Mixotrophic Conditions Research Articles

Optimization of Chlorella vulgaris cultivation grown in waste molasses syrup using mixture design

AbstractThe aim of this study was to determine and optimize culture media for Chlorella vulgaris microalgae under mixotrophic conditions using waste molasses as a cheap carbon source containing both organic carbons and other nutrients. In the current study, at first the growth and lipid productivity of C. vulgaris were assessed in different culture media and the best media was selected for mixotrophic growth conditions. Significant medium ingredients were screened through Plackett–Burman design. Then ingredients with positive effect were considered as a mixture component and their combinations were evaluated on lipid productivity using mixture design. According to results, Zarrouk medium was considered as the base medium with the highest biomass and lipid productivity of 72 and 7.1 mg L−1 d−1, respectively. Based on the Plackett–Burman design, out of 11 factors, molasses, NaNO3 and K2HPO4 demonstrated key roles in biomass and lipid productivity in mixotrophic conditions. Consequently, the selected three factors were investigated by mixture design. The results showed that high concentration of molasses causes decrease in biomass and lipid productivity due to high turbidity and a blend consisting of approximately 9.5 g L−1 molasses, 5 g L−1 NaNO3 and 0.15 g L−1 K2HPO4 was found as the optimum mixture with obtained lipid productivity of 115 mg L−1 d−1. In conclusion, waste molasses can be used as a promising feedstock for cost effective cultivation of C. vulgaris.

A universal dynamical metabolic model representing mixotrophic growth of Chlorella sp. on wastes

An emerging idea is to couple wastewater treatment and biofuel production using microalgae to achieve higher productivities and lower costs. This paper proposes a metabolic modeling of Chlorella sp. growing on fermentation wastes (blend of acetate, butyrate and other acids) in mixotrophic conditions, accounting also for the possible inhibitory substrates. This model extends previous works by modifying the metabolic network to include the consumption of glycerol and glucose by Chlorella sp., with the goal to test the addition of these substrates in order to overcome butyrate inhibition. The metabolic model was built using the DRUM framework and consists of 188 reactions and 173 metabolites. After a calibration phase, the model was successfully challenged with data from 122 experiments collected from scientific literature in autotrophic, heterotrophic and mixotrophic conditions. The optimal feeding strategy estimated with the model reduces the time to consume the volatile fatty acids from 16 days to 2 days. The high prediction capability of this model opens new routes for enhancing design and operation in waste valorization using microalgae.

Effects of N-acyl homoserine lactone on immobilized Scenedesmus quadricauda bead using Ca-alginate for wastewater treatment

During wastewater treatment using microalgae, microalgae are inevitably exposed to bacteria and their autoinducers (AIs). There is limited evidence regarding the interaction between microalgae and AIs in wastewater treatment processes. In this study, the effect of N-acyl homoserine lactone (AHL), an AI of Gram-negative bacteria, on the immobilization of Scenedesmus quadricauda using calcium alginate was investigated and compared between heterotrophic and mixotrophic conditions. AHL did not affect the performance of the microalgal bead reactors under heterotrophic and mixotrophic conditions. Removal efficiencies of chemical oxygen demand, nitrogen, and phosphorus under mixotrophic conditions were 96 ± 1.2 %, 39 ± 6.5 %, and 95 ± 5.4 %, respectively (n = 18). Aggregation of microalgae was observed in reactors fed with AHL. The cell concentration of microalgae in the effluent was decreased by 42–44 %. The cell concentration of microalgae in the bead was increased by 16 % under mixotrophic conditions, and the disruption of beads was only 0.8 % of total microalgal beads during the time of study. Furthermore, microalgal aggregate formation was more effective under mixotrophic conditions.

The Nitrogen Removal Performance and Functional Bacteria in Heterotrophic Denitrification and Mixotrophic Denitrification Process

The heterotrophic and autotrophic synergistic denitrification (HAD) system can effectively remove sulfide, nitrate, and organic carbon pollutants from municipal wastewater. However, the effect of sulfide on the functional bacteria in the denitrification system is still unclear. To better understand the mechanism of sulfide affected on bacteria in the system, the up-flow anaerobic sludge blanket (UASB) reactor was operated continuously under heterotrophic (no sulfide added) and mixotrophic conditions (with increased sulfide contents) for 120 days. The contents of protein (PN) in extracellular polymeric substances (EPS) were significantly increased with the addition of sulfide, which enhanced the flocculation of sludge and was beneficial to the formation of high-density microorganism communities. The dominant bacteria showed large differences under different nutrient conditions. The abundances of Thauera increased from 4.13% to over 12.94%, and that of Dechloromonas and Thiobacillus were 2.61–3.01% and 1.04–2.66% respectively after added sulfide. And the efficient performance of the system in mixotrophic conditions was accomplished with the interaction of heterotrophic sulfide-oxidizing, nitrate-reducing bacteria (Thauera, Dechloromonas), autotrophic sulfide-oxidizing, nitrate-reducing bacteria (Thiobacillus) and heterotrophic nitrate-reducing bacteria (Rubrivivax, Acidovorax, Simplicispira, Alicycliphilus). Moreover, the abundances of Nar G, Nap A, Nir S, Nor B, and Nos Z were significantly enhanced in mixotrophic conditions, indicating that the nitrogen metabolism potential of the system was also improved after added sulfide. These results elucidated the reasons for the enhanced denitrifying capacity of the system by adding S2− from the microbiological point of view and provided a theoretical basis for the establishment of an efficient denitrification system.

The effects of acetate and glucose on carbon fixation and carbon utilization in mixotrophy of Haematococcus pluvialis

The culture method using sodium acetate and glucose, widely used as organic carbon sources in the mixotrophy of Haematococcus pluvialis, was compared with its autotrophy. In the 12-day culture, mixotrophy using sodium acetate and glucose increased by 40.4% and 77.1%, respectively, compared to autotrophy, but the mechanisms for the increasing biomass were different. The analysis of the mechanism was divided into autotrophic and heterotrophic metabolism. The mixotrophy with glucose increased the biomass by directly supplying the substrate and ATP to the TCA cycle while inhibiting photosynthesis. Gene expressions related to glycolysis and carbon fixation pathway were confirmed in autotrophy and mixotrophy with glucose and acetate. The metabolism predicted in the mixotrophy with acetate and glucose was proposed via autotrophic and heterotrophic metabolism analysis. The mechanism of Haematococcus pluvialis under mixotrophic conditions with high CO2 concentration was confirmed through this study.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants’ load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Microalgal production under mixotrophic conditions using cheese whey as substrate

Microalgae are known for producing various biotechnological products. Moreover, they absorb nutrients from dairy wastewater, grow well, and accumulate valuable compounds faster. In this study, photoautotrophic and mixotrophic cultivation with different initial lactose concentrations present in cheese whey (CW) were established to investigate their effect on cell concentration (Xm, mg L-1), cell productivity (Px, mg L-1day-1), and specific cell growth (µmax, day-1) of Chlorella vulgaris, Dunaliella tertiolecta, and Tetradesmus obliquus. The biomass production of C. vulgaris (Xm= 1,520 ± 30.3 mg L-1, Px = 147 ± 3.00 mg L-1, and µmax = 0.150 ± 0.00 mg L-1) in mixotrophic culture with 10.0 g L-1 of lactose, the main constituent of CW, was notably enhanced by 55% in comparison with their photoautotrophic cultures, whereas a lower effect of these lactose concentrations on cell growth was observed in T. obliquus and D. tertiolecta. Thus, mixotrophic cultivation of C. vulgaris using CW as a carbon and energy source could be considered a feasible alternative to obtain high value-added biomass.

Pyrolysis-GCMS of Spirulina platensis: Evaluation of biomasses cultivated under autotrophic and mixotrophic conditions.

Microalgae are autotrophs and CO2 fixers with great potential to produce biofuels in a sustainable way, however the high cost of biomass production is a challenge. Mixotrophic growth of microalgae has been presented as a great alternative to achieve economic sustainability. Thus, the present work reports the energetic characterization of S. platensis biomasses cultivated under autotrophic (A) and mixotrophic conditions using cheese whey waste at different concentrations, 2.5 (M2.5), 5.0 (M5) and 10.0% (M10), in order to analyze the potential production of valuable chemicals and bio-oil by TGA/DTG and Py-GC/MS. The biochemical compositions of the studied biomasses were different due to the influence of different culture mediums. As the whey concentration increased, there was an increase in the carbohydrate content and a decrease in the protein content, which influenced the elemental composition, calorific value, TGA and volatile compounds evaluated by Py-GC/MS at 450°C, 550°C and 650°C. Sample M10 had lower protein content and formed a smaller amount of nitrogenates compounds by pyrolysis at all temperatures evaluated. There was a reduction of 43.8% (450º), 45.6% (550ºC) and 23.8% (650ºC) in the formation of nitrogenates compounds in relation to sample A. Moreover, the temperature also showed a considerable effect in the formation of volatile compounds. The highest yields of nitrogenates compounds, phenols and aromatic and non-aromatic hydrocarbons were observed at 650ºC. The oxygenated, and N and O containing compounds decreased as the temperature increased. Hydrocarbons such as toluene, heptadecane and heneicosane were produced by S.platensis pyrolysis, which makes this biomass attractive for production of high quality bio-oil and valuable chemicals. Therefore, the results showed that it is possible to decrease the formation of nitrogen compounds via manipulation of growth conditions and temperature.

PH induced stress enhances lipid accumulation in microalgae grown under mixotrophic and autotrophic condition

Production of biodiesel together with wastewater treatment and CO2 sequestration is a promising technology. The growing levels of carbon dioxide in the atmosphere increase the amount of dissolved CO2 in natural watercourses, triggering the increase in concentrations of bicarbonate and hydrogen ions while dropping those of carbonate and hydroxyl ions. The active carbon cycling in coastal areas, which can result in periodic and daily fluctuations in pH and CO2 concentrations that may surpass those anticipated for the extensive marine ecosystems, is regarded as one of the consequences of climate change. Studies were conducted to examine the effects of various pH levels on algal growth and lipid production in order to better understand how the growth of algae may be influenced in such conditions. In the present study, the influence of three different pH levels (6, 8, and 10) was studied to evaluate microalgae’s carbohydrate utilisation and lipid accumulation during the operation’s starvation phase (SP). Microalgae, in the study, were cultivated in two modes, namely mixotrophic [growth phase (GP)] and autotrophic [pH-induced (SP)] conditions. Enhancement in biomass formation, and intracellular carbohydrate accumulation were recorded during the GP operation, while noticeable lipid productivities (Total/neutral, 26.93/10.3%) were observed during SP operation at pH 8. Pigment analysis showed variations in both the procedures where higher Chl a concentration was noticed in GP, and higher Chl b was detected during SP. Nile red fluorescent staining strongly supports the existence of intracellular lipid bodies (LB). GC analysis of fatty acid methyl esters (FAME) showed the existence of a substantial amount of saturated fatty acids (SFA) compared with unsaturated fatty acids (USFA). Efficient wastewater treatment with nutrient assimilation was reported during the GP operation, demonstrating the phyco-remediation.

Growth behavior, phenol removal and lipid productivity of microalgae in mixotrophic and heterotrophic conditions under synergistic effect of phenol and bicarbonate for biodiesel production

Growth behavior, phenol removal and lipid productivity of microalgae in mixotrophic and heterotrophic conditions under synergistic effect of phenol and bicarbonate for biodiesel production

Different Concentration Organic Carbon Waste Cassava in Mixotrophic Cultivation on Protein and Beta Carotene Content of Dunaliella sp.

Dunaliella sp. is one type of green microalgae that can be used as natural feed because it is easy to digest. Inmixotrophic culture, microalgae in their growth carry outthe process of photosynthesis and use organiccarbon nutrients to produce energy. Choice of organiccarbon sources for growing Dunaliella sp. namelyusing waste cassava. The organic carbon content in wastecassava is still very complex, so that Dunaliella sp.for its growth, it can be done by breaking downcarbohydrates into simple glucose using hydrolysis withthe addition of -amylase and glucoamylase enzymes. The purpose of this study was to explain the effectof giving waste cassava hydrolyzate under Mixotrophic conditions to the protein and beta carotene contentof Dunaliella sp. The results showed that the administration of glucose organic carbon from different wastecassava under mixotrophic conditions had a significanteffect on the protein and beta carotene content ofDunaliella sp. The best glucose concentration of 0.30 g/lresulted in 34.69% protein content and 19.84 g/mlbeta carotene.

Growth Performance and Biochemical Composition of Waste-Isolated Microalgae Consortia Grown on Nano-Filtered Pig Slurry and Cheese Whey under Mixotrophic Conditions

The cultivation mode plays a vital role in algal growth and composition. This paper assessed the growth ability of twelve algae–microbial consortia (ACs) originally selected from organic wastes when nano-filtered pig slurry wastewater (NFP) and cheese whey (CW) were used as growth substrates in a mixotrophic mode in comparison with a photoautotrophic mode. Nutrient uptake ability, biochemical composition, fatty acids, and amino acid profiles of ACs were compared between both cultivation conditions. On average, 47% higher growth rates and 35% higher N uptake were found in mixotrophic cultivation along with significant P and TOC removal rates. Changing the cultivation mode did not affect AA and FA composition but improved EAA content, providing the potential for AC_5 and AC_4 to be used as local protein feed supplements. The results also showed the possibility for AC_6 and AC_1 to be used as omega-3 supplements due to their low ω-6–ω-3 ratio.

Mixotrophic Cultivation of a Native Cyanobacterium, Pseudanabaena mucicola GO0704, to Produce Phycobiliprotein and Biodiesel.

Global warming has accelerated in recent decades due to the continuous consumption of petroleum-based fuels. Cyanobacteria-derived biofuels are a promising carbon-neutral alternative to fossil fuels that may help achieve a cleaner environment. Here, we propose an effective strategy based on the large-scale cultivation of a newly isolated cyanobacterial strain to produce phycobiliprotein and biodiesel, thus demonstrating the potential commercial applicability of the isolated microalgal strain. A native cyanobacterium was isolated from Goryeong, Korea, and identified as Pseudanabaena mucicola GO0704 through 16s RNA analysis. The potential exploitation of P. mucicola GO0704 was explored by analyzing several parameters for mixotrophic culture, and optimal growth was achieved through the addition of sodium acetate (1 g/l) to the BG-11 medium. Next, the cultures were scaled up to a stirred-tank bioreactor in mixotrophic conditions to maximize the productivity of biomass and metabolites. The biomass, phycobiliprotein, and fatty acids concentrations in sodium acetate-treated cells were enhanced, and the highest biodiesel productivity (8.1 mg/l/d) was achieved at 96 h. Finally, the properties of the fuel derived from P. mucicola GO0704 were estimated with converted biodiesels according to the composition of fatty acids. Most of the characteristics of the final product, except for the cloud point, were compliant with international biodiesel standards [ASTM 6761 (US) and EN 14214 (Europe)].

Real textile industrial wastewater treatment and biodiesel production using microalgae

Microalgae are promising feedstocks capable to simultaneously treat wastewater and produce biodiesel. The focus current studyis the treatment of real textile wastewater (RTWW) and successive biodiesel production using microalgae (Chlorella vulgaris). Cultivation was carried out in unsterilized 100% (without dilution) and diluted (25%, 50%, 75%) RTWW. Microalgae cultivation in defined media (BG-11) was set as a control. In results, 50% dilution showed the highest decolorization efficiency (99 ± 0.13%), COD removal (82%), and Fatty Acid Methyl Esters (FAMEs) content (32.62 mg g−1 of biomass). Cultivation was carried out in mixotrophic and heterotrophic conditions to improve microalgae performance. Mixotrophic cultivation showed 99 ± 0.29% decolorization, 94% COD removal, and 61.65 mg g−1 of biomass as FAMEs, which was higher (p < 0.05) than the heterotrophic condition. FAME content and COD removal in mixotrophic conditions were higher (p < 0.05) than in photo-autotrophic conditions; however, there was no significant difference (p > 0.05) in the decolorization efficiency. Thus, it turned out that 50% diluted RTWW under mixotrophic conditions was the most suitable choice to achieve high treatment performance and the FAMEs yield. This study demonstrates that RTWW could be used as a microalgae feedstock without sterilization and less freshwater addition (50% of RTWW). Thus, it can be considered a promising feedstock for economical biodiesel production.

Deciphering mixotrophic microbial electrosynthesis with shifting product spectrum by genome-centric metagenomics

Microbial electrosynthesis (MES) is a promising platform for renewable energy storage, carbon fixing, and chemicals production. However, the generation of longer chain carboxylates of which their values are higher than acetate remains a grand challenge in traditional autotrophic MES feeding CO2 as the sole carbon source. The present study describes the employment of mixotrophic MES as an important strategy for the production of chemicals with longer carbon chain. With pre-enriched acetogens, the caproate (C6) specificity was increased from 0 % (autotrophic MES) to 12.8 ± 1.5 % (mixotrophic MES). Without pre-enriched acetogens, no caproate was detected, while the propionate (C3) specificity was increased from 17.1 ± 7.8 % (autotrophic MES) to 40.1 ± 0.1 % (mixotrophic MES). Metagenomic sequencing indicated that this strategy increased the abundance of functional microbes capable of chain elongation via the fatty acid biosynthesis (FAB), although the mixotrophic condition slightly decreased the carbon metabolic pathways via Wood-Ljungdahl (WL) pathways and reverse β-oxidation (RBO). Genome-centric analysis located 60 functional microbes who possessed WL and/or FAB pathways, and 27 of them were significantly enriched in mixotrophic conditions (p < 0.001). In addition, compared with the abundance of these functional microbes, it was proposed that the pre-enriched acetogens were more critical than that of mixotrophic conditions for a shift in product spectrum. These results demonstrate the great potential of mixotrophic MES, as a novel renewable-electricity-driven technology, to produce long-chain compounds from the simultaneous valorization of CO2 and organic waste.

PH spurring microalgal cells to subsist onto palm kernel expeller for growing into biodiesel feedstock

The potentiality of microalgae as a feedstock for biodiesel production is actively being explored to resolve the inadequacy of biomass and lipid indexes conundrum, and economic infeasibility associated to the conventional cultivation system. Current study is an extension of a pre-optimized cultivation condition which has further elaborated the impact of pH on attached microalgal cultivation onto nutritional lignocellulosic waste; palm kernel expeller (PKE) by employing a novel periphytic growth and harvesting technique. The highest microalgal density was achieved at 10.9 ± 0.8 g/g-PKE in pH 5 cultivation medium with highest carbon-PKE assimilation. In fact, the microalgal growths under mixotrophic condition demonstrated a positive correlation between pH of cultivation medium and carbon-PKE assimilation by microalgae. The maximum lipid productivity was obtained at 33.1 ± 3.3 mg/L day from the attached microalgae of pH 11 medium. However, the lowest microalgal density was likewise attained at similar pH due to the trigger by which the carbon metabolic activity shifted towards lipid production instead of growth. Owing to the highest microalgal density attained at pH 5 medium, the gap of lipid productivities with pH 11 was narrowed down to merely 7.0 mg/L day. The attached microalgal feedstock harvested from this study was eventually found satiating most of the essential biodiesel properties in compliance with the international standards decreed by ASTM D6751-03 and EN 14214.

Unchanged nitrate and nitrite isotope fractionation during heterotrophic and Fe(II)-mixotrophic denitrification suggest a non-enzymatic link between denitrification and Fe(II) oxidation

Natural-abundance measurements of nitrate and nitrite (NOx) isotope ratios (δ15N and δ18O) can be a valuable tool to study the biogeochemical fate of NOx species in the environment. A prerequisite for using NOx isotopes in this regard is an understanding of the mechanistic details of isotope fractionation (15ε, 18ε) associated with the biotic and abiotic NOx transformation processes involved (e.g., denitrification). However, possible impacts on isotope fractionation resulting from changing growth conditions during denitrification, different carbon substrates, or simply the presence of compounds that may be involved in NOx reduction as co-substrates [e.g., Fe(II)] remain uncertain. Here we investigated whether the type of organic substrate, i.e., short-chained organic acids, and the presence/absence of Fe(II) (mixotrophic vs. heterotrophic growth conditions) affect N and O isotope fractionation dynamics during nitrate (NO3–) and nitrite (NO2–) reduction in laboratory experiments with three strains of putative nitrate-dependent Fe(II)-oxidizing bacteria and one canonical denitrifier. Our results revealed that 15ε and 18ε values obtained for heterotrophic (15ε-NO3–: 17.6 ± 2.8‰, 18ε-NO3–:18.1 ± 2.5‰; 15ε-NO2–: 14.4 ± 3.2‰) vs. mixotrophic (15ε-NO3–: 20.2 ± 1.4‰, 18ε-NO3–: 19.5 ± 1.5‰; 15ε-NO2–: 16.1 ± 1.4‰) growth conditions are very similar and fall within the range previously reported for classical heterotrophic denitrification. Moreover, availability of different short-chain organic acids (succinate vs. acetate), while slightly affecting the NOx reduction dynamics, did not produce distinct differences in N and O isotope effects. N isotope fractionation in abiotic controls, although exhibiting fluctuating results, even expressed transient inverse isotope dynamics (15ε-NO2–: –12.4 ± 1.3 ‰). These findings imply that neither the mechanisms ordaining cellular uptake of short-chain organic acids nor the presence of Fe(II) seem to systematically impact the overall N and O isotope effect during NOx reduction. The similar isotope effects detected during mixotrophic and heterotrophic NOx reduction, as well as the results obtained from the abiotic controls, may not only imply that the enzymatic control of NOx reduction in putative NDFeOx bacteria is decoupled from Fe(II) oxidation, but also that Fe(II) oxidation is indirectly driven by biologically (i.e., via organic compounds) or abiotically (catalysis via reactive surfaces) mediated processes co-occurring during heterotrophic denitrification.

Entner-Doudoroff pathway in Synechocystis PCC 6803: Proposed regulatory roles and enzyme multifunctionalities.

The Entner-Doudoroff pathway (ED-P) was established in 2016 as the fourth glycolytic pathway in Synechocystis sp. PCC 6803. ED-P consists of two reactions, the first catalyzed by 6-phosphogluconate dehydratase (EDD), the second by keto3-deoxygluconate-6-phosphate aldolase/4-hydroxy-2-oxoglutarate aldolase (EDA). ED-P was previously concluded to be a widespread (∼92%) pathway among cyanobacteria, but current bioinformatic analysis estimated the occurrence of ED-P to be either scarce (∼1%) or uncommon (∼47%), depending if dihydroxy-acid dehydratase (ilvD) also functions as EDD (currently assumed). Thus, the biochemical characterization of ilvD is a task pending to resolve this uncertainty. Next, we have provided new insights into several single and double glycolytic mutants based on kinetic model of central carbon metabolism of Synechocystis. The model predicted that silencing 6-phosphogluconate dehydrogenase (gnd) could be coupled with ∼90% down-regulation of G6P-dehydrogenase, also limiting the metabolic flux via ED-P. Furthermore, our metabolic flux estimation implied that growth impairment linked to silenced EDA under mixotrophic conditions is not caused by diminished carbon flux via ED-P but rather by a missing mechanism related to the role of EDA in metabolism. We proposed two possible, mutually non-exclusive explanations: (i) Δeda leads to disrupted carbon catabolite repression, regulated by 2-keto3-deoxygluconate-6-phosphate (ED-P intermediate), and (ii) EDA catalyzes the interconversion between glyoxylate and 4-hydroxy-2-oxoglutarate + pyruvate in the proximity of TCA cycle, possibly effecting the levels of 2-oxoglutarate under Δeda. We have also proposed a new pathway from EDA toward proline, which could explain the proline accumulation under Δeda. In addition, the presented in silico method provides an alternative to 13C metabolic flux analysis for marginal metabolic pathways around/below the threshold of ultrasensitive LC-MS. Finally, our in silico analysis provided alternative explanations for the role of ED-P in Synechocystis while identifying some severe uncertainties.

Mixotrophic Cultivation Optimization of Microalga Euglena pisciformis AEW501 for Paramylon Production.

Euglena, a flagellated unicellular protist, has recently received widespread attention for various high-value metabolites, especially paramylon, which was only found in Euglenophyta. The limited species and low biomass of Euglena has impeded paramylon exploitation and utilization. This study established an optimal cultivation method of Euglena pisciformis AEW501 for paramylon production under mixotrophic cultivation. The results showed that the optimum mixotrophic conditions were 20 °C, pH 7.0, and 63 μmol photons m−2∙s−1, and the concentrations of sodium acetate and diammonium hydrogen phosphate were 0.98 g L−1 and 0.79 g L−1, respectively. The maximal biomass and paramylon content were 0.72 g L−1 and 71.39% of dry weight. The algal powder contained more than 16 amino acids, 6 vitamins, and 10 unsaturated fatty acids under the optimal cultivation. E. pisciformis paramylon was pure β-1,3-glucan-type polysaccharide (the purity was up to 99.13 ± 0.61%) composed of linear glucose chains linked together by β-1,3-glycosidic bonds. These findings present a valuable basis for the industrial exploitation of paramylon with E. pisciformis AEW501.

Effects of organic carbon sources on growth and oil accumulation by Desmodesmus subspicatus LC172266 under mixotrophic condition.

Energy crisis and environmental sustainability have attracted global attention to microalgal biofuels. The present study investigated the impact of organic carbon sources on growth and bio-oil accumulation by an oleaginous microalga Desmodesmus subspicatus LC172266 under mixotrophic culture condition. Glucose and glycerol supported higher growth rates and lipid productivities than sucrose, fructose, mannitol and acetate. Each of the organic carbon source tested supported significantly (P < 0.05) higher growth rates and lipid productivities than the photoautotrophic culture (without organic carbon source). The lipid productivity obtained with a mixture of optima concentrations of glucose and glycerol (5.0gL-1 glycerol + 10.0gL-1glucose) (0.14875 ± 0.002g/L/day) was about 25% and 66% higher than the values obtained with only 10.0gL-1glucose and 5.0gL-1glycerol, respectively. When a batch culture with 5gL-1glycerol was fed with 0.5gL-1glucose daily the cell growth and lipid productivity were lower than the values obtained in a batch culture with a mixture of glucose and glycerol. The lipid productivity obtained in a 4-L photobioreactor was 94% (0.217gL-1day-1), higher than the value obtained in a flask culture with 10.0g/Lglucose (0.112gL-1day-1) and 46% higher than the value obtained in a flask culture with 5.0gL-1glycerol (0.086gL-1day-1).