minutum blooms disappearing from the Harbour of Alexandria. Overall, main HAB risks derive from cases of massive development of microalgal biomass and consequent impacts of reduced coastal water quality on tourism, which represents the largest part of the marine economy along the MS coasts.

Digging out molecular markers associated with low salinity tolerance of Nannochloropsis oceanica through bulked mutant analysis

Nannochloropsis oceanica is a marine microalgal species with both economic value and biological importance. It grows fast, contains rich oils, reproduces asexually, holds a small and haploidy genome, and is easy to be modified genetically. However, the genetic study of N. oceanica is scarce. Very less genetic bases of its traits have been deciphered, and no gene has been isolated from it with the function verified simultaneously via either genetic or reverse genetic approaches or both (de novo cloned). Changing medium salinity may aid to control harmful organisms met during large scale cultivation. As a stress, it may also facilitate the accumulation of desirable chemicals including fatty acids. In order to decipher the genetic basis of the low salinity tolerance of N. oceanica, we mutated N. oceanica with Zeocin. In total, five mutant bulks were constructed at equal number of cells, 100 mutants each, which were tolerant to a discontinuous serial of salinities from that of 100% of f/2 to that of a mixture of 4% of f/2 and 94% of BG11. The bulks were genotyped through whole genome re-sequencing and analyzed with bulked mutant analysis (BMA) newly modified from bulked segregant analysis (BSA). In total, 47 SNPs and 112 InDels were found to associate with the low salinity tolerance, and around them a set of low salinity tolerance associating genes were identified. A set of annotatable genes commonly found between control and different salinities indicated that the genes functioning in gene expression, energy metabolism and cellular structure may be involved in the low salinity tolerance. These associating molecular markers and genes around them were not enough for outlining the physiological mechanism underlining the tolerance; however they should aid to improve N. oceanica genetically.

Photosynthesis enhancement in four marine microalgal species exposed to expanded polystyrene leachate.

Due to its widespread use, large amounts of expanded polystyrene (EPS) have been released into the marine environment, where it is broken down into small pieces with large surface areas. As such, chemical additives may be released into the environment, which can affect marine organisms; however, studies of the effects of such additives are lacking. We assessed the effects of leachate from EPS on the photosynthetic activities of four microalgal species (Dunaliella salina, Scenedesmus rubescens, Chlorella saccharophila, and Stichococcus bacillaris). They were exposed to EPS leachate for seven days and their photosynthetic activities were analyzed based on seven parameters. Overall, leachate exposure increased photosynthetic activity in all four species, albeit to different degrees and showing slightly different trends among the seven parameters. Based on chemical analysis, hexabromocyclododecane concentrations were higher in small-fragment leachate, whereas UV326 concentrations were higher in low-concentration-large-sphere leachate; bisphenol-A and total organic carbon showed no major differences among leachates. Thus, we speculate that exposure to trace chemicals influenced microalgal photosynthesis and overall growth. These results support further investigation of the impacts of plastic debris and chemical additives on marine ecosystems and organisms.

Relating nitrogen concentration and light intensity to the growth and lipid accumulation of Dunaliella viridis in a photobioreactor

The marine microalgal species Dunaliella viridis is a promising source of biofuels because of its ability to accumulate neutral lipids without freshwater resources for growth. Less energy for biofuel production from D. viridis may also be required because of the possible extraction of lipids through osmotic lysis. However, there is a lack of experimental data on the growth of D. viridis that can be used in mathematical models for process design. In this study, experiments were performed in a 3.2 L photobioreactor with both pH and temperature tightly controlled at 7.6 and 25 °C, respectively. Levels of neutral lipids, biomass, carbohydrate, chlorophyll, and cell counts of D. viridis were evaluated for ten days at various initial light intensities (100, 300, 400, and 600 μmol photons m−2 s−1) and nitrogen levels (9 and 60 g m−3 as nitrogen). The maximum lipid production observed was 26.9 g m−3 with 3.15 g m−3 day−1 average lipid productivity at an initial nitrogen concentration of 9 g m−3 and initial light intensity of 300 μmol photons m−2 s−1. The data show that D. viridis accumulates cellular carbohydrates as a primary carbon and energy storage product and then converts the cellular carbohydrates into cellular lipids as a secondary storage product when nitrogen is depleted. The on-line light data revealed linear relationships between real-time light intensity and biomass concentration (r = 0.96, p < 0.01) and between real-time light intensity and chlorophyll a concentration (r = − 0.89, p < 0.01), suggesting the possible use of real-time light data as a method for in situ quantification of biomass concentration and chlorophyll a concentration.

Semi-continuous anaerobic digestion of the marine micro-algal species I. galbana and D. salina grown under low and high sulphate conditions

Anaerobic digestion of marine micro-algae is a necessary step for their incorporation into the future portfolio of biofuels. Digestion of marine feedstocks can pose operational issues associated with competition and toxicity to the microbial consortium. This research examined the marine species Isochrysis galbana and Dunaliella salina continuously cultivated in a tubular photobioreactor using a low sulphate medium; D. salina was also cultivated with a high sulphate medium (4.7 g SO4 L−1). Harvested micro-algal biomass was used as feedstock in semi-continuous digestion with a salt-adapted inoculum. Stable operation was achieved with reasonable specific methane production (SMP) despite a short (15-day) retention time. SMP for I. galbana and D. salina was 0.244 and 0.233 L CH4 g−1 volatile solids (VS), with VS destruction 32% and 48% respectively. SMP ranged from 62 to 94% of the biochemical methane potential, but was only 32–49% of theoretical methane yields, indicating pre-treatments may be beneficial. Changing from low to high sulphate D. salina reduced the SMP to 0.193 L CH4 g−1 VS with a rise in H2S production. Under semi-continuous digestion, evidence for sulphide precipitation and oxidation was observed, which were not seen in batch analyses. This highlights the importance of conducting continuous rather than batch studies, to avoid overlooking these effects.