Nutritional value of Chlorella vulgaris: Effects of ultrasonication and electroporation on digestibility in rats

Enhancing Digestibility of Chlorella vulgaris Biomass in Monogastric Diets: Strategies and Insights

Microalgae, such as Chlorella vulgaris (CV), have been identified as promising animal feed sources due to their high content of essential nutrients, including proteins, total lipids, n-3 polyunsaturated fatty acids, and pigments. This study aimed to review the digestibility, bioaccessibility, and bioavailability of nutrients from CV biomass, and to analyse strategies to enhance their digestibility in monogastric animal diets. The study conducted a systematic review of the literature from databases such as PubMed, Scopus, Google Scholar, and Web of Science, up until the end of January 2023. The results of adding CV to poultry and swine diets were diverse and depended on a number of variables. However, pre-treatments applied to CV biomass improved nutrient digestibility and accessibility. CV biomass, produced in a cost-effective manner, has the potential to serve as a supplement or substitute for expensive feed ingredients and improve animal health, physiology, and immune status. Variations in results may be due to differences in microalgal strain, cultivation conditions, and dietary inclusion levels, among other factors. This study provides new insights and perspectives into the utilization of CV biomass in animal diets, highlighting its potential as a valuable ingredient to improve nutrient utilization.

Chlorella vulgaris microalgae in Ruminant Nutrition: a Review of the Chemical Composition and Nutritive Value

Recently, microalgae, natural marine resources, have gained increasing interests as a feed for animals. Chlorella vulgaris microalgae are single-cell microorganisms that have been used to provide nutrition to humans and animals for centuries. In the present review, we unveil the composition and nutritive value of C. vulgaris microalgae as a feed for ruminants. Research has shown that inclusion of C. vulgaris microalgae in diets improved feed utilization, milk production and quality, growth performance, and meat quality in ruminants, as a result of improved diet nutritive value. Very low doses of C. vulgaris in feed enhance growth and lactational performance of ruminants. Additionally, C. vulgaris showed very promising results as an alternative to corn and soybean meal; however, it is an expensive protein feed. Therefore, the main constraint to use of C. vulgaris as a feedstuff is its high cost of production, making improvement of cultivation technology to reduce the production costs a critical issue in the near future.

Cyanobacterial Biomass Produced in the Wastewater of the Dairy Industry and Its Evaluation in Anaerobic Co-Digestion with Cattle Manure for Enhanced Methane Production

The unique perspective that microalgae biomass presents for bioenergy production is currently being strongly considered. This type of biomass production involves large amounts of nutrients, due to nitrogen and phosphorous fertilizers, which impose production limitations. A viable alternative to fertilizers is wastewater, rich in essential nutrients (carbon, nitrogen, phosphorus, potassium). Therefore, Arthrospira platensis was cultivated in 150 mL photobioreactors with 70% (v/v) with the wastewater from a dairy industry, under a regime of light:dark cycles (12 h:12 h), with an irradiance of 140 μmol m−2 s−1 photon. The discontinuous cultures were inoculated with an average concentration of chlorophyll-a of 13.19 ± 0.19 mg L−1. High biomass productivity was achieved in the cultures with wastewater from the dairy industry (1.1 ± 0.02 g L−1 d−1). This biomass was subjected to thermal and physical treatments, to be used in co-digestion with cattle manure. Co-digestion was carried out in a mesophilic regime (35 °C) with a C: N ratio of 19:1, reaching a high methane yield of 482.54 ± 8.27 mL of CH4 g−1 volatile solids (VS), compared with control (cattle manure). The results demonstrate the effectiveness of the use of cyanobacterial biomass grown in wastewater to obtain bioenergy.

Protein and amino acid digestibility of 15N Spirulina in rats

PURPOSE

Spirulina is often used as dietary supplement for its protein content and quality. However, in vivo data on protein digestibility are lacking. This study aims to determine nitrogen and amino acid digestibility in rats. A secondary objective was to test the effect of sonication prior to ingestion to break cell walls.

METHODS

Wistar rats were fed a single test meal containing ¹⁵N Spirulina that was either sonicated (n = 11) or not (control, n = 13). Rats were euthanized 6 h after the meal ingestion. Spirulina nitrogen digestibility was measured by assessment of ¹⁵N recovery in digestive contents. Amino acid digestibility was measured by quantification of the caecal amino acid content and their ¹⁵N enrichment.

RESULTS

Real fecal nitrogen digestibility was 86.0 ± 0.7%, without any differences between groups. Mean ¹⁵N amino acid caecal digestibility was 82.8 ± 1.3%, and values ranged between 77.9 ± 1.9% for serine and 89.4 ± 1.0% for methionine. No effect of sonication was observed. The most limiting AA was histidine, with a chemical score of 0.98 and a PD-CAAS of 0.84. Lysine was also limiting in a lesser extent.

CONCLUSION

The nitrogen and amino acid digestibility of Spirulina is relatively low, and showed no effect of prior sonication. Its amino acid composition is relatively well balanced but not enough to compensate for the poor digestibility.

Characterization of the mitochondrion genome of a Chlorella vulgaris strain isolated from rubber processing wastewater

Chlorella vulgaris ITBBA3-12 was isolated from the rubber processing wastewater and has a role in wastewater purification. Its complete mitogenome contains 88754 bp, with a G + C content of 29.7%. A total of 64 genes were annotated, including 34 protein-coding genes, 27 tRNA genes, three rRNA (rrn23, rrn16, and rrn5). Phylogenetic analysis using the mitogenomes of Trebouxiophyceae species indicated that the strain ITBBA3-12 is closely related to C. vulgaris strain UTEX259 and NJ-7, and they clustered in the Chlorella lineage.

High density long-term cultivation of Chlorella vulgaris SAG 211-12 in a novel microgravity-capable membrane raceway photobioreactor for future bioregenerative life support in SPACE

Hybrid life support systems are of great interest for future far-distant space exploration missions to planetary surfaces, e.g. Mars, planned until 2050. By synergistically combining physicochemical and biotechnological algae-based subsystems, an essential step towards the closure of the carbon loop in environmental control and life support systems (ECLSS) shall be accomplished, offering a wide beneficial potential for ECLSS through the utilization of oxygenic photosynthesis: O₂ and potential human food can be formed in-situ from CO₂ and water. The wild type green alga Chlorella vulgaris strain SAG 211-12 was selected as model microorganism due to its photoautotrophic growth, high biomass yield, cultivation flexibility and long-term cultivation robustness. The current study presents for the first time a stable xenic long-term processing of microalgae in a novel microgravity capable membrane raceway photobioreactor for 188 days with the focus on algal growth kinetics and gas evolution. In particular, culture homogeneity and viability were monitored and evaluated during the whole cultivation process due to their putative crucial impact on long-term functionality and efficiency of a closed cultivation system. Based on a specially designed cyclic batch cultivation process for SAG 211-12, a successive biomass growth up to a maximum of 12.2 g l^-1 with a max. global volumetric productivity of 1.3 g l^-1 d^-1 was reached within the closed loop system. The photosynthetic capacity was assessed to a global molar photosynthetic quotient of 0.31. Furthermore, cultivation parameters for a change from batch to continuous processing at high biomass densities and proliferation rates are introduced. The presented µgPBR miniature plant and the developed high throughput cultivation process are planned to be tested under real space conditions within the PBR@LSR project (microgravity and cosmic radiation) aboard the International Space Station with an operation period of up to 180 days to investigate the impact on long-term system stability.

Using microalgae in the circular economy to valorise anaerobic digestate: challenges and opportunities

Managing organic waste streams is a major challenge for the agricultural industry. Anaerobic digestion (AD) of organicwastes is a preferred option in the waste management hierarchy, as this processcangenerate renewableenergy, reduce emissions from wastestorage, andproduce fertiliser material.However, Nitrate Vulnerable Zone legislation and seasonal restrictions can limit the use of digestate on agricultural land. In this paper we demonstrate the potential of cultivating microalgae on digestate as a feedstock, either directlyafter dilution, or indirectlyfromeffluent remaining after biofertiliser extraction. Resultant microalgal biomass can then be used to produce livestock feed, biofuel or for higher value bio-products. The approach could mitigate for possible regional excesses, and substitute conventional high-impactproducts with bio-resources, enhancing sustainability withinacircular economy. Recycling nutrients from digestate with algal technology is at an early stage. We present and discuss challenges and opportunities associated with developing this new technology.

Variability in nutrient composition and in vitro crude protein digestibility of 16 microalgae products

The chemical composition of 16 microalgae products of four genera, Arthrospira (n = 2), Chlorella (n = 8), Nannochloropsis (n = 4) and Phaeodactylum (n = 2), was assayed to evaluate the intra- and inter-genera variation of nutrient profiles of commercial microalgae products. Crude protein was the main component in all genera, followed by ether extract and crude ash. Mean crude protein concentrations were 690, 502, 431 and 446 g/kg dry matter, and mean ether extract concentrations were 63, 157, 188 and 113 g/kg dry matter for Arthrospira, Chlorella, Nannochloropsis and Phaeodactylum respectively. However, there was considerable inter- and intra-genera variation. The concentration of α-linked glucose was low (0-143 g/kg dry matter). There was high variation between and within genera in the crude ash concentration (22-237 g/kg dry matter), which was also observed for the mineral composition. In contrast to the crude protein concentration, the amino acid composition of the protein (g amino acid/16 g N) was less variable. The investigated samples possessed high concentrations of Glx, Asx and Leu, and low concentrations of Cys and Met. The mean concentration of non-protein nitrogen compounds was highest in Phaeodactylum (110 g/kg dry matter) and lowest in Nannochloropsis (47 g/kg dry matter) products, and as with proximate nutrients, high variability between and within genera was observed. In vitro crude protein digestibility varied between 54% (non-cell-disrupted Nannochloropsis) and 84% (cell-disrupted Chlorella). Inositol phosphate isomers were not detectable in any sample (concentration <1 μmol/g dry matter). The predominant fatty acids were C16:0 in Arthrospira products, C18:2 n-6+ C19:1 t7 and C18:3 n-3 in Chlorella products, and C20:5 n-3 in Nannochloropsis and Phaeodactylum products; however, the relative proportions of fatty acids varied within genera. Commercially available microalgae products appear to be valuable alternative food and feed products. However, because of the high variability in nutrient profiles, attention should be given to the analytical characterization of the products.

Chlorella vulgaris as a Source of Essential Fatty Acids and Micronutrients: A Brief Commentary

Polyunsaturated fatty acids (PUFAs) comprise about 35-40% of the total lipid content from green algaeChlorella, reaching up to 24% linoleic acid and 27% α-linolenic acid inC. vulgaris. Also, microalgae nutrient composition may be modulated by changes in the culture medium, increasing fatty acid and microelement concentrations in the algae biomass. PUFAs, such as α-linolenic (n-3) and linoleic (n-6) acids, as well as its derivatives, are considered essential for dietary consumption, and their ability to regulate body chemistry has been recently explored in depth. A balanced fatty acid consumption is shown to counteract the negative effects of western diets, such as chronic inflammation and glucose intolerance. In this brief commentary, technological and practical uses ofC. vulgarisare explored as means to improve dietary quality and, ultimately, human health.

Investigation of in vitro digestibility of dietary microalga Chlorella vulgaris and cyanobacterium Spirulina platensis as a nutritional supplement

Microalgal proteins are promising sources for functional nutrition and a sustainable candidate for nutraceutical formulations. They also gain importance due to emerging focus on a healthy nutrition and increase in the number of chronic diseases. In this study, dried dietary species of microalga, Chlorella vulgaris, and cyanobacterium Spirulina platensis were hydrolyzed with pancreatin enzyme to obtain protein hydrolysates. The hydrolysis yield of biomass was 55.1 ± 0.1 and 64.8 ± 3.6% for C. vulgaris and S. platensis; respectively. Digestibility, as an indicator for dietary utilization, was also investigated. In vitro protein digestibility (IVPD) values depicted that cell wall structure due to the taxonomical differences affected both hydrolysis and digestibility yield of the crude biomass (p < 0.05). Epithelial cells (Vero) maintained their viability around 70%, even in relatively higher concentrations of hydrolysates in the culture. The protein hydrolysates showed no any antimicrobial activities. This study clearly shows that the conventional protein sources in nutraceutical formulations such as soy, whey, and fish proteins can be replaced by enzymatic hydrolysates of microalgae, which shows elevated digestibility values as a sustainable and reliable source.

Biology and Industrial Applications of Chlorella: Advances and Prospects

Chlorella represents a group of eukaryotic green microalgae that has been receiving increasing scientific and commercial interest. It possesses high photosynthetic ability and is capable of growing robustly under mixotrophic and heterotrophic conditions as well. Chlorella has long been considered as a source of protein and is now industrially produced for human food and animal feed. Chlorella is also rich in oil, an ideal feedstock for biofuels. The exploration of biofuel production by Chlorella is underway. Chlorella has the ability to fix carbon dioxide efficiently and to remove nutrients of nitrogen and phosphorous, making it a good candidate for greenhouse gas biomitigation and wastewater bioremediation. In addition, Chlorella shows potential as an alternative expression host for recombinant protein production, though challenges remain to be addressed. Currently, omics analyses of certain Chlorella strains are being performed, which will help to unravel the biological implications of Chlorella and facilitate the future exploration of industrial applications.

Candida utilis and Chlorella vulgaris counteract intestinal inflammation in Atlantic salmon (Salmo salar L.)

Intestinal inflammation, caused by impaired intestinal homeostasis, is a serious condition in both animals and humans. The use of conventional extracted soybean meal (SBM) in diets for Atlantic salmon and several other fish species is known to induce enteropathy in the distal intestine, a condition often referred to as SBM induced enteropathy (SBMIE). In the present study, we investigated the potential of different microbial ingredients to alleviate SBMIE in Atlantic salmon, as a model of feed-induced inflammation. The dietary treatments consisted of a negative control based on fish meal (FM), a positive control based on 20% SBM, and four experimental diets combining 20% SBM with either one of the three yeasts Candida utilis (CU), Kluyveromyces marxianus (KM), Saccharomyces cerevisiae (SC) or the microalgae Chlorella vulgaris (CV). Histopathological examination of the distal intestine showed that all fish fed the SC or SBM diets developed characteristic signs of SBMIE, while those fed the FM, CV or CU diets showed a healthy intestine. Fish fed the KM diet showed intermediate signs of SBMIE. Corroborating results were obtained when measuring the relative length of PCNA positive cells in the crypts of the distal intestine. Gene set enrichment analysis revealed decreased expression of amino acid, fat and drug metabolism pathways as well as increased expression of the pathways for NOD-like receptor signalling and chemokine signalling in both the SC and SBM groups while CV and CU were similar to FM and KM was intermediate. Gene expression of antimicrobial peptides was reduced in the groups showing SBMIE. The characterisation of microbial communities using PCR-DGGE showed a relative increased abundance of Firmicutes bacteria in fish fed the SC or SBM diets. Overall, our results show that both CU and CV were highly effective to counteract SBMIE, while KM had less effect and SC had no functional effects.

Comparative effect of Piper betle, Chlorella vulgaris and tocotrienol-rich fraction on antioxidant enzymes activity in cellular ageing of human diploid fibroblasts

Background

Human diploid fibroblasts (HDFs) undergo a limited number of cellular divisions in culture and progressively reach a state of irreversible growth arrest, a process termed cellular ageing. Even though beneficial effects of Piper betle, Chlorella vulgaris and tocotrienol-rich fraction (TRF) have been reported, ongoing studies in relation to ageing is of interest to determine possible protective effects that may reverse the effect of ageing. The aim of this study was to evaluate the effect of P. betle, C. vulgaris and TRF in preventing cellular ageing of HDFs by determining the activity of antioxidant enzymes viz.; catalase, superoxide dismutase (SOD) and glutathione peroxidase.

Methods

Different passages of HDFs were treated with P. betle, C. vulgaris and TRF for 24 h prior to enzymes activity determination. Senescence-associated beta-galactosidase (SA β-gal) expression was assayed to validate cellular ageing.

Results

In cellular ageing of HDFs, catalase and glutathione peroxidase activities were reduced, but SOD activity was heightened during pre-senescence. P. betle exhibited the strongest antioxidant activity by reducing SA β-gal expression, catalase activities in all age groups, and SOD activity. TRF exhibited a strong antioxidant activity by reducing SA β-gal expression, and SOD activity in senescent HDFs. C. vulgaris extract managed to reduce SOD activity in senescent HDFs.

Conclusion

P. betle, C. vulgaris, and TRF have the potential as anti-ageing entities which compensated the role of antioxidant enzymes in cellular ageing of HDFs.

Highly valuable microalgae: biochemical and topological aspects

The past decade has seen a surge in the interest in microalgae culture for biodiesel production and other applications as renewable biofuels as an alternative to petroleum transport fuels. The development of new technologies for the culture of these photosynthetic microorganisms and improved knowledge of their biochemical composition has spurred innovation in the field of high-value biomolecules. These developments are only economically viable if all the microalgae fractions are valorized in a biorefinery strategy. Achieving this objective requires an understanding of microalgae content and the cellular localization of the main biomolecular families in order to develop efficient harvest and sequential recovery technologies. This review summarizes the state of the art in microalgae compositions and topologies using some examples of the main industrially farmed microalgae.

Potential for green microalgae to produce hydrogen, pharmaceuticals and other high value products in a combined process

Green microalgae for several decades have been produced for commercial exploitation, with applications ranging from health food for human consumption, aquaculture and animal feed, to coloring agents, cosmetics and others. Several products from green algae which are used today consist of secondary metabolites that can be extracted from the algal biomass. The best known examples are the carotenoids astaxanthin and β-carotene, which are used as coloring agents and for health-promoting purposes. Many species of green algae are able to produce valuable metabolites for different uses; examples are antioxidants, several different carotenoids, polyunsaturated fatty acids, vitamins, anticancer and antiviral drugs. In many cases, these substances are secondary metabolites that are produced when the algae are exposed to stress conditions linked to nutrient deprivation, light intensity, temperature, salinity and pH. In other cases, the metabolites have been detected in algae grown under optimal conditions, and little is known about optimization of the production of each product, or the effects of stress conditions on their production. Some green algae have shown the ability to produce significant amounts of hydrogen gas during sulfur deprivation, a process which is currently studied extensively worldwide. At the moment, the majority of research in this field has focused on the model organism, Chlamydomonas reinhardtii, but other species of green algae also have this ability. Currently there is little information available regarding the possibility for producing hydrogen and other valuable metabolites in the same process. This study aims to explore which stress conditions are known to induce the production of different valuable products in comparison to stress reactions leading to hydrogen production. Wild type species of green microalgae with known ability to produce high amounts of certain valuable metabolites are listed and linked to species with ability to produce hydrogen during general anaerobic conditions, and during sulfur deprivation. Species used today for commercial purposes are also described. This information is analyzed in order to form a basis for selection of wild type species for a future multi-step process, where hydrogen production from solar energy is combined with the production of valuable metabolites and other commercial uses of the algal biomass.

High pressure thermal hydrolysis as pre-treatment to increase the methane yield during anaerobic digestion of microalgae

Anaerobic digestion of algal biomass will be an essential component of algal biofuel production systems, yet the methane yield from digestion of algae is typically much lower than the theoretical potential. In this work, high pressure thermal hydrolysis (HPTH) is shown to enhance methane yield during algae digestion. HPTH pre-treatment was applied to both raw algae and algal residue resulting from lipid extraction. HPTH and even the lipid extraction process itself increased methane yield, by 81% and 33% respectively; in combination they increased yield by 110% over that of the raw algae (18L CH4 gVS(-1) substrate). HPTH had little effect on the rate of anaerobic digestion, however lipid extraction enhanced it by 33% over that for raw algae (0.21day(-1)). Digestion resulted in solubilisation of nitrogen (and phosphorous to a lesser degree) in all cases, showing that there is potential for nutrient recycling for algal growth.

Nutritional evaluation of single-cell protein produced by Aphanothece microscopica Nägeli

The aim of this research was to evaluate the nutritional characteristics of Aphanothece microscopica Nägeli microalgae developed in the effluent of parboiled rice. The biomass was biologically evaluated by rat growth, during 10 days for nitrogen balance studies and 28 days for blood analysis. The feeding of Aphanothece biomass diets resulted in a nitrogen balance of 1.42 g/rat/day, an apparent biological value of 73.33%, an apparent digestibility of 82.12%, an apparent net protein utilization of 60.21% and a net protein retention of 2.40. Significant differences between the glycemic indices of rats fed with the Aphanothece and those fed with the control diet were not observed. However, the total cholesterol levels in the plasma of rats fed the test diet proved to be significantly lower. These results suggest the use of A. microscopica Nägeli developed in parboiled rice effluent as a potential source of single-cell protein.

Microbial community composition of the crop and ceca contents of laying hens fed diets supplemented with Chlorella vulgaris

It is generally accepted that the intestinal microbiota plays an important role in sustaining health and productivity of animals. Chlorella vulgaris, a naturally occurring green microalga, is believed to influence performance and health, including bird reproduction and egg quality. The nutritive value of open or indoor cultured C. vulgaris depends upon the technological process used to treat the algal mass. In the present paper, it is presented and discussed how 2 differentially processed C. vulgaris powders (spray-dried: SD-CV; bullet-milled and spray-dried: BMSD-CV) affected crop and cecal microbiota in laying hens. Polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) of bacterial 16S rRNA gene fragments was applied. The diversity of the crop universal bacterial DGGE fingerprints was not affected (6.4 +/- 1.65, 5.4 +/- 1.19, and 5.5 +/- 1.35 in the control, SD-CV, and BMSD-CV, respectively). Most of the bands from the corresponding positions in the gels were closely related to Lactobacillus sp. The DGGE fingerprints of V2-V3 fragments of 16S rRNA of crop lactobacilli had lower diversity in the control hens (8.7 +/- 1.22) than in the SD-CV (9.2 +/- 1.77) and BMSD-CV (9.9 +/- 1.88); thus, feeding C. vulgaris resulted in increased lactobacilli diversity in crop. A band closely related to Lactobacillus ingluviei was present in 9 out of 12 hens in the control group but in only 1 bird in the SD-CV and in 5 out of 11 birds in the BMSD-CV, suggesting a negative effect of C. vulgaris on this lactobacillus. Feeding C. vulgaris to laying hens also resulted in increased bacterial community diversity in the ceca. No effect of the technological processing of the microalgae on the microbial diversity could be observed. The diversity of the ceca universal bacterial DGGE fingerprints was lower in the control group than in the SD-CV and BMSD-CV (5.6 +/- 1.72 vs. 9.16 +/- 2.64 and 9.31 +/- 2.41, respectively). Most of the sequences retrieved from the DGGE bands formed ceca that were closely related to Ruminococcaceae, Lachnospiraceae, and lactobacilli, giving further insight into still poorly discovered intestinal microbiota of laying hens.

Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable

The potential of microalgae as a source of biofuels and as a technological solution for CO2 fixation is subject to intense academic and industrial research. In the perspective of setting up massive cultures, the management of large quantities of residual biomass and the high amounts of fertilizers must be considered. Anaerobic digestion is a key process that can solve this waste issue as well as the economical and energetic balance of such a promising technology. Indeed, the conversion of algal biomass after lipid extraction into methane is a process that can recover more energy than the energy from the cell lipids. Three main bottlenecks are identified to digest microalgae. First, the biodegradability of microalgae can be low depending on both the biochemical composition and the nature of the cell wall. Then, the high cellular protein content results in ammonia release which can lead to potential toxicity. Finally, the presence of sodium for marine species can also affect the digester performance. Physico-chemical pretreatment, co-digestion, or control of gross composition are strategies that can significantly and efficiently increase the conversion yield of the algal organic matter into methane. When the cell lipid content does not exceed 40%, anaerobic digestion of the whole biomass appears to be the optimal strategy on an energy balance basis, for the energetic recovery of cell biomass. Lastly, the ability of these CO2 consuming microalgae to purify biogas and concentrate methane is discussed.

Polysaccharides as a protective response against microcystin-induced oxidative stress in Chlorella vulgaris and Scenedesmus quadricauda and their possible significance in the aquatic ecosystem

Toxic cyanobacteria occur worldwide in aquatic ecosystem, and their toxins have adverse effects on most aquatic organisms. However, some species of green algae can grow and flourish at environmentally relevant concentrations of microcystins (MCYSTs). Therefore, the present study aimed to investigate the possible adaptive response of two representatives of green algae, Chlorella vulgaris and Scenedesmus quadricauda to these toxins. Growth and antioxidative biomarkers of these algae were studied over a 14-day exposure to different concentrations of pure microcystin-LR (MCYST-LR) and crude MCYSTs. Both pure and crude MCYSTs significantly decreased the growth of the two algae compared to control cultures during the first 3 days of incubation. Meanwhile, increases in glutathione-S-transferase (GST), glutathione peroxidase (GPX) and lipid peroxidation, and decreases in glutathione (GSH) were also observed in toxin-treated cultures. All growth and biochemical variables were restored to control levels after 3 days of incubation and remained at levels near to those of control cultures during the remaining period of experiment. The changes in these variables correlated with polysaccharide contents of toxin-treated cultures, indicating the involvement of these polysaccharides in protecting the algal cells against MCYST-induced oxidative stress. The results of in vitro assay of antioxidant activity revealed that these polysaccharides had different activities, depending on their sulfate contents. This study provides an evidence for the first time that polysaccharides play a protective role in some microalgae against MCYST-induced oxidative stress.

Effects of magnetic field on the antioxidant defense system of recirculation-cultured Chlorella vulgaris

Little is known about the influence of magnetic fields (MF) on growth of microalgae such as Chlorella vulgaris, which has been consumed as health food for various nutritional and pharmacological effects. This preliminary study investigated whether static MF can modulate the antioxidant system in C. vulgaris by exposing the cells to static MF generated by dual yoke electromagnets with magnetic flux density of 10-50 mT for 12 h. After exposure to 10-35 mT for 12 h, the activity of superoxide dismutases and peroxidase increased significantly compared to control cells. However, a remarkable increase of catalase activity occurred at 45 and 50 mT. The lipid peroxidation of algae cells determined by production of thiobarbituric acid-reactive substances was much increased when exposed to 35, 45, and 50 mT of MF. The scavenging ability of 2,2-diphenyl-1-picrylhydrazyl radical was decreased markedly while there was no variation of total carotenoids content in C. vulgaris cells. Assay of specific growth rate in 72 h cultivation after MF exposure was also conducted. In groups after exposure to 10-35 mT of MF, specific growth rate was significantly increased. These results suggest that 10-35 mT of static MF exposure could promote the growth of C. vulgaris and regulate its antioxidant defense system to protect cells efficiently, which could possibly enhance the growth of C. vulgaris in industrialized cultivation by MF.