Mixotrophic Mode Research Articles

Carbon and energy metabolism for the mixotrophic culture of Chlorella vulgaris using sodium acetate as a carbon source.

There has been an emergence of a diversity of microalgal mixotrophic synergistic mechanisms due to substrate differences. In this study, the effects of the mixotrophic culture of Chlorella vulgaris were examined. The maximum values of cell density, specific growth rate, and cell dry weight of Chlorella vulgaris were 3.52*107 cells/mL, 0.75 d-1, and 3.48 g/L in the mixotrophic mode, respectively. These were higher than the corresponding values of photoautotrophic or heterotrophic modes. Moreover, it was found that the concentrations of sodium bicarbonate consumed by the Chlorella vulgaris under mixotrophic and photoautotrophic modes were 635 mg/L/d and 505 mg/L/d, respectively; the concentrations of sodium acetate consumed by the Chlorella vulgaris under mixotrophic and heterotrophic modes were 614 mg/L/d and 645 mg/L/d, respectively. The activity of Rubisco was 9.36 U/mL in the mixotrophic culture, which was 3.09 and 4.85 times higher than that of the photoautotrophic and heterotrophic modes, respectively. This indicated that the differences for the carbon source absorption efficiency of Chlorella vulgaris in the mixotrophy led to different internal metabolic efficiencies when compared to photoautotroph or heterotrophy. Additionally, Chlorella vulgaris exhibits a more rapid energy metabolism efficiency when operating in the mixotrophic mode.

An assessment of the autotrophic/heterotrophic synergism in microalgae under mixotrophic mode and its contribution in high-rate phosphate recovery from wastewater

Dual carbon metabolisms and the synergism contribute to improving nutrient recovery under mixotrophy. However, how synergism influences nutrient recovery has yet to be understood, which is revealed in the current study. Due to dual carbon metabolisms and synergism,the PO4−-P recovery rate under mixotrophy reached 0.34 mg L−1 h−1. Due to the internal cycling of respiratory CO2, the mutualistic index (MI) in terms of synergism helped Scenedesmus accumulate 27.49 % more biomass under mixotrophy than sum of the two controls. In contrast, MI contributed 0.26 g L−1 d−1 to the total modeled mixotrophic productivity of 1.15 g L−1 d−1. To total modeled PO4−-P recovery, mixotrophic-auto, and mixotrophic-hetero shares were 42 % and 58 %. The synergism under mixotrophy contributed 20 % in total PO4−-P recovery. The PO4−-P recovery rate under mixotrophywas comparable to other biological P removal methods. These findings emphasize the potential of synergism in improving productivityand promoting resource recovery for sustainable wastewater treatment.

Microalgal production and nutrient recovery under mixotrophic mode using cheese whey permeate

Mixotrophic microalgal solutions are efficient nutrient recovery methods, with potential to prolong the cultivation seasons in temperate climates. To improve operation sustainability, the study used landfill leachate for nitrogen source and whey permeate for phosphorus and organic carbon. A non-axenic polyculture, dominated by green algae, was cultivated in mixotrophic mode on glucose or whey permeate compared to a photoautotrophic control in outdoor pilot-scaled raceway ponds during Nordic spring and autumn. The whey permeate treatment had the highest algal growth rate and productivity (0.48 d−1, 183.8 mg L−1 d−1), nutrient removal (total nitrogen: 21.71 mg L−1 d−1, total phosphorus: 3.05 mg L−1 d−1) and recovery rate (carbon: 85.19 mg L−1 d−1, nitrogen: 17.01 mg L−1 d−1, phosphorus: 2.58 mg L−1 d−1). When grown in whey permeate, algal cultures demonstrated consistent productivity and biochemical composition in high (spring) and low light conditions (autumn), suggesting the feasibility of year-round production in Nordic conditions.

Growth and Cell Size of Microalga Auxenochlorella protothecoides AS-1 under Different Trophic Modes.

Certain microalgal species can grow with different trophic strategies depending on the availability of nutrient resources. They can use the energy from light or an organic substrate, or both, and can therefore be called autotrophs, heterotrophs, or mixotrophs. We recently isolated a microalgal strain from the microplastic biofilm, which was identified as Auxenochlorella protothecoides, AS-1. Strain AS-1 grew rapidly in bacterial culture media and exhibited different growth rates and cell sizes under different trophic conditions. We compared the growth performance of AS-1 under the three different trophic modes. AS-1 reached a high biomass (>4 g/L) in 6 days under mixotrophic growth conditions with a few organic carbons as a substrate. In contrast, poor autotrophic growth was observed for AS-1. Different cell sizes, including daughter and mother cells, were observed under the different growth modes. We applied a Coulter Counter to measure the size distribution patterns of AS-1 under different trophic modes. We showed that the cell size distribution of AS-1 was affected by different growth modes. Compared to the auto-, hetero- and mixotrophic modes, AS-1 achieved higher biomass productivity by increasing cell number and cell size in the presence of organic substrate. The mechanisms and advantages of having more mother cells with organic substrates are still unclear and warrant further investigations. The work here provides the growth information of a newly isolated A. protothecoides AS-1 which will be beneficial to future downstream applications.

Amino acids rich biomass cultivation: Trophic mode influence on Chlorella Growth Factor (CGF) production

Nutritional supplement derived from protein-rich microalgae holds significant promise for both livestock and mankind. Chlorella sp. is unique and advantageous due to its ease of cultivation and presence of high composition of proteins, amino acids, and essential micronutrients. A comprehensive three-stage evaluation was conducted to assess different trophic modes (autotrophic, mixotrophic, and photoheterotrophic) and their impact on biomass production and nutritive value. These stages involved trophic mode cultivation (Stage-I) with varied carbon and nitrogen concentrations compared to nutrient deprived condition (control (N1)), CGF production and extraction (Stage-II), and CGF application (Stage-III). In Stage I, mixotrophic modes (M1 and M2) demonstrated the highest biomass production at 4.91 and 4.98 g L-1, surpassing autotrophic (A1 and A2), photoheterotrophic (H1), and nutrient-deprived (N1) conditions. Kinetic modelling revealed a correlative dependence of Chlorella sorokiniana growth on the supplemented nutrients. Scaling up the condition (M1) in a 5 L photobioreactor in Stage-II yielded a biomass of 4.63 g L-1 which was subjected to CGF extraction. In stage-II, C. sorokiniana exhibited a higher quantum efficiency of photosystem II (Fv/Fm: 0.77) and nutritive value, including 412.2 mg g-1 protein and 308 mg g-1 carbohydrate. Extracted CGF constituted of 54.4 % protein having eight essential amino acids (EAA) at 26.36 %, with a total EAA content of 13.7 g/100 g, slightly exceeding commercially available soy meal (12.5 g/100 g). In Stage-III, the applicability of CGF as a substrate for ethanol production using Saccharomyces cerevisiae was assessed, resulting in a biomass of 1.71 g L-1 and ethanol production of 4.5 %. This underscores the potential of C. sorokiniana not only as a rich nutritional source but also for the production of biobased products.

Optimizing ciprofloxacin removal through regulations of trophic modes and FNA levels in a moving bed biofilm reactor performing sidestream partial nitritation

The performance of partial nitritation (PN)-moving bed biofilm reactor (MBBR) in removal of antibiotics in the sidestream wastewater has not been investigated so far. In this work, the removal of ciprofloxacin was assessed under varying free nitrous acid (FNA) levels and different trophic modes. For the first time, a positive correlation was observed between ciprofloxacin removal and FNA levels, either in the autotrophic PN-MBBR or in the mixotrophic PN-MBBR, mainly ascribed to the FNA-stimulating effect on heterotrophic bacteria (HB)-induced biodegradation. The maximum ciprofloxacin removal efficiency (∼98 %) and removal rate constant (0.021 L g−1 SS h−1) were obtained in the mixotrophic PN-MBBR at an average FNA level of 0.056 mg-N L−1, which were 5.8 and 51.2 times higher than the corresponding values in the autotrophic PN-MBBR at 0 mg FNA-N L−1. Increasing FNA from 0.006 to 0.056 mg-N L−1 would inhibit ammonia oxidizing bacteria (AOB)-induced cometabolism and metabolism from 10.2 % and 6.9 % to 6.2 % and 6.4 %, respectively, while HB-induced cometabolism and metabolism increased from 31.2 % and 22.7 % to 41.9 % and 34.5 %, respectively. HB-induced cometabolism became the predominant biodegradation pathway (75.9 %-85.8 %) in the mixotrophic mode. Less antimicrobial biotransformation products without the piperazine or fluorine were newly identified to propose potential degradation pathways, corresponding to microbial-induced metabolic types and FNA levels. This work shed light on enhancing antibiotic removal via regulating both FNA accumulation and organic carbon addition in the PN-MBBR process treating sidestream wastewater.

Biomass Accumulation and Physiological Characteristics of Chlorella pyrenoidosa with Different Forms of Organic Phosphorus under the Mixotrophic Mode

Biomass Accumulation and Physiological Characteristics of <i>Chlorella pyrenoidosa</i> with Different Forms of Organic Phosphorus under the Mixotrophic Mode

Microbial protein production under mixotrophic mode: ammonium assimilation pathway and C/N ratio optimization

Producing microbial protein (MP) is considered as a promising method to alleviate the demand for the global protein supply. The conversion of carbon dioxide (CO2) and organic carbon into MP by hydrogen oxidizing bacteria (HOB) is considered as a potent solution. In this study, under mixotrophic condition, MP production was 2.4 g/L, higher than the sum of that in autotrophic and heterotrophic mode (1.9 g/L), showing the mutualistic relationship of two pathways. According to functional enzyme analysis, the abundance of glutamate dehydrogenase and glutamine synthetase in the heterotrophic and mixotrophic modes was obviously enhanced (80%−800% increment), indicating that adding soluble organics could enhance both the direct (“NH4+ → L-Glutamate”) and the indirect pathway (“NH4+ → L-Glutamine → L-Glutamate”) of NH4+ assimilation in the mixed HOB consortium. For further enhancing MP production, different C/N ratio was evaluated based on mixotrophic mode, achieving amino acid production of 3.3 ± 0.1 g/L and high protein content (58.1%) in C/N-9 reactor. Corynebacterium was dominant (91.4%). In nitrogen assimilation pathway, the higher abundance of glutamine synthetase than glutamate dehydrogenase suggested that NH4+-N was mainly converted via the indirect pathway. With the increase of C/N ratio, 24–48% increment was obtained on glutamine synthetase, along with the decrement of glutamate dehydrogenase. Thus, high C/N ratio could boost the indirect pathway, while performing the negative effect on the direct pathway.

Interchangeable modular design and operation of photo-bioreactors for Chlorella vulgaris cultivation towards a zero-waste biorefinery

This study explores diverse cultivation modes for Chlorella vulgaris within a biorefinery at pilot scale that produces both biodiesel by transesterification of waste frying oils and syngas by gasification of organic wood waste. Given microalgae's comparatively modest biofuel yield relative to principal biorefinery products, the microalgae cultivation process is designed on the biofuels production rates. Liquid and gaseous waste streams are recycled inside the biorefinery: crude glycerol is mixed with wood to enhance the quality of syngas, wastewater is fed to microalgae so as flue gas. Also, the oil extracted from microalgae contributes to produce biodiesel and the waste cells are gasified.Considering that the optimal fit for each cultivation mode varies with the shape of the reactor, we propose a modular approach to assemble them in batteries of tubular, bubble flow, and airlift reactors, and present an operating design criterion that can fulfill the mass balance of the plant by adding/transforming the number of units inside the different batteries. Methods to adjust the operating conditions and control the operating parameters are also discussed.The designed configurations were operated recycling nominal waste streams of about 30 L d−1 of wastewater and 90 Nm3 h−1 of flue gas. Results confirm that the most advantageous one, in terms of volume per recycled waste streams, is a battery of 16 airlift reactors, operating in mixotrophic mode, with growing rate of 0.427 d−1, yield of 3.06, glycerol conversion 39 %, CO2 removal 64 % of inlet 6–10 %(mol) concentration. The same nominal waste streams can also be managed by 40 tubular reactors in almost heterotrophic conditions coupled with 12 bubble columns in autotrophic conditions; working respectively at growing rates of 0.395 d−1 and 0.362 d−1 and yields of 2.94 and 2.84. The battery of tubular reactors reached a glycerol conversion of 45 % and the array of bubble columns removed about 51 % of inlet 12–20 %(mol) CO2 concentration. A complete comparison is reported also in terms of dimensionless numbers and pumping/mixing requirements.

Mixotrophic culture of Chaetoceros sp. and the synergistic carbon and energy metabolism

This research studied the metabolic mechanism of the mixotrophic Chaetoceros sp. The results showed this alga had the highest cell density and growth rate of 47.72 × 105 cells mL−1 and 0.41 d-1, respectively, with a maximum dry weight of 2.90 g/L, when compared to photoautotrophic and photoheterotrophic modes. Compared to photoheterotrophy, transcriptomics results showed the Rubisco, PGK, and GAPDH related genes were separately up-regulated by 1.03, 2.36, and 1.36 times in CBB cycle in mixotrophic mode, suggesting intermediate metabolites of EMP and PPP can enter the chloroplast via transporter proteins, or membrane permeation, and feedback inhibition regulates the reduction of multiple reactions in CBB cycle. Chaetoceros sp. achieves high biomass by utilizing ATP and carbon structures from EMP and PPP pathways, and the addition of NaHCO3 leads to an up-regulation of CBB cycle for the mixotrophic alga, resulting in higher biomass compared to the photoheterotrophic mode.

Evaluation of Growth and Production of High-Value-Added Metabolites in Scenedesmus quadricauda and Chlorella vulgaris Grown on Crude Glycerol under Heterotrophic and Mixotrophic Conditions Using Monochromatic Light-Emitting Diodes (LEDs).

This study aimed to examine the impact of crude glycerol as the main carbon source on the growth, cell morphology, and production of high-value-added metabolites of two microalgal species, namely Chlorella vulgaris and Scenedesmus quadricauda, under heterotrophic and mixotrophic conditions, using monochromatic illumination from light-emitting diodes (LEDs) emitting blue, red, yellow, and white (control) light. The findings indicated that both microalgae strains exhibited higher biomass yield on the mixotrophic growth system when compared to the heterotrophic one, while S. quadricauda generally performed better than C. vulgaris. In mixotrophic mode, the use of different monochromatic illumination affected biomass production differently on both strains. In S. quadricauda, growth rate was higher under red light (μmax = 0.89 d-1), while the highest biomass concentration and yield per gram of consumed glycerol were achieved under yellow light, reaching 1.86 g/L and Yx/s = 0.18, respectively. On the other hand, C. vulgaris demonstrated a higher growth rate on blue light (μmax = 0.45 d-1) and a higher biomass production on white (control) lighting (1.34 g/L). Regarding the production of metabolites, higher yields were achieved during mixotrophic mode in both strains. In C. vulgaris, the highest lipid (26.5% of dry cell weight), protein (63%), and carbohydrate (20.3%) contents were obtained under blue, red, and yellow light, respectively, thus indicating that different light wavelengths probably activate different metabolic pathways. Similar results were obtained for S. quadricauda with red light leading to higher lipid content, while white lighting caused higher production of proteins and carbohydrates. Overall, the study demonstrated the potential of utilizing crude glycerol as a carbon source for the growth and metabolite production of microalgae and, furthermore, revealed that the strains' behavior varied depending on lighting conditions.

Biomass Fuel Production through Cultivation of Microalgae Coccomyxa dispar and Scenedesmus parvus in Palm Oil Mill Effluent and Simultaneous Phycoremediation

Palm oil mill effluent (POME) is a potential alternative sources of biomass fuel upon phycoremediation treatment using microorganisms. In this study, Coccomyxa dispar and Scenedesmus parvus, as acidophilic microalgae, were used to investigate growth and the production of biomass fuel from the cultivation of POME, as well the effectiveness of removing contaminants from POME. Individual cultivation was conducted at 26 ± 3 °C for 14 days under three growth modes (mixotrophic, heterotrophic, and autotrophic). To elucidate the potential phycoremediation properties, the characteristics of treated POME were compared, such as optical density (OD), cell dry weight (CDW), calorific energy values (CEV), chemical oxygen demand (COD), biochemical oxygen demand (BOD), carbon, hydrogen, and nitrogen (CHN) elemental analysis, including oil and grease content. S. parvus exhibits an outstanding growth profile for all growth modes compared to C. dispar, with measurements of 228.8, 37.08, and 118.2 mg/L observed at day 14 of cultivation. The highest CEV is 32.30 MJ/kg, which was obtained from S. parvus in the mixotrophic mode. Maximum removal efficiency for COD and BOD was 81% and 19% in the mixotrophic growth mode with S. parvus. These results pinpoint that S. parvus has the potential to be utilized for biomass fuel production with high CEV and effective POME phycoremediation.

CO2 capture and lipid production performance of microalgae in the S-shaped photobioreactor under different culture modes

An S-shaped photobioreactor was designed by adding grooves and baffles in the traditional photobioreactor to improve the culture efficiency of microalgae. After that, the parameters of the characterization of the S-shaped photobioreactor, such as the mixing time, gas holdup, and gas-liquid mass transfer coefficient, were determined. The biomass, lipid production rate, and average CO2 capture rate of microalgae were then analyzed under different culture modes. Finally, the feasibility of using digested piggery wastewater combined with simulated flue gas was explored as a culture mode for the microalgae and the lipid properties of the microalgae were analyzed. The results revealed that, at a flow rate of 0.08 vvm, the mixing time was reduced by 8.5 s, the gas hold-up increased by 44.6% and the gas–liquid mass transfer ability was also improved. Improvements were also observed in the biomass values, lipid production rate, and average CO2 capture rate of the microalgae under different culture conditions, with respective values reaching 0.23 g·(L·d)–1, 70.28 mg·(L·d)–1, and 0.43 g·(L·d)–1 under the mixotrophic mode. Additionally, digested piggery wastewater combined with the simulated microalgae flue gas culture was determined to be feasible. The biomass, lipid production rate, and the average CO2 capture rate of microalgae, the values of which were 0.22 g·(L·d)–1, 52.55 mg·(L·d)–1, and 0.41 g·(L·d)–1, respectively. Lipid was observed to have the potential to produce high-quality biofuel.

Altering autotrophic carbon metabolism of Nitzschia closterium to mixotrophic mode for high-value product improvement

An adaptive laboratory evolution (ALE) strategy was designed to evolve autotrophic Nitzschia closterium to mixotrophic growth for high productivity of essential amino acid (EAA), eicosapentaenoic acid (EPA) and fucoxanthin. The N. closterium growth was limited under glucose initially, but a red light emitting diode was innovatively applied to modify carbon metabolism and obtain mixotrophic strain of N. closterium GM. The N. closterium GM biomass concentration was improved by 65.07% comparing with wild type, but exhibited weak photosynthesis and strong glucose metabolism. At carbon metabolism levels, ALE promoted NADPH oxidase activity and induced protein degradation to lipid biosynthesis by elevating acetyl-CoA and pyruvate contents. It also improved carbon flux to TCA cycle, and elevated contents of glucose-6-phosphate, fructose-6-phosphate, glyceraldehyde-3-phosphate for providing sufficient ATP and NADPH. Productivities of EPA, EAA and fucoxanthin were increased by 41.0%, 18.8% and 20.4%, respectively. This ALE strategy was promising in microalgal production of high-value products.

Oil-rich filamentous algae cultivation in anaerobic digestate effluent: Inhibition effect of undissociated fatty acids

Microalgae cultivation using organic carbon waste has been proved as a promising way to enhance filamentous algal biomass bio-protection. However, the carbon source in anaerobic digestate (AD; the effluent of biogas plants) contains various organic carbon source and other components, with a complex metabolic process in algae. The utilization of organic carbon including volatile fatty acids (VFAs) and glycerin by Tribonema minus were investigated. The results showed that the utilization of VFAs as the carbon source by T. minus with the addition of 0.3% CO2 decreased pH value below 6.0 and accumulated the undissociated VFAs (UVFAs) (UVFAs contents: 99.29 ± 8.34 mg L−1, 176.52 ± 4.05 mg L−1, 115.02 ± 5.86 mg L−1, and 127.52 ± 7.24 mg L−1 for acetic acid, propanoic acid, butyric acid, and valeric acid, respectively after 1st day cultivation), which inhibited T. minus growth. However, this inhibition effect was not observed when using glycerin as a carbon source (Biomass: 2.95 g L−1). To study the inhibition mechanism of UVFAs on the algae, the growth and metabolism of algae using acetic acid and butyric acid as carbon source was studied under different pH (4.5, 5.5, 6.5). The study found that the UVFAs content at pH 4.5–5.5 was higher than that at pH 6.5 with the same carbon concentrations. UVFAs inhibited the biomass accumulation of T. minus and decreased photosynthetic and enzymatic activities. This study concluded that T. minus can be cultivated with a mixotrophic mode using AD that contains VFAs with controlled pH value around neutral.

The growth and lipid accumulation of Scenedesmus quadricauda under nitrogen starvation stress during xylose mixotrophic/heterotrophic cultivation.

In order to conquer the block of high cost and low yields which limit to realize the commercialization of microalgal biodiesel, the mixotrophic and heterotrophic cultivation of Scenedesmus quadricauda FACHB-1297 fed on xylose was separately studied employing six forms of media: phosphorus sufficient, phosphorus restricted, and phosphorus starvation were combined with nitrogen sufficient and nitrogen starvation conditions. The maximum lipid content (about 41% of dry weight) was obtained on the 5th day (heterotrophic cultivation) and 8th day (mixotrophic cultivation) under the nitrogen starved and phosphorus sufficient (N0&P) conditions, which was about twofold in comparison to the final lipid content on the sufficient nitrogen condition (control). Under mixotrophic and heterotrophic modes, the highest lipid production was achieved in the N0&P trial, with the value of 274.96mg/L and 193.77mg/L, respectively. Xylose utilization rate of 30-96% under heterotrophic modes was apparently higher than that of 20-50% in mixotrophic modes. In contrast, phosphorus uptake rate of 100% under mixotrophic cultivation was significantly more than that of 60-90% in heterotrophic cultivation. Furthermore, under the condition of heterotrophic cultivation using xylose as a carbon source, the phosphorus had a positive impact on microalgae cell synthesis and the lipid content enhanced with the augmentation in phosphorus concentrations. We suggested that sufficient phosphorus should be supplied for obtaining higher microalgal lipid production in the lack of nitrogen under xylose heterotrophic/mixotrophic condition. This was a highly effective way to obtain efficient microalgae lipid production.

Co-cultivation of microalgae-cyanobacterium under various nitrogen and phosphorus regimes to concurrently improve biomass, lipid accumulation and easy harvesting

Due to due to high-cost harvesting method, low biomass productivity (BP), and lipid yield (LY), commercialization of microalgae biomass is still impeded. Some researchers discovered that the combined effects of low nitrogen (N) and high phosphorus (P) resulted to an increase in biomass and lipid production. However, the choice of a balanced N:P ratio is still ambiguous between microalgal species and is up for debate. Here, we set various ranges of N:P ratios from 2:1–44.11:1 with the addition of glucose in the BG 11 medium to examine its influence on the growth of microalgae. The investigation was performed by subjecting a novel strain, Scenedesmus sp. DDVG I to these various mediums under heterotrophic and mixotrophic modes. The N:P of 100:50 or N-deficient P-over excessive (Ndef Poexcs) condition under mixotrophic mode had the highest growth rate of 0.15 d−1 ± 0.01, with a maximum BP and LY of 41.1 ± 0.5 mg/L. d and 39.1 ± 1.2 % dry cell weight (DCW), respectively. Further, in attempting to facilitate the harvesting step, we co-cultured Scenedesmus sp. with Limnothrix sp. DDVG II mixotrophically under inoculum ratio of 1:1, 1:2, 2:1 in the Ndef Poexcs condition. The co-culture 1:1 system achieved the maximum biomass harvesting efficiency of 99.9± 0.5 % with an increase in BP and LY up to 42.0 ± 0.9 mg/L. d and 40.2 ± 1.0 % DCW, respectively. The fatty acid methyl ester compositions of co-culture 1:1 was rich in C18:2 (36.05 %), C16:0 (32.25 %), C18:1 (16.86 %), and C18:0 (7.68 %). The biodiesel derived from the co-culture 1:1 also complied with standard specifications, making it appropriate for the production of biodiesel. The overall findings demonstrated a unique co-culture approach toward easy harvesting while concurrently maximizing biomass and lipid yield when grown in a balanced N:P ratio of 100:50. The techno-economic analysis of the system, biodiesel cost, and its implementation toward biorefinery approach can be envisaged in the future study.

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 growth regime of novel strain Scenedesmus sp. DDVG I in municipal wastewater for concomitant bioremediation and valorization of biomass

Availability of cost-effective nutrients for the commercial cultivation of microalgae is one of the major challenges. The present study investigated the feasibility of primary municipal wastewater (PMWW) collected from a local wastewater treatment plant in Minnesota, USA as an alternative to fresh-water microalgae growth media towards high-value bioenergy feedstock production. The novel strain Scenedesmus sp. DDVG I was cultivated in the PMWW under heterotrophic and mixotrophic modes in 250 mL Erlenmeyer flasks. The optimized cultivation mode was further scaled up to the 3-L bubbled bioreactor. The study confirmed the wastewater as a potential growth medium while Scenedesmus sp. DDVG I showed superior biomass productivity (0.069 g/L d), lipid yield (22.5%), and FAME content (22.04% in dry cell weight) over 10 days in the mixotrophic mode. The biomass also showed high essential amino acid content (159.8 mg/g DCW). The corresponding values for bioremediation efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) by Scenedesmus sp. were 75.6% and 99.8% respectively. Meanwhile, ammonia nitrogen (NH3–N) and total phosphorus (TP) were removed at up to 100% removal efficiencies. Analyses of fatty acid profile and different parameters that were required for biodiesel characterization revealed the high-quality nature of the Scenedesmus-derived oil. Overall, the study concluded effective bioremediation of municipal wastewater by Scenedesmus sp. DDVG I with the recovery of valuable resources from the biomass.

High oleic acid biosynthesis and its absolute quantification by GC/MS in oleaginous Scenedesmus sp. SVMIICT1 cultivated in dual stress phase

High photosynthetic rates and high lipid content make microalgae a promising source for the industrial production of edible oils. Enhancement of oleic acid production in microalgae is an important area in the algae-based edible oils research. This study employed the mixotrophic mode of nutrition with a nutrient-rich growth phase (GP) followed by two different stress phases (SPs), including nitrate depletion (single stress phase; SSP) and nitrate depletion with salinity (dual stress phase; DSP). In DSP, higher oleic acid (C18:1) content was observed and considered the same for autotrophic mode. In addition to DSP, it evaluated the role of nitrate to phosphate ratio in GP towards fatty acid biosynthesis. The relative and absolute quantities of fatty acids were measured in mixotrophic and autotrophic cultivations. Higher oleic acid was obtained at 250 mM NaCl DSP condition in mixotrophic cultivation compared to other conditions. Whereas autotrophic mode microalgae cultivated in dual stress phase (DSP for A-GP-1N1P, DSP for A-GP-1N2P, DSP for A-GP-1N4P, and DSP for A-GP-1N6P) resulted in ~30 % (w/w) of total fatty acids with 55 % of Oleic acid in absolute quantity. Overall, the study depicted a distinct influence of nitrate, nitrate to phosphate ratio, nitrate depletion (single stress), and dual stress on the oleic acid yield. The application of dual stress to microalgae cultivation is a new approach to oleic acid enhancement. • Nitrate depletion and salinity in stress phase influenced oleic acid biosynthesis. • Study achieved 30 % of total fatty acids with 55 % of Oleic acid in absolute quantity. • Nitrates and phosphates in growth phase also influenced fatty acids production. • Nitrates increment in mixotrophic growth phase negligibly affected oleogenesis. • Biosynthesis of fatty acids is interdependent with growth phase and stress phase.