Photoautotrophic Microalgae Research Articles

The Crucial Impact of Microbial Growth and Bioenergy Conversion on Treating Livestock Manure and Antibiotics Using Chlorella sorokiniana

The residual antibiotics in livestock excreta (LE) have been regarded as a potential threat to the ecosystem and human society. Some photoautotrophic microalgae, however, were found to metabolize them during active biomass photosynthesis. This study investigates how the strength of the antibiotics impacts the overall biodiesel yield and composition of the harvested microalgal biomass grown from LE. The microalgal growth results demonstrate that increasing the concentration of residual antibiotics suppresses the microalgal growth rate from 0.87 d−1 to 0.34 d−1. This 61% lower biomass production rate supports the proposition that the kinetic impact of antibiotics may slow lipid synthesis. Moreover, the analytical results of fatty acid methyl ester (FAME) demonstrate that amoxicillin substantially reduces the C16:0 content by over 96%. This study evidences that the functional group similarity of amoxicillin may competitively inhibit the esterification reaction by consuming methanol. This explanation further highlights that residual antibiotics interfere with microalgal lipid synthesis and its transesterification. Moreover, it was confirmed that the presence of residual antibiotics may not affect the major nutrient removal (total nitrogen: 74.5~78.0%, total phosphorus: 95.6~96.8%). This indicates that residual antibiotics inhibit the metabolism associated with carbon rather than those associated with nitrogen and phosphorus, which is connected to the decrease in the biodiesel yield. Overall, these results reveal that the frequent abuse of antibiotics in livestock may harm the eco-friendly conversion of waste-into-bioenergy strategy.

Shaping Sustainable Bioplastics: Illuminating Chlorella sp. Growth with Light Variations and NPK Levels

this study delved into the exploration of a biodegradable alternative to synthetic plastics through the production of biodegradable bioplastics derived from microalgae. The investigation suggests that utilizing <i>Chlorella </i>sp. as a viable source for sustainable biomass in bioplastic creation holds promise due to the convenience of microalgae cultivation and its rapid growth rate. However, the large-scale cultivation of microalgae requires a considerable amount of nutrients, posing challenges to its economic viability. To address this hurdle, it becomes imperative to prioritize the enhancement of growth parameters for microalgae development. This study endeavors to identify the optimal NPK (nitrogen, phosphorus, and potassium) concentration and light spectrum for <i>Chlorella </i>sp. using a cost-effective NPK fertilizer medium. Various combinations of light spectra and NPK levels were examined to optimize growth conditions. Cultures of <i>Chlorella</i> sp. were subjected to red (660 nm), blue (460 nm), and white light (380 ~ 760 nm) which acted as experimental control over a span of 10 days. Among these, blue light yielded the highest optical density at 0.687, while red light exhibited the lowest optical density at 0.349. The findings underscore that the quantity of NPK fertilizer employed as a growth medium correlate directly with the observed cellular growth in <i>Chlorella</i> sp. cultures. The study also encompassed tensile strength and biodegradability assessments to characterize the resulting bioplastics. Tensile tests disclosed that bioplastics synthesized with sorbitol displayed a lower tensile strength of 0.106 MPa, in contrast to bioplastics containing both sorbitol and chitosan, which demonstrated a tensile strength of 0.167 MPa. In conclusion, both the appropriate light wavelengths and NPK nutrients emerge as pivotal factors influencing photosynthesis and the growth of photoautotrophic microalgae. The overarching objective of this research was achieved by successfully producing bioplastics using microalgae biomass residue cultivated under optimized parameters.

Interkingdom network analyses reveal microalgae and protostomes as keystone taxa involved in nutrient cycling in large freshwater lake sediment.

Few studies have explored the role of interkingdom interactions between bacteria and microeukaryotes in nutrient cycling in lake ecosystems. We conducted sediment sampling from 40 locations covering Hongze Lake and analyzed their chemical properties. Intra- and interkingdom networks were constructed using 16S and 18S rRNA gene amplicon sequencing. Microeukaryotic intranetworks were more complex in spring than in autumn, while no clear variation in the complexity of bacterial intranetworks was found between autumn and spring. Larger and more complex bacterial-microeukaryotic bipartite networks emerged in spring than in autumn, correlated with lower carbon, nitrogen, and phosphorus levels in spring, likely resulting in intense microbial competition. Bacteria and microeukaryotes played different topological roles in interkingdom networks, with microeukaryotes contributing to the networks' greater complexity. Seven keystone modules were identified in spring and autumn nutrient cycling. Importantly, keystone taxa in these modules belonged to photoautotrophic microalgae or predatory protostomes, indicating that these organisms are key drivers in lake sediment nutrient cycling. Our results suggested that nutrient content variation in autumn and spring changes interkingdom networks' topological structure between bacteria and microeukaryotes. Microalgae and protostomes are essential in freshwater lake nutrient cycling and may be targeted to modulate nutrient cycling in large freshwater ecosystems.

Enhancing the bio-prospective of microalgae by different light systems and photoperiods.

Microalgae are a source of highly valuable bioactive metabolites and a high-potential feedstock for environmentally friendly and sustainable biofuel production. Recent research has shown that microalgae benefit the environment using less water than conventional crops while increasing oxygen production and lowering CO2 emissions. Microalgae are an excellent source of value-added compounds, such as proteins, pigments, lipids, and polysaccharides, as well as a high-potential feedstock for environmentally friendly and sustainable biofuel production. Various factors, such as nutrient concentration, temperature, light, pH, and cultivation method, effect the biomass cultivation and accumulation of high-value-added compounds in microalgae. Among the aforementioned factors, light is a key and essential factor for microalgae growth. Since photoautotrophic microalgae rely on light to absorb energy and transform it into chemical energy, light has a significant impact on algal growth. During micro-algal culture, spectral quality may be tailored to improve biomass composition for use in downstream bio-refineries and boost production. The light regime, which includes changes in intensity and photoperiod, has an impact on the growth and metabolic composition of microalgae. In this review, we investigate the effects of red, blue, and UV light wavelengths, different photoperiod, and different lighting systems on micro-algal growth and their valuable compounds. It also focuses on different micro-algal growth, photosynthesis systems, cultivation methods, and current market shares.

Mass Cultivation of Microalgae: II. A Large Species Pulsing Blue Light Concept.

If mass cultivation of photoautotrophic microalgae is to gain momentum and find its place in the new "green future", exceptional optimizations to reduce production costs must be implemented. Issues related to illumination should therefore constitute the main focus, since it is the availability of photons in time and space that drives synthesis of biomass. Further, artificial illumination (e.g., LEDs) is needed to transport enough photons into dense algae cultures contained in large photobioreactors. In the present research project, we employed short-term O2 production and 7-day batch cultivation experiments to evaluate the potential to reduce illumination light energy by applying blue flashing light to cultures of large and small diatoms. Our results show that large diatom cells allow more light penetration for growth compared to smaller cells. PAR (400-700 nm) scans yielded twice as much biovolume-specific absorbance for small biovolume (avg. 7070 μm3) than for large biovolume (avg. 18,703 μm3) cells. The dry weight (DW) to biovolume ratio was 17% lower for large than small cells, resulting in a DW specific absorbance that was 1.75 times higher for small cells compared to large cells. Blue 100 Hz square flashing light yielded the same biovolume production as blue linear light in both the O2 production and batch experiments at the same maximum light intensities. We therefore suggest that, in the future, more focus should be placed on researching optical issues in photobioreactors, and that cell size and flashing blue light should be central in this.

Preparation and Characterization of Microalgae Styrene-Butadiene Composites Using Chlorella vulgaris and Arthrospira platensis Biomass.

The food industry is a high consumer of polymer packing materials, sealing materials, and engineering components used in production equipment. Biobased polymer composites used in the food industry are obtained by incorporating different biogenic materials into the structure of a base polymer matrix. Renewable resources such as microalgae, bacteria, and plants may be used as biogenic materials for this purpose. Photoautotrophic microalgae are valuable microorganisms that are able to harvest sunlight energy and capture CO2 into biomass. They are characterized by their metabolic adaptability to environmental conditions, higher photosynthetic efficiency than terrestrial plants, and natural macromolecules and pigments. The flexibility of microalgae to grow in either low-nutrient or nutrient-rich environments (including wastewater) has led to the attention for their use in various biotechnological applications. Carbohydrates, proteins, and lipids are the main three classes of macromolecular compounds contained in microalgal biomass. The content in each of these components depends on their growth conditions. In general, proteins represent 40-70% of microalgae dry biomass, followed by carbohydrates (10-30%) and lipids (5-20%). A distinctive feature of microalgae cells is the presence of light-harvesting compounds such as photosynthetic pigments carotenoids, chlorophylls, and phycobilins, which are also receiving growing interest for applications in various industrial fields. The study comparatively reports on polymer composites obtained with biomass made of two species of green microalgae: Chlorella vulgaris and filamentous, gram-negative cyanobacterium Arthrospira. Experiments were conducted to reach an incorporation ratio of the biogenic material into the matrix in the 5-30% range, and the resulting materials were characterized by their mechanical and physicochemical properties.

High cell density culture of Neochloris oleoabundans in novel horizontal thin-layer algal reactor: Effects of localized aeration, nitrate concentration and mixing frequency

A horizontal thin-layer algal reactor was designed, constructed and tested for high cell density culture of an oil-rich green alga, Neochloris oleoabundans, at a thickness of 6 mm. A hollow fiber membrane sparger was used for localized aeration with CO2-enriched air, which allowed control of culture pH at a narrow range of pH 7.0–7.5. The optimal nitrate concentration under the investigated conditions was 345 mg-N/L with a cell density of ∼6.6 × 108 cells/mL and biomass concentration of ∼8 g/L. The volumetric and areal biomass productivities were 1.81 g/L/day and 10.85 g m− 2/day, respectively, and the maximum volumetric and areal productivities 3.57 g/L/day and 21.42 g m− 2/day, respectively. Intermittent mixing at a frequency of once every two hours (five min mixing each time) produced a cell growth profile similar to that of continuous mixing. Such intermittent mixing resulted in 98.38 % saving on mixing energy and 33.9 % reduction in water evaporation. It was observed that metabolic stress such as high pH and high nitrate concentration could inhibit cell division while causing cell size to enlarge abnormally. The results indicate that it is technically feasible to have high cell density culture of photoautotrophic microalgae with intermittent mixing and no culture circulation, opening the door towards the development of open algal farming systems of low capital, operational, and maintenance costs.

Development of a bench-scale photobioreactor with a novel recirculation system for continuous cultivation of microalgae

Microalgae cultivation can be used to increase the sustainability of carbon emitting processes, converting the CO2 from exhaust gases into fuels, food and chemicals. Many of the carbon emitting industries operate in a continuous manner, for periods that can span days or months, resulting in a continuous stream of gas emissions. Biogenic CO2 from industrial microbiological processes is one example, since in many cases it becomes unsustainable to stop these processes on a daily or weekly basis. To correctly sequester these emissions, microalgae systems must be operated under continuous constant conditions, requiring photobioreactors (PBRs) that can act as chemostats for long periods of time. However, in order to optimize culture parameters or study metabolic responses, bench-scale setups are necessary. Currently there is a lack of studies and design alternatives using chemostat, since most works focus on batch assays or semi-continuous cultures. Therefore, this work focused on the development of a continuous bench-scale PBR, which combines a retention vessel, a photocollector and a degasser, with an innovative recirculation system, that allows it to operate as an autotrophic chemostat, to study carbon sequestration from a biogenic CO2-rich constant air stream. To assess its applicability, the PBR was used to cultivate the green microalga Haematococcus pluvialis using as sole carbon source the CO2 produced by a coupled heterotrophic bacterial chemostat. An air stream containing ≈0.35 vol% of CO2, was fed to the system, and it was evaluated in terms of stability, carbon fixation and biomass productivity, for dilution rates ranging from 0.1 to 0.5 d−1. The PBR was able to operate under chemostat conditions for more than 100 days, producing a stable culture that generated proportional responses to the stimuli it was subjected to, attaining a maximum biomass productivity of 183 mg/L/d with a carbon fixation efficiency of ≈39% at 0.3 d−1. These results reinforce the effectiveness of the developed PBR system, making it suitable for laboratory-scale studies of continuous photoautotrophic microalgae cultivation.

Characterization and in vitro anticancer potential of exopolysaccharide extracted from a freshwater diatom Nitzschia palea (Kütz.) W.Sm. 1856

Diatoms are photoautotrophic microalgae classified under class Bacillariophyceae, engulfed by hard silicate frustules, which give mechanical support and protection from bacterial infections. They exude polysaccharides extracellularly that help them with their gliding motion (locomotion). However, the bioactivity of such compounds was least explored from freshwater diatoms. In the present study, a single species of pennate diatom identified as Nitzschia palea was isolated and molecularly characterized by 18S rRNA smaller subunit gene (partial) sequencing and submitted to GenBank NCBI and accession number retrieved as ON360983. Based on logarithmic growth curve analysis, the exponential phase was obtained from 3rd to 4th day of diatom culture. The exopolysaccharide was extracted by the hot-water extraction method, and characterized by FT-IR. The total yield of exopolysaccharide from Nitzschia palea was estimated as 1.56 mg in 100 mL of culture after 7 days of incubation. The estimated carbohydrate content was 51.35 µg/100 µL. The monosaccharide constituents were determined by acid hydrolysis of exopolysaccharide, silylation (derivatization), followed by GC–MS analysis and tabulated. The extracted exopolysaccharide was evaluated for its anti-cancer potential against the Human Adenocarcinoma lung cancer cell line (A549) and the estimated IC50 value was 62.64 µg/mL. Acridine orange staining assay and DNA fragmentation assay also confirmed the apoptotic activity of exopolysaccharide derived from the diatom Nitzschia palea.

Antioxidative capacity of microalgal carotenoids for stabilizing n-3 LC-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.

Microalgae production in human urine: Fundamentals, opportunities, and perspectives.

The biological treatment of source-separated human urine to produce biofuel, nutraceutical, and high-value chemicals is getting increasing attention. Especially, photoautotrophic microalgae can use human urine as media to achieve environmentally and economically viable large-scale cultivation. This review presents a comprehensive overview of the up-to-date advancements in microalgae cultivation employing urine in photobioreactors (PBRs). The standard matrices describing algal growth and nutrient removal/recovery have been summarized to provide a platform for fair comparison among different studies. Specific consideration has been given to the critical operating factors to understand how the PBRs should be maintained to achieve high efficiencies. Finally, we discuss the perspectives that emphasize the impacts of co-existing bacteria, contamination by human metabolites, and genetic engineering on the practical microalgal biomass production in urine.

Insight into the comprehensive effect of carbon dioxide, light intensity and glucose on heterotrophic-assisted phototrophic microalgae biofilm growth: A multifactorial kinetic model

Heterotrophic-assisted photoautotrophic microalgae biofilm cultivation was an alternative way to realize CO2 reduction and wastewater treatment. Growth kinetics supplied a channel to better understand how the cultivation conditions affect microalgal growth and CO2 reduction. However, the two growth modes (heterotroph and photoautotroph) have different needs for organic and inorganic nutrients. Thus, combining the threshold theory and multiplication theory, an integral multifactorial kinetic model that looking insight into the comprehensive effect of glucose, CO2, light intensity, and nitrate was developed for heterotrophic-assisted photoautotrophic microalgae biofilm growth in this study. R2 between model and experiment was 0.99. It predicted the maximum specific growth rate and maximum CO2 consumption rate of heterotrophic-assisted photoautotrophic microalgae biofilm was 1.868 h−1 and 1.02 h−1, respectively. This model fully explained the influence of the main factors on microalgae biofilm growth and reasonably predicted the growth rate of microalgae biofilm under different growth conditions.

Chlorella vulgaris cultivation under super high light intensity: An application of the flashing light effect

Chlorella vulgaris was grown under super high illumination (7000 μmolPhotonPAR/m2/s). Continuous and flashing light patterns were applied to investigate potential gain originating from the flashing light effect (square pattern, duty cycle of 0.5). Three control configurations were tested, all under continuous light: 200 μmolPhotonPAR/m2/s (conventional cultivation conditions), 4000 μmolPhotonPAR/m2/s (about the same average amount of energy), and 7000 μmolPhotonPAR/m2/s (maximum incident light intensity, cells did not grow). The experiments were conducted in ultra-thin flat-panel photobioreactors to ensure isoactinic growth conditions. After acclimation, the monitored outcomes were: growth rate, macronutrient composition (proteins, carbohydrates, lipids), pigment content, and transient fluorescence (OJIP assays). The results showed that Chlorella vulgaris can grow at a similar rate under 200 μmolPhotonPAR/m2/s of continuous light and under 7000 μmolPhotonPAR/m2/s of flashing light for frequencies between 0.1 and 100 Hz. Acclimation mechanisms did not alter cell macronutrient composition, yet, chlorophyll contents decreased while carotenoids increased (allegedly linked to an increased expression of the VAZ cycle). OJIP tests also revealed potential up-regulation of the water-water cycle (featuring PTOX enzyme), which would allow faster repletion of the PQ pool, delaying photosynthetic apparatus saturation. Above 100 Hz (1000 Hz in this study), cells exhibited the same growth rate as under the equivalent amount of continuous light. It suggests that light alternation is too fast for the cells to perceive it. On the contrary, too low frequencies (0.01 Hz) showed lower performances than under the same average intensity. In this condition, during the light phase, cells are exposed to harmful conditions (continuous 7000 μmolPhotonPAR/m2/s), and the too-long dark phase only allows the cells some rest but does not bring any benefits. In terms of applicability, these results pave the way for the use of super high light (either artificial or by sunlight concentration) to overcome the energy limitation burdening photoautotrophic microalgae cultivation.

Cultivation of Chlorella pyrenoidosa with different phosphorus forms under photoautotrophic and mixotrophic modes: Biochemical component synthesis and phosphorus bioavailability appraisement

Microalgae cultivation with wastewater could reduce the water pollution and relieve global energy crisis. Nowadays, there is few study on the bioavailability of phosphorus forms in wastewater for microalgae growth and biochemical component synthesis. In this study, Chlorella pyrenoidosa was cultivated under photoautotrophic and mixotrophic modes with five phosphorus forms, including K 2 HPO 4 (Pi), sodium tripolyphosphate (STPP), glucose-6-phosphate (G-6-P), β-sodium glycerophosphate (β-glycerol-P), and adenosine triphosphate (ATP). Results showed that Chlorella pyrenoidosa could utilize all phosphorus forms to sustain its growth. Pi was the preferred phosphorus form that could be absorbed directly, while monophosphates (G-6-P and β-glycerol-P) could promote the accumulation of carbohydrate, protein and chlorophyll- a . Regarding phosphorus absorption and utilization, most of phosphorus in mixotrophic bulk were transformed and stored in intracellular phosphorus pool, whereas photoautotrophic microalgae absorbed excess phosphorus in a short time and released subsequently. The G-6-P enhanced the AKP activity and improved organic phosphorus hydrolysis. Results will provide valuable information for mixotrophic microalgae cultivation with different phosphorus forms, and further for phosphorus recovery and high density microalgae cultivation in wastewater. • Effect of phosphorus forms on microalgae growth and intracellular component. • Different bioavailability and utilization strategy of phosphorus forms. • Mixotrophy improved the performance of phosphorus absorption and utilization. • G-6-P was more effective for protein and carbohydrate accumulation.

Nutrient Deprivation Coupled with High Light Exposure for Bioactive Chrysolaminarin Production in the Marine Microalga Isochrysis zhangjiangensis.

Chrysolaminarin, a kind of water-soluble bioactive β-glucan produced by certain microalgae, is a potential candidate for food/pharmaceutical applications. This study identified a marine microalga Isochrysis zhangjiangensis, in which chrysolaminarin production was investigated via nutrient (nitrogen, phosphorus, or sulfur) deprivations (-N, -P, or -S conditions) along with an increase in light intensity. A characterization of the antioxidant activities of the chrysolaminarin produced under each condition was also conducted. The results showed that nutrient deprivation caused a significant increase in chrysolaminarin accumulation, though this was accompanied by diminished biomass production and photosynthetic activity. -S was the best strategy to induce chrysolaminarin accumulation. An increase in light intensity from 80 (LL) to 150 (HL) µE·m−2·s−1 further enhanced chrysolaminarin production. Compared with -N, -S caused more suitable stress and reduced carbon allocation toward neutral lipid production, which enabled a higher chrysolaminarin accumulation capacity. The highest chrysolaminarin content and concentration reached 41.7% of dry weight (%DW) and 632.2 mg/L, respectively, under HL-S, with a corresponding productivity of 155.1 mg/L/day achieved, which exceeds most of the photoautotrophic microalgae previously reported. The chrysolaminarin produced under HL-N (Iz-N) had a relatively competitive hydroxyl radical scavenging activity at low concentrations, while the chrysolaminarin produced under HL-S (Iz-S) exhibited an overall better activity, comparable to the commercial yeast β-glucan, demonstrating I. zhangjiangensis as a promising bioactive chrysolaminarin producer from CO2.

Microalgal Biomass as Feedstock for Bacterial Production of PHA: Advances and Future Prospects.

The search for biodegradable plastics has become the focus in combating the global plastic pollution crisis. Polyhydroxyalkanoates (PHAs) are renewable substitutes to petroleum-based plastics with the ability to completely mineralize in soil, compost, and marine environments. The preferred choice of PHA synthesis is from bacteria or archaea. However, microbial production of PHAs faces a major drawback due to high production costs attributed to the high price of organic substrates as compared to synthetic plastics. As such, microalgal biomass presents a low-cost solution as feedstock for PHA synthesis. Photoautotrophic microalgae are ubiquitous in our ecosystem and thrive from utilizing easily accessible light, carbon dioxide and inorganic nutrients. Biomass production from microalgae offers advantages that include high yields, effective carbon dioxide capture, efficient treatment of effluents and the usage of infertile land. Nevertheless, the success of large-scale PHA synthesis using microalgal biomass faces constraints that encompass the entire flow of the microalgal biomass production, i.e., from molecular aspects of the microalgae to cultivation conditions to harvesting and drying microalgal biomass along with the conversion of the biomass into PHA. This review discusses approaches such as optimization of growth conditions, improvement of the microalgal biomass manufacturing technologies as well as the genetic engineering of both microalgae and PHA-producing bacteria with the purpose of refining PHA production from microalgal biomass.

Optimisation and growth kinetic analysis of Microalgae, Arthrospira platensis in 2-L Photobioreactors

In recent years, photoautotrophic microalgae are widely recognised due to their diverse yet significant natural values, particularly in healthcare, including pharmaceuticals, cosmetics and feedstock industries. One of the most exploited blue-green microalgae, Arthrospira sp. has been addressed as a potent superfood. However, the microalgal mass-production requires suitable inoculum strain and controlled cultivation conditions for enhanced growth performance. Hence, this study aimed to maximise biomass of Arthrospira platensis chosen strain in a 2 litres indoor photobioreactor under three different parameters which were aeration rate, light intensity and pH of the medium. In the present study, a comparative study of growth performance between helical (S1) and straight form (S2) of A. platensis was conducted and the results revealed that morphological differences did not affect growth performances. Meanwhile, the optimisation based on the parameters studied shows that cultivation of A. platensis with aeration of 0.5 L/min and medium of pH 9.0 yielded the highest biomass production which were 1.500 ± 0.049 g/L. Under different light intensity, A. platensis produced the highest biomass and maximum specific growth rate of 1.142 ± 0.037 g/L and 0.716 ± 0.018 1/day, respectively when cultivated under irradiance of 6000 Lux. In conclusion, compared to before optimisation, biomass and maximum specific growth rate after optimisation was 137% and 24% increased, respectively.

Autotrophic vs. Heterotrophic Cultivation of the Marine Diatom Cyclotella cryptica for EPA Production.

Recently, the marketable value of ω-3 fatty acid, particularly eicosapentaenoic acid (EPA), increased considering their health effects for human consumption. Microalgae are considered a valuable and “green” source of EPA alternative to fish oils, but considerable efforts are necessary for their exploitation at an industrial level. Due to the high operation costs of photoautotrophic microalgae cultivation, heterotrophic growth represents a promising economic solution. Marine diatoms are the major ecological producers of ω-3 fatty acids. Few species of diatoms are capable to grow in the dark using organic carbon sources. The marine diatom Cyclotella cryptica was cultivated for 14 days under photoautotrophic and heterotrophic conditions to define the effects on growth parameters, lipid production, total fatty acids and EPA content. Photoautotrophic conditions led to a total EPA production of 1.6% of dry weight, 12.2 mg L−1 culture and productivity of 0.9 mg L−1 day−1. The heterotrophy cultures reported a total EPA production of 2.7% of dry cell weight, 18 mg L−1 culture, a productivity of 1.3 mg L−1 day−1, which are promising values in the prospective of improving culture parameters for the biotechnological exploitation of dark cultivation. C. cryptica could be a potential candidate for the heterotrophic production of EPA, also considering its robustness, capacity to resist to bacterial contaminations and plasticity of lipid metabolism.

Performance of led with mixed wavelengths or two-phase culture on the growth and lipid accumulation of chlorella pyrenoidosa.

Chlorella pyrenoidosa, a type of lipid-rich green algae, features broad prospects for application in such fields as healthy foods, biodiesel and so on. The light-utilizing efficiency of the cells is a critical factor that influences the biomass and lipid contents of photoautotrophic microalgae. Inconsistent illumination wavelengths hinder microalgal growth. The patterns about the impacts of mixed light emitting diode (LED) wavelengths or two-phase culture over the growth and lipid accumulation of Chlorella pyrenoidosa were reported. Among the different LED wavelengths (white, purple, blue, green, yellow and red) at the light intensity of 200 μmol/m2·s tested, red and green gave maximum biomass and lipid contents, respectively. Based on the discovery, two-phase (red was illuminated for 12 d in the first phase, and then shifted to green light for 8 d in the second phase, R→G) or mixed LED (R:G=3:7 or R:G=7:3) culture protocol was adopted for the high lipid-accumulation of Chlorella pyrenoidosa. The results indicated that the lipid contents of Chlorella pyrenoidosa treated with two-phase (R→G) or mixed LED culture was significantly higher than that of white light with the same intensity (p<0.05), and the highest lipid-accumulation rate was 26.37 mg/L·d in the two-phase culture. Fatty acid (FA) analysis showed that 13 types FAs were detected and unsaturated FAs were over 50% (w/w). 26.8%-27.7% (w/w) palmitic acid (C16:0) was the major saturated FA, while the largest proportions of monounsaturated FA and polyunsaturated FA were oleic acid (C18:1) and linoleic acid (C18:2), respectively. Additionally, although no difference in the FA composition of Chlorella pyrenoidosa treated with different protocols was found, the absolute content did differ significantly, coinciding with that of the total lipids. Furthermore, the ratio of unsaturated FAs in Chlorella pyrenoidosa was significantly increased under the mixed LED (R:G=7:3) (p<0.05). Keywords: Chlorella pyrenoidosa, mixed LED wavelength, two-phase, biomass, lipid, fatty acid DOI: 10.25165/j.ijabe.20211401.6098 Citation: Chu B Q, Zhao J W, Zheng H M, Gong J Y, Chen K, Zhang S W, et al. Performance of LED with mixed wavelengths or two-phase culture on the growth and lipid accumulation of Chlorella pyrenoidosa. Int J Agric & Biol Eng, 2021; 14(1): 90–96.

Performance of LED with mixed wavelengths or two-phase culture on the growth and lipid accumulation of Chlorella pyrenoidosa

Chlorella pyrenoidosa, a type of lipid-rich green algae, features broad prospects for application in such fields as healthy foods, biodiesel and so on. The light-utilizing efficiency of the cells is a critical factor that influences the biomass and lipid contents of photoautotrophic microalgae. Inconsistent illumination wavelengths hinder microalgal growth. The patterns about the impacts of mixed light emitting diode (LED) wavelengths or two-phase culture over the growth and lipid accumulation of Chlorella pyrenoidosa were reported. Among the different LED wavelengths (white, purple, blue, green, yellow and red) at the light intensity of 200 μmol/m2·s tested, red and green gave maximum biomass and lipid contents, respectively. Based on the discovery, two-phase (red was illuminated for 12 d in the first phase, and then shifted to green light for 8 d in the second phase, R→G) or mixed LED (R:G=3:7 or R:G=7:3) culture protocol was adopted for the high lipid-accumulation of Chlorella pyrenoidosa. The results indicated that the lipid contents of Chlorella pyrenoidosa treated with two-phase (R→G) or mixed LED culture was significantly higher than that of white light with the same intensity (p<0.05), and the highest lipid-accumulation rate was 26.37 mg/L·d in the two-phase culture. Fatty acid (FA) analysis showed that 13 types FAs were detected and unsaturated FAs were over 50% (w/w). 26.8%-27.7% (w/w) palmitic acid (C16:0) was the major saturated FA, while the largest proportions of monounsaturated FA and polyunsaturated FA were oleic acid (C18:1) and linoleic acid (C18:2), respectively. Additionally, although no difference in the FA composition of Chlorella pyrenoidosa treated with different protocols was found, the absolute content did differ significantly, coinciding with that of the total lipids. Furthermore, the ratio of unsaturated FAs in Chlorella pyrenoidosa was significantly increased under the mixed LED (R:G=7:3) (p<0.05). Keywords: Chlorella pyrenoidosa, mixed LED wavelength, two-phase, biomass, lipid, fatty acid DOI: 10.25165/j.ijabe.20211401.6098 Citation: Chu B Q, Zhao J W, Zheng H M, Gong J Y, Chen K, Zhang S W, et al. Performance of LED with mixed wavelengths or two-phase culture on the growth and lipid accumulation of Chlorella pyrenoidosa. Int J Agric & Biol Eng, 2021; 14(1): 90–96.