Optimization of a Nile Red method for rapid lipid determination in autotrophic, marine microalgae is species dependent

Nannochloropsis Lipids and Polyunsaturated Fatty Acids: Potential Applications and Strain Improvement

The genus Nannochloropsis comprises a group of oleaginous microalgae that accumulate polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA). These molecules are essential for the correct development and health of humans and animals. Thanks to their attractive lipid profile, Nannochloropsis is mainly marketed as a feed ingredient in aquaculture. In microalgae of this genus, contents and cellular location of PUFAs are affected by the growth conditions and gene expression. Strain improvement through non-recombinant approaches can generate more productive strains and efficient bioprocesses for PUFA production. Nevertheless, the lack of specific markers, detection methods, and selective pressure for isolating such mutants remains a bottleneck in classical mutagenesis approaches or lipid quality assessment during cultivation. This review encompasses the importance of PUFAs and lipid classes from Nannochloropsis species and their potential applications. Additionally, a revision of the different ways to increase PUFA content in Nannochloropsis sp. by using classical mutagenesis and adaptive laboratory evolution is also presented, as well as various methods to label and quantify lipids and PUFAs from Nannochloropsis microalgae.

Antioxidative capacity of microalgal carotenoids for stabilizing n-3LC-PUFA rich oil: Initial quantity is key

The health-beneficial long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA) are easily affected by the undesired process of lipid oxidation in fish oil, while being stable in the lipid extracts of photoautotrophic microalgae. The current research investigates the role of carotenoids by evaluating the oxidative stability of mixtures of fish oil with total lipid extracts of two different microalgae (Phaeodactylum and Isochrysis) throughout an accelerated storage experiment of 4 weeks at 37 °C. A clear separation between oxidatively stable and oxidatively unstable mixtures was observed for which the initial amount of carotenoids relative to the amount of n-3LC-PUFA was a good indicator. The lipid class composition, clearly differing between the two algae, was probably of minor influence. The antioxidative role of fucoxanthin, and diatoxanthin and β-carotene as minor carotenoids, was illustrated by their gradual degradation throughout storage. However, when their initial contents were too low, this role could not be exerted leading to thorough lipid oxidation.

Marine enzymes: Classification and application in various industries

Oceans are regarded as a plentiful and sustainable source of biological compounds. Enzymes are a group of marine biomaterials that have recently drawn more attention because they are produced in harsh environmental conditions such as high salinity, extensive pH, a wide temperature range, and high pressure. Hence, marine-derived enzymes are capable of exhibiting remarkable properties due to their unique composition. In this review, we overviewed and discussed characteristics of marine enzymes as well as the sources of marine enzymes, ranging from primitive organisms to vertebrates, and presented the importance, advantages, and challenges of using marine enzymes with a summary of their applications in a variety of industries. Current biotechnological advancements need the study of novel marine enzymes that could be applied in a variety of ways. Resources of marine enzyme can benefit greatly for biotechnological applications duo to their biocompatible, ecofriendly and high effectiveness. It is beneficial to use the unique characteristics offered by marine enzymes to either develop new processes and products or improve existing ones. As a result, marine-derived enzymes have promising potential and are an excellent candidate for a variety of biotechnology applications and a future rise in the use of marine enzymes is to be anticipated.

Physiological and Biochemical Responses of Bicarbonate Supplementation on Biomass and Lipid Content of Green Algae Scenedesmus sp. BHU1 Isolated From Wastewater for Renewable Biofuel Feedstock

In the present study, different microalgae were isolated from wastewater environment and evaluated for higher growth and lipid accumulation. The growth adaptability of all the isolated microalgae were tested for carbon source with supplementation of sodium bicarbonate in BG-11 N⁺ medium. Further based on the uptake rate of sodium bicarbonate and growth behavior, microalgal strains were selected for biofuel feedstock. During the study, growth parameters of all the isolates were screened after supplementation with various carbon sources, in which strain Scenedesmus sp. BHU1 was found highly effective among all. The efficacy of Scenedesmus sp. BHU1 strain under different sodium bicarbonate (4–20 mM) concentration, in which higher growth 1.4 times greater than control was observed at the concentration 12 mM sodium bicarbonate. In addition, total chlorophyll content (Chl-a + Chl-b), chlorophyll fluorescence (Fv/Fm, Y(II), ETR max, and NPQmax), and biomass productivity were found to be 11.514 μg/ml, 0.673, 0.675, and 31.167 μmol electrons m⁻² s⁻¹, 1.399, 59.167 mg/L/day, respectively, at the 12 mM sodium bicarbonate. However, under optimum sodium bicarbonate supplementation, 56.920% carbohydrate and 34.693% lipid content were accumulated, which showed potential of sodium bicarbonate supplementation in renewable biofuel feedstock by using Scenedesmus sp. BHU1 strain.

Rapid Lipid Content Screening in Neochloris oleoabundans Utilizing Carbon-Based Dielectrophoresis

In this study, we carried out a heterogeneous cytoplasmic lipid content screening of Neochloris oleoabundans microalgae by dielectrophoresis (DEP), using castellated glassy carbon microelectrodes in a PDMS microchannel. For this purpose, microalgae were cultured in nitrogen-replete (N+) and nitrogen-deplete (N−) suspensions to promote low and high cytoplasmic lipid production in cells, respectively. Experiments were carried out over a wide frequency window (100 kHz–30 MHz) at a fixed amplitude of 7 V_PP. The results showed a statistically significant difference between the dielectrophoretic behavior of N+ and N− cells at low frequencies (100–800 kHz), whereas a weak response was observed for mid- and high frequencies (1–30 MHz). Additionally, a finite element analysis using a 3D model was conducted to determine the dielectrophoretic trapping zones across the electrode gaps. These results suggest that low-cost glassy carbon is a reliable material for microalgae classification—between low and high cytoplasmic lipid content—through DEP, providing a fast and straightforward mechanism.

Accurate method for rapid biomass quantification based on specific absorbance of microalgae species with biofuel importance

The development of microalgae culture technology has been an integral part to produce biomass feedstock to biofuel production. Due to this, numerous attempts have been made to improve some operational parameters of microalgae production. Despite this, specialized research in cell growth monitoring, considered as a fundamental parameter to achieve profitable applications of microalgae for biofuels production, presents some opportunity areas mainly related to the development of specific and accurate methodologies for growth monitoring. In this work, predictive models were developed through statistical tools that correlate a specific micro-algal absorbance with cell density measured by cell count (cells∙per ml), for three species of interest for biofuels production. The results allow the precise prediction of cell density through a logistic model based on spectrophotometry, valid for all the kinetics analysed. The adjusted determination coefficients ( r adj 2 ) for the developed models were 0·993, 0·995 and 0·994 for Dunaliella tertiolecta, Nannochloropsis oculata and Chaetoceros muelleri respectively. The results showed that the equations obtained here can be used with an extremely low error (≤2%) for all the cell growth ranges analysed, with low operational cost and high potential of automation. Finally, a user-friendly software was designed to give practical use to the developed predictive models.

Nile Red Incubation Time Before Reading Fluorescence Greatly Influences the Yeast Neutral Lipids Quantification

High-throughput screening methodologies to estimate lipid content in oleaginous yeasts use Nile red fluorescence in a given solvent and optimized excitation/emission wavelengths. However, Nile red fluorescence stabilization has been poorly analyzed, and high variability occurs when relative fluorescence is measured immediately or a few minutes after dye addition. The aim of this work was to analyze the fluorescence of Nile red at different incubation times using a variety of solvents and oleaginous/non-oleaginous yeast strains. We showed that fluorescence stabilization occurs between 20 and 30 min, depending on the strain and solvent. Therefore, we suggest that fluorescence measurements should be followed until stabilization, where Relative Fluorescence Units should be considered after stabilization for lipid content estimation.

Electro-Fenton Based Technique to Enhance Cell Harvest and Lipid Extraction from Microalgae

Currently, lipid extraction remains a major bottleneck in microalgae technology for biofuel production. In this study, an effective and easily controlled cell wall disruption method based on electro-Fenton reaction was used to enhance lipid extraction from the wet biomass of Nannochloropsis oceanica IMET1. The results showed that 1.27 mM of hydroxide radical (HO•) was generated under the optimal conditions with 9.1 mM FeSO4 in a 16.4 mA·cm−2 current density for 37.0 min. After the electro-Fenton treatment, the neutral lipid extraction yield of microalgae (~155 mg) increased from 40% to 87.5%, equal to from 12.2% to 26.7% dry cell weight (DCW). In particular, the fatty acid composition remained stable. The cell wall disruption and lipid extraction processes were displayed by the transmission electron microscope (TEM) and fluorescence microscopy (FM) observations, respectively. Meanwhile, the removal efficiency of algal cells reached 85.2% within 2 h after the reaction was terminated. Furthermore, the biomass of the microalgae cultured in the electrolysis wastewater treated with fresh nutrients reached 3 g/L, which is 12-fold higher than that of the initial after 24 days. These finds provided an economic and efficient method for lipid extraction from wet microalgae, which could be easily controlled by current magnitude regulation.

Neutral Lipid Content in Lipid Droplets: Potential Biomarker of Cordycepin Accumulation in Cordycepin-Producing Fungi

To clarify the relationship between neutral lipid content and cordycepin accumulation in Cordyceps militaris, mutants were generated from mixed spores of two C. militaris strains with varying cordycepin-producing capacities. Fifteen stable mutants producing from 0.001 to 2.363 mg/mL cordycepin were finally selected. The relative fluorescence intensities of the 15 mutants, two C. militaris strains and an Aspergillus nidulans strain at different concentrations of lyophilized mycelium powder were then investigated using the Nile red method. The mutant CM1-1-1 with the highest relative fluorescence intensity among the eighteen strains was selected for optimizing the Nile red method. Relative fluorescence intensity was linearly correlated with cordycepin concentration in liquid broth (R² = 0.9514) and in lyophilized mycelium powder (R² = 0.9378) for the 18 cordycepin-producing strains under identical culture conditions and with cordycepin concentration in liquid broth (R² = 0.9727) and in lyophilized mycelium powder (R² = 0.9613) for CM1-1-1 under eight different sets of conditions. In addition, the cordycepin content in lyophilized mycelium powder measured by the Nile red method was linearly correlated with that determined by an HPLC method (R² = 0.9627). In conclusion, neutral lipids in lipid droplets are required during cordycepin accumulation; these neutral lipids are potential biomarkers of cordycepin biosynthesis.

Determining intracellular lipid content of different oleaginous yeasts by one simple and accurate Nile Red fluorescent method

A simple and accurate Nile Red fluorescent method was built to evaluate the lipid content of three different oleaginous yeasts by one standard curve. The staining of cells can be observed clearly by laser scanning confocal microscope, showing that Nile Red can enter into the cells of oleaginous yeasts easily. A series of conditions such as pretreating temperature, cell suspension concentration (OD₆₀₀), staining time, Nile Red concentration and the type of suspension solvent were learnt systematically to obtain the optimal process parameters for Nile Red staining. After optimization, the fitting curve of Nile Red fluorescent method was established under suitable conditions (pretreating temperature: 50 °C, OD₆₀₀: 1.0; staining time: 5 mins; Nile Red concentration: 1.0 μg/mL; suspension solvent: PBS) and it had a suitable correlation coefficient (R² = 0.95) for lipid content measurement of different oleaginous yeasts. By this study, the possibility of lipid content determination of different oleaginous yeasts by one fitting curve can be proven and this will improve the efficiency of researches related to microbial lipid production.

How to use Nile Red, a selective fluorescent stain for microalgal neutral lipids

The use of Nile Red for rapid monitoring of the neutral lipid content in microalgae has gained interest over the last decade, since neutral lipids are feedstock for renewable transportation fuel. In this review, we discuss the main considerations needed to make an NR protocol reliable for staining neutral lipids in microalgae. Cell wall permeability must be enhanced by using stain carriers: DMSO (5% v/v to 25% v/v), glycerol (0.1 to 0.125mg/mL), or EDTA (3.0 to 3.8mg/mL). Temperatures between 30 and 40°C facilitate the diffusion of NR through the cell wall without incurring excess quenching. Good NR-lipid interaction requires using a low NR/cell ratio; the NR concentration must be between 0.25μg/mL and 2.0μg/mL, and the cell concentration >5×10(4)cells/mL. In order to have the maximum and stable NR fluorescence, it is necessary to scan the excitation/emission wavelengths for up to a 40-min of incubation time. We outline a five-step method to customize the Nile Red protocol to a specific strain: 1) Evaluate the strain's suitability by checking for the presence of neutral lipid, 2) Select of the best excitation/emission wavelength, 3) Optimization of incubation time, stain carrier, dye concentration, and temperature, 4) Prepare single-strain algal cultures with different lipid contents to calibrate NR fluorescence with neutral-lipid content, and 5) Correlate NR fluorescence intensity to neutral lipid content for the same strain. Once the protocol is customized, the NR method allows for rapid and reliable monitoring of neutral lipid content of a microalgae strain.