Effects of carbon source and light intensity on the growth and total lipid production of three microalgae under different culture conditions

Lipids productivity of cyanobacterium Anabaena vaginicola in an internally illuminated photobioreactor using LED bar lights

Concerns over environmental issues exists and desire to decrease of their extent, have directed efforts toward green energy production. Growth behavior of Anabaena vaginicola was determined in a photobioreator which illuminated internally (IIPBR) using LED bar light. Excessive heat generated in the IIPBR was taken care of by applying a novel air-cooled system. Further note in experimentation was to find favorable cultivation conditions in the IIPBR for A. vaginicola growth and its lipids production capacity. The following results are expressed: 80 µmol photons m-2 s-1 as light intensity, 0.5 g/l as NaNO3, and 120 ml/min as CO2 amount being expressed in terms of aeration rate. The findings were interpreted in terms of a two-component system where the genes encoded to the relevant proteins are present in cyanobacteria and their expressiveness depends on environmental stress. By determining growth rate constant as 0.11 d-1, the productivity in terms of biomass formation was calculated as 202.6 mg L-1 d-1. While rate of lipids production by the test cyanobacterium is 15.65 mg L-1 d-1. Based on total energy used for IIPBR performance, biomass productivity per unit power input equals to 0.74 g W-1 d-1 and this is in favorable position compared with other photobioreactors.

Cultivation of microalgae-bacteria consortium by waste gas-waste water to achieve CO2 fixation, wastewater purification and bioproducts production

The cultivation of microalgae and microalgae-bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae-bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae-bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae-bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing.

Characterization of exogenous lactate addition on the growth, photosynthetic performance, and biochemical composition of four bait microalgae strains

AIMS

To quickly obtain the biomass of bait microalgae with high value-added products, researchers have examined the influence of biochemical and environmental factors on the growth rates and biochemical composition of microalgae. Previous studies have shown that lactate plays an important role in metabolic regulation in Phaeodactylum tricornutum. In this study, we investigated the effect of exogenous lactate on the growth rates, photosynthetic efficiency, and biochemical composition of four commonly used bait microalgae in aquaculture.

METHODS AND RESULTS

The optical density of the algal cultures at specific time points, YII, Fv/Fm, and the total lipid, protein, soluble sugar, insoluble sugar, chlorophyll a, and carotenoid content of P. tricornutum, Isochrysis galbana (I. galbana), Chaetoceros muelleri, and Cylindrotheca fusiformis were determined. In I. galbana, the growth rate was enhanced with the addition of lactate, even though higher concentrations of lactate were associated with a decrease in YII and Fv/Fm. In general, the total lipid content of these microalgal strains increased gradually in a concentration-dependent manner over the range of lactate concentrations. In addition, higher concentrations of lactate also induced significant changes in the total soluble and insoluble sugar levels in all microalgal strains. However, chlorophyll a and carotenoid contents increased at lower but decreased at higher concentrations of lactate in all microalgal strains. The total protein content was significantly elevated at all concentrations of lactate in P. tricornutum, whereas there were no significant differences in that of C. fusiformis.

CONCLUSIONS

Lactate effective influences in the growth, metabolism, and synthesis of important biochemical components in the four microalgal strains under investigation.

Enhancement for the synthesis of bio-energy molecules (carbohydrates and lipids) in Desmodesmus subspicatus: experiments and optimization techniques

Microalgae are regarded as renewable resources of energy, foods and high-valued compounds using a biorefinery approach. In the present study, we explored isolated microalgae (Desmodesmus subspicatus) for the production of bio-energy molecules (carbohydrate and lipid). Optimizations of media (BG-11) components have been made using the Taguchi orthogonal array (TOA) technique to maximize biomass, carbohydrate and lipid production. Optimized results showed that biomass, carbohydrates and lipid productivity increased by 1.3 times at optimal combinations of media components than standard BG-11 media. Further, the influence of various carbon and nitrogen sources as nutritional supplement with optimum media composition under different light intensities was investigated for productivity of carbohydrate and lipid. Results demonstrated that 1.5 times higher productivity of carbohydrate and lipids were achieved in the presence optimum BG-11 under a broad range of light intensities (84-504 µmol m-2 s-1). Among different nitrogen sources, glycine was found to give higher productivity (1.5 times) followed by urea. Use of the cellulose as a carbon source in the media significantly increases biomass (2.4 times), carbohydrates (2.3 times) and lipids (2.3 times) productivity. Investigations revealed that cultivating Desmodesmus subspicatus under optimum culture conditions has the potential for large-scale bio-ethanol and bio-diesel production.

Advanced treatment of toluene emissions with a cutting-edge algal bacterial photo-bioreactor: Performance assessment in a circular economy perspective

A novel approach for the treatment of VOCs (by using toluene used as a model compound) and the simultaneous conversion of carbon dioxide into valuable biomass has been investigated by using a combination of an activated sludge moving bed bioreactor (MBBR) and an algal photo-bioreactor (PBR). The first unit (MBBR, R1) promoted toluene removal up to 99.9 % for inlet load (IL) of 119.91 g m^-3 d^-1. The CO₂ resulting from the degradation of toluene was then fixed in PBR (R2), with a fixation rate up to 95.8 %. The CO₂ uptake was promoted by algae, with average production of algal biomass in Stage VI of 1.3 g L^-1 d^-1. In the contest of the circular economy, alternative sources of nutrients have been assessed, using synthetic urban wastewater (UWW) and dairy wastewater (DWW) for liquid renewal. The produced biomass with DWW showed a high lipid content, with a maximum productivity of 450.25 mg of lipids L^-1 d^-1. The solution proposed may be thus regarded as a sustainable and profitable strategy for VOCs treatment in a circular economy perspective.

Influence of light intensity and photoperiod on the pigment and, lipid production of Dunaliella tertiolecta and Nannochloropsis oculata under three different culture medium

Microalgal biomass has the ability to store huge amount of triacylglycerides as fatty ester methyl esters (FAME) and carotenoids which has made algae as potential candidate for biorefinery approach. Essential fatty acid such as palmitic acid, stearic acid, arachidonic acid and eicospentanoic acid have been produced which are known for their various applications. The present study was aimed to evaluate the influence of different light intensities (120 and 250 μE/m²/s) and photoperiod (16:8h and 13:11h light/dark cycle) on the production of lipid, biomass and lutein. Dunaliella tertiolecta and Nannochloropsis oculata was grown for 23 days in F/2, sea salt media (SSM, Distilled water (DW) and SSM (natural seawater media,NSW) under two different light intensities and photoperiod regimes at 25 ᵒC. SSM (NSW) showed maximum accumulation of lipid in D.tertiolecta (34.56 mg/L/d). SSM (DW)- biomass showed 1.5 times higher lutein productivity of 0.253 mg/L/d under 13:11h light/dark cycle at 250 μE/m²/s compared to same medium under 16:8h light/dark cycles at 120 μE/m²/s. Where as in N.oculata, F/2 biomass showed higher lipid and lutein productivity of 15.69 and 0.279 mg/L/d, respectively The laboratory scale cultivation parameters and related media cost showed the suitability of different culture media adaptation to large scale production.

Air-liquid interface cultivation of Navicula incerta using hollow fiber membranes

Microalgae cultivation in open ponds requires a large footprint, while most photobioreactors need improvement in the ratio of surface to volume and energy consumption. In this study, polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) hollow fiber membranes with a large surface area were rearranged into open-ended and dead-ended configurations to improve the air-liquid interface cultivation of Navicula incerta. N. incerta were successfully grown on the porous membrane surface with the nutrients circulating inside the lumen. Fourier-transform infrared spectra showed the accumulation of polysaccharides, proteins and humic acids. Hydrophilic polysaccharides reduced water contact angles on PES and PVDF membranes to 37.2 ± 2.6° and 55.7 ± 3.3°, respectively. However, the porosity of PES (80.1 ± 1.1%) and PVDF (61.3 ± 4.5%) membranes were not significantly affected even after cultivation and harvesting of N. incerta. Scanning electron images further confirmed that N. incerta, cell debris and extracellular organic matter accumulated on the membrane. With large pores and a hydrophobic surface, PVDF hollow fiber membranes offered a greater improvement in N. incerta cell growth rate compared to PES hollow fiber membranes despite using different configurations. In the dead-ended configuration, they even attained the greatest improvement in N. incerta growth rate, up to 54.0%. However, PES hollow fiber membranes only achieved improvement in harvesting efficiency within the range of 18.7-38.0% due to weak cell adhesion. PVDF hollow fiber membranes significantly promoted the growth of microalgae N. incerta through the air-liquid interface system, leading to potential applications in wastewater treatment.

Organic Carbon Is Ineffective in Enhancing the Growth of Dunaliella

(1) Background: Mixotrophic growth is commonly associated with higher biomass productivity and lower energy consumption. This paper evaluates the impact of using different carbon sources on growth, protein profile, and nutrient uptake for Dunaliella tertiolecta CCAP 19/30 to assess the potential for mixotrophic growth. (2) Methods: Two experimental sets were conducted. The first assessed the contribution of atmospheric carbon to D. tertiolecta growth and the microalgae capacity to grow heterotrophically with an organic carbon source to provide both carbon and energy. The second set evaluated the impact of using different carbon sources on its growth, protein yield and quality. (3) Results: D. tertiolecta could not grow heterotrophically. Cell and optical density, ash-free dry weight, and essential amino acids index were inferior for all treatments using organic carbon compared to NaHCO3. Neither cell nor optical density presented significant differences among the treatments containing organic carbon, demonstrating that organic carbon does not boost D. tertiolecta growth. All the treatments presented similar nitrogen, phosphorus, sulfur recovery, and relative carbohydrate content. (4) Conclusions: Based on the results of this paper, D. tertiolecta CCAP 19/30 is an obligated autotroph that cannot grow mixotrophically using organic carbon.

Cultivation of Arthrospira platensis in Brewery Wastewater

Cultivation of photosynthetic microorganisms in wastewater is a potential cost-effective method of treating wastewater and simultaneously providing the essential nutrients for high-value biomass production. This study investigates the cultivation of the cyanobacterium Arthrospira platensis in non-diluted and non-pretreated brewery wastewater under non-sterile and alkaline growth conditions. The system’s performance in terms of biomass productivity, pollutant consumption, pigment production and biomass composition was evaluated under different media formulations (i.e., addition of sodium chloride and/or bicarbonate) and different irradiation conditions (i.e., continuous illumination and 16:8 light:dark photoperiod). It was observed that the combination of sodium bicarbonate with sodium chloride resulted in maximum pigment production recorded at the end of the experiments, and the use of the photoperiod led to increased pollutant removal (up to 90% of initial concentrations) and biomass concentration (950 mg/L). The composition of the microbial communities established during the experiments was also determined. It was observed that heterotrophic bacteria dominated by the phyla of Pseudomonadota, Bacillota, and Bacteroidota prevailed, while the cyanobacteria population showcased a dynamic behavior throughout the experiments, as it increased towards the end of cultivation (relative abundance of 10% and 30% under continuous illumination and photoperiod application, respectively). Overall, Arthrospira platensis-based cultivation proved to be an effective method of brewery wastewater treatment, although the large numbers of heterotrophic bacteria limit the usage of the produced biomass to applications such as biofuel and biofertilizer production.

Bright as day and dark as night: light-dependant energy for lipid biosynthesis and production in microalgae

Microalgae are photosynthetic organisms functioning as the green bio-factories for various pharmaceutical and biofuel products. To date, numerous attempts have been carried out to manipulate culture conditions to maximize the production of the desired metabolites. Because light is the energy source of microalgae for their growth and metabolites biosynthesis, it has been one of the most investigated variables emphasized on the deep understanding of how microalgae respond towards light changes as an external stimulus. This review discusses the effects of different light sources, light intensities, light wavelengths and length of photoperiod on various microalgae species, especially in terms of biomass and lipid productivity. Additionally, the relationship between photoregulation processes and lipid productivity of microalgae are also deliberated. The current available approaches of microalgae mass cultivation, including different types of open and closed systems are recapitulated with the intention to highlight the significant insights for the design of future photoreactors.

Simultaneous nutrient recovery and algal biomass production from anaerobically digested sludge centrate using a membrane photobioreactor

This study aims to evaluate the performance of C. vulgaris microalgae to simultaneously recover nutrients from sludge centrate and produce biomass in a membrane photobioreactor (MPR). Microalgae growth and nutrient removal were evaluated at two different nutrient loading rates (sludge centrate). The results show that C. vulgaris microalgae could thrive in sludge centrate. Nutrient loading has an indiscernible impact on biomass growth and a notable impact on nutrient removal efficiency. Nutrient removal increased as the nutrient loading rate decreased and hydraulic retention time increased. There was no membrane fouling observed in the MPR and the membrane water flux was fully restored by backwashing using only water. However, the membrane permeability varies with the hydraulic retention time (HRT) and biomass concentration in the reactor. Longer HRT offers higher permeability. Therefore, it is recommended to operate the MPR system in lower HRT to improve the membrane resistance and energy consumption.

Enhancing growth and oil accumulation of a palmitoleic acid-rich Scenedesmus obliquus in mixotrophic cultivation with acetate and its potential for ammonium-containing wastewater purification and biodiesel production

A palmitoleic acid-rich Scenedesmus obliquus strain SXND-02 was isolated from ammonium-containing wastewater. Biomass and lipid production were examined for this microalgal strain in photoautotrophic, heterotrophic, and mixotrophic cultivations, respectively, in order to extend its application in wastewater purification coupled with production of valued bio-products. Among the tested conditions, the microalga had better growth and higher lipid accumulation in mixotrophy. NH₄Cl inhibited the microalgal growth in photoautotrophic cultivation. However, NaAc alleviated this inhibition in both heterotrophy and mixotrophy. Using 7 g L^-1 NaAc and 0.5 g L^-1 NH₄Cl as carbon and nitrogen sources significantly increased the algal biomass and lipid yields under mixotrophic cultivation, with the highest levels up to 1.0 g L^-1 and 59.88%, respectively. Fatty acid profiling indicated that palmitoleic acid was 23% in the S. obliquus SXND-02 under mixotrophic condition, which was about 21-fold higher than that in the control S. obliquus. Furthermore, this microalgal strain was tested in the chicken farm wastewater (CFW) containing high ammonium. Compared with other treatments, the S. obliquus SXND-02 cultivated in the 1/2 CFW + NaAc medium produced larger amounts of biomass (2.18 g L^-1) and lipids (50.22%), and simultaneously higher removal rates of total nitrogen (TN) (80%), total ammonium nitrogen (TAN) (68%), total phosphate (TP) (82%), biological oxygen demand (BOD) (86%) and chemical oxygen demand (COD) (89%) from wastewater. The present data indicate that this excellent microalga can be used in mixotrophic cultivation for wastewater purification coupled with commercial production of valued biomass and high-quality algal oils.

Influence of Light Conditions on Microalgae Growth and Content of Lipids, Carotenoids, and Fatty Acid Composition

Microalgae are a valuable natural resource for a variety of value-added products. The growth of microalgae is determined by the impact of many factors, but, from the point of view of the implementation of autotrophic growth, light is of primary importance. This work presents an overview of the influence of light conditions on the growth of microalgae, the content of lipids, carotenoids, and the composition of fatty acids in their biomass, taking into account parameters such as the intensity, duration of lighting, and use of rays of different spectral composition. The optimal light intensity for the growth of microalgae lies in the following range: 26-400 µmol photons m-2 s-1. An increase in light intensity leads to an activation of lipid synthesis. For maximum lipid productivity, various microalgae species and strains need lighting of different intensities: from 60 to 700 µmol photons m-2 s-1. Strong light preferentially increases the triacylglyceride content. The intensity of lighting has a regulating effect on the synthesis of fatty acids, carotenoids, including β-carotene, lutein and astaxanthin. In intense lighting conditions, saturated fatty acids usually accumulate, as well as monounsaturated ones, and the number of polyunsaturated fatty acids decreases. Red as well as blue LED lighting improves the biomass productivity of microalgae of various taxonomic groups. Changing the duration of the photoperiod, the use of pulsed light can stimulate microalgae growth, the production of lipids, and carotenoids. The simultaneous use of light and other stresses contributes to a stronger effect on the productivity of algae.

Simultaneous Application of Mixotrophic Culture and Magnetic Fields as a Strategy to Improve Spirulina sp. LEB 18 Phycocyanin Synthesis

Spirulina is a filamentous microalga which is considered a promising alternative source of essential nutrients and active biomolecules. High production cost and the space required to install a photobioreactor are two of the greatest challenges in the industrial application of microalga-based products. Thus, this study aimed to improve Spirulina sp. LEB 18 biomass and phycocyanin content by combining the application of mixotrophic culture and magnetic fields (MF). Zarrouk medium was modified with 1 and 3 g/L liquid molasses and the application of 30 mT for 1·h/d was investigated. Mixotrophic culture with 1 g/L molasses showed the highest biomass concentration (1.62 g/L), carbohydrate content (25.6%), and lipid contents (8.7%) after 15 days. Although the combination of 30 mT and 1 g/L liquid molasses decreased biomass production (1.44 g/L), there was increase in protein yield (76.9%) and protein productivity (73.8 mg/L·d). The proposed method increased phycocyanin production by 145% and its purity from 0.584 in the control culture to 0.627. Data described by this study show that the combination of mixotrophic culture and MF application is a promising alternative to increase microalga protein and phycocyanin production.

Enhanced biomass production through a repeated sequential auto-and heterotrophic culture mode in Chlorella protothecoides

A repeated sequential auto-and heterotrophic (RSAH) culture mode was designed to enhancebiomass ofChlorella protothecoides. Based on the result that the photosynthesis system may receive damage if the light period is more than 16 h, autotrophy was applied in the 16 h of the light cycle and mixotrophy using acetic acid and glucose in the 8 h of dark cycle. In the dark cycle, an organic carbon source was added according to the Monod equation to maintain activation of the TCA cycle and organic carbon source-to-cell conversion. When acetic acid and glucose were used as organic carbon sources, this culture method was found to be 32.3% and 12.6% higher in biomass, 2.59 and 2.67 times higher in the organic carbon source-to-cell conversion factor, and 2.17 and 2.32 times higher in ATP/ADP ratio, respectively, compared to mixotrophy. Through this new culture method, economic feasibility and carbon reduction capabilities in large-scale cultures can be achieved.

Changes in Growth, Photosynthesis Performance, Pigments, and Toxin Contents of Bloom-Forming Cyanobacteria after Exposure to Macroalgal Allelochemicals

Macroalgae can directly restrict the growth of various phytoplankton species by releasing allelopathic compounds; therefore, considerable attention should be paid to the allelopathic potential of these organisms against harmful and bloom-forming cyanobacteria. The main aim of this study was to demonstrate for the first time the allelopathic activity of Ulva intestinalis on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (F_v/F_m) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll a (Chl a) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, Aphanizomenon sp., Nodularia spumigena, and Nostoc sp. We found both negative and positive allelopathic effects of U. intestinalis on tested cyanobacteria. The study clearly showed that the addition of the filtrate of U. intestinalis significantly inhibited growth, decreased pigment content and F_v/F_m and ΦPSII values of N. spumigena and Nostoc sp., and stimulated Aphanizomenon sp. The addition of different concentrations of aqueous extract also stimulated the cyanobacterial growth. It was also shown that the addition of extract obtained from U. intestinalis caused a significant decrease in the MC-LR content in Nostoc sp. cells. Moreover, it the phenol content in N. spumigena cells was increased. On the other hand, the cell-specific phenol content for Aphanizomenon sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of U. intestinalis depends on the target species’ identity as well as the type of allelopathic method used. The study of the allelopathic Baltic macroalgae may help to identify their possible role as a significant biological factor influencing harmful cyanobacterial blooms in brackish ecosystems.

Cultivation of microalgae on unhydrolysed waste molasses syrup using mass cultivation strategy for improved biodiesel

High cultivation cost and low lipid yield are framed as a major bottleneck for the production of microalgae biodiesel. Hence, we first and foremost highlight a trophic mode transition, coupled with a combinatorial effect of organic carbon, nitrogen and light (C/N/L) on an isolated microalga Chlorococcum sp. SVF in a one pot tri-phasic intermittent feeding system by developing a lab scale Raceway tank (40L). Hitherto, waste molasses syrup without hydrolysis is unexplored in algal bioenergy arena. The direct utilisation capability of sucrose, served by waste unhydrolysed molasses syrup (WUMS), effectively modulates the intrinsic biochemical and physiological characteristics towards microalgae biomass and lipid assimilation. Response surface methodology-central composite design (RSM-CCD) tool has been employed to observe the cumulative impact of light irradiation and nutrient sources (carbon and nitrogen) on cellular stoichiometric analysis. Experimental results exhibit a potentially achievable biomass (18.88 g L^-1) and lipid accumulation (80.34%) under the light intensity of 75.5 µmol m^-2 s^-1 with stepwise light attenuation strategy. Characterisation of fatty acid methyl esters (FAME) reveals the dominance of oleic acid (32.72%) and palmitic acid methyl esters (32.49%) in mixotrophic condition, which are considered as the upmost indicators of quality biodiesel. The biofuel properties were obtained in acquiescence with American and European standard. These findings are therefore a way forward towards the effective growth of Chlorococcum sp. SVF in sucrose rich inexpensive industrial waste stream that positively influences the lipid yield for large scale sustainable biodiesel production.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02823-7.

Optimization of culture conditions for enhanced Dunaliella salina productions in mixotrophic culture

Dunaliella salina (D. salina) is a green microalga known for its tendency to produce lipid and β-carotene. Fatty acid profile, lipid and β-carotene productions of the microalga D. salina cultivated under different mixotrophic conditions were assayed. Notably, in spite of a broad spectrum of substrates served, mixotrophic cultivations slightly affected the fatty acid composition, and as a result C16:0 and C18:0, C18:1, C18:2 and C18:3 were identified as main fatty acids. Lipid in dry weight biomass (DWB) hit a high of 24.3% at 5% of NaCL and linolenic acid in lipid reached a peak of 9.15% at 15% of NaCL in medium containing glucose and equal amounts of yeast extract and soy bean powder. One-factor-at-a-time was applied to elucidate the substrates which had noticeable impacts on β-carotene production. Glucose, meat peptone, titanium dioxide nanoparticles (TiO₂ NPs), pH 7.5 and 5% NaCL were identified as key process parameters impacting β-carotene production. Following, the concentration of glucose, meat peptone and TiO₂ NPs were optimized by using response surface method. The highest content of β-carotene, 25.23 mg/g DWB, was obtained in medium composed of (g/L); 22.92 glucose, 5 meat peptone and 0.002 TiO₂ NPs.

Synergistic effect of growth conditions and organic carbon sources for improving biomass production and biodiesel quality by the microalga Choricystis minor var. minor

In the search for microalgae species with potential for biodiesel production, Choricystis minor var. minor has been seen as a promising source of biomass due to its high lipid content and the satisfactory characteristics of its fatty acid methyl esters (FAMEs). For this reason, the objective of this study was to investigate the synergistic effect of growth conditions and organic carbon sources on cultivation of this microalga. To do so, experimental cultivations were conducted in photoautotrophic, heterotrophic and mixotrophic metabolisms using glucose, fructose, glycerol or sucrose - in growth conditions that use organic carbon. Thus, growth parameters of the cultures were evaluated and at the end of the cultivations, FAMEs yield and profile were determined by gas chromatography, the efficiency of carbon conversion into biomass was evaluated and a microbial analysis was conducted. Regarding growth conditions, the findings have confirmed that, regardless of the organic carbon source used, the heterotrophic and mixotrophic metabolisms can present advantages over the photoautotrophic one. In addition, biomass production was higher with the use of glucose than with other organic carbon sources, regardless of growth condition (heterotrophic or mixotrophic). Moreover, cultivations with the addition of CO₂ have converted carbon into biomass less efficiently. On the other hand, photoautotrophic cultures presented the lowest bacterial load. In comparison to photoautotrophic and mixotrophic, heterotrophic cultures have led to lower FAMEs content and higher yields of unsaturated fatty acids. The most satisfactory FAMEs profile for biodiesel production was obtained with mixotrophic growth using fructose.

Municipal Wastewater: A Sustainable Source for the Green Microalgae Chlorella vulgaris Biomass Production

The need to reduce the costs associated with microalgae cultivation encouraged scientific research into coupling this process with wastewater treatment. Thus, the aim of this work was to assess the growth of Chlorella vulgaris (Chlorophyta) in different effluents from a municipal wastewater treatment plant (WWTP), namely secondary effluent (SE) and sludge run-off (SR). Assays were performed, under the same conditions, in triplicate with 4 dilution ratios of the wastewaters (25%, 50%, 75% and 100%) with the standard culture medium bold basal medium double nitrated (BBM2N) as a control. The capability of C. vulgaris for biomass production, chlorophyll synthesis and nutrients removal in the SE and SR was evaluated. The 25% SE and 25% SR showed increased specific growth rates (0.47 and 0.55 day−1, respectively) and higher biomass yields (8.64 × 107 and 1.95 × 107 cells/mL, respectively). Regarding the chlorophyll content, the 100% SR promoted the highest concentration of this pigment (2378 µg/L). This green microalga was also able to remove 94.8% of total phosphorus of SE, while in 50% SR, 31.2% was removed. Removal of 73.9% and 65.9% of total nitrogen in 50% and 100% SR, respectively, was also observed. C. vulgaris growth can, therefore, be maximized with the addition of municipal effluents, to optimize biomass production, while cleansing the effluents.

A brief period of darkness induces changes in fatty acid biosynthesis towards accumulation of saturated fatty acids in Chlorella vulgaris UMT-M1 at stationary growth phase

OBJECTIVE

The effects of a brief (3 days) and prolonged (6 days) period of incubation in darkness and light on the biomass content, lipid content and fatty acid profile in Chlorella vulgaris UMT-M1 were determined.

RESULTS

Three days of incubation in darkness increased saturated fatty acid (SFA) content from 34.0 to 41.4% but decreased monounsaturated fatty acid (MUFA) content from 36.7 to 29.8%. Palmitic acid (C16:0) content was increased from 23.2 to 28.9%, whereas oleic acid (C18:1) content was reduced from 35.4 to 28.8%. Total oil content was slightly decreased from 20.4 to 18.7% after 3 days of darkness, without a significant reduction in biomass compared to 3 days of incubation in light. Biomass and oil content was highest in cultures incubated for 6 days in light, however the stimulatory and inhibitory effects of darkness (or light) on SFA and MUFA content was no longer present at 6 days of incubation.

CONCLUSIONS

Findings from this study suggests that fatty acid composition in C. vulgaris could be modulated to favor either C16:0 or C18:1 by a brief period of either darkness or light incubation, prior to harvesting.

An integrated digital microfluidic bioreactor for fully automatic screening of microalgal growth and stress-induced lipid accumulation

Algae are the promising feedstock of biofuel. The screening of competent species and proper fertilizer supply is of the most important tasks. To accelerate this rather slow and laborious step, we developed an integrated high-throughput digital microfluidic (DMF) system that uses a discrete droplet to serve as a microbioreactor, encapsulating microalgal cells. On the basis of fundamental understanding of various droplet hydrodynamics induced by the existence of different sorts of ions and biological species, incorporation of capacitance-based position estimator, electrode-saving-based compensation, and deterministic splitting approach, was performed to optimize the DMF bioreactor. Thus, it enables all processes (e.g., nutrient gradient generation, algae culturing, and analyzing of growth and lipid accumulation) occurring automatically on-chip especially in a high-fidelity way. The ability of the system to compare different microalgal strains on-chip was investigated. Also, the Chlorella sp. were stressed by various conditions and then growth and oil accumulation were analyzed and compared, which demonstrated its potential as a powerful tool to investigate microalgal lipid accumulation at significantly lower laborites and reduced time.

CRISPR/Cas technology promotes the various application of Dunaliella salina system

Dunaliella salina (D. salina) has been widely applied in various fields because of its inherent advantages, such as the study of halotolerant mechanism, wastewater treatment, recombinant proteins expression, biofuel production, preparation of natural materials, and others. However, owing to the existence of low yield or in the laboratory exploration stage, D. salina system has been greatly restricted for practical production of various components. In past decade, significant progresses have been achieved for research of D. salina in these fields. Among them, D. salina as a novel expression system demonstrated a bright prospect, especially for large-scale production of foreign proteins, like the vaccines, antibodies, and other therapeutic proteins. Due to the low efficiency, application of traditional regulation tools is also greatly limited for exploration of D. salina system. The emergence of the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas system offers a precise editing tool to overcome the obstacles of D. salina system. This review not only comprehensively summarizes the recent progresses of D. salina in domain of gene engineering but also gives a deep analysis of problems and deficiencies in different fields of D. salina. Moreover, further prospects of CRISPR/Cas system and its significant challenges have been discussed in various aspects of D. salina. It provides a great referencing value for speeding up the maturity of D. salina system, and also supplies practical guiding significance to expand the new application fields for D. salina. KEY POINTS: • The review provides recent research progresses of various applications of D. salina. • The problems and deficiencies in different fields of D. salina were deeply analyzed. • The further prospects of CRISPR/Cas technology in D. salina system were predicted. • CRISPR/Cas system will promote the new application fields and maturity for D. salina.

Cultivation of Microalgae and Cyanobacteria: Effect of Operating Conditions on Growth and Biomass Composition

The purpose of this work is to define optimal growth conditions to maximise biomass for batch culture of the cyanobacterium Arthrospira maxima and the microalgae Chlorella vulgaris, Isochrysis galbana and Nannochloropsis gaditana. Thus, we study the effect of three variables on cell growth: i.e., inoculum:culture medium volume ratio (5:45, 10:40, 15:35 and 20:30 mL:mL), light:dark photoperiod (8:16, 12:12 and 16:8 h) and type of culture medium, including both synthetic media (Guillard’s F/2 and Walne’s) and wastewaters. The results showed that the initial inoculum:culture medium volume ratio, within the range 5:45 to 20:30, did not affect the amount of biomass at the end of the growth (14 days), whereas high (18 h) or low (6 h) number of hours of daily light was important for cell growth. The contribution of nutrients from different culture media could increase the growth rate of the different species. A. maxima was favoured in seawater enriched with Guillard’s F/2 as well as C. vulgaris and N. gaditana, but in freshwater medium. I. galbana had the greatest growth in the marine environment enriched with Walne’s media. Nitrogen was the limiting nutrient for growth at the end of the exponential phase of growth for C. vulgaris and N. gaditana, while iron was for A. maxima and I. galbana. The growth in different synthetic culture media also determines the biochemical composition of each of the microalgae. All species demonstrated their capability to grow in effluents from a wastewater treatment plant and they efficiently consume nitrogen, especially the three microalga species.

Organic wastes/by-products as alternative to CO2 for producing mixotrophic microalgae enhancing lipid production

In this work, white wine lees (WWL), cheese whey (CW), and glycerol (GLY) were used as carbon (C) sources to mixotrophically support the production of the microalga Nannochloropsis salina, replacing CO₂ supply. In doing so, the alga was allowed to grow on C sources dosed at 2 g L^-1, 3 g L^-1, and 4 g L^-1 of C, in the presence and absence of CO₂ supply. WWL and CW were not able to support the algal growth due to a fungal contamination that was genomically identified, while GLY gave interesting results in particular with 3 g L^-1 of C. GLY-C was able to replace CO₂-C completely when the latter was omitted, showing an algal biomass production similar to those obtained in autotrophy. If CO₂-C was provided jointly with GLY-C, biomass production and lipid contents increased more than 30% and 23%, respectively, compared to autotrophy.

Effects of light intensity on growth and lipid production in microalgae grown in wastewater

BACKGROUND

Cultivation of microalgae in wastewater could significantly contribute to wastewater treatment, biodiesel production, and thus the transition to renewable energy. However, more information on effects of environmental factors, including light intensity, on their growth and composition (particularly fatty acid contents) is required. Therefore, we investigated the biomass and fatty acid production of four microalgal species, isolated in the Northern hemisphere and grown at three light intensities (50, 150 and 300 μE m^-2 s^-1).

RESULTS

Increases in light intensities resulted in higher biomass of all four species and, importantly, raised fatty acid contents of both Desmodesmus sp. and Scenedesmus obliquus. Fourier-transform IR spectrometry analysis showed that the increases in fatty acid content were associated with reductions in protein, but not carbohydrate, contents. Assessment of fatty acid composition revealed that increasing light intensity led to higher and lower contents of oleic (18:1) and linolenic (18:3) acids, respectively. The microalgae consumed more than 75% of the nitrogen and phosphorus present in the wastewater used as growth medium.

CONCLUSION

The results show the importance of optimizing light intensities to improve fatty acid production by microalgae and their quality as sources of biodiesel. In addition, increase in fatty acid content is associated with decrease in protein content.

Immobilized oleaginous microalgae as effective two-phase purify unit for biogas and anaerobic digester effluent coupling with lipid production

Oleaginous microalga Scenedesmus sp. was immobilized in alginate-gel beads and applied as two-phase purify unit for biogas and anaerobic digester effluent from palm oil mill. Optimal microalgal cell concentration and bead volume ratio were 10⁶ cells mL^-1 and 25% v/v, respectively. The use of 20% effluent and light intensity at 128 µmol·proton·m^-2 s^-1 most promoted CO₂ removal by immobilized microalgae and achieved the maximum CO₂ removal rate of 4.63 kg-CO₂ day^-1 m^-3. This process upgraded methane content in biogas (>95%) and completely remove nitrogen and phosphorus in the effluent. After process operation, 2.98 g L^-1 microalgal biomass with 35.92% lipid content were recovered by simple sieving method. Microalgal lipids are composed of C16-C18 (>98%) with prospect high cetane number and short ignition delay time. This study has shown the promising biorefinery concept which is effective not only in CO₂ fixation, biogas upgrading and pollutant removal but also cost-effective production of microalgae-based biofuel.

Bacterial Community Diversity and Screening of Growth-Affecting Bacteria From Isochrysis galbana Following Antibiotic Treatment

Algal cultures are generally co-cultures of algae and bacteria, especially when considering outdoor cultivation. However, the effects of associated bacteria on algal growth remain largely unexplored, particularly in the context of Isochrysis galbana. In the present study, we investigated the effects of antibiotic on the growth of I. galbana and its associated bacterial community. We found advantageous responses of I. galbana to antibiotic exposure, evidenced by the increased growth, and the maximal photochemical efficiency of PSII (Fv/Fm). Since antibiotics can cause major disturbances within bacterial community, we further conducted 16S rDNA amplicon sequencing to determine the changes of bacterial community diversity following antibiotic treatment. We found that antibiotic treatment considerably and negatively affected the abundance and diversity of bacterial community, and 17 significantly decreased bacterial species in the antibiotic-treated medium, including Pseudomonas stutzeri, were identified. Further co-culture experiments revealed that P. stutzeri inhibited the growth of I. galbana, and the inhibitory activity was retained in the cell-free bacterial filtrate. These results indicated that the negative effect of bacteria was not exclusively transmitted through contact with I. galbana but could be also mediated via secretory compounds. Taken together, our findings not only fully characterized the bacterial community associated with I. galbana and how the bacterial community changed in response to antibiotic perturbations, but also provided a valuable information about the interactions between I. galbana and its associated bacteria, which might help improve the yield, and quality of I. galbana during its cultivation processes.

Impact of culture conditions on the chlorophyll content of microalgae for biotechnological applications

Chlorophyll is a commercially important natural green pigment responsible for the absorption of light energy and its conversion into chemical energy via photosynthesis in plants and algae. This bioactive compound is widely used in the food, cosmetic, and pharmaceutical industries. Chlorophyll has been consumed for health benefits as a nutraceutical agent with antioxidant, anti-inflammatory, antimutagenic, and antimicrobial properties. Microalgae are photosynthesizing microorganisms which can be extracted for several high-value bioproducts in the biotechnology industry. These microorganisms are highly efficient at adapting to physicochemical variations in the local environment. This allows optimization of culture conditions for inducing microalgal growth and biomass production as well as for changing their biochemical composition. The modulation of microalgal culture under controlled conditions has been proposed to maximize chlorophyll accumulation. Strategies reported in the literature to promote the chlorophyll content in microalgae include variation in light intensity, culture agitation, and changes in temperature and nutrient availability. These factors affect chlorophyll concentration in a species-specific manner; therefore, optimization of culture conditions has become an essential requirement. This paper provides an overview of the current knowledge on the effects of key environmental factors on microalgal chlorophyll accumulation, focusing on small-scale laboratory experiments.

Glucose supplementation-induced changes in the Auxenochlorella protothecoides fatty acid composition suitable for biodiesel production

This study evaluates the effect of different concentrations of glucose supplementation on growth, lipid accumulation, and the fatty acid profile in the Auxenochlorella protothecoides. Addition of glucose promoted the growth rate and decreased the chlorophyll content. Compared with photoautotrophic cells, an increase in the lipid content was observed in mixotrophic cells. The glucose addition induced changes in the fatty acid profile. Higher content of saturated fatty acids was found in the case of cells growing in the glucose-free medium. Oleic acid was the predominant component in mixotrophic cells supplemented with 5gL(-1) glucose, while linoleic acids dominated in cultures supplemented with both 1 and 3gL(-1) glucose. The use of glucose was associated with decreased levels of linolenic acid and PUFA. The changes in the fatty acid profile in mixotrophic cells are favourable for biodiesel production.