Marine Microalgae Research Articles

AlgaeClass_Net: Optimizing Few-Shot Marine Microalgae Classification with Multi-Scale Feature Enhancement Network

AlgaeClass_Net: Optimizing Few-Shot Marine Microalgae Classification with Multi-Scale Feature Enhancement Network

Growth and Lipid Production of Marine Microalgae Tetraselmis Chuii Cultured in Different Phosphorus Concentrations

Lipid produced in the marine microalgae, Tetraselmis chuii has the potential to be processed into biofuels which can replace the use of fossil fuels that contributes to the global warming on earth. The purpose of this study was to determine the effects of phosphorus on lipid production in Tetraselmis chuii. Therefore, Tetraselmis chuii was cultured under normal concentration of phosphorus in the Conway medium. The cell was harvested on the fourth day and then transferred and cultured under different concentrations of phosphorus (10g, 15g, 20g, 25g and 30g of NaH2 PO4 .2H2 O in 1 L Conway medium). The cell density and optical density analysis of the culture were analyzed daily whereas the biomass (dry weight) analysis and lipid extractions were carried out on every alternate day. Result of the study showed that the highest lipid production in Tetraselmis chuii was achieved on day 4 in the phosphorus sufficient culture medium (25 g/L of NaH2 PO4 .2H2 O). Under the deficiency of phosphorus in the culture medium especially when the growth reached the stationary phase, more lipids accumulated in all the treatments. Therefore, our findings illustrated that phosphorus was important in regulating the growth of Tetraselmis chuii and the lipid accumulation was higher when the growth of Tetraselmis chuii was limited by the depleted phosphorus. In addition, total lipid yields also increased with the presence of excess phosphorus in the culture medium.

Exopolysaccharide from marine microalgae belonging to the Glossomastix genus: fragile gel behavior and suspension stability

ABSTRACT With the aim to find new polysaccharides of rheological interest with innovated properties, rhamnofucans produced as exopolysaccharides (EPS) in a photobioreactor (PBR) and an airlift bioreactor (ABR) by the marine microalgae Glossomastix sp. RCC3707 and RCC3688 were fully studied. Chemical characterizations have been conducted (UHPLC – MS HR). Analyses by size-exclusion chromatography (SEC) coupled online with a multiangle light scattering detector (MALS) and a differential refractive index detector showed the presence of large structures with molar masses higher than 106 g.mol−1. The rheological studies of these EPS solutions, conducted at different concentrations and salinities, have evidenced interesting and rare behavior characteristic of weak and fragile hydrogels i.e. gel behavior with very low elastic moduli (between 10−2 and 10 Pa) and yield stresses (between 10−2 and 2 Pa) according to the EPS source, concentration, and salinity. These results were confirmed by diffusing wave spectroscopy. Finally, as one of potential application, solutions of EPS from Glossomastix sp. have evidenced very good properties as anti-settling stabilizers, using microcrystalline cellulose particles as model, studied by multiple light scattering (MLS) with utilization in cosmetic or food industry. Compared to alginate solution with same viscosity for which sedimentation is observed over few hours, microalgae EPS leads to a stable suspension over few days.

Preservation and hydrocarbon generation potential of microalgal organic matter in product aggregates induced by Chlorella sp. MASCC-0008

Microalgae are one of the important sources of organic matter which, if preserved well in sediments, can generate hydrocarbons during burial diagenesis. However, the preservation mode of microalgal organic matter within product aggregates induced by marine microalgae has rarely been examined. Herein, a strain of eukaryotic marine microalgae, Chlorella sp. MASCC-0008, was used to conduct biomineralization experiments in an f/2 medium with a 0.02 mol/L Ca2+ ion concentration and various Mg2+ ion concentrations of 0.05, 0.06, 0.07 and 0.10 mol/L. It was found that the soluble organic matter of the microalgae contains amino acids and fulvic acids which can attract and absorb cations. With an increase in Mg2+ ion concentration in the experimental group with Chlorella sp., the aragonite content of the mineral precipitates increased whereas the calcite content decreased. In contrast, calcite was the sole mineral precipitated in the control experiments with no Chlorella sp.. Due to the porous structure of minerals, their organic matters were preferred to be preserved in aragonite aggregates compared to calcite aggregates. The TOC content of the minerals aggregates is the highest (0.45%) and the hydrocarbon generation potential (S1 + S2) of organic matter is the greatest (3.66 mg/g) in those precipitated in the medium with a Mg2+ ion concentration of 0.10 mol/L. Microalgal organic matter has significant hydrocarbon generation potential due to its effective preservation in the product aggregates formed by the microalgal biomineralization. Squalene is the most abundant alkene detected in the pyrolytic products. These results suggest that microalgae can induce precipitation of carbonate minerals, a process that facilitates the sequestration of organic matter within the product aggregates precipitated, thus potentially preserving this microalgal organic matter into the burial diagenetic realm where, if conditions are appropriate, hydrocarbons may be developed.

Integrating wet stirred-bead milling for Tetraselmis suecica biorefinery: Operating parameters influence and specific energy efficiency

Stirred bead milling proved to be an efficient cell destruction technique in a biorefinery unit for the extraction of over 95 % of proteins and 60 % of carbohydrates from the green marine microalga Tetraselmis suecica. Optimum conditions, expressed in terms of metabolite yield and energy consumption, were found for average values of bead size and agitator rotation speed. The higher the microalgae concentration, up to 100 g.L−1, which is adequate for biofilm algae growth in an industrial unit, the more efficient the cell destruction process. Cell destruction rates and metabolite extraction yields are similar in pendular and recycling modes, but the pendular configuration reduces the residence time of the suspension in the grinding chamber, which is less costly. With regard to the cell destruction mechanism, it was concluded that bead shocks first damage cells by permeabilizing them, and that after a longer period, all cells are shredded and destroyed, forming elongated debris.

Lipid Enhancement in Oleaginous Nannochloropsis sp. under Nitrate Limitation for Future Bioenergy Production

Microalgae possess high oil content, exhibit rapid growth rates and biomass productivity, and leave a minimal environmental footprint, making them highly attractive for biofuel applications. Consequently, this present study is aimed at evaluating the impact of nitrogen starvation on the marine microalgae Nannochloropsis sp. to enhance lipid accumulation. The microalga culture was grown under an irradiance of 120 μmol photon m-2 s-1, temperature 25 ± 1 °C, continuous air-CO2, and with different concentrations of sodium nitrites over a 14-day cultivation period. From the results, it was found that the growth of the strain decreased under limited nitrogen conditions. After harvesting, the cells in the supernatant were regenerated by cultivating in double concentration of media. The results showed that on the 12th day, the highest lipid content was achieved, reaching 68.0 ± 2.3 wt.% of the dry weight under nitrogen limitation. The composition of the obtained lipid consisted of 18.0 wt.% saturated fatty acids, 72.38 wt.% monounsaturated fatty acids, and 8.95 wt.% polyunsaturated fatty acids. The lipid composition was dominated by monounsaturated oleic acid ( 70.97 ± 4.6 wt.%), saturated palmitic acid ( 13.68 ± 1.0 wt.%), and polyunsaturated linoleic acid ( 8.41 ± 0.4 wt.%). The findings of this study demonstrated that limiting nitrogen availability enhanced lipid accumulation in Nannochloropsis sp. Despite experiencing inhibited growth, this microalga species shows great potential for the large-scale cultivation of lipids and essential fatty acids. These results contribute to understanding the relationship between nitrogen availability and lipid metabolism in microalgae, providing valuable insights for optimizing lipid production in the context of biofuel and biotechnology applications.

Physiological and transcriptomic analysis reveals the toxic and protective mechanisms of marine microalga Chlorella pyrenoidosa in response to TiO2 nanoparticles and UV-B radiation

Concerns have been raised regarding the adverse effects of nanoparticles (NPs) on marine organisms, as an increasing number of NPs inevitably enter the marine environment with the development of nanotechnology. Owing to the photocatalytic properties, TiO2 NPs' toxicity may be aggravated by enhanced UV-B resulting from stratospheric ozone depletion. However, the molecular mechanisms of phytoplankton in response to TiO2 NPs under UV-B remains poorly understood. In this study, we integrated whole transcriptome analysis with physiological data to provide understanding on the toxic and protective mechanisms of marine Chlorella pyrenoidosa in response to TiO2 NPs under UV-B. The results indicated that the changes in gene expression could be related to the growth inhibition and TiO2 NP internalization in C. pyrenoidosa, and several molecular mechanisms were identified as toxicity response to TiO2 NPs and UV-B. Differential expression of genes involved in glycerophospholipids metabolism indicated that cell membrane disruption allowed TiO2 NPs to enter the algal cell under UV-B exposure, although the up-regulation of genes involved in the general secretory dependent pathway and the ATP-binding cassette transporter family drove cellular secretion of extracellular polymeric substances, acting as a barrier that prevent TiO2 NP internalization. The absence of changes in gene expression related to the antioxidant system may be responsible for the severe oxidative stress observed in algal cells following exposure to TiO2 NPs under UV-B irradiation. Moreover, differential expression of genes involved in pathways such as photosynthesis and energy metabolism were up-regulated, including the light-harvesting, photosynthetic electron transport coupled to photophosphorylation, carbon fixation, glycolysis, pentose phosphate pathway, tricarboxylic acid cycle, and oxidative phosphorylation, indicating that more energy and metabolites were supplied to cope with the toxicity of TiO2 NPs and UV-B. The obtained results provide valuable information on the molecular mechanisms of response of marine phytoplankton exposed to TiO2 NPs and UV-B.

Strategic Agro-Waste Valorization for Sustainable Production of Bioactives and Biofuel by Marine Microalgae

Strategic Agro-Waste Valorization for Sustainable Production of Bioactives and Biofuel by Marine Microalgae

Polar Lipids of Marine Microalgae Nannochloropsis oceanica and Chlorococcum amblystomatis Mitigate the LPS-Induced Pro-Inflammatory Response in Macrophages.

Microalgae are recognized as a relevant source of bioactive compounds. Among these bioactive products, lipids, mainly glycolipids, have been shown to present immunomodulatory properties with the potential to mitigate chronic inflammation. This study aimed to evaluate the anti-inflammatory effect of polar lipids isolated from Nannochloropsis oceanica and Chlorococcum amblystomatis. Three fractions enriched in (1) digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG), (2) monogalactosyldiacylglycerol (MGDG), and (3) diacylglyceryl-trimethylhomoserine (DGTS) and phospholipids (PL) were obtained from the total lipid extracts (TE) of N. oceanica and C. amblystomatis, and their anti-inflammatory effect was assessed by analyzing their capacity to counteract nitric oxide (NO) production and transcription of pro-inflammatory genes Nos2, Ptgs2, Tnfa, and Il1b in lipopolysaccharide (LPS)-activated macrophages. For both microalgae, TE and Fractions 1 and 3 strongly inhibited NO production, although to different extents. A strong reduction in the LPS-induced transcription of Nos2, Ptgs2, Tnfa, and Il1b was observed for N. oceanica and C. amblystomatis lipids. The most active fractions were the DGTS-and-PL-enriched fraction from N. oceanica and the DGDG-and-SQDG-enriched fraction from C. amblystomatis. Our results reveal that microalgae lipids have strong anti-inflammatory capacity and may be explored as functional ingredients or nutraceuticals, offering a natural solution to tackle chronic inflammation-associated diseases.

Physicochemical and Microstructural Characteristics of Sulfated Polysaccharide from Marine Microalga

Marine algae are a valuable source of polysaccharides. However, the information available on sulfated polysaccharides from microalgae is limited. Navicula sp. is a microalga present in the Sea of Cortez, of which little is known regarding their polysaccharides’ properties. This study investigated the physicochemical and microstructural characteristics of Navicula sp. sulfated polysaccharide (NSP). The Fourier transform infrared spectrum of NSP showed distinctive bands (1225 and 820 cm−1, assigned to S–O and C–O–S stretching, respectively), confirming the molecular identity. NSP registered molecular weight, intrinsic viscosity, a radius of gyration, and a hydrodynamic radius of 1650 kDa, 197 mL/g, 61 nm, and 36 nm, respectively. The zeta potential, electrophoretic mobility, conductivity, and diffusion coefficient of the molecule were −5.8 mV, −0.45 µm cm/s V, 0.70 mS/cm, and 2.9 × 10−9 cm2/s, respectively. The characteristic ratio and persistence length calculated for NSP were 4.2 and 1.3 nm, suggesting a nonstiff polysaccharide chain conformation. The Mark–Houwink–Sakurada α and K constants were 0.5 and 1.67 × 10−1, respectively, indicating a molecular random coil structure. NSP scanning electron microscopy revealed a rough and porous surface. Knowing these polysaccharides’ physicochemical and microstructural characteristics can be the starting point for elucidating their structure–function relationship as a valuable tool in advanced biomaterial design.

Enhanced microalgal growth and metabolites through co-cultivation with Escherichia coli in algal organic matter solution

Studies of how symbiotic bacteria interact with microalgae have been an area of interest for some time. However, there is still a knowledge gap on the role of algal organic matters in algal growth promotion and adaptive mechanisms of the co-cultures in medium containing high abundancy of dissolved algal organic matters. It remains unclear if high extra- and intra-cellular organic substances concentration influences algal development or subsequent algal organic matter productivity in the presence of bacteria. Therefore, this study aims to co-cultivate Escherichia coli NEB 5-alpha with broad range of marine and freshwater microalgae in fresh medium (T), soluble EPS (sEPS) and internal organic matter solution (IOM). Among screened species, only the growth of Cylindrotheca fusiformis and Chlorella vulgaris was promoted by E. coli at 1.15×106±2.08×104 cells mL−1 and 7.79×106±1.27×105 cells mL−1after 96 h. Xenic algal growth was further enhanced about 10 % more utilizing sEPS and IOM. However, the net EPS accumulation of the cells cultivated in sEPS and IOM was comparatively lower than that of the cells in T medium due to metabolite consumption. Elevation in the transparent exopolymer particles, total chlorophyll, total carbohydrate, total protein and lipid productivity up to 3.54-fold by cultivating the co-cultures in sEPS and IOM indicated an alteration of the microalgae's physiology. This is a new paradigm on how algal extracts promote xenic algal growth and metabolite production which pave a way for cost-effective biotechnological applications by reusing the algae medium with abundant organic matters.

Untargeted metabolomics to expand the chemical space of the marine diatom Skeletonema marinoi.

Diatoms (Bacillariophyceae) are aquatic photosynthetic microalgae with an ecological role as primary producers in the aquatic food web. They account substantially for global carbon, nitrogen, and silicon cycling. Elucidating the chemical space of diatoms is crucial to understanding their physiology and ecology. To expand the known chemical space of a cosmopolitan marine diatom, Skeletonema marinoi, we performed High-Resolution Liquid Chromatography-Tandem Mass Spectrometry (LC-MS2) for untargeted metabolomics data acquisition. The spectral data from LC-MS2 was used as input for the Metabolome Annotation Workflow (MAW) to obtain putative annotations for all measured features. A suspect list of metabolites previously identified in the Skeletonema spp. was generated to verify the results. These known metabolites were then added to the putative candidate list from LC-MS2 data to represent an expanded catalog of 1970 metabolites estimated to be produced by S. marinoi. The most prevalent chemical superclasses, based on the ChemONT ontology in this expanded dataset, were organic acids and derivatives, organoheterocyclic compounds, lipids and lipid-like molecules, and organic oxygen compounds. The metabolic profile from this study can aid the bioprospecting of marine microalgae for medicine, biofuel production, agriculture, and environmental conservation. The proposed analysis can be applicable for assessing the chemical space of other microalgae, which can also provide molecular insights into the interaction between marine organisms and their role in the functioning of ecosystems.

Detection of Fe(III) ion based on bifunctionalized silver nanoparticles: Sensitivity, selectivity and environmental safety

Functionalized silver nanoparticles (AgNPs) are widely used as optical sensors for heavy metal ions in water, due to their versatile, easy and cheap preparations and due to their peculiar physico-chemical properties. Surface functionalization plays a key role in AgNPs chemical-physical behavior as capping agents can affect sensitivity, selectivity but alsoenvironmental safety. In this framework, AgNPs are synthetised and properly functionalized using two capping agents to induce hydrophilic behavior and selectivity, respectively citrate (cit) and glutathione (GSH). The opportune choice of these capping agents induces size control and stability for AgNPs-cit-GSH in water (Ø = 4 ± 0.2 nm; ζ-potential = - 60 ± 1 mV) and make available selectively detection of Fe (III) in the range 0.5–10.0 ppm. Environmental safety was also evaluated using standardized ecotoxicity assays (ecosafety) with freshwater and marine microalgae which show a low-to-negligible effects, with exception only at the highest tested concentration (10 mg/L) but only for the freshwater one.

Double step method in lipid extraction from biomass <i>Aurantiochytrium sp</i> powder

<p><em><span>Aurantiochytrium sp</span></em><span> is a marine microalgae that is rich in lipids. Extraction of lipids from microalgae requires effort to select a suitable solvent and extraction method. This research used a double-step extraction method to study a mixture of n-hexane and methanol as a solvent. The variables studied were stirring time, the n-hexane to methanol (H/M) mixture ratio, and the solvent-to-biomass ratio (S/B). This research concluded that an optimum stirring time was 30 min, and a mixture of n-hexane and methanol solvents with a volume ratio of 1:1 is optimum. The optimum solvent-to-biomass ratio was S/B=20 mL/g dry microalgae. Under these conditions, the yield of oil was 83.88%. Double-step extraction can increase the yield by 10-40%.</span></p>

Marine Microalgae Assemblages of the East Java Coast Based on Sub-Habitats Representatives and Their Relationship to the Environmental Factors

Marine Microalgae Assemblages of the East Java Coast Based on Sub-Habitats Representatives and Their Relationship to the Environmental Factors

Population and functional changes in a multispecies co-culture of marine microalgae and cyanobacteria under a combination of different salinity and temperature levels

Changes in the temperature or salinity of ocean waters can affect marine organisms at multiple trophic levels. Both environmental variables could have an impact on marine microalgae populations. Therefore, the effect of the combination of three levels of temperature (20, 24 and 28 °C), and three levels of salinity (33, 36, and 39 PSU) were evaluated on the growth of a multispecies community of five common species of phytoplankton: (one cyanobacteria, Synechococcus sp., and four microalgae, Chaetoceros gracilis, Amphidinium carterae, Pleurochrysis roscoffensis and Rhodomonas baltica). The co-culture was monitored by flow cytometry under controlled conditions in a 96 h study. The effect of both variables on dissolved oxygen concentrations was measured using the SDR SensorDish Reader system. The results demonstrated that Synechococcus sp., C. gracilis, and A. carterae displayed a high growth at the temperature of 28 °C combined with the lowest salinity assayed. However, salinity increases negatively affected the growth of P. roscoffensis and R. baltica. Decreased salinity combined with decreased temperature exhibited a higher net O2 production. The interaction of two environmental factors related to global change such as temperature and salinity can cause structural (community growth) and functional (net oxygen production) changes in a phytoplanktonic community.

Oxidative stress and energy metabolic response of Isochrysis galbana induced by different types of pristine and aging microplastics and their leachates

The aging process and leachate composition of different types of MPs (PS, PS-NH2, PS-COOH and PMMA) with a particle size of 1.0 μm were characterized, and marine microalgae Isochrysis galbana OA3011(I. galbana) was used as test organism to investigate the 96 h toxic effects of MPs before and after aging as well as leachate exposure. Except for polymethyl methacrylate (PMMA), all other tested microplastics showed significant aggregation in seawater, which increased with the presence of surface amino and carboxyl groups, in addition, the increase in polymer dispersibility index (PDI) values after aging reflected more severe aggregation. Fourier transform infrared spectrometer (FTIR) showed that the surface amino groups were shed during the aging of PS-NH2, which can likewise be demonstrated by the change in surface electric potential from positive to negative before and after aging. PMMA, due to the addition of plasticizers (HEHP and DIBP detected in high concentration) and its own structure, has stronger resistance to aging than the other three microplastics, and no significant aging phenomenon occurs. As for I. galbana, growth inhibition, oxidative stress and energy metabolism were tested after exposure to different microplastics and their leachate. It was found that high concentrations of A-PS had a greater negative impact on I. galbana, while the toxic effects of PS-NH2 and PS-COOH on I. galbana behaved in a diametrically opposite way before and after aging compared to PS with the inhibitory effect decreasing after aging, which was caused by the shedding of surface groups. As for PMMA, the differences in the toxic effects on microalgae before and after aging were not significant. The inhibitory effect of low concentrations of PAEs (Phthalate acid esters) in the leachate of PS-COOH on I. galbana was not significant, and the stronger inhibitory effect of 4 d L-PS-NH2 was presumed to be the shedding of positively charged groups.

Physiological responses and altered halocarbon production in Phaeodactylum tricornutum after exposure to polystyrene microplastics

Oceanic emissions are a major source of atmospheric, very short-lived, ozone-depleting, brominated substances. These substances can be produced by marine microalgae, estimates of their current and future emissions are imperfect, because the processes by which marine microalgae respond to environmental changes are rarely account for environmental pollutants. Here, concurrent measurements of the potential effects of polystyrene (PS) microplastics with concentrations of 25–100 mg/L on the growth of Phaeodactylum tricornutum and their volatile halocarbons (VHCs) production were made over a 20-day culture period. The maximum inhibition rates (IR) due to 0.1 µm and 0.5 µm PS microplastics on cell density were 40.11 % and 32.87 %, on Chl a content were 25.89 % and 20.73 %, and on Fv/Fm were 9.74 % and 9.00 %, respectively. All IR showed dose-dependent effects with maxima occurring in the logarithmic phase. However, in the stationary phase, P. tricornutum exposed to PS microplastics exhibited improved attributes. Enhanced biogenesis of VHCs was induced by the excess reactive oxygen species in algal cells due to microplastics exposure, and their production rates were higher in the logarithmic phase than stationary phase. This represents that oxidative stress to cells plays a dominant role in determining the release of CHBrCl2, CHBr2Cl, and CHBr3. Hence, we suggest that the widespread microplastics in the ocean may be partly responsible for the increase in the emission of VHCs by marine phytoplankton, thereby affecting the ozone layer recovery in the future.

Nanoplastics increase the adverse impacts of lead on the growth, morphological structure and photosynthesis of marine microalga Platymonashelgolandica

Nanoplastics and heavy metals are common pollutants in coastal environments with high concerns, but their joint ecological risk to marine primary productivity remains unclear. In this study, the effects of 7, 70, 700 μg/L lead (Pb) single exposure and in combination with 200 μg/L polystyrene nanoplastics (NPs, 70 nm) on marine microalga Platymonas helgolandica were investigated. Pb single exposure induced a dose-dependent inhibition on the growth of P. helgolandica, which was associated with the reduced photosynthetic efficiency and nutrient accumulation. Compared to Pb single exposure, the addition of NPs significantly reduced the photosynthetic efficiency and aggravated the damage to cell structure. Reduced esterase activity and increased membrane permeability also indicated that NPs exacerbated the adverse effects of Pb on P. helgolandica. Thus, co-exposure to NPs and Pb induced more severe impacts on marine microalgae, suggesting that the joint ecological risk of NPs and heavy metals to marine primary productivity merits more attention.

Oxidative stress responses in two marine diatoms during sulfamethoxazole exposure and the toxicological evaluation using the IBRv2 index

Sulfamethoxazole (SMX) is widely present in water systems, and its stable properties and poor biodegradability can result in high residues of SMX in the water environment. This, in turn, can have detrimental effects on the entire aquatic habitat and human life and health. This study aimed to investigate the toxic effects of SMX on the growth, photosynthetic pigment content, and oxidative stress of two marine microalgae species: Skeletonema costatum and Phaeodactylum tricornutum. SMX demonstrated a significant inhibitory effect on microalgae proliferation, with 96-h median effective concentration (EC50) values of 0.93 mg/L and 4.65 mg/L for S. costatum and P. tricornutum, respectively. At low concentrations, SMX significantly increased the production of Chl a in both microalgae species. However, in the higher concentration SMX treatment group, Chl a content in P. tricornutum experienced a significant decrease, whereas Chl c showed no sensitivity to SMX. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), along with the glutathione (GSH) content, exhibited a significant increasing trend in response to higher SMX concentrations. However, these changes effectively inhibited the accumulation of malondialdehyde (MDA) content. In the treatment group with the highest SMX concentration, MDA content in both microalgae species was significantly higher compared to the control group. The Integrated Biomarker Response Version 2 (IBRv2) index showed a significant positive correlation with SMX concentration, suggesting its potential for assessing the ecotoxicological effects of lower SMX concentrations on marine microalgae.