Effect of photoperiod, light intensity and carbon sources on biomass and lipid productivities of Isochrysis galbana

Effects of disturbance modes and carbon sources on the physiological traits and nutrient removal performance of microalgae (S. obliquus) for treating low C/N ratio wastewater

Wastewater treatment with microalgae is an ecologically sustainable process. In this study, the growth characteristics, nutrient removal, and spectral changes of dissolved organic matter (DOM) in microalgae bioreactors were investigated for treating low C/N ratio wastewater under different disturbance modes (agitation and aeration) and carbon sources (sucrose and humic acid). The results showed that the biomass and chlorophyll-a contents of Scenedesmus obliquus in the aeration condition (725.32-811.16 × 104 cells mL-1, 1.58-1.69 mg L-1) were higher than those in the agitation condition (426.06-465.14 × 104 cells mL-1, 1.48-1.61 mg L-1). The better removal of nutrients (TN, 29.62-36.39 mg L-1, TP, 1.84-2.30 mg L-1) by microalgae in sucrose-containing wastewater under agitation conditions occurred on the second day, with removal efficiencies of 21.33-30.67% and 44.84-58.51%, respectively; while it was on the fifth day both in sucrose and humic acid-containing wastewater under aeration conditions (TN, 19.56-31.20 mg L-1, TP, 0.26-0.30 mg L-1), with removal efficiencies of 13.92-46.75% and 88.36-90.50%, respectively. The wastewater DOM primarily consisted of humic-like substances under agitation and aeration conditions characterized by high levels of aromaticity, molecular weight and humification. Furthermore, the aromatization and humification properties of DOM in humic acid wastewater were higher than those in sucrose wastewater, which was corresponding with the lower removal and availability of pollutants by algae. Microalgae showed good biomass accumulation and nutrients removal at incubation time of 2 days (agitation condition) and 5 days (aeration condition), respectively. Consequently, a technical reference is provided for the microalgae coupled with other treatment processes.

Mixotrophy of Algae: More Algal Biomass and More Biofertilization for Plants

Background: The use of algae as biofertilizers is fast-spreading in order to meet the excessive demands for agricultural products. To achieve this, enough algal biomass needs to be supplied year-round. Hence, algal nutritional components must be optimized through mixotrophic conditions. Materials and methods: Two algal isolates, namely, Phormidium sp. and Synechocystis sp. were tested for their ability to produce mixotrophic growth using different supplementations including molasses, aqueous Lepidium sativum, Trigonella foenum graecum seed extract and liquorice root extract, as well as acetate salt solution. The algae that showed highest growth under optimized mixotrophic conditions was further used in cantaloupe seed growth experiments. GC-MS was also carried out on the biomass of Phormidium on one of the fractions of extract using solvent system to reveal some dominant novel bioactive compounds in algal biomass. Results: The sugarcane molasses significantly enhanced the growth of the two algal strains, followed by Lepidium sativum extract only in case of Phormidium sp. Therefore, it was used in subsequent experiments. All growth parameters for that algae were significantly enhanced by the addition of these nutritional sources with molasses being the best supplement. The Phormidium sp. was rich in its content of chlorophyll, proteins, sugars as well as some novel bioactive compounds as revealed by GC–MS. The germination percentage of seeds treated with Phormidium sp. showed a significant increase over that of control. The different growth-related metabolites of total soluble proteins, total soluble sugars and all photosynthetic pigment contents of the seedlings were all significantly increased using this algal treatment. Discussion: The sugarcane molasses was superior in enhancing the algal growth due to its rich content not only of sugars but also of minerals and nitrogenous compounds. The use of aqueous extracts of seeds of Lepidium sativum enhanced growth significantly more than that of the control set as seeds are rich in proteins, omega-3 fatty acids, phytochemicals and other essential nutrients. In growth experiments carried out on cantaloupe seeds, there was a significant increase in germination percentage as well as all growth parameters due to the rich nutritional content of Phormidium sp. Conclusion: Mixotrophic growth achieved better algal biomass production than autotrophy in the case of Phormidium sp. The use of cheap resources such as sugarcane molasses, which is the waste from the sugar industry, as well as the common herb extract of Lepidium sativum, is a cost-effective approach. The use of this mixotrophically grown blue-green alga as a biofertilizer significantly enhanced plant growth and seed germination, indicating the usefulness of this eco-friendly agricultural strategy for achieving both food security and environmental sustainability.

Immunomodulatory effects of Isochrysis galbana incorporated diet on Oreochromis sp. (red hybrid tilapia) via Sera-1H NMR metabolomics study

Tilapia is one of the most common fish species that is intensively produced all over the world. However, significant measures at improving aquaculture health must be taken since disease outbreaks are often encountered in the rapidly developing aquaculture industry. Therefore, the objective of the study was designed to evaluate the metabolite changes in tilapia' sera through ¹H NMR metabolomics in identifying the potential biomarkers responsible for immunomodulatory effect by the indigenous species of Malaysian microalgae Isochrysis galbana (IG). The results showed that IG-incorporated diet mainly at 5.0% has improved the immune response of innate immunity as observed in serum bactericidal activity (SBA) and serum lysozyme activity (SLA). The orthogonal partial least squares (OPLS) analysis indicated 5 important metabolites significantly upregulated namely as ethanol, lipoprotein, lipid, α-glucose and unsaturated fatty acid (UFA) in the 5.0% IG-incorporated diet compared to control. In conclusion, this study had successfully determined IG in improving aquaculture health through its potential use as an immune modulator. This work also demonstrated the effective use of metabolomics approach in the development of alternative nutritious diet from microalgae species to boost fish health in fulfilling the aquaculture's long-term goals.

Complementary Analytical Platforms of NMR Spectroscopy and LCMS Analysis in the Metabolite Profiling of Isochrysis galbana

This study was designed to profile the metabolites of Isochrysis galbana, an indigenous and less explored microalgae species. ¹H Nuclear Magnetic Resonance (NMR) spectroscopy and Liquid Chromatography-Mass Spectrometry (LCMS) were used to establish the metabolite profiles of five different extracts of this microalga, which are hexane (Hex), ethyl acetate (EtOAc), absolute ethanol (EtOH), EtOH:water 1:1 (AqE), and 100% water (Aq). Partial least square discriminant analysis (PLS–DA) of the generated profiles revealed that EtOAc and Aq extracts contain a diverse range of metabolites as compared to the other extracts with a total of twenty-one metabolites, comprising carotenoids, polyunsaturated fatty acids, and amino acids, that were putatively identified from the NMR spectra. Meanwhile, thirty-two metabolites were successfully annotated from the LCMS/MS data, ten of which (palmitic acid, oleic acid, α-linolenic acid, arachidic acid, cholesterol, DHA, DPA, fucoxanthin, astaxanthin, and pheophytin) were similar to those present in the NMR profile. Another eleven glycerophospholipids were discovered using MS/MS-based molecular network (MN) platform. The results of this study, besides providing a better understanding of I.galbana’s chemical make-up, will be of importance in exploring this species potential as a feed ingredient in the aquaculture industry.

Process optimization of fucoxanthin production with Tisochrysis lutea

To optimize fucoxanthin production in Tisochrysis lutea, the effect of different process parameters on fucoxanthin productivity (Pfx) were evaluated using batch and continuous experiments. In batch, the highest Pfx was found at 30 °C and 300 μmol m^-2 s^-1, allowing to design continuous experiments to optimize the dilution rate. The highest ever reported Pfx (9.43-9.81 mg L^-1 d^-1) was achieved at dilution rates of 0.53 and 0.80 d^-1. Irradiance was varied (50-500 μmol m^-2 s^-1) to result in a range of absorbed light between 2.23 and 25.80 mol m^-2 d^-1 at a fixed dilution rate (0.53 d^-1). These experiments validated the hypothesis that light absorbed can be used to predict fucoxanthin content, resulting in 2.23 mol m^-2 d^-1 triggering the highest fucoxanthin content (16.39 mg/g). The highest Pfx was found with 18.38 mol m^-2 d^-1. These results can be used to achieve high Pfx or fucoxanthin content during cultivation of Tisochrysis lutea.

Optimization of light intensity and photoperiod for Isochrysis galbana culture to improve the biomass and lipid production using 14-L photobioreactors with mixed light emitting diodes (LEDs) wavelength under two-phase culture system

The optimal light intensity and photoperiod required to produce high biomass and lipid contents in Isochrysis galbana cultured in a 14-L bioreactor with LED wavelengths was studied. The cell biomass production was monitored in the first phase comprising of mixed blue (465 nm) and red (640 nm) LED wavelengths, then green (520 nm) LED were used in the second phase for lipid production. The optimal light intensity was 400 µmol/m²/s giving a maximum cell biomass of 1.05 g dcw/L and total lipid content of 65.2% (w/w) cultured under 12:12 h L/D cycle. The optimal light intensity of 400 µmol/m²/s was applied at different L/D cycles, the maximum cell biomass (1.25 g dcw/L) and lipid content (71.1% w/w) were obtained at 18:6 h L/D cycle. Stearic acid was the main fatty acid ranging from 42.91 (500 µmol/m²/s) to 65.57% w/w (100 µmol/m²/s) and 53.84 (18:6 h) to 65.44% w/w (24:0 h).

Bacterial Community Diversity and Screening of Growth-Affecting Bacteria From Isochrysis galbana Following Antibiotic Treatment

Algal cultures are generally co-cultures of algae and bacteria, especially when considering outdoor cultivation. However, the effects of associated bacteria on algal growth remain largely unexplored, particularly in the context of Isochrysis galbana. In the present study, we investigated the effects of antibiotic on the growth of I. galbana and its associated bacterial community. We found advantageous responses of I. galbana to antibiotic exposure, evidenced by the increased growth, and the maximal photochemical efficiency of PSII (Fv/Fm). Since antibiotics can cause major disturbances within bacterial community, we further conducted 16S rDNA amplicon sequencing to determine the changes of bacterial community diversity following antibiotic treatment. We found that antibiotic treatment considerably and negatively affected the abundance and diversity of bacterial community, and 17 significantly decreased bacterial species in the antibiotic-treated medium, including Pseudomonas stutzeri, were identified. Further co-culture experiments revealed that P. stutzeri inhibited the growth of I. galbana, and the inhibitory activity was retained in the cell-free bacterial filtrate. These results indicated that the negative effect of bacteria was not exclusively transmitted through contact with I. galbana but could be also mediated via secretory compounds. Taken together, our findings not only fully characterized the bacterial community associated with I. galbana and how the bacterial community changed in response to antibiotic perturbations, but also provided a valuable information about the interactions between I. galbana and its associated bacteria, which might help improve the yield, and quality of I. galbana during its cultivation processes.

Effects of wavelength mixing ratio and photoperiod on microalgal biomass and lipid production in a two-phase culture system using LED illumination

Blue and red light-emitting diodes (LEDs) were used to study the effects of wavelength mixing ratios, photoperiod regimes, and green wavelength stress on Nannochloropsis salina, Isochrysis galbana, and Phaeodactylum tricornutum cell biomass and lipid production. The maximum specific growth rates of I. galbana and P. tricornutum were obtained under a 50:50 mixing ratio of blue and red wavelength LEDs; that of N. salina was obtained under red LED. Maximum cell biomass for N. salina and P. tricornutum was 0.75 and 1.07 g dcw/L, respectively, obtained under a 24:0 h light/dark cycle. However, the maximum I. galbana biomass was 0.89 g dcw/L under an 18:6 h light/dark cycle. The maximum lipid contents for N. salina, I. galbana, and P. tricornutum were 49.4, 63.3 and 62.0% (w/w), respectively, after exposure to green LED. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were obtained 1% in P. tricornutum and 2% in I. galbana.

Effect of cultivation mode on the production of docosahexaenoic acid by Tisochrysis lutea

In this study, Tisochrysis lutea was cultivated in mixotrophic and heterotrophic cultures with glycerol as a carbon source and with glucose and acetate for comparison; autotrophic cultivation was the control group without a carbon source. It was found that T. lutea used glycerol and did not use glucose and acetate under mixotrophy. Mixotrophy slightly elevated the docosahexaenoic acid (DHA) and total fatty acids (TFA) content in the dry-weight and enhanced the DHA and TFA production in medium (41.3 and 31.9% respectively) at the end of a 16-day cultivation, while heterotrophy reduced the DHA content and TFA production. Under the mixotrophy, the glycerol contribution to the DHA production (16.19 mg/L) and the TFA production (97.8 mg/L) was not very high and the DHA yield [2.63% chemical oxygen demand (COD)] and TFA yield (13.1% COD) were also very low. Furthermore, T. lutea using glycerol had a period of adaptation, indicating that T. lutea was not an ideal microalga for organic carbon utilization.

Combining glucose and sodium acetate improves the growth of Neochloris oleoabundans under mixotrophic conditions

Mixotrophic cultivation is a potential approach to produce microalgal biomass that can be used as raw materials for renewable biofuels and animal feed, although using a suitable, cost-effective organic carbon source is crucial. Here, we used a Box–Behnken design with three factors, the glucose and sodium acetate concentrations, and the percentage of Bold’s basal medium (BBM), to evaluate the effects of different carbon sources on biomass productivity and the protein and lipid contents of Neochloris oleoabundans (UTEX#1185). When grow at optimal levels of these factors, 100 % BBM plus 7.5 g L⁻¹ each of glucose and sodium acetate, N. oleoabundans yielded 1.75 g L⁻¹ of dry biomass, with 4.88 ± 0.09 % N, 24.01 ± 0.29–30.5 ± 0.38 % protein, and 34.4 % ± 0.81 lipids. A nuclear magnetic resonance spectrum (¹H-NMR) of a lipid extract showed that the free fatty acid content was 11.25 %. Thus, combining glucose and sodium acetate during the mixotrophic cultivation of N. oleoabundans can yield greater amounts of biomass, proteins, and lipids for biofuel production.