Search Results (8)

Microalgae are considered as sustainable starch producers, yet the carbon sources for this process in terms of starch productivity and functionality require further elucidation. The present study investigated the roles of CO₂ and acetate on the starch production in a marine microalga Tetraselmis subcordiformis, and the ordered structure and digestibility of the starches obtained were characterized. CO₂ and acetate could serve as efficient carbon sources for T. subcordiformis to accumulate starch, with the maximum starch content, yield, and productivity reaching 66.0%, 2.16 g/L, and 0.71 g/L/day on day 3 and the maximum biomass productivity reaching 0.94 g/L/day on day 2, respectively, when 2.5 g/L sodium acetate and 2% CO₂ were simultaneously applied. The addition of acetate under 2% CO₂ improved the photosynthetic efficiency and enhanced the activity of ADP-glucose pyrophosphorylase, facilitating the biomass and starch production. The supply of CO₂ and acetate changed the amylose/amylopectin ratio by affecting the activity of starch branching enzymes and isoamylases. FTIR and XRD analyzes showed that the supply of CO₂ reduced the long- and short-range ordered structure of starch, while acetate promoted the production of additional B- and V-type starch, resulting in a reduced digestibility. The combined supply of 2% CO₂ and 5 g/L sodium acetate enabled the most efficient production of functional resistant starch (RS) measured with Englyst’s method, with a maximum RS content and yield reaching 13.7%DW and 0.40 g/L, respectively, on day 3. This study provided novel insights into the efficient production of high value-added functional starch (RS) from microalgae. Full article

Carbon dioxide (CO₂) is often a limiting factor for the growth of microalgal biomass. Consequently, the search for new CO₂ sources that do not contain components inhibitory to microalgal metabolism remains a priority. An alternative to the solutions tested thus far may involve the use of CO₂-rich gas derived from microbial fuel cells (MFCs). This concept served as the basis for the original experimental work described in this study. The objective of the research was to evaluate the effect of using gases from the anode chamber of an MFC as a CO₂ source in the autotrophic cultivation of Tetraselmis subcordiformis. The highest biomass growth efficiency was observed when the CO₂ concentration in the culture medium was maintained at 220.0 ± 8.0 mg/L. Under these conditions, the microalga proliferation rate reached 0.52 ± 0.03 g VS/(L∙day) and 11.54 ± 0.42 mg chl-a/(L∙day), with a final biomass concentration of 2.68 ± 0.10 g VS/L and 63.53 ± 2.44 mg chl-a/L at the end of the cultivation cycle. Moreover, the highest total hydrogen (H₂) production of 312 ± 38 mL was achieved in the same experimental variant, corresponding to an H₂ production rate of 62.4 ± 6.1 mL/day. The removal efficiency of ammonium nitrogen (N-NH₄) was notably high in experimental variants using MFC-derived biogas, ranging from 97.0 ± 2.2% to 98.2 ± 1.8%. Additionally, the growing microalgal biomass effectively utilized phosphate phosphorus (P-PO₄) and iron, further highlighting its potential for nutrient recovery. Full article

The development and implementation of innovative production technologies have a direct influence on the creation of new sources of pollution and types of waste. An example of this is the wastewater from soil-less agriculture and the effluent from microbial fuel cells. An important topic is the development and application of methods for their neutralisation that take into account the assumptions of global environmental policy. The aim of the present study was to determine the possibilities of utilising this type of pollution in the process of autotrophic cultivation of the biohydrogen-producing microalgae Tetraselmis subcordiformis. The highest biomass concentration of 3030 ± 183 mgVS/L and 67.9 ± 3.5 mg chl-a/L was observed when the culture medium was wastewater from soil-less agriculture. The growth rate in the logarithmic growth phase was 270 ± 16 mgVS/L-day and 5.95 ± 0.24 mg chl-a/L-day. In the same scenario, the highest total H₂ production of 161 ± 8 mL was also achieved, with an observed H₂ production rate of 4.67 ± 0.23 mL/h. Significantly lower effects in terms of biomass production of T. subcordiformis and H₂ yield were observed when fermented dairy wastewater from the anode chamber of the microbial fuel cell was added to the culture medium. Full article

Extracellular polymeric substances (EPS) produced by microorganisms contain polymers that are used for the bioflocculation of microalgae; however, these polymers are also organic compounds that might be used as carbon sources. The study analyzed two strategies for the introduction of EPS for Tetraselmis subcordiformis, Chlorella sp., and Arthrospira platensis biomass harvesting. In the first variant, EPS in the dose of 100 mg TOC/g were added to the photobioreactor every other day from the beginning of the cultivation, while in the second variant, EPS in the two doses of 100 mg TOC/g and 300 mg TOC/g were only added at the end of cultivation. In the first variant, the results proved that microalgae/cyanobacteria can use the EPS as external carbon sources. The cultures were characterized by a faster increase in biomass concentration, which contained less chlorophyll. However, the EPS content did not change. In the second variant, the addition of EPS did not affect the EPS content and the sedimentation of the Chlorella sp. biomass. The biomass of T. subcordiformis was characterized by a much better sedimentation coefficient. The greatest differences were observed in the A. platensis culture: the biomass concentration increased from 1.2 ± 0.2 g/L to 1.9 ± 0.2 g/L, EPS content increased by 16%, and sedimentation efficiency increased to 72%. Full article

The performance of microalgae-based wastewater treatment processes for ammonium-N (NH₄⁺-N) removal depends on the maintenance of a favorable pH that is critical for minimizing nitrogen escape in the form of free ammonia (NH₃) and preventing high-NH₃ or extreme-pH stress. This study developed a CO₂-inorganic carbon (CO₂-IC) buffering system that automatically stabilized pH with the supply of a carbon source for efficient photosynthetic reclamation of NH₄⁺-N by a euryhaline microalga Tetraselmis subcordiformis. The soluble (NaHCO₃) and insoluble (CaCO₃ and MgCO₃) ICs were compared for this purpose. The pH was well controlled in the range of 6.5~8.5 in the CO₂-IC system, which was suitable for the photosynthetic growth of T. subcordiformis. The NH₄⁺-N (100 mg/L) was almost completely removed in three days, with the maximum removal rate of 60.13 mg N/L/day and minimal N escape of 19.65% obtained in the CO₂-NaHCO₃ system. The CO₂-IC system also restricted the release of extracellular organic matter by preventing stress conditions. The CO₂-NaHCO₃ system enabled the highest “normal” starch production suitable for fermentation, while the CO₂-CaCO₃/MgCO₃ system facilitated high-amylose starch accumulation that was conducive to producing bio-based materials and health-promoting ingredients. The proteins accumulated in T. subcordiformis were of good quality for animal feeds. Full article

The development of wastewater treatment systems, including competitive methods for nitrogen and phosphorus removal, is focused on intensifying final technological effects with due care taken for economic and environmental concerns. Given the possibility of integrating wastewater treatment processes with biofuel production, the prospective seems to be technologies harnessing microalgal biomass. The present study aimed to verify the feasibility of applying T. subcordiformis genus microalgae as the third stage of the dairy wastewater treatment process and to determine microalgae biomass production effectiveness and hydrogen yield in the biophotolysis process. The study proved that microalgae cultivation with dairy wastewater was nearly 35% less effective compared to that with a chemically pure medium. Nitrogen and phosphorus compounds contaminating wastewater were found to represent an available source of nutrients for T. subcordiformis population. The volume of hydrogen produced ranged from 116 ± 7 cm³ to 162 ± 7 cm³, and the percentage of H₂ content in the biogas ranged from 55.4 ± 2.2% to 57.2 ± 4.1%. A significantly higher hydrogen yield per initial biomass concentration, reaching 69 ± 4.2 cm³/g_o.d.m., was determined in the variant with wastewater accounting for 50% of the culture medium. The respective value noted in the control respirometer was 54 ± 2.1 cm³/g_o.d.m. Full article

We found the euryhaline microalga, Tetraselmis jejuensis sp. nov., which was adapted to supralittoral tide pools with salinities varying from 0.3–3.1%. Fifteen strains of T. jejuensis were isolated from Daejeong (DJ) and Yongduam (YO), and clonal cultures were established in the laboratory. Morphological characterization revealed that the cells have a compressed shape, four flagella emerging from a depression near the apex in two opposite pairs, a cup-shaped chloroplast containing one pyrenoid surrounded by starch, and eyespot regions not located near the flagellar base. T. jejuensis cells showed distinct characteristics compared to other Tetraselmis species. First, a regular subunit pattern with honeycomb-like structures was predominantly displayed on the surface in the middle of the cell body. Second, the pyrenoid was invaded by both cytoplasmic channels comprising electron-dense material separated from the cytoplasm, and two branches of small cytoplasmic channels (canaliculi) in various directions, which characterize the subgenus Tetrathele. Eyespot regions containing a large number of osmiophilic globules, packed closely together and arranged in subcircular close packing of diverse sizes, were dispersed throughout the chloroplast. In the phylogenetic analysis of small subunit (SSU) rDNA sequences, the 15 strains isolated from DJ and YO separated a newly branched clade in the Chlorodendrophyceae at the base of a clade comprising the T. carteriiformi/subcordiformis clade, T. chuii/suecica clade, and T. striata/convolutae clade. The strains in the diverging clade were considered to belong to the same species. The SSU rDNA sequences of the DJ and YO strains showed a maximum difference of 1.53% and 1.19% compared to Tetraselmis suecica (MK541745), the closest species of the family based on the phylogenetic analysis, respectively. Based on morphological, molecular, and physiological features, we suggest a new species in the genus Tetraselmis named Tetraselmis jejuensis, with the species name “jejuensis” referring to the collection site, Jeju Island, Korea. Full article

Tetraselmis subcordiformis, a unicellular marine green alga, is used widely in aquaculture as an initial feeding for fish, bivalve mollusks, penaeid shrimp larvae, and rotifers because of its rich content of amino acids and fatty acids. A stable nuclear transformation system using the herbicide phosphinothricin (PPT) as a selective reagent was established previously. In this research, the recombinant expression in T. subcordiformis was investigated by particle bombardment with the rt-PA gene that encodes the recombinant human tissue-type plasminogen activator (Reteplase), which is a thrombolytic agent for acute myocardial infarction treatment. Transgenic algal strains were selected by their resistance to PPT, and expression of rt-PA was validated by PCR, Southern blotting, and Western blotting, and bioactivity of rt-PA was confirmed by the fibrin agarose plate assay for bioactivity. The results showed that rt-PA was integrated into the genome of T. subcordiformis, and the expression product was bioactive, indicating proper post-transcriptional modification of rt-PA in T. subcordiformis. This report contributes to efforts that take advantage of marine microalgae as cell factories to prepare recombinant drugs and in establishing a characteristic pathway of oral administration in aquaculture. Full article