Physiological-phased kinetic characteristics of microalgae Chlorella vulgaris growth and lipid synthesis considering synergistic effects of light, carbon and nutrients

Effect of interactions between humic acid and cerium oxide nanoparticles on the toxicity to the Chlorella sp

With the wide application of nanomaterials, the concentration of nanomaterials in natural water continues to increase, which poses a severe threat to the water environment. However, the influence of organic matter and nanomaterials rich in natural water on the toxic effect of algae growth is still unclear. In this study, the effects of humic acid (HA) and nano-cerium oxide (nCeO2) on the physiology and transcriptome of Chlorella sp. were analyzed, and the mechanism of the toxic effect of HA on Chlorella sp. under nCeO2 stress was revealed. Under 20-200 mg/L nCeO2 stress, the growth of Chlorella cells was inhibited and the highest inhibition rate reached 52% within 200 mg/L nCeO2. The Fv/Fm and ETRmax values of Chlorella sp. decreased from 0.490 and 24.45 (20 mg/L nCeO2) to 0.488 and 23.4 (100 mg/L nCeO2), respectively. Under the stimulation of nCeO2, the level of reactive oxygen species in algal cells was increased, accompanied by lipid peroxidation and membrane damage. However, the addition of HA at concentrations of 5-10 mg/L effectively alleviated the toxic effect of nCeO2 on Chlorella sp. Transcriptome analysis showed that 10 mg/L HA could alleviate the cellular stress at 100 mg/L nCeO2 on Chlorella sp. by regulating genes related to photosynthesis and metabolism pathways. Moreover, the downregulation of genes (e.g., Lhca1, Lhcb1, AOC3, and AOC2) indicated that HA reduced the level of oxidative stress in Chlorella sp. These findings offer novel insights of evaluating the ecotoxicity nCeO2 and HA in natural water environment and their impact on Chlorella sp.

Regulatory mechanisms of autophagy on DHA and carotenoid accumulation in Crypthecodinium sp. SUN

BACKGROUND

Autophagy is a crucial process of cellular self-destruction and component reutilization that can affect the accumulation of total fatty acids (TFAs) and carotenoids in microalgae. The regulatory effects of autophagy process in a docosahexaenoic acid (DHA) and carotenoids simultaneously producing microalga, Crypthecodinium sp. SUN, has not been studied. Thus, the autophagy inhibitor (3-methyladenine (MA)) and activator (rapamycin) were used to regulate autophagy in Crypthecodinium sp. SUN.

RESULTS

The inhibition of autophagy by 3-MA was verified by transmission electron microscopy, with fewer autophagy vacuoles observed. Besides, 3-MA reduced the glucose absorption and intracellular acetyl-CoA level, which resulting in the decrease of TFA and DHA levels by 15.83 and 26.73% respectively; Surprisingly, 3-MA increased intracellular reactive oxygen species level but decreased the carotenoids level. Comparative transcriptome analysis showed that the downregulation of the glycolysis, pentose phosphate pathway and tricarboxylic acid cycle may underlie the decrease of acetyl-CoA, NADPH and ATP supply for fatty acid biosynthesis; the downregulation of PSY and HMGCR may underlie the decreased carotenoids level. In addition, the class I PI3K-AKT signaling pathway may be crucial for the regulation of carbon and energy metabolism. At last, rapamycin was used to activate autophagy, which significantly enhanced the cell growth and TFA level and eventually resulted in 1.70-fold increase in DHA content.

CONCLUSIONS

Our findings indicate the mechanisms of autophagy in Crypthecodinium sp. SUN and highlight a way to manipulate cell metabolism by regulating autophagy. Overall, this study provides valuable insights to guide further research on autophagy-regulated TFA and carotenoids accumulation in Crypthecodinium sp. SUN.

Responses of microalgae under different physiological phases to struvite as a buffering nutrient source for biomass and lipid production

Microalgae cultivation for biodiesel production is promising, but the high demand for nutrients, such as nitrogen and phosphorus, remains a limiting factor. This study investigated effects of struvite, a low-cost nutrient source, on microalgae production under different physiological phases. Changes in element concentrations were determined to characterize the controllable nutrient release properties of struvite. Results showed that nutrient elements could be effectively supplemented by struvite. However, responses of microalgae under different growth stages to struvite varied obviously, achieving the highest biomass (0.53 g/L) and the lowest (0.32 g/L). Moreover, the microalgal lipid production was obviously increased by adding struvite during the growth phase, providing the first evidence that struvite could serve as an alternative buffering nutrient source to culture microalgae. The integration of microalgae cultivation with struvite as a buffering nutrient source provides a novel strategy for high ammonia nitrogen wastewater treatment with microalgae for biodiesel production.

Enhancing carbon dioxide fixation and co-production of protein and lutein in oleaginous Coccomyxa subellipsoidea by a stepwise light intensity and nutrients feeding strategy

To achieve high-efficient CO₂ fixation and co-production of protein and lutein, a stepwise light intensity and nutrients feeding strategy in two-phase cultivation was developed after optimization in one-phase culture of oleaginous C. subellipsoidea in this work. Results showed the incremental light intensity and CO₂ feeding boosted biomass production in phase 1, then a decreased light intensity and CO₂ feeding with nitrate addition enhanced protein and lutein synthesis in phase2. The highest biomass (9.40 g/L) and average CO₂ fixation rate (1.4 g/L/d) were achieved with excellent content and productivity of protein (52.36% DW, 435.72 mg/L/d) and lutein (1.65 mg/g, 1.37 mg/L/d) with 40.27% of light-energy saved. While the highest contents of total amino acids (42.38% DW) and essential amino acids (17.65% DW) were obtained with an essential amino acid index (1.2) compared with FAO/WHO reference. This study provided a promising application scenario of oleaginous microalgae for carbon neutrality and multiple high-value compounds co-production.

Optimized infrared-assisted extraction to obtain total lipid from microalgae Scenedesmus obliquus: a green approach

Microalgae oil has great potential to address the growing energy demand and dependence on fossil fuels. However, the multilayered cell walls of microalgae hinder efficient extraction and enhanced lipid recovery. In this study, we develop a novel protocol based on near infrared-assisted extraction (NIRAE) technology to extract efficiently total lipids from Scenedesmus obliquus. Under a greener solvent extraction approach, the effect of nine non-polar/polar solvent systems in various ratios on lipid yield was tested, and the results were compared with Soxhlet, Folch, and Bligh–Dyer methods. The highest oil yields were NIRAE 15.43%, and Soxhlet 22.24%, using AcoEt/MeOH (1:2 v/v). For Folch and Bligh–Dyer, 9.11 and 10%, respectively. The optimized NIRAE conditions obtained using response surface methodology (RSM): 43.8 min, solvent/biomass 129.90:1 (m/v), and AcOEt/MeOH 0.57:2.43 (v/v) increased the oil yield significantly to 24.20%. In contrast to conventional methods, the overall optimized NIRAE process satisfied the requirements of a green extraction because of the simple and safe operation, less solvent toxicity, lower extraction time, and solvent and energy consumption.

Study on high-CO2 tolerant Dunaliella salina and its mechanism via transcriptomic analysis

Microalgae has been regarded as a promising method for reducing CO2 emission. High CO2 concentration generally inhibits algal growth, and previous studies have mostly focused on breeding freshwater algae with high CO2 tolerance. In this study, one marine algal strain Dunaliella salina (D. salina) was grown under 0.03%-30 % CO2 and 3% NaCl conditions, and was evaluated to determine its potential for CO2 assimilation. The results showed that D. salina could tolerate 30% CO2 , and its maximum biomass concentration could reach 1.13 g·L-1 after 8 days incubation, which was 1.85 times higher than that of incubation in air (0.03%). The phenomenon of high-CO2 tolerance in D. salina culture was discussed basing on transcriptome analysis. The results showed that D. salina was subjected to oxidative stress under 30% CO2 conditions, and the majority genes involving in antioxidant system, such as SOD, CAT, and APX genes were up-regulated to scavenge ROS. In addition, most of the key enzyme genes related to photosynthesis, carbon fixation and metabolism were up-regulated, which are consistent with the higher physiological and biochemical values for D. salina incubation under 30% CO2 .

Enhancing nitrogen removal in mature landfill leachate by mixed microalgae through elimination of inhibiting factors

Nitrogen removal from landfill leachate (LL) using microalgae is a promising method and can realize CO₂ mitigation. But the performances are usually inhibited by high chromaticity, high free ammonia (FAN) and some complex macro molecular organic matter (MOM) in the LL. To achieve efficient nitrogen removal from LL, this study firstly pretreated the mature LL with ozone, decolorizer and activated sludge (AS) respectively, and then inoculated with mixed microalgae. The results showed that the synergistic effect of ozonation and microalgae was the best among the three, with 99.7% ammonia removal, 0.77 g/L (dry weight) microalgae biomass, and a maximum growth rate of 160 mg/L/d. Ozonation pretreatment significantly reduced the chromaticity and macromolecular organic matter of LL, with the chromaticity reduced from 2225 to 225 times and the 3D fluorescence intensity representing MOM reduced from 4089 a.u. to 986.1 a.u.. And it was found that the mixed microalgae grown after pretreatment by three different methods all were mostly Chlorella and very few Microcystis, and the density of microalgal populations (number of cells per unit volume) after ozonation was up to 10,650 cells/μL. This work provides a feasible and an economical way to remove ammonia nitrogen (NH+ 4-N) from landfill leachate.

Revealing the synergistic effects of cells, pigments, and light spectra on light transfer during microalgae growth: A comprehensive light attenuation model

As the sole energy for photosynthesis, light decrease rapidly with path due to absorption by pigments and scattering by cells in microalgal suspensions. By comprehensively considering cell concentrations, pigment components, and light spectra, a modified Cornet model for light transmission in microalgal suspensions is established. The developed model better fits experimental data with a higher adjusted R², which is 5% higher than the model that is based only on cell concentration. The attenuation of blue light is the most severe, followed by red and green light. Among the three main pigments, total carotenoids contribute the most to the absorption of blue and green light (with contribution coefficients of 89.26 ± 4.53% and 46.04 ± 3.77%, respectively), and chlorophyll a contributes the most to the absorption of red light (with a contribution coefficient of 75.33 ± 5.08%). This study provides a better understanding and prediction of light transmission during microalgal cultivation.

Effect of phosphorus concentration and light/dark condition on phosphorus uptake and distribution with microalgae

In this study, the effects of P concentration and light/dark condition on the distribution of P in microalgae were tracked with Scenedesmus sp.393. Results showed that different culture conditions affected the accumulation capacity and transformation of P in intracellular polymeric substances (IPS), extracellular polymeric substances (EPS), and soluble microbial products (SMP). At low P concentration (0.70 mg P/L), inorganic phosphorus (IP) absorbed in EPS (19.40%) and organic phosphorus (OP) accumulated in IPS (70.98%) were mainly P forms in microalgae. High P concentration (>21.42 mg P/L) promoted the luxury uptake and accumulation of IP by IPS, and the conversion of IP to OP. However, the adsorption of IP by EPS was inhibited when exposed to high external P concentration. Continuous illumination promoted the microalgae growth, and dark condition stimulated the P accumulation in microalgae biomass. The results of this study could provide valuable information for P recovery with microalgae.

Boosting photo-biochemical conversion and carbon dioxide bio-fixation of Chlorella vulgaris in an optimized photobioreactor with airfoil-shaped deflectors

Aiming at ameliorating the poor hydrodynamic regimes and uneven light distribution in the conventional airlift flat-plate photobioreactor (AFP-PBR), a novel PBR with static airfoil-shaped deflectors (ASD-PBR) is proposed in this study to boost the microalgal biomass manipulation and hence the photo-biochemical conversion. The ASD module accelerated the circulation of microalgal suspension from the center to two sides with the help of bubbling so that the microalgal cells got more opportunities to access the light source. Compared with the control PBR, the solution velocity along the incident light direction increased by 114.8% in the newly-proposed ASD-PBR. Furthermore, the ASD module also served as a static mixer, which resulted in an increment of 11.5% in mass transfer coefficient and a decrement of 21.4% in mixing time. The amended hydrodynamic characteristics eventually contributed to an improvement of 18.3% and 10.9% in the maximum algal biomass yield and CO₂ fixation rate, respectively.

A survey on experiences in leachate treatment: Common practices, differences worldwide and future perspectives

The necessity for landfill leachate treatment is a requisite to reduce the environmental impact related to municipal solid waste landfills and different aspects must be considered while deciding for an appropriate treatment process. For example, it was demonstrated that the landfill leachate stabilization in tropical regions is achieved right after its first year of operation, requiring technologies capable of treating leachates of a higher recalcitrant character if compared to those leachates from temperate regions and same landfill age. In view of its complexity and variability, stand-alone processes (either biological or physicochemical) are often ineffective in attaining the threshold values for its discharge in receiving bodies. Due to that fact, full-scale facilities have adopted integrated routes, harvesting the benefits of both biological and physicochemical processes. The implementation of membrane bioreactors followed by polishing membrane separation process (nanofiltration and reverse osmosis) seems to be a trend in leachate treatment by full-scale treatment plants. This technology is widely employed in China, European countries, and tropical countries as Brazil, generally with a treatment cost lower than the costs related to its disposal in domestic effluent collection systems. From the technologies already employed by full-scale facilities, four integrated routes were proposed for a sensitive analysis considering the treatment of a landfill leachate of different physicochemical characteristics. From all routes, those employing the membrane separation process as a polishing step had a better efficacy in attaining the threshold values for leachate disposal, being that an interesting alternative for leachate polishing by full-scale facilities.

Enhancing CO2 photo-biochemical conversion in a newly-designed attached photobioreactor characterized by stacked horizontal planar waveguide modules

Aiming at alleviating the adverse effects on attached microalgae biofilm growth caused by heterogeneous spatial light distributions within the attached cultivation photobioreactors (PBRs), an innovative PBR integrated with stacked horizontal planar waveguide modules (SHPW-PBR) was proposed in this work. Different from the conventional PBR, the emergent light from the external LED light bars were guided and evenly redistributed within the SHPW-PBR by the planar waveguides and hence provided light energy for microalgae cells photoautotrophic growth. In comparison with the control PBR, the average light intensity illuminating the attached Chlorella vulgaris biofilm in the SHPW-PBR was elevated by 204.11% and contributed to a 145.20% improvement on areal C. vulgaris biofilm production. Thereafter, responses of attached C. vulgaris biofilm growth in the SHPW-PBR to various light intensities were evaluated and the maximum areal C. vulgaris biofilm density reached 90.43 g m^-2 under the light intensity of 136 μmol m^-2 s^-1 after 9 days cultivation. Furthermore, the SHPW-PBR can be easily scaled-up by increasing the quantity of the stacked planar waveguide modules and thus shows great potential in biofilm-based biomass production.

Removal of copper improves the lipid content in Nannochloropsis oculata culture

Mining is an important activity for the economic development of many countries. However, this activity produces toxic residues that pollute water and the environment. The heavy metal removal from effluents of acid mine water is crucial to avoid environmental pollution. The microalga Nannochloropsis oculata was cultured in algal medium, with the addition of 1.16, 1.74, 2.32, 3.48, and 4.64 mg Cu²⁺ L^-1 coming from acid mine water to assess its removal capacity and the effect of copper content on the cell density and lipid productivity. The results showed that N. oculata removed up to 94.88 ± 0.43% at copper concentration than 1.74 mg Cu²⁺ L^-1; additionally, a positive effect on the lipid content was found at copper concentration to be higher, 4.64 mg Cu²⁺ L^-1, yielding 77.04 ± 2.60% of lipid content, twice as high as that achieved in the control culture of 33.058 ± 5.398%, thus potentiating the biodiesel production. These findings are favorable because they indicate that microalgae can remove copper added in the culture and present in acid mine water and can yield high lipid content at the same time. The cell density and growth rate decreased with increased concentrations of copper in the culture medium.

Removal of pollutants from biogas slurry and CO2 capture in biogas by microalgae-based technology: a systematic review

Recent research interest has focused on microalgae cultivation for biogas slurry purification and biogas upgrading due to the requirement of high efficiency for nutrient uptake and CO₂ capture, with economic feasibility and environmental benefits. Numerous studies have suggested that biogas slurry purification and biogas upgrading can occur simultaneously via microalgae-based technology. However, there is no comprehensive review on this technology with respect to the nutrient removal from biogas slurry and biogas upgrading. This article summarizes microalgal cultivation with biogas slurry and biogas from anaerobic digestion. The parameters, techniques, and modes of microalgae cultivation have been discussed in detail to achieve high efficiency in biogas slurry purification and biogas upgrading. In addition, the evaluation of energy efficiency and safety has also been explored. Compared with mono-cultivation of microalgae and co-cultivation of microalgae and bacteria, microalgae-fungi symbiosis has demonstrated greater development prospect and higher energy efficiency and the energy consumption for pollutants and CO₂ removal were 14.2-39.0% · USD^-1 and 19.9-23.3% · USD^-1, respectively. Further, a sustainable recycling scheme is proposed for the purification of biogas slurry from anaerobic digestion process and biogas upgrading via microalgae-based technology.

Development of a single helical baffle to increase CO2 gas and microalgal solution mixing and Chlorella PY-ZU1 biomass yield

A single helical baffle (SHB), consisting of twisted turns, was developed to convert straight flow into spiral flow in a Chlorella PY-ZU1 open raceway pond (ORWP) bubbled with 15% CO₂. Microalgal solution flowing through the SHB alternative helical interspaces generated whirling flow both vertically and horizontally, which decreased mixing and increased mass transfer rates. The optimized SHB had a pitch length to total SHB length ratio of 0.13 and SHB diameter to ORWP single channel width ratio of 0.30, which decreased mixing times and increased mass transfer coefficients by 41.1% and 38.4% respectively. SHB moved Chlorella PY-ZU1 from the ORWP bottom to the top, increasing light exposure for photosynthesis. Cellular electron transfer rates and photochemical efficiency (φPSII) increased by 18%, chlorophyll a content increased by 16% and variable to maximum fluorescence ratio increased by 13%. The microalgal biomass of SHB ORWP was 23% higher than that of conventional ORWP.

Light-Emitting Diode Power Conversion Capability and CO2 Fixation Rate of Microalgae Biofilm Cultured Under Different Light Spectra

Microalgae biofilm-based culture has attracted much interest due to its high harvest efficiency and low energy requirements. Using light-emitting diodes (LEDs) as light source for microalgae culture has been considered as a promising choice to enhance the economic feasibility of microalgae-based commodities. In this work, the LED power conversion capability and CO2 fixation rate of microalgae biofilms (Chlorella ellipsoidea and Chlorella pyrenoidosa) cultured under different light spectra (white, blue, green and red) were studied. The results indicated that the power-to-biomass conversion capabilities of these two microalgae biofilms cultured under blue and white LEDs were much higher than those under green and red LEDs (C. ellipsoidea: 32%–33% higher, C. pyrenoidosa: 34%–46% higher), and their power-to-lipid conversion capabilities cultured under blue LEDs were 61%–66% higher than those under green LEDs. The CO2 fixation rates of these two biofilms cultured under blue LEDs were 13% and 31% higher, respectively, than those under green LEDs. The results of this study have important implications for selecting the optimal energy-efficient LEDs using in microalgae biofilm-based culture systems.

Photo-bioreactor design for microalgae: A review from the aspect of CO2 transfer and conversion

Photobioreactor (PBR) is the most critical equipment for microalgal photosynthetic fixation of CO₂. It provides suitable environmental conditions, such as CO₂, light and nutrients, for microalgal growth. As the major carbon source for microalgae, CO₂ gas is pumped into PBR with the formation of bubbles and formed gas-liquid flow. The gas-liquid flow affects CO₂ and nutrients transmission as well as microalgae cells distribution in PBR, thereby affecting the biochemical reaction of microalgae. While the migration and transport of biochemical reaction products affect the two-phase flow, phase distribution and flow resistance in the PBR in return, thus affecting the transport of light and nutrients. Therefore, microalgal photosynthetic rate is determined synthetically by two-phase flow and the transport of CO₂, light and nutrients in PBR. Deep understanding of gas-liquid two-phase flow, energy and mass transfer coupling with microalgal growth in PBR is the cornerstone for the design of an efficient microalgae PBR.

Analyzing the effect of pH on microalgae adhesion by identifying the dominant interaction between cell and surface

Microalgae adhesion plays a critical role in developing effective photobioreactors for large-scale production of microalgae biofuel. This study focused on elucidating the influencing mechanism of liquid medium pH on microalgae adhesion by identifying the dominant interactions between cell and substratum using a criterion. Herein, the adhesion of three microalgae onto two substrata at a series of pH was observed using a flow chamber. The results indicated that the adhesion of freshwater Chlorella sp. onto PVC and glass and marine Chlorella sp. and N. oculata onto glass decreased with increasing pH, because these adhesions were dominated by the EL interaction, and the pH would influence the adhesion primarily by affecting the ζ potential of the cell and substratum. Whereas, the adhesion of marine Chlorella sp. and N. oculata onto PVC increased with increasing pH, because these adhesions were dominated by Lewis acid-base (AB) interaction, and the pH would influence the adhesion primarily by affecting the components of surface free energy of cell. The study demonstrated that the influencing mechanism of pH on adhesion can be conclusively elucidated by identifying the dominant interaction between the cell and the surface, and may have significant implications for predicting cell adhesion in various applications.

Microalgal lipids production and nutrients recovery from landfill leachate using membrane photobioreactor

The aim of this work was to realize high-efficiency nutrients recovery from landfill leachate (LL) for microalgal lipids production. Negative effects of LL on microalgal lipid synthesis was revealed and a scalable membrane-based tubular photobioreactor (SM-PBR) was proposed to offset these negative effects. Microalgal biomass concentration was improved from 0 g/L in the traditional PBR to 2.13 g/L in the SM-PBR. Major operating conditions were optimized to enhance nutrients recovery and lipid productivity. The maximum N recovery efficiency of 74.31% and the maximum daily lipid production of 404.98 mg/d were obtained under the volume ratio of 5:3 (microalgae culture/LL stream) and phosphate feeding concentration of 50 mg/L. The obtained lipid was convinced to have a good combustion and anti-degradation property, with high cetane number (>52%) and low linolenic acid content (<12%). The SM-PBR provided a feasible approach for large-scale microalgal lipid production with LL.

Uptake of copper from acid mine drainage by the microalgae Nannochloropsis oculata

The removal of heavy metals from acid mine drainage is a key factor for avoiding damage to the environment. The microalga Nannochloropsis oculata was cultured in an algal medium with 0.05, 0.1, 0.15, 0.2, and 0.25 mM copper under completely defined conditions to assess its removal capacity; the effects of copper on the cell density and lipid productivity of N. oculata were also evaluated. The results showed that N. oculata was able to remove up to 99.92 ± 0.04% of the copper content in the culture medium. A total of 89.29 ± 1.92% was eliminated through metabolism, and 10.70 ± 1.92% was removed by adsorption. These findings are favorable because they indicate that a large amount of copper was extracted due to the ability of the microalga to metabolize copper ions. The cell density, growth rate, and lipid content decreased with increased concentrations of copper in the culture medium. A positive effect on the fatty acid profile was found, as the saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) content improved when the copper concentration was higher than 0.1 mmol L^-1, which can potentiate the production of high-quality biodiesel. N. oculata is a good option for the treatment of acid mine drainage due to its ability to eliminate a substantial percentage of the copper present. Moreover, combining different culture systems such that heavy metals are removed to non-toxic levels in the first stage and high cell densities, which promote lipid production, is obtained in the second stage would be an advantageous strategy.

High-efficiency nutrients reclamation from landfill leachate by microalgae Chlorella vulgaris in membrane photobioreactor for bio-lipid production

Using microalgae to treat landfill leachate is a promising approach due to the effective nutrients reclamation ability and additional profit of bio-lipid production. To offset the negative effect of landfill leachate on microalgae cells, a membrane photobioreactor (m-PBR) was adopted in the study, in which microalgae biomass concentration was improved from 0.66 in traditional photobioreactor (T-PBR) to 0.95 g/L. Nutrients reclamation efficiencies of leachate were analyzed according to elemental balance, and the results showed that nitrogen reclamation efficiency was generally lower than 50% while phosphorus reclamation efficiency was higher than 70% due to elemental availability. The nitrogen and phosphorus reclamation efficiencies in the m-PBR were much higher than that in the T-PBR. Besides, lipid produced from the m-PBR had a high cetane number of 60.96% and low linolenic acid content of 8.32%, which demonstrated good combustion properties of the microalgae-based lipid when using landfill leachate as nutrients source.

Enhancing microalgae biofilm formation and growth by fabricating microgrooves onto the substrate surface

Attachment of cells to substrate surface is the premise for biofilm formation. To shelter microalgae cells from fluid shear stress and offer larger areas for microalgae attachment, the inerratic microgrooves, which can act as anchor points that offer larger areas for microalgae attachment and induce vortex to protect cells from hydraulic shear stress, were designed and fabricated into substrate surface. The results indicated that the shear stress on the surface with V-grooves was weaker than that on the surface with U-grooves, and 45° V-grooves with the width of 200 μm were benefit for cells attachment. The initial attachment time was shortened to 50 min under the hydraulic shear stress of 0.02 Pa compared to that of 135 min on the surface without microgrooves. Subsequently, the biofilm biomass concentration on the surface with 45° V-grooves increased by 14.29% to 165.84 g m^-2 compared with that on flat substrates.

Chlorella vulgaris mixotrophic growth enhanced biomass productivity and reduced toxicity from agro-industrial by-products

Algal wastewater remediation has become attractive for a couple of years now, however the effectiveness of genetic toxicity reducing of some by-products through microalgae are still not well reported. This study aimed to evaluate the growth, nutrients and toxicity removal of Chlorella vulgaris cultivated under autotrophic and mixotrophic conditions in three agro-industrial by-products. Mixotrophic culture using corn steep liquor showed higher cell concentration, specific growth rate, maximum cell productivity and biomass protein content when compared to cheese whey and vinasse. Nutrient removal results showed that C. vulgaris was able to completely remove corn steep liquor nutrients, while in cheese whey and vinasse culture this removal was not as efficient, observing remaining COD. This work evaluated for the first time the corn steep liquor and cheese whey genetic toxicity through Allium cepa seeds assay. These results demonstrate that corn steep liquor toxicity was totally eliminated by C. vulgaris cultivation, and cheese whey and vinasse toxicity were minimized. This study proves that the mixotrophic cultivation of C. vulgaris can increase cellular productivity, as well as it is a suitable and economic alternative to remove the toxicity from agroindustrial by-products.

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.

Application of growth-phase based light-feeding strategies to simultaneously enhance Chlorella vulgaris growth and lipid accumulation

Considering the variations of optimal light intensity required by microalgae cells along with growth phases, growth-phase light-feeding strategies were proposed and verified in this paper, aiming at boosting microalgae lipid productivity from the perspective of light conditions optimization. Experimental results demonstrate that under an identical time-averaged light intensity, the light-feeding strategies characterized by stepwise incremental light intensities showed a positive effect on biomass and lipid accumulation. The lipid productivity (235.49 mg L^-1 d^-1) attained under light-feeding strategy V (time-averaged light intensity: 225 μmol m^-2 s^-1) was 52.38% higher over that obtained under a constant light intensity of 225 μmol m^-2 s^-1. Subsequently, based on light-feeding strategy V, microalgae lipid productivity was further elevated to 312.92 mg L^-1 d^-1 employing a two-stage based light-feeding strategy V₅₆₀ (time-averaged light intensity: 360 μmol m^-2 s^-1), which was 79.63% higher relative to that achieved under a constant light intensity of 360 μmol m^-2 s^-1.