mixotrophic conditions
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2022 ◽  
Vol 12 ◽  
Author(s):  
Qingling Zhu ◽  
Mengmeng Zhang ◽  
Bingying Liu ◽  
Fang Wen ◽  
Zhili Yang ◽  
...  

Chlorella sorokiniana is one of the most productive microalgal species with a high potential for the production of biofuels and other high value-added molecules. Many studies have focused on its capability of mixotrophic growth using reduced organic carbon and growth pattern shift between autotrophic and mixotrophic conditions. In this study, we investigated growth patterns of a novel isolate, C. sorokiniana G32, under mixotrophic growth conditions supplemented with a low level (1.25 g L–1) and a high level (5 g L–1) of glucose. Physiological, transcriptomic (i.e., RNA-seq), and metabolomic (i.e., LC-MS/MS) methods were used. We showed that peak growth based on OD680nm absorbance is ∼4-fold higher with high glucose vs. low glucose supplementation. Photosynthetic efficiency (Fv/Fm) in G32 mixotrophic cultures with high or low glucose supplementation remains identical to that of G32 phototrophic growth. We also found that the conversion rate between absorbance-based cell density and cell dry weight with high glucose supplementation was lower than with low glucose. This suggests that more cell biomass is produced under high glucose treatment than with low glucose. The result was confirmed via sucrose density gradient centrifugation. It is likely that accumulation of high concentration of starch may account for this effect. Transcriptomic analysis of G32 cultures (i.e., via RNA-seq) in response to reciprocal change of glucose levels reveals that expression of a subset of differentially expressed genes (DEGs) is correlated with the amount of glucose supplementation. These DEGs are designated as glucose-specific responsive (GSR) genes. GSR genes are enriched for a number of energy metabolic pathways. Together with metabolomics data (i.e., LC-MS/MS), we show that under high-level supplementation, glucose is preferentially oxidized through an oxidative pentose phosphate pathway. Collectively, our results indicate the mechanism of regulation of glucose assimilation and energy metabolism in G32 under mixotrophic conditions with different levels of glucose supplementation revealed by transcriptomic and metabolomic analyses. We propose that C. sorokiniana G32 has the potential for the production of high value-added molecules.


Author(s):  
Hyun-Sik Yun ◽  
Young-Saeng Kim ◽  
Ho-Sung Yoon

In the past, biomass production using microalgae culture was dependent on inorganic carbon sources as microalgae are photosynthetic organisms. However, microalgae utilize both organic and inorganic carbon sources, such as glucose. Glucose is an excellent source of organic carbon that enhances biomass yield and the content of useful substances in microalgae. In this study, photoautotrophic, mixotrophic, and heterotrophic cultivation conditions were applied to three well-known strains of Chlorella (KNUA104, KNUA114, and KNUA122) to assess biomass productivity, and compositional changes (lipid, protein, and pigment) were evaluated in BG11 media under photoautotrophic, mixotrophic, and heterotrophic conditions utilizing different initial concentrations of glucose (5, 10, 15, 20, and 25 g L−1). Compared to the photoautotrophic condition (biomass yield: KNUA104, 0.35 ± 0.04 g/L/d; KNUA114, 0.40 ± 0.08 g/L/d; KNUA122, 0.38 ± 0.05 g/L/d) glucose was absent, and the biomass yield improved in the mixotrophic (glucose: 20 g L−1; biomass yield: KNUA104, 2.99 ± 0.10 g/L/d; KNUA114, 5.18 ± 0.81 g/L/d; KNUA122, 5.07 ± 0.22 g/L/d) and heterotrophic conditions (glucose: 20 g L−1; biomass yield: KNUA104, 1.72 ± 0.26 g/L/d; KNUA114, 4.26 ± 0.27 g/L/d; KNUA122, 4.32 ± 0.32 g/L/d). All strains under mixotrophic and heterotrophic conditions were optimally cultured when 15–20 g L−1 initial glucose was provided. Although bioresourse productivity improved under both mixotrophic and heterotrophic conditions where mixotrophic conditions were found to be optimal as the yields of lipid and pigment were also enhanced. Protein content was less affected by the presence of light or the concentration of glucose. Under mixotrophic conditions, the highest lipid content (glucose: 15 g L−1; lipid content: 68.80 ± 0.54%) was obtained with Chlorella vulgaris KNUA104, and enhanced pigment productivity of Chlorella sorokiniana KNUA114 and KNUA122 (additional pigment yield obtained with 15 g L−1 glucose: KNUA 114, 0.33 ± 0.01 g L−1; KNUA122, 0.21 ± 0.01 g L−1). Also, saturated fatty acid (SFA) content was enhanced in all strains (SFA: KNUA104, 29.76 ± 1.31%; KNUA114, 37.01 ± 0.98%; KNUA122, 33.37 ± 0.17%) under mixotrophic conditions. These results suggest that mixotrophic cultivation of Chlorella vulgaris and Chlorella sorokiniana could improve biomass yield and the raw material quality of biomass.


Metabolites ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 866
Author(s):  
Willian Capa-Robles ◽  
Ernesto García-Mendoza ◽  
José de Jesús Paniagua-Michel

Current mixotrophic culture systems for Dunaliella salina have technical limitations to achieve high growth and productivity. The purpose of this study was to optimize the mixotrophic conditions imposed by glycerol, light, and salinity that lead to the highest biomass and β-carotene yields in D. salina. The combination of 12.5 mM glycerol, 3.0 M salinity, and 50 μmol photons m−2 s−1 light intensity enabled significant assimilation of glycerol by D. salina and consequently enhanced growth (2.1 × 106 cell mL−1) and β-carotene accumulation (4.43 pg cell−1). The saline and light shock induced the assimilation of glycerol by this microalga. At last stage of growth, the increase in light intensity (300 μmol photons m−2 s−1) caused the β-carotene to reach values higher than 30 pg cell−1 and tripled the β-carotene values obtained from photoautotrophic cultures using the same light intensity. Increasing the salt concentration from 1.5 to 3.0 M NaCl (non-isosmotic salinity) produced higher growth and microalgal β-carotene than the isosmotic salinity 3.0 M NaCl. The mixotrophic strategy developed in this work is evidenced in the metabolic capability of D. salina to use both photosynthesis and organic carbon, viz., glycerol that leads to higher biomass and β-carotene productivity than that of an either phototrophic or heterotrophic process alone. The findings provide insights into the key role of exogenous glycerol with a strategic combination of salinity and light, which evidenced unknown roles of this polyol other than that in osmoregulation, mainly on the growth, pigment accumulation, and carotenogenesis of D. salina.


Author(s):  
Nashwa A. H. Fetyan ◽  
Abo El-Khair B. El-Sayed ◽  
Fatma M. Ibrahim ◽  
Yasser A. Attia ◽  
Mahmoud W. Sadik

2021 ◽  
Vol 9 (7) ◽  
pp. 1496
Author(s):  
Rubiyatno ◽  
Kazuhiro Mori ◽  
Daisuke Inoue ◽  
Sunah Kim ◽  
Jaecheul Yu ◽  
...  

Euglena gracilis produces paramylon, which is a feedstock for high-value functional foods and nutritional supplements. The enhancement of paramylon productivity is a critical challenge. Microalgae growth-promoting bacteria (MGPB) can improve microalgal productivity; however, the MGPB for E. gracilis remain unclear. This study isolated bacteria capable of enhancing E. gracilis growth and paramylon production under mixotrophic conditions. Enterobacter sp. CA3 and Emticicia sp. CN5 were isolated from E. gracilis grown with sewage-effluent bacteria under mixotrophic conditions at pH 4.5 or 7.5, respectively. In a 7-day E. gracilis mixotrophic culture with glucose, CA3 increased E. gracilis biomass and paramylon production 1.8-fold and 3.5-fold, respectively (at pH 4.5), or 1.9-fold and 3.5-fold, respectively (at pH 7.5). CN5 increased E. gracilis biomass and paramylon production 2.0-fold and 4.1-fold, respectively (at pH 7.5). However, the strains did not show such effects on E. gracilis under autotrophic conditions without glucose. The results suggest that CA3 and CN5 promoted both E. gracilis growth and paramylon production under mixotrophic conditions with glucose at pH 4.5 and 7.5 (CA3) or pH 7.5 (CN5). This study also provides an isolation method for E. gracilis MGPB that enables the construction of an effective E. gracilis–MGPB-association system for increasing the paramylon yield of E. gracilis.


2021 ◽  
Vol 12 ◽  
Author(s):  
Martin Lehmann ◽  
Evgenia Vamvaka ◽  
Alejandro Torrado ◽  
Peter Jahns ◽  
Marcel Dann ◽  
...  

Lutein, made by the α-branch of the methyl-erythritol phosphate (MEP) pathway, is one of the most abundant xanthophylls in plants. It is involved in the structural stabilization of light-harvesting complexes, transfer of excitation energy to chlorophylls and photoprotection. In contrast, lutein and the α-branch of the MEP pathway are not present in cyanobacteria. In this study, we genetically engineered the cyanobacterium Synechocystis for the missing MEP α-branch resulting in lutein accumulation. A cassette comprising four Arabidopsis thaliana genes coding for two lycopene cyclases (AtLCYe and AtLCYb) and two hydroxylases (AtCYP97A and AtCYP97C) was introduced into a Synechocystis strain that lacks the endogenous, cyanobacterial lycopene cyclase cruA. The resulting synlut strain showed wild-type growth and only moderate changes in total pigment composition under mixotrophic conditions, indicating that the cruA deficiency can be complemented by Arabidopsis lycopene cyclases leaving the endogenous β-branch intact. A combination of liquid chromatography, UV-Vis detection and mass spectrometry confirmed a low but distinct synthesis of lutein at rates of 4.8 ± 1.5 nmol per liter culture at OD730 (1.03 ± 0.47 mmol mol–1 chlorophyll). In conclusion, synlut provides a suitable platform to study the α-branch of the plastidic MEP pathway and other functions related to lutein in a cyanobacterial host system.


2021 ◽  
Vol 57 ◽  
pp. 102344
Author(s):  
Priscila P. Dario ◽  
Wellington Balmant ◽  
Fabiana R. Lírio ◽  
Luiz P. Ramos ◽  
Johana G. Blanco ◽  
...  

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