Screening of Diatom Strains and Characterization of Cyclotella cryptica as A Potential Fucoxanthin Producer

Novel insights into mixotrophic cultivation of Nitzschia laevis for co-production of fucoxanthin and eicosapentaenoic acid

The aim of this study was to determine a compatible method for co-production of fucoxanthin and eicosapentaenoic acid of diatom Nitzschia laevis by mixotrophic and heterotrophic cultivation modes in view of cell growth, targeting products' contents, photosynthesis-related characteristics and carbon partitioning. The results showed that mixotrophic mode enhanced fucoxanthin and eicosapentaenoic acid yields by increasing their precursors of pyruvate and acetyl-CoA at the expense of starch. The increase of chlorophylls and glyceraldehyde 3-phosphate indicated the development of Calvin cycle and carbon repartitioning in mixotrophic mode. Consequently, microalgal cells in mixotrophic mode achieved much higher fucoxanthin (60.12%) and eicosapentaenoic acid (50.67%) contents, and lower starch content (30.2%) compared with heterotrophic mode. Furthermore, fucoxanthin content was positively correlated with eicosapentaenoic acid content (adjusted R² = 0.96). Taken together, these results showed that the mixotrophic mode could be a promising approach for the co-production of fucoxanthin and eicosapentaenoic acid by Nitzschia laevis.

Transgenic microalgae as bioreactors

Microalgae are unicellular organisms that act as the crucial primary producers all over the world, typically found in marine and freshwater environments. Most of them can live photo-autotrophically, reproduce rapidly, and accumulate biomass in a short period efficiently. To adapt to the uninterrupted change of the environment, they evolve and differentiate continuously. As a result, some of them evolve special abilities such as toleration of extreme environment, generation of sophisticated structure to adapt to the environment, and avoid predators. Microalgae are believed to be promising bioreactors because of their high lipid and pigment contents. Genetic engineering technologies have given revolutions in the microalgal industry, which decoded the secrets of microalgal genes, express recombinant genes in microalgal genomes, and largely soar the accumulation of interested components in transgenic microalgae. However, owing to several obstructions, the industry of transgenic microalgae is still immature. Here, we provide an overview to emphasize the advantage and imperfection of the existing transgenic microalgal bioreactors.

Storage carbon metabolism of Isochrysis zhangjiangensis under different light intensities and its application for co-production of fucoxanthin and stearidonic acid

This study explored the co-production of fucoxanthin and stearidonic acid from Isochrysis zhangjiangensis by investigating its carbon metabolism under different light intensities. Results showed high light inhibited the synthesis of fucoxanthin and stearidonic acid, while promoted cell growth and enhanced cellular lipid content compared with low light, achieving 2.4 g/L and 28.55%, respectively. Low light accelerated the accumulation of fucoxanthin and stearidonic acid, which obtained 23.29 mg/g and 17.16% (of total fatty acid). In combination with the molecular analysis, low light redirected carbon skeletons into glyceraldehyde-3-phosphate and diverted into carotenoid especially fucoxanthin. While, high light redistributed the skeletons to Malonyl CoA, citrate and α-Ketoglutarate and then oriented into lipid metabolism. The highest fucoxanthin and stearidonic acid productivity was 2.94 mg L^-1 d^-1 and 4.33 mg L^-1 d^-1, respectively, which revealed I. zhanjiangensis is a potential strain for the co-production of fucoxanthin and stearidonic acid.

OPTIMIZATION OF EXTRACTION PARAMETERS FOR FUCOXANTHIN, GALLIC ACID AND RUTIN FROM NITZSCHIA THERMALIS

Recently, microalgae have become important in their health, and cosmetic applications since they are viewed as new sources of carotenoids. Fucoxanthin is also a type of carotenoid. The anti-diabetic, anti-obesity, anti-cancer, and antioxidant properties of fucoxanthin have been widely reported. Since these valuable properties, they also represent a valuable resource of nutraceuticals for functional food applications. This study aims to determine the amount of fucoxanthin, gallic acid, and rutin in Nitzschia thermalis obtained from the Ege University Microalgae Culture Collection. The extraction parameters have been optimized using response surface methodology. The extraction temperature (25, 35, and 45°C), the extraction time (10, 20, and 30 min) and the biomass/solvent ratio (0.005, 0.001, and 0.015 g ml-1) have been assessed as response variables in the Box – Behnken design. The amount of fucoxanthin was determined by the C30 column at 450 nm, while both the amount of gallic acid and rutin were separated in the C18 column at 275 nm by HPLC-DAD. In the present study, the optimum extraction conditions providing the maximum amount of fucoxantin, gallic acid, and rutin were selected by applying the “desirability” function approach in response surface methodology. Finally, the temperature has been determined to be 27.30°C, the extraction time 10 minutes, and the biomass ratio 0.05 g ml-1. Under these conditions, the optimum fucoxanthin level has been determined as 5.8702 mg g-1, the gallic acid level as 0.0140 mg g-1, and the rutin level as 0.0496 mg g-1. The findings are in good agreement with international published values for fucoxanthin content. In addition, response surface methodology was shown to be an effective technique for optimising extraction conditions for maximum fucoxanthin yield. In conclusion, these findings may be applied in the development of extraction methodologies for value added microalgea products as well as can serve as a reference for the extraction of fucoxanthin having high gallic acid and rutin from other brown microalgae, and therefore it could potentially be applied in both pharmaceutical and food industries.

Biological aspects and biotechnological potential of marine diatoms in relation to different light regimens

As major primary producers in marine environments, diatoms are considered a valuable feedstock of biologically active compounds for application in several biotechnological fields. Due to their metabolic plasticity, especially for light perception and use and in order to make microalgal production more environmentally sustainable, marine diatoms are considered good candidates for the large-scale cultivation. Among physical parameters, light plays a primary role. Even if sunlight is cost-effective, the employment of artificial light becomes a winning strategy if a high-value microalgal biomass is produced. Several researches on marine diatoms are designed to study the influence of different light regimens to increase biomass production enriched in biotechnologically high-value compounds (lipids, carotenoids, proteins, polysaccharides), or with emphasised photonic properties of the frustule.

Extract of the Microalga Nitzschia laevis Prevents High-Fat-Diet-Induced Obesity in Mice by Modulating the Composition of Gut Microbiota

SCOPE

The aim of the present study is to investigate the efficacy of Nitzschia laevis extract (NLE) in preventing obesity in mice fed with a high-fat diet (HFD), and the potential underlying mechanisms focusing on modulation of the gut microbiota profile.

METHODS AND RESULTS

Physiological, histological, and biochemical parameters and gut microbiota compositions are compared among four experimental groups fed respectively with the following diets for 8 weeks: Normal chow diet, HFD, HFD + low concentration of NLE, and HFD + high concentration of NLE. The results demonstrate that NLE supplementation significantly reduces body weight gain and effectively prevents lipid accumulation in the white adipose tissue and liver of the mice. Mechanistic analysis reveals that NLE promotes the expression of uncoupling protein 1 and peroxisome proliferators-activated receptor-γ coactivator-1 mRNA in brown adipose tissue. Furthermore, NLE protects the gut epithelium and positively reshapes the gut microbiota composition against the damaging effect of HFD.

CONCLUSIONS

NLE supplementation demonstrates a protective effect against HFD-induced obesity in mice, which is associated with reshaping the profile of gut microbiota. To the best of our knowledge, this has been the first report on the potential of microalgal extract to prevent obesity by modulating gut microbiota.

Changes in the fucoxanthin production and protein profiles in Cylindrotheca closterium in response to blue light-emitting diode light

BACKGROUND

Marine diatoms have a higher fucoxanthin content in comparison to macroalgae. Fucoxanthin features many potent bioactive properties, particularly anti-obesity properties. Despite the great potential for harvesting larger amounts of fucoxanthin, the impacts of light quality (light source, intensity, and photoperiod) on fucoxanthin production and the essential proteins involved in fucoxanthin biosynthesis in marine diatoms remain unclear.

RESULTS

In the present study, Cylindrotheca closterium was selected from four different species of diatoms based on its high fucoxanthin content and productivity. Optimal light conditions (light source, intensity, and regime) were determined by a "Design of Experiment" approach (software MODDE Pro 11 was used). The model indicated that an 18/6 light/darkness regime increased fucoxanthin productivity remarkably as opposed to a 12/12 or 24/0 regime. Eventually, blue light-emitting diode light, as an alternative to fluorescent light, at 100 μmol/m2/s and 18/6 light/darkness regime yielded maximum fucoxanthin productivity and minimal energy consumption. The fucoxanthin production of C. closterium under the predicted optimal light conditions was assessed both in bottle and bag photobioreactors (PBRs). The high fucoxanthin content (25.5 mg/g) obtained from bag PBRs demonstrated the feasibility of large-scale production. The proteomes of C. closterium under the most favorable and unfavorable fucoxanthin biosynthesis light/darkness regimes (18/6 and 24/0, respectively) were compared to identify the essential proteins associated with fucoxanthin accumulation by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry. Six proteins that were up-regulated in the 18/6 regime but down-regulated in the 24/0 were identified as important chloroplastic proteins involved in photosynthesis, energy metabolism, and cellular processes.

CONCLUSIONS

Blue light-emitting diode light at 100 μmol/m2/s and 18/6 light/darkness regime induced maximum fucoxanthin productivity in C. closterium and minimized energy consumption. The high fucoxanthin production in the bag photobioreactor under optimal light conditions demonstrated the possibility of commercialization. Proteomics suggests that fucoxanthin biosynthesis is intimately associated with the photosynthetic efficiency of the diatom, providing another technical and bioengineering outlook on fucoxanthin enhancement.

A Hetero-Photoautotrophic Two-Stage Cultivation Process for Production of Fucoxanthin by the Marine Diatom Nitzschia laevis

There is currently much interest in fucoxanthin due to its broad beneficial health effects. The major commercial source of fucoxanthin is marine seaweed, which has many shortcomings, and has thus restricted its large-scale production and more diversified applications. In this study, growth characteristics and fucoxanthin accumulation were evaluated to explore the potential of the marine diatom Nitzschia laevis in fucoxanthin production. The results suggested that heterotrophic culture was more effective for cell growth, while the mixotrophic culture was favorable for fucoxanthin accumulation. A two-stage culture strategy was consequently established. A model of exponential fed-batch culture led to a biomass concentration of 17.25 g/L. A mix of white and blue light significantly increased fucoxanthin content. These outcomes were translated into a superior fucoxanthin productivity of 16.5 mg/(L·d), which was more than 2-fold of the best value reported thus far. The culture method established herein therefore represents a promising strategy to boost fucoxanthin production in N. laevis, which might prove to be a valuable natural source of commercial fucoxanthin.

Industrial potential of carotenoid pigments from microalgae: Current trends and future prospects

Microalgae are rich source of various bioactive molecules such as carotenoids, lipids, fatty acids, hydrocarbons, proteins, carbohydrates, amino acids, etc. and in recent Years carotenoids from algae gained commercial recognition in the global market for food and cosmeceutical applications. However, the production of carotenoids from algae is not yet fully cost effective to compete with synthetic ones. In this context the present review examines the technologies/methods in relation to mass production of algae, cell harvesting for extraction of carotenoids, optimizing extraction methods etc. Research studies from different microalgal species such as Spirulina platensis, Haematococcus pluvialis, Dunaliella salina, Chlorella sps., Nannochloropsis sps., Scenedesmus sps., Chlorococcum sps., Botryococcus braunii and Diatoms in relation to carotenoid content, chemical structure, extraction and processing of carotenoids are discussed. Further these carotenoid pigments, are useful in various health applications and their use in food, feed, nutraceutical, pharmaceutical and cosmeceutical industries was briefly touched upon. The commercial value of algal carotenoids has also been discussed in this review. Possible recommendations for future research studies are proposed.

A Rapid Method for the Determination of Fucoxanthin in Diatom

Fucoxanthin is a natural pigment found in microalgae, especially diatoms and Chrysophyta. Recently, it has been shown to have anti-inflammatory, anti-tumor, and anti-obesityactivity in humans. Phaeodactylum tricornutum is a diatom with high economic potential due to its high content of fucoxanthin and eicosapentaenoic acid. In order to improve fucoxanthin production, physical and chemical mutagenesis could be applied to generate mutants. An accurate and rapid method to assess the fucoxanthin content is a prerequisite for a high-throughput screen of mutants. In this work, the content of fucoxanthin in P. tricornutum was determined using spectrophotometry instead of high performance liquid chromatography (HPLC). This spectrophotometric method is easier and faster than liquid chromatography and the standard error was less than 5% when compared to the HPLC results. Also, this method can be applied to other diatoms, with standard errors of 3-14.6%. It provides a high throughput screening method for microalgae strains producing fucoxanthin.

Carotenoid profile of three microalgae/cyanobacteria species with peroxyl radical scavenger capacity

Carotenoids from cyanobacteria Aphanothece microscopica Nageli and green microalgae Chlorella vulgaris and Scenedesmus obliquus were identified. The total carotenoid content, based on dry weight of biomass, of A. microscopica Nägeli, C. vulgaris and S. obliquus were 1398.88μg/g, 1977.02μg/g and 2650.70μg/g, respectively. A total of 23 different carotenoids were separated in all the extracts, the major ones being all-trans-β-carotene (29.3%) and all-trans-lutein (28.1%) in Scenedesmus; all-trans-echinenone (22.8%) and all-trans-β-carotene (17.7%) in Chlorella; all-trans-echinenone (28.3%) and all-trans-β-carotene (26.2%) in Aphanothece. The carotenoid extracts were shown to be a potent scavenger of peroxyl radical, with values of 31.1 (Chlorella), 14.0 (Scenedesmus) and 7.3 (Aphanothece) times more potent than α-tocopherol.