Pre-concentration of microalga Euglena gracilis by alkalescent pH treatment and flocculation mechanism of Ca3(PO4)2, Mg3(PO4)2, and derivatives

Wu, Mingcan; Li, Jing; Qin, Huan; Lei, Anping; Zhu, Hongxiang; Hu, Zhangli; Wang, Jiangxin

doi:10.1186/s13068-020-01734-8

Cited by 26 publications

(12 citation statements)

References 46 publications

(70 reference statements)

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“…However, for some economic microalgae such as single-celled Euglena gracilis aquatic environmental pH would be reduced when cultured under photoautotrophic conditions. For example, when the initial pH was as low as 3.5 to 2, the biomass of E. gracilis gradually increased [9]. This phenomenon is contrary to traditional theory.…”

Section: Open Accessmentioning

confidence: 57%

Microalgal photoautotrophic growth induces pH decrease in the aquatic environment by acidic metabolites secretion

et al. 2022

Biotechnol Biofuels

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Background Microalgae can absorb CO2 during photosynthesis, which causes the aquatic environmental pH to rise. However, the pH is reduced when microalga Euglena gracilis (EG) is cultivated under photoautotrophic conditions. The mechanism behind this unique phenomenon is not yet elucidated. Results The present study evaluated the growth of EG, compared to Chlorella vulgaris (CV), as the control group; analyzed the dissolved organic matter (DOM) in the aquatic environment; finally revealed the mechanism of the decrease in the aquatic environmental pH via comparative metabolomics analysis. Although the CV cell density was 28.3-fold that of EG, the secreted-DOM content from EG cell was 49.8-fold that of CV (p-value < 0.001). The main component of EG’s DOM was rich in humic acids, which contained more DOM composed of chemical bonds such as N–H, O–H, C–H, C=O, C–O–C, and C–OH than that of CV. Essentially, the 24 candidate biomarkers metabolites secreted by EG into the aquatic environment were acidic substances, mainly lipids and lipid-like molecules, organoheterocyclic compounds, organic acids, and derivatives. Moreover, six potential critical secreted-metabolic pathways were identified. Conclusions This study demonstrated that EG secreted acidic metabolites, resulting in decreased aquatic environmental pH. This study provides novel insights into a new understanding of the ecological niche of EG and the rule of pH change in the microalgae aquatic environment.

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Section: Open Accessmentioning

confidence: 57%

Microalgal photoautotrophic growth induces pH decrease in the aquatic environment by acidic metabolites secretion

et al. 2022

Biotechnol Biofuels

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“…Euglena gracilis CCAP 1224/5Z was obtained from the Culture Collection of Algae and Protozoa (CCAP) and maintained in our lab at Shenzhen University [ 30 ]. This strain was cultured in a modified photoautotrophic Euglena medium (PEM) according to Cramer and Myers [ 31 ].…”

Section: Methodsmentioning

confidence: 99%

“…Paramylon content was quantified using the method of Takenaka et al [ 37 ] and Wu et al [ 30 ] with the following modification: 2 mL, 30 mmol/L of EDTA chelating agent was added to 15 mL the algae cells suspensions. After each cell suspension was centrifuged and freeze-dried, 10 mg freeze-dried algae powder and 5 mL of acetone were transferred to a 15 mL of centrifuge tube and shaken for 30 s, then placed in a shaker for 2 h. After the tube was centrifuged at 2000× g for 5 min, the supernatant was removed.…”

Section: Methodsmentioning

confidence: 99%

Water reuse and growth inhibition mechanisms for cultivation of microalga Euglena gracilis

et al. 2021

Biotechnol Biofuels

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Background Microalgae can contribute to more than 40% of global primary biomass production and are suitable candidates for various biotechnology applications such as food, feed products, drugs, fuels, and wastewater treatment. However, the primary limitation for large-scale algae production is the fact that algae requires large amounts of fresh water for cultivation. To address this issue, scientists around the world are working on ways to reuse the water to grow microalgae so that it can be grown in successive cycles without the need for fresh water. Results In this study, we present the results when we cultivate microalgae with cultivation water that is purified and reused. Specifically, we purify the cultivation water using an ultrafiltration membrane (UFM) treatment and investigate how this treatment affects: the biomass and biochemical components of the microalgae; characteristics of microalgae growth inhibitors; the mechanism whereby potential growth inhibitors are secreted (followed using metabolomics analysis); the effect of activated carbon (AC) treatment and advanced oxidation processes (AOPs) on the removal of growth inhibitors of Euglena gracilis. Firstly, the results show that E. gracilis can be only cultivated through two growth cycles with water that has been filtered and reused, and the growth of E. gracilis is significantly inhibited when the water is used a third time. Secondly, as the number of reused water cycles increases, the Cl− concentration gradually increases in the cultivation water. When the Cl− concentration accumulates to a level of fivefold higher than that of the control, growth of E. gracilis is inhibited as the osmolality tolerance range is exceeded. Interestingly, the osmolality of the reused water can be reduced by replacing NH4Cl with urea as the source of nitrogen in the cultivation water. Thirdly, E. gracilis secretes humic acid (HA)—which is produced by the metabolic pathways for valine, leucine, and isoleucine biosynthesis and by linoleic acid metabolism—into the cultivation water. Because HA contains large fluorescent functional groups, specifically extended π(pi)-systems containing C=C and C=O groups and aromatic rings, we were able to observe a positive correlation between HA concentration and the rate of inhibition of E. gracilis growth using fluorescence spectroscopy. Moreover, photosynthetic efficiency is adversely interfered by HA, thereby reductions in the synthetic efficiency of paramylon and lipid in E. gracilis. In this way, we are able to confirm that HA is the main growth inhibitor of E. gracilis. Finally, we verify that all the HA is removed or converted into nutrients efficiently by AC or UV/H2O2/O3 treatments, respectively. As a result of these treatments, growth of E. gracilis is restored (AC treatment) and the amount of biomass is promoted (UV/H2O2/O3 treatment). Conclusions These studies have important practical and theoretical significance for the cyclic cultivation of E. gracilis and for saving water resources. Our work may also provide a useful reference for other microalgae cultivation.

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“…The differences in flocculation rates and times of arrival at T max could have been related to pH as it is known that pH affects flocculation via its effect on the Zeta potentials and hydrophobicity of both fungal and algal cells (Chu et al 2021a). Under acidic conditions, the surface charge of algal cells becomes less negative, increasing destabilization of the cells in suspension (Bhattacharya et al 2017;Wu et al 2020). Fungi excrete organic acids which can help lower the pH, destabilizing the algae, and increasing the likelihood that the different cell types will be attracted to each other and flocculate (Chu et al 2021a).…”

Section: Flocculationmentioning

confidence: 99%

Bioflocculation of Euglena gracilis via direct application of fungal filaments: a rapid harvesting method

et al. 2021

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The high cost and environmental impact of traditional microalgal harvesting methods limit commercialization of microalgal biomass. Fungal bioflocculation of microalgae is a promising low-cost, eco-friendly method but the range of fungal and microalgal species tested to date is narrow. Here, eight non-pathogenic, filamentous fungi were screened for their ability to self-pelletize and flocculate Euglena gracilis (ca.50 µm motile microalga) in suspension. Self-pelletization was tested under various rotational speeds, and species which formed pellets (Ø > 0.5 cm) were selected for harvesting tests. Filaments of each species were combined with E. gracilis at various ratios based on dry weight. Harvesting efficiency was determined by measuring the change in cell counts over time, and settling of the flocs was evaluated by batch settling tests. Three fungal species, Ganoderma lucidum, Pleurotus ostreatus, and Penicillium restrictum, were able to reliably flocculate and harvest 62–75% of the microalgae while leaving it unharmed. The results demonstrated that self-pelletization, harvesting, and settling were dependent on the fungal species. The fungi to algae ratio also had significant but contrasting effects on harvesting and settling. In balancing the needs to both harvest and settle the biomass, the optimal fungi to algae ratio was 1:2. The application of fungal filaments to microalgae in suspension produced readily settling flocs and was less time-consuming than other commonly used methods. This method is especially attractive for harvesting microalgal biomass for low-value products where speed, low cost, and cell integrity is vital.

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Pre-concentration of microalga Euglena gracilis by alkalescent pH treatment and flocculation mechanism of Ca3(PO4)2, Mg3(PO4)2, and derivatives

Cited by 26 publications

References 46 publications

Microalgal photoautotrophic growth induces pH decrease in the aquatic environment by acidic metabolites secretion

Microalgal photoautotrophic growth induces pH decrease in the aquatic environment by acidic metabolites secretion

Water reuse and growth inhibition mechanisms for cultivation of microalga Euglena gracilis

Bioflocculation of Euglena gracilis via direct application of fungal filaments: a rapid harvesting method

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