Mixotrophic Cultivation Research Articles

Third generation biobutanol production by Clostridium beijerinckii in a medium containing mixotrophically cultivated Dunaliella salina biomass

This study aims the third generation biobutanol production in P2 medium supplemented D. salina biomass mixotrophically cultivated with marble waste (MW). The wastes derived from the marble industry contain approximately 90% of carbon-rich compounds. Microalgal growth in mixotrophic conditions was optimized in the 0.4-2 g/L of MW concentration range. The highest microalgal concentration was obtained as 0.481 g/L in the presence of 1 g/L MW. Furthermore, some important parameters for the production of biobutanol, such as microalgal cultivation conditions, initial mixotrophic microalgal biomass loading (50-300 g/L), and fermentation time (24-96 h) were optimized. The highest biobutanol, total ABE, biobutanol yield and productivity were determined as 11.88 g/L, 13.89 g/L, 0.331 g/g and 0.165 g/L/h at the end of 72 h in P2 medium including 60 g/L glucose and 200 g/L microalgal biomass cultivated in 1 g/L MW, respectively. The results show that D. salina is a suitable raw material for supporting Clostridium beijerinckii DSMZ 6422 cells on biobutanol production. To the best of our knowledge, this is the first study on the use of MW which is a promising feedstock on the mixotrophic cultivation of D. salina for biobutanol production.

Harnessing Diesel-Degrading Potential of an Antarctic Microalga from Greenwich Island and Its Physiological Adaptation.

Microalgae are well known for their metal sorption capacities, but their potential in the remediation of hydrophobic organic compounds has received little attention in polar regions. We evaluated in the laboratory the ability of an Antarctic microalga to remediate diesel hydrocarbons and also investigated physiological changes consequent upon diesel exposure. Using a polyphasic taxonomic approach, the microalgal isolate, WCY_AQ5_1, originally sampled from Greenwich Island (South Shetland Islands, maritime Antarctica) was identified as Tritostichococcus sp. (OQ225631), a recently erected lineage within the redefined Stichococcus clade. Over a nine-day experimental incubation, 57.6% of diesel (~3.47 g/L) was removed via biosorption and biodegradation, demonstrating the strain's potential for phytoremediation. Fourier transform infrared spectroscopy confirmed the adsorption of oil in accordance with its hydrophobic characteristics. Overall, degradation predominated over sorption of diesel. Chromatographic analysis confirmed that the strain efficiently metabolised medium-chain length n-alkanes (C-7 to C-21), particularly n-heneicosane. Mixotrophic cultivation using diesel as the organic carbon source under a constant light regime altered the car/chl-a ratio and triggered vacuolar activities. A small number of intracellular lipid droplets were observed on the seventh day of cultivation in transmission electron microscopic imaging. This is the first confirmation of diesel remediation ability in an Antarctic green microalga.

Enhancing Lipid Production of Chlorella sp. by Mixotrophic Cultivation Optimization

Mixotrophic microalgal cultivation can utilize CO2 and organic carbon sources. This study optimized the cultivation nitrogen source (peptone, urea, yeast extract, NH4Cl, (NH4)2SO4, NH4NO3, NaNO3 and KNO3), carbon combination (glucose, glycerol, sucrose), (NH4)2SO4 nitrogen source and pH (6–11) in a local microalgae species with three characteristics (high pH-resistant, high growth rate and high lipid content). Chlorella sp. G3H3-1-2 biomass production and lipid accumulation were estimated using the fatty acid methyl esters (FAMEs) concentration. The Chlorella sp. G3H3-1-2 FAME content was strongly influenced by the carbon, nitrogen sources and pH variations. The pH ranged from 6.0 to 8.0, which produced the highest specific growth rate of 1.22 day−1 for Chlorella sp. G3H3-1-2 while using glucose as the single carbon source. However, the highest total FAMEs content of 59% in the Chlorella sp. G3H3-1-2 biomass of 1.75 g/L was obtained while using the combination of 1 g-glucose/L as the carbon source and 0.2 g-(NH4)2SO4/L as the nitrogen source at the high pH value of 10.

System metabolic tools reveal fucoxanthin metabolism in Nitzschia laevis for the improvement of fucoxanthin productivity

The production of fucoxanthin from microalgae is rapidly gaining popularity due to its exceptional productivity, lack of contamination, and straightforward extraction process. However, the optimal conditions for increasing biomass concentration and/or fucoxanthin content through the manipulation of light and carbon sources are context specific. This study explored fucoxanthin metabolism in Nitzschia laevis under heterotrophic and mixotrophic conditions using 13C tracer-based metabolic flux analysis, targeted metabolomics, and transcriptome analysis. Mixotrophic culture at 10 μmol m-2 s-1 improved fucoxanthin content by 27.54% but decreased biomass concentration by 15.65% compared to heterotrophic culture. At the molecular level, exposure to low light results in a reduction in carbon flux in the TCA cycle, leading to an increased flux toward carotenoid and fatty acid biosynthesis. The accumulation of high levels of citrate, isocitrate, and α-ketoglutaric acid is attributed to the reduced activity of the TCA cycle. Moreover, the metabolism of glyceraldehyde-3-phosphate and phosphoenolpyruvate was found to be more active under mixotrophic cultivation than heterotrophic ones, resulting in a substantial accumulation of fucoxanthin. The higher ATP and NADPH consumption provided sufficient energy for fucoxanthin and fatty acid biosynthesis. Furthermore, gene expression analysis revealed that low light upregulated the genes involved in fucoxanthin biosynthesis and promoted the violaxanthin cycle, especially after 12 h of cultivation. To improve fucoxanthin productivity, low light conditions were applied after a fed-batch culture, resulting in a 22.92% increase in fucoxanthin accumulation. The findings of this study offer valuable insights into the advantages of employing multi-stage cultivation techniques to improve microalgal production.

Mechanism of lactose assimilation in microalgae for the bioremediation of dairy processing side-streams and co-production of valuable food products

Abstract This study investigated the mechanism of lactose assimilation in Nannochloropsis oceanica for dairy-wastewater bioremediation and co-production of valuable feed/food ingredients in a circular dairy system (β-galactosidase and omega-3 polyunsaturated fatty acids). Mixotrophic cultivation was found to be mandatory for lactose assimilation in N. oceanica, with biomass production in mixotrophic cultures reaching a fourfold increase over that under heterotrophic conditions. Under mixotrophic conditions, the microalgae were able to produce β-galactosidase enzyme to hydrolyse lactose, with maximum extracellular secretion recorded on day 8 of growth cycle at 41.47 ± 0.33 U gbiomass−1. No increase in the concentration of glucose or galactose was observed in the medium, confirming the ability of microalgae to indiscriminately absorb the resultant monosaccharides derived from lactose breakdown. Population analysis revealed that microalgae cells were able to maintain dominance in the mixotrophic culture, with bacteria accounting for < 12% of biomass. On the other hand, under heterotrophic conditions, native bacteria took over the culture (occupying over 95% of total biomass). The bacteria, however, were also unable to effectively assimilate lactose, resulting in limited biomass increase and negligible production of extracellular β-galactosidase. Results from the study indicate that N. oceanica can be effectively applied for onsite dairy wastewater treatment under strict mixotrophic conditions. This is commercially disadvantageous as it rules out the possibility of deploying heterotrophic fermentation with low-cost bioreactors and smaller areal footprint.

Nannochloris sp. Microalgae Strain for Treatment of Dairy Wastewaters.

This paper focuses on a process for dairy wastewater treatment by mixotrophic cultivation of microalgae Nannochloris sp., using cheese whey obtained as a side flow from cheese production as an organic carbon source. The microalgae samples were prepared by adding to the standard growth medium increasing amounts of cheese whey, calculated to ensure a lactose concentration between 0 and 10 g/L. The samples were incubated at a constant temperature of 28 °C and 175 rpm stirring speed for a total time of seven days. Two LED (Light Emitting Diode) illumination schemes were applied in order to assess the effect of this parameter on microalgae development and bioactive compound accumulation: continuous illumination (light stress) versus alternative cycles of 12 h light-12 h dark (day-night cycle). The growth medium was analyzed before and after microalgae cultivation in order to determine the reduction of carbon, nitrogen, and phosphorus. The results obtained for this process, after a seven-day cultivation period, were as follows: reduction of 99-100% of lactose from the growth medium, up to 96% reduction in chemical oxygen demand, up to 91% reduction in nitrogen content, and up to 70% reduction in phosphorus content.

Simulation and Economic Analysis of the Biotechnological Potential of Biomass Production from a Microalgal Consortium

The biomass of microalgae and the compounds that can be obtained from their processing are of great interest for various economic sectors. Chlorophyll from green microalgae has biotechnological applications of great potential in different industrial areas such as food, animal feed, pharmaceuticals, cosmetics, and agriculture. In this paper, the experimental, technical and economic performance of biomass production from a microalgal consortium (Scenedesmus sp., Chlorella sp., Schroderia sp., Spirulina sp., Pediastrum sp., and Chlamydomonas sp.) was investigated in three cultivation systems (phototrophic, heterotrophic and mixotrophic) in combination with the extraction of chlorophyll (a and b) on a large scale using simulation; 1 ha was established as the area for cultivation. In the laboratory-scale experimental stage, biomass and chlorophyll concentrations were determined for 12 days. In the simulation stage, two retention times in the photobioreactor were considered, which generated six case studies for the culture stage. Subsequently, a simulation proposal for the chlorophyll extraction process was evaluated. The highest microalgae biomass concentration was 2.06 g/L in heterotrophic culture, followed by mixotrophic (1.98 g/L). Phototrophic and mixotrophic cultures showed the highest chlorophyll concentrations of 20.5 µg/mL and 13.5 µg/mL, respectively. The simulation shows that higher biomass and chlorophyll production is attained when using the mixotrophic culture with 72 h of retention that we considered to evaluate chlorophyll production (a and b). The operating cost of the entire process is very high; the cultivation stage has the highest operating cost (78%), mainly due to the high energy consumption of the photobioreactors.

Phytoremediation of Domestic Sewage in Constructed Wetland Integrated with Cultivation of Chlorella sp.: A Novel Technique for Remediation and Resource Recovery

Domestic sewage-based constructed wetland (CW) showed that the effluent from CW-system contain enough plant nutrients and enhanced the growth of microalgae. Hence, a pilot CW system employing Typha latifolia in domestic sewage, integrated with the cultivation wild type Chlorella sp. was investigated. Phytoremediation at 48 hours of detention time caused significant changes in its physicochemical properties and the generated effluent was notably attractive for the cultivation of microalgae. The microalga was grown in 6 treatments: treated-mixotrophic (T1), treated-heterotrophic (T2), treated-autotrophic (T3), control-mixotrophic (T4), control-heterotrophic (T5) and control-autotrophic (T6) conditions for 8 days inside an incubator. The results suggested that phytoremediation effluents integrated with mixotrophic cultivation of microalgae, utilising both light and carbon sources could be the most efficient, environmentally safe, sustainable and novel technique for synergistic resource generation and bioremediation.

Characterization of nongxiang- and soy sauce-type distilled grains and their application in enhancing polyunsaturated fatty acid and triacylglyceride production from Chlorella sp. 038F

A sustainable method of handling large quantities of distilled grains in the Chinese baijiu industry is bioconverting these distilled grains into value-added products. We here compared the properties of two distilled grains, soy sauce-type (DGSB) and nongxiang-type (DGNB). Results revealed that DGSB had higher contents of crude protein, crude fat, soluble sugars, free amino acids, and antioxidants than DGNB. Mixotrophic cultivation of Chlorella sp. 038F was performed using aqueous crude extracts of distilled grains. Biomass, total lipid, and fatty acid production with DGSB crude extracts was approximately 2.43, 1.40, and 1.69 times higher than that with photoautotrophic culture, respectively, whereas DGNB crude extracts only improved the biomass by 1.64 times. Detailed profile analysis revealed that DGSB crude extracts remarkably increased the proportions of polyunsaturated fatty acids, especially linoleic and α-linolenic acids, and triacylglycerides in total lipids. Interestingly, DGNB crude extracts did not enhance total lipid accumulation but increased triacylglyceride accumulation. Comparative transcriptomics revealed that genes encoding photosynthetic pigments and proteins were downregulated, suggesting the decreased anabolism of the photosynthetic light reaction. Genes involved in fatty acid biosynthesis, the Calvin cycle, and glycolysis were upregulated, indicating sufficient accumulation of the building blocks acyl-CoA and glycerol-3-phosphate for triacylglyceride biosynthesis. All transcriptional trends of triacylglyceride biosynthesis-related genes were consistent with the triacylglyceride accumulation patterns. This study provides insights into the potential use of microalgae for the bioconversion of distilled grains into high-value products and highlights the role of distilled grains in improving polyunsaturated fatty acid and triacylglyceride production.

Recovery of carbon from rice straw for production of high-value products by Chlorella sorokiniana TH01 through mixotrophic cultivation

Rice straw is an abundant agricultural by-product in Viet Nam. Rice straw mainly contains carbohydrate (e.g., hemicellulose and cellulose), an abundant carbon source for biological production of high-value products, which is being used for animal feeding, burning or disposal in most suburban and rural areas of Viet Nam. The treatment of rice straw by burning and/or disposal has caused environmental pollution due to emission of greenhouse gases (e.g., CO2, CH4), toxic gases (CO, SOx, NOx) and dust. It is critical to apply technological measures replacing the traditional method to sustainably treat the huge volume of rice straw. In this study, rice straw carbohydrate was transformed to sugar-rich hydrolysate via a different chemical and enzymatic treatment methods for cultivation of Chlorella sorokiniana TH01 to produce lutein, lipid and protein. Data showed that the combined treatment of NaOH/H2SO4/Enzyme resulted in the maximal glucose and xylose hydrolysis efficiency of 96.32% and 93.43%, respectively. C. sorokiniana TH01 displayed the best growth in the hydrolysate with initial sugar concentration of 15 g/L diluted in BG-11 medium, achieving the maximal biomass concentration of 6.5 g/L (biomass yield of 0.44 g DCW/g substrate). Lutein, lipid, carbohydrate and protein contents were determined as 7.2, 350, 220 and 260 mg/g biomass, respectively. The sugar utilization efficiency by C. sorokiniana TH01 was determined as 94.67%. C. sorokiniana TH01 exhibited a promising capability in recovery of carbon from rice straw for production of high-value multiple commercial products, keeping rice straw in a circular economy and finally reaching a carbon-neutral process.

Mixotrophic culture of Chaetoceros sp. and its response to circadian rhythm

Chaetoceros sp. is widely used in aquaculture due to its high nutritional value. However, the low growth rate and poor light adaptability of Chaetoceros sp. limit their applications as aquatic food. In this study, the effects of different carbon and nitrogen sources on the growth of algal cells were studied. The highest algal cell density was 5.25*l06 cells/mL when glycerol concentration was 5.0 g/L in the mixotrophic culture. Correspondingly, the maximum algal cell density was 6.23*106 cells/mL when the concentration of nitrogen urea was 0.075 g/L. The lipid content was significantly increased to 156.5 mg/L under the mixotrophic culture. The characteristics of the response of Chaetoceros sp. to circadian rhythm were further studied. The dynamic analysis of cell volume showed that algal cell volume varied greatly under various culture conditions. Compared with the autotrophic model, the algal cell volume of the mixotrophic culture had a faster growth rate in the dark stage, with a peak at 8 h, which confirmed that there was sufficient energy for further cell growth in the dark stage under the mixotrophic culture.

Biomass productivity of Microchloropsis gaditana cultivated in a variety of modes and effect of cobalt and molybdenum on its lipid distribution

The autotropic, heterotrophic and mixotrophic cultivation mode of the microalgae Microchloropsis gaditana was studied. Three sets of experiments were carried out: In the first set, six experimental groups were tested; one autotrophic, one heterotrophic and four mixotrophic where cultivation modes carried out and biomass productivities were compared to each other. In the second and in the third set of experiments, the algae were exposed to four or five concentrations of cobalt (Co) or of molybdenum (Mo) respectively; in these sets of experiments the effect of Co and Mo on the biomass productivity and on the lipid content and distribution of M. gaditana was examined. In the 1st set of experiments, the mixotrophic cultivations, the initial carbon concentration, C(0), was equal to 2.87 g/L, 2.92 g/L, 3.96 g/L and 4.96 g/L and in the heterotrophic cultivation C(0) was equal to 2.24 g/L. Nitrogen initial concentration, Ν(0), was held constant at 77.1 mg/L. For the heterotrophic and the three mixotrophic cultivations, the biomass yield, when expressed as g/(per L-g of added carbon) was highest for the heterotrophic growth. In the 2nd and 3rd sets of experiments it was found that both Co and Mo affect biomass productivity and lipid distribution. Co, even at relatively medium concentrations, strongly inhibited the growth. On the other hand, Mo, even at relatively high concentrations, did not affect substantially the growth rate of M. gaditana. The lipid distribution showed that for most treatments with varying concentrations of Co and Mo, MUFA prevailed while, n-3 PUFA up to 26.6% and 19.4% of the total FA were obtained. Lipid and protein contents of the biomass for the treatments with Co were up to 8.18% and 14.97% respectively, while the respective values for the treatments with Mo were higher up to 16.67% and 17.76%.

Microalga Coelastrella sp. Cultivation on Unhydrolyzed Molasses-Based Medium towards the Optimization of Conditions for Growth and Biomass Production under Mixotrophic Cultivation.

Improving biomass production with the utilization of low-cost substrate is a crucial approach to overcome the hindrance of high cost in developing large-scale microalgae production. The microalga Coelastrella sp. KKU-P1 was mixotrophically cultivated using unhydrolyzed molasses as a carbon source, with the key environmental conditions being varied in order to maximize biomass production. The batch cultivation in flasks achieved the highest biomass production of 3.81 g/L, under an initial pH 5.0, a substrate to inoculum ratio of 100:3, an initial total sugar concentration of 10 g/L, and a sodium nitrate concentration of 1.5 g/L with continuous light illumination at 23.7 W/m2. The photobioreactor cultivation results indicated that CO2 supplementation did not improve biomass production. An ambient concentration of CO2 was sufficient to promote the mixotrophic growth of the microalga as indicated by the highest biomass production of 4.28 g/L with 33.91% protein, 46.71% carbohydrate, and 15.10% lipid. The results of the biochemical composition analysis suggest that the microalgal biomass obtained is promising as a source of essential amino acids and pigments as well as saturated and monounsaturated fatty acids. This research highlights the potential for bioresource production via microalgal mixotrophic cultivation using untreated molasses as a low-cost raw material.

Research on the Tolerance and Degradation of o-Cresol by Microalgae

o-Cresol shows high toxicity and stability. To explore a better degradation method of o-cresol, the degradation of o-cresol by three kinds of microalgae (Selenastrum capricornutum, Scenedesmus obliquus, and Microcystis aeruginosa) was researched in this paper. The growth status and degradation rate were used to reflect the tolerance and degradation effect of microalgae. The effects of the medium’s initial pH, microalgal density, and different exogenous pollutants on the degradation of o-cresol by Selenastrum capricornutum were investigated. The results showed that Selenastrum capricornutum had the best degradation effect on o-cresol. microalgal density increased after adaptation to different concentrations of o-cresol for some time. At pH 7.0 as the initial condition, the microalgal exhibited the best results of degradation. When the microalgal density OD680 was 0.20, o-cresol was the first to be completely degraded within 5 days. At higher initial concentrations of o-cresol, the microalgae preferentially degraded glucose to promote the growth of the microalgae under mixotrophic cultivation. Selenastrum capricornutum could degrade phenol and o-cresol at the same time, and the degradation was completed within 8 days when the initial concentration of o-cresol and phenol were 100 and 120 mg/L. It was proven that the degradation of o-cresol by Selenastrum capricornutum is feasible under suitable conditions.

Scale-down of oxygen and glucose fluctuations in a tubular photobioreactor operated under oxygen-balanced mixotrophy.

Oxygen-balanced mixotrophy (OBM) is a novel type of microalgal cultivation that improves autotrophic productivity while reducing aeration costs and achieving high biomass yields on substrate. The scale-up of this process is not straightforward, as non-ideal mixing in large photobioreactors might have unwanted effects in cell physiology. We simulated at lab scale dissolved oxygen and glucose fluctuations in a tubular photobioreactor operated under OBM where glucose is injected at the beginning of the tubular section. We ran repeated batch experiments with the strain Galdieria sulphuraria ACUF 064 under glucose pulse feeding of different lengths, representing different retention times: 112, 71 and 21 minutes. During the long and medium tube retention time simulations, dissolved oxygen was depleted 15 to 25 minutes after every glucose pulse. These periods of oxygen limitation resulted in the accumulation of coproporphyrin III in the supernatant, an indication of disruption in the chlorophyll synthesis pathway. Accordingly, the absorption cross section of the cultures decreased steeply, going from values of 150 - 180 m2 ·kg-1 at the end of the first batch down to 50 - 70 m2 ·kg-1 in the last batches of both conditions. In the short tube retention time simulation, dissolved oxygen always stayed above 10% air saturation and no pigment reduction nor coproporphyrin III accumulation were observed. Concerning glucose utilization efficiency, glucose pulse feeding caused a reduction of biomass yield on substrate in the range of 4 to 22% compared to the maximum levels previously obtained with continuous glucose feeding (0.9 C-g·C-g-1 ). The missing carbon was excreted to the supernatant as extracellular polymeric substances constituted by carbohydrates and proteins. Overall, the results point out the importance of studying large-scale conditions in a controlled environment and the need for a highly controlled glucose feeding strategy in the scale-up of mixotrophic cultivation. This article is protected by copyright. All rights reserved.

Engineered production of isoprene from the model green microalga Chlamydomonas reinhardtii

Isoprene is a clear, colorless, volatile 5-carbon hydrocarbon that is one monomer of all cellular isoprenoids and a platform chemical with multiple applications in industry. Many plants have evolved isoprene synthases (IspSs) with the capacity to liberate isoprene from dimethylallyl diphosphate (DMADP) as part of cellular thermotolerance mechanisms. Isoprene is hydrophobic and volatile, rapidly leaves plant tissues and is one of the main carbon emission sources from vegetation globally. The universality of isoprenoid metabolism allows volatile isoprene production from microbes expressing heterologous IspSs. Here, we compared heterologous overexpression from the nuclear genome and localization into the plastid of four plant terpene synthases (TPs) in the green microalga Chlamydomonas reinhardtii. Using sealed vial mixotrophic cultivation, direct quantification of isoprene production was achieved from the headspace of living cultures, with the highest isoprene production observed in algae expressing the Ipomoea batatas IspS. Perturbations of the downstream carotenoid pathway through keto carotenoid biosynthesis enhanced isoprene titers, which could be further enhanced by increasing flux towards DMADP through heterologous co-expression of a yeast isopentenyl-DP delta isomerase. Multiplexed controlled-environment testing revealed that cultivation temperature, rather than illumination intensity, was the main factor affecting isoprene yield from the engineered alga. This is the first report of heterologous isoprene production from a eukaryotic alga and sets a foundation for further exploration of carbon conversion to this commodity chemical.

Effects of Some Nutritional Factors on the Growth of Chlorella vulgaris in a Mixotrophic Cultivation

The microalgae Chlorella vulgaris is not only known as a source of lipid compounds for the biofuel industry but also as a potential source of biomass production for aquaculture. This study investigated the influence of some nutritional factors (organic carbon source and C:N ratio) on the growth rate of Chlorella vulgaris. Glucose, sodium acetate, and sucrose were used to check the effect of the carbon sources. Meanwhile, five different ratios of C:N (1:1, 6:1, 12:1, 18:1, and 24:1) were tested. Results showed that glucose was the most suitable source of organic carbon for the biomass development of the Chlorella vulgaris; the ratio C:N=18:1 equivalent to 52.92 mmol/L carbon and 2.94 mmol/L nitrogen is the most appropriate ratio to promote biomass increase. The maximum growth rate of C. vulgaris recorded in this study was 0.58±0.03 day-1 in treatment supplemented with glucose at ratio C:N=18:1.

Optimizing mixotrophic cultivation of oil-rich Tribonema minus using volatile fatty acids and glycerin: A promising approach for pH-controlling and enhancing lipid productivity

Volatile Fatty Acids (VFAs) have become a subject of significant interest recently, primarily because they can serve as a carbon source for microorganisms that produce bioactive compounds, biodegradable materials, and energy. VFAs can be produced from various waste streams via anaerobic fermentation (AF) in a cost-effective manner, providing a potential avenue for producing biofuels and biochemicals while reducing waste volume. In this study, different VFAs and glycerin individually or in combination were used as the sole carbon source in the mixotrophic cultivation of oil-rich filamentous Tribonema minus. Using different VFAs or glycerin individually caused pH fluctuation in the culture, which led to the accumulation of free ammonia, which produced protons, acidifying the environment and inhibiting microalgae growth. To minimize pH fluctuation, different proportions of organic carbon sources were combined. Under combined organic carbon sources, the growth and photosynthetic performance of T. minus were all higher than those of the single carbon source groups. When Cacetic acid:Cbutyric acid:Cglycerin was set to 0.5:0.5:1, pH in the culture remained close to neutrality, and the removal of NH4+-N and carbon reached the maximum of 81.17 and 97.79%, respectively. The microalgal biomass and lipid productivity reached the highest of 223.80 and 108.16 mg L−1 d−1, respectively. Under the optimized carbon source condition, the fatty acids and biodiesel-related qualities of T. minus were improved. This study provided a reference for the precise design of carbon sources to maximize the resource utilization of butyric acid-type AF effluent by oil-rich T. minus. These conditions also can be achieved on a large scale by adding glycerin wastes to butyric acid-type AF effluent, mainly composed of acetic and butyric acids to get the recommended ratio for microalgae cultivation.

Biochemical composition of <i>Euglena gracilis</i> cells during mixotrophic growth in the presence of various organic substrates

The general biochemical composition and profile of low molecular weight metabolites of euglena (Euglena gracilis Klebs.) cells grown in a mixotrophic culture supplemented with 0.5% ethanol, glucose, butanol, glycine, or glycerol was studied. Ethanol and glucose significantly stimulated the growth of the Euglena culture and the accumulation of storage compounds (paramylon and wax esters) in the cells. Butanol also contributed to the division of euglena cells and increased biosynthesis of protein, mono- and disaccharides, carotenoids, and tocopherols. Glycine and glycerol were metabolized more slowly than other substrates, and they accumulated in E. gracilis cells along with their direct derivatives. Glycine did not stimulate the growth of the culture, but it caused the accumulation of paramylon, organic acids of the Krebs cycle, and nitrogen-containing metabolites (chlorophyll, free amino acids, and nitrogenous bases) in the cells. Apparently, glycine is equally effectively used by Euglena as an additional source of both carbon and nitrogen under the conditions of mixotrophy. Assimilation of glycerol was accompanied by the accumulation of wax esters and the amino acids proline and ornithine in Euglena cells. In general, the results obtained demonstrate the ability of Euglena to significantly rearrange its metabolism during the assimilation of organic substrates of various chemical nature. Our data can be used in the context of E. gracilis practical applications.

Optimization of the culture of Chlorella sorokiniana PA.91 by RSM: effect of temperature, light intensity, and MgAC-NPs.

The unique physicochemical properties of magnesium amino clay nanoparticles (MgAC-NPs) tends to be beneficial in the application as a co-additive in treating microalgae. Also, MgAC-NPs can create oxidative stress in the environment, concurrently elective control bacteria in mixotrophic culture, and stimulate CO2 biofixation. The condition of the cultivation of newly isolated strains, Chlorella sorokiniana PA.91, was optimized for the first time for MgAC-NPs at various temperatures and light intensities in the culture medium of municipal wastewater (MWW) by central composite design in the response surface methodology (RSM-CCD). This study examined synthesized MgAC-NP with their FE-SEM, EDX, XRD, and FT-IR characteristics. The synthesized MgAC-NPs were naturally stable, cubic shaped, and within the size range of 30-60nm. The optimization results show that at culture conditions of 20°C, 37μmolm-2s-1, and 0.05g L-1, microalga MgAC-NPs have the best growth productivity and biomass performance. Maximum dry biomass weight (55.41%), specific growth rate (30.26%), chlorophyll (81.26%), and carotenoids (35.71%) were achieved under the optimized condition. Experimental results displayed that C.S. PA.91 has a high capacity for lipid extraction (1.36g L-1) and significant lipid efficiency (45.1%). Also, in 0.2 and 0.05g L-1 of the MgAC-NPs, COD removal efficiency 91.1% and 81.34% from C.S. PA.91 showed, respectively. These results showed the potential of C.S. PA.91-MgAC-NPs for nutrient removal in wastewater treatment plants and their quality as sources of biodiesel.