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Food production is facing challenging times due to the pandemic, and climate change. With production expected to double by 2050, there is a need for a new paradigm in sustainable animal feed supply. Seaweeds offer a highly valuable opportunity in this regard. Seaweeds are classified into three categories: brown (Phaeophyceae), red (Rhodophyceae), and green (Chlorophyceae). While they have traditionally been used in aquafeed, their demand in the feed market is growing, parallelly increasing according to the food demand. Additionally, seaweeds are being promoted for their nutritional benefits, which contribute to the health, growth, and performance of animals intended for human consumption. Moreover, seaweeds contain biologically active compounds such as polyunsaturated fatty acids, antioxidants (polyphenols), and pigments (chlorophylls and carotenoids), which possess beneficial properties, including antibacterial, antifungal, antiviral, antioxidant, and anti-inflammatory effects and act as prebiotics. This review offers a new perspective on the valorization of macroalgae biomass due to their nutritional profile and bioactive components, which have the potential to play a crucial role in animal growth and making possible new sources of healthy food ingredients.

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The present study shows the characterization of the bacterial communities associated with different systems during the cultivation of the microalga Tetradesmus obliquus. For that, sequential cultivation was performed in three different systems: (1) Photobioreactor bench-scale; (2) flat-panel photobioreactor; and (3) thin-layer cascade. Cultures were monitored daily for growth parameters and biomass samples were collected for characterization of bacterial communities using metagenomic. A total of 195,177 reads were produced, resulting in the identification of 72 OTUs. In the grouping of bacterial communities, 3 phyla, 6 classes, 28 families, and 35 taxa were found. The bacteria Brevundimonas and Porphyrobacter had a higher relative abundance compared with other taxa found. These taxa were present in all cultivation systems forming a possible core community. Bacterial communities associated with different cultivation systems of the microalga T. obliquus showed an increase in taxa richness and diversity in the super-intensive and intensive systems.

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Each phytoplankton species presents a different behavior and tolerance to the cryopreservation process. Therefore, in a species-specific protocol, it is essential to ensure both growth and post-thawing cell viability. In this study, we explored the effect of cryopreservation of Scenedesmus sp. with two cryoprotectants, dimethyl sulfoxide (DMSO) and methanol (MET), at 5% and 10% inclusion for each. In the control treatment, the microalgae were not exposed to cryoprotective agents (Control). Three post-thawing cell viability criteria were used: no cell damage (NCD), cell damage (CD), and marked lesions (LM), and mitochondrial and cell membrane damage was evaluated by flow cytometry. The study was a 2 × 2 factorial design, with five replications by treatments, population growth, and cell damage evaluated from the fifth day after thawing. On the fifth day, the highest percentage of NCD was observed when the microalgae were cryopreserved with DMSO 5% (50%); Regarding the control group, it showed 0% NCD. Flow cytometry analysis reveals minor damage at the membrane and mitochondria (9-10.7%) when DMSO is used at both inclusion percentages (5-10%) after thawing. In the exponential phase, the highest growth rates, doubling time, and yield was observed in cryopreserved cells with MET 5%. The results suggest that DMSO 5% is an ideal treatment for cryopreserving microalgae Scenedesmus sp.

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Microalgae are known for producing various biotechnological products. Moreover, they absorb nutrients from dairy wastewater, grow well, and accumulate valuable compounds faster. In this study, photoautotrophic and mixotrophic cultivation with different initial lactose concentrations present in cheese whey (CW) were established to investigate their effect on cell concentration (Xm, mg L-1), cell productivity (Px, mg L-1day-1), and specific cell growth (µmax, day-1) of Chlorella vulgaris, Dunaliella tertiolecta,and Tetradesmus obliquus. The biomass production of C. vulgaris(Xm= 1,520 ± 30.3 mg L-1, Px = 147 ± 3.00 mg L-1, and µmax= 0.150 ± 0.00 mg L-1) in mixotrophic culture with 10.0 g L-1 of lactose, the main constituent of CW, was notably enhanced by 55% in comparison with their photoautotrophic cultures, whereas a lower effect of these lactose concentrations on cell growth was observed in T. obliquus and D. tertiolecta. Thus, mixotrophic cultivation of C. vulgarisusing CW as a carbon and energy source could be considered a feasible alternative to obtain high value-added biomass.(AU)

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Bioactive compounds, synthesized by photosynthetic microorganisms, have drawn the attention of the pharmaceutical field. This study aimed at evaluating synthesis and in vitro antioxidant capacity of phenolic compounds produced by a microalgae species P. boryanum, which was grown in six different culture media (standard BG11, modified BG11/MBG11, standard WC, modified WC, WC*2 and basal). The highest concentrations of biomass (1.75 ± 0.01 g.L-1) and phenolic content (3.18 ± 0.00 mg.g-1) were obtained when P. boryanum was grown in MBG11 and phenolic acids were identified: gallic, protocatechuic, chlorogenic, hydroxybenzoic and vanillic ones. All extracts exhibited scavenger activity in the ABTS assay and inhibited peroxidase. However, phenolic compounds from P. boryanum grown in BG11 and MBG11 had the most potent scavenger activity in the DPPH assay. In sum, P. boryanum can be a new source of free phenolic compounds with potential antioxidant activity when grown in MBG11, since it yields high amounts of biomass and phenolic compounds.

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Ciprofloxacin (CIP) is an antimicrobial "pseudo-persistent" in aquatic ecosystems. Once dispersed in the water compartments, it can also affect the microalgae. Thus, the evaluation of its long-term ecotoxicological effects is necessary. CIP interactions with other pharmaceuticals are not well known. In this study, we investigated the toxic effects of CIP alone and combined with caffeine (CAF), using the modified Gompertz model parameters and the chlorophyll-a production of the microalga Raphidocelis subcapitata as endpoints, throughout a 16-day exposure assay. The exposure to CIP alone led to significant reductions of the growth rate and the cell density of the microalgae compared to control groups. The combination with CAF lowered the adverse effects of CIP to R. subcapitata. However, as the toxicity is dynamic, our results indicated that the toxic effects in respect to the studied endpoints changed throughout the exposure period, reinforcing the need for longer-term ecotoxicity assessments.

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Atrazine (ATZ) is one of the most widely used herbicides in the world. A scientometric study was conducted to analyze the evolution of research on ATZ. The study also looked at the use of microalgae and cyanobacteria as biological models for toxicity tests during the period from 1959 to 2019, in the category of toxicology of Web of Science. The results show an increase in the number of scientific publications mainly in the USA, Canada, and China. The majority of papers was published in journals with high impact factors, demonstrating the relevance of such studies. About 83% of the studies aimed to evaluate the effect of ATZ on non-target organisms. From those, 7.5% included microalgae and cyanobacteria. The majority of them worked with chlorophyceae to perform toxicity bioassays of ATZ and analyze its sublethal effects. The gaps identified by this analysis included a small number of collaborations between research groups from different countries; the number of studies with terrestrial organisms, which are larger in comparison to aquatic organisms; and the fact that none of the studies with ATZ and microalgae was performed in the field. These findings can point out to researchers and funding agencies the gaps in knowledge on the toxic effects of ATZ and guide the development of new research projects as well as environmental policies.

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A method to simultaneously extract polar (PC) and non-polar compounds (NPC) from microalgae was developed for further determination of intracellular metabolites by gas chromatography. The proposed method was validated and used to characterize two Chlorophyceae, Chlorella vulgaris and Scenedesmus obliquus, and two Cyanobacteria, Aphanothece microscopica Nagëli and Phormidium autumnale. The compounds were extracted with a reduced amount of organic solvent mixture (methanol-chloroform), compared to the reference method, under different conditions of homogenization and/or cell disruption. The NPC were derivatized by acid catalysis, whereas the PC fraction was derivatized using N-methyl,N-tert-Butyldimethylsilyltrifluoroacetamide (MTBSTFA) in alkaline medium. The following parameters for method validation were considered: selectivity, linearity, limit of detection (LOD), limit of quantitation (LOQ), precision, and accuracy. All methods of homogenization and cell disruption extracted both PC and NPC from Chlorophyceae and Cyanobacteria. Derivatization of PC presented satisfactory validation parameters. Eleven fatty acids, six free amino acids, and three organic acids were found within the evaluated microalgae species, succinic, malic, and citric acids, important intermediates of the tricarboxylic acid cycle. Glutamic acid was the amino acid found in greatest quantities in all species. Chlorophyceae presented a higher concentration of unsaturated fatty acids, while Cyanobacteria had more saturated fatty acids. Thus, the proposed method was suitable to metabolically characterize both PC and NPC from microalgae.

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RESUMO Neste trabalho foi avaliado o crescimento da microalga Pseudokirchneriella subcapitata em meio de cultivo alternativo NPK (20:05:20) contaminado com metais pesados. O primeiro tratamento consiste do controle sem a adição de contaminante, enquanto os demais foram contaminados com AlCl3, FeSO4 e ZnSO4 e os três metais. Nos resultados obtidos, o controle foi o único que apresentou crescimento positivo contínuo, enquanto o tratamento contendo todos os metais obteve maior densidade e maior taxa de crescimento exponencial. O tratamento contaminado com ZnSO4 obteve o menor potencial de produção. Apesar dos valores apresentados, todos os tratamentos apresentaram crescimento positivo no final do ensaio, sendo possível atribuir à microalga um elevado potencial de produção em água contaminado por metais.

ABSTRACT This study evaluated the growth of microalgae Pseudokirchneriella subcapitata amid growing alternative NPK (20:05:20) contaminated with heavy metals. The first treatment consists of the control without addition of dopant, while others were infected with AlCl3, FeSO4 e ZnSO4 and the three metals. Of the results obtained, the control was the only one that showed continued positive growth, while all metal-containing treatment had a higher density and a higher rate of exponential growth. Treatment contaminated with ZnSO4 had the lowest production potential. Despite the figures, all treatments showed positive growth at the end of the test, so it is possible to assign a high potential for microalgae production in water contaminated by metals.

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Copper is an essential metal for several physiological and metabolic processes, but a narrow range regulate its effect in phytoplankton cells. It can affect the production of biomolecules and be toxic at concentrations slightly above those required, e.g. decreasing photosynthesis and increasing respiration. The aims of this study were to analyse the changes in growth and chlorophyll a synthesis, and in biochemistry (total carbohydrates, proteins, lipids and fatty acids) of the freshwater microalga Selenastrum gracile after exposure to copper. Exponentially growing cells were exposed to 5 concentrations of free copper ions (Cu2+) ranging from 0.7 (control) to 13 × 10-8 M for up to 120 h. Free Cu2+ ion concentrations were calculated through the chemical equilibrium model MINEQL+. We observed that copper was responsible for a decrease in cell density and an increase in total protein and lipid production, but no effect on total carbohydrates was detected. The increase in phospholipids and sterols and a decrease in saturated fatty acids under copper exposure suggest a change in conformation of the cell membrane, by decreasing its fluidity. We suggest this serves the cell as a system to avoid the internalization of metal, thereby acting as a detoxifying mechanism.

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