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The thraustochytrids, the heterotrophic marine microorganisms, have received increasing attention because of their capacity for the production of high‐value products such as docosahexaenoic acid (DHA), carotenoids, and sterols. In this study, three potential Δ5,7‐sterols, showing similar UV absorption spectra to that of ergosterol, in the thraustochytrid Schizochytrium sp. S31, were estimated by the ultraperformance liquid chromatography (UPLC) − APCI−MS/MS method. The proposed structures of three Δ5,7‐sterols were ergosta‐5,7,24(28)‐trien‐3β‐ol, ergosta‐5,7‐dien‐3β‐ol, and 24‐ethylcholesta‐5,7,22‐trien‐3β‐ol. The contents of astaxanthin, ergosterol, and the other three Δ5,7‐sterols in Schizochytrium sp. S31 during the cultivation performed in three separate batches were analyzed by a fast UPLC–PDA method. The results demonstrated that astaxanthin, ergosterol, and ergosta‐5,7‐dien‐3β‐ol were the predominant carotenoid and Δ5,7‐sterols, respectively, and their contents kept increasing during the growth and reached a maximum after 23 days of cultivation. The estimated maximum contents of astaxanthin and four Δ5,7‐sterols, including ergosterol, ergosta‐5,7‐dien‐3β‐ol, ergosta‐5,7,24(28)‐trien‐3β‐ol, and 24‐ethylcholesta‐5,7,22‐trien‐3β‐ol were 2.31, 4.02, 3.43, 0.30, and 0.97 mg g−1 dry biomass, respectively. These findings are different to other strains reported in the composition and accumulation of Δ5,7‐sterols and carotenoids. The present study suggests that Schizochytrium sp. S31 might be a promising marine microorganism for the productions of high‐value natural pigment astaxanthin, the provitamin D2 ergosterol, and the provitamin D4 ergosta‐5,7‐dien‐3β‐ol, and taken as a model organism to study the sterologenesis of the microorganisms because of its complexity of sterol compositions. [ABSTRACT FROM AUTHOR]

Chlorella zofingiensis has great potential for astaxanthin and fatty acid production. This study investigated the accumulation of astaxanthin and total fatty acids (TFA), the fatty acid compositions of astaxanthin esters and TFA in photoautotrophic and heterotrophic C. zofingiensis, respectively. The results displayed that in photoautotrophic cells, 18:3 was the most predominant fatty acid, followed by 16:0, 18:2, and 18:1, while astaxanthin mono‐esters (mono‐AE) contained only 16:0 and 18:0, and astaxanthin di‐esters (di‐AE) contained 16:0 mostly, followed by 18:1, 18:0, 18:2, and 18:3. C. zofingiensis accumulated the highest level of astaxanthin and TFA under heterotrophic conditions fed with 30 g L−1 glucose. The percentage of 18:1 in TFA, mono‐AE, and di‐AE increased from 10.05%, 0%, and 17.76% to 35.80%, 14.84%, and 50.12%, respectively; in contrast, the percentages of 18:3 in TFA and di‐AE were observed to decrease from 40.42% and 7.59% to 9.56% and 1.30%, respectively, in comparison with those in photoautotrophic ones. The RNA sequencing (RNA‐seq) results showed that the expressions of the genes in astaxanthin and fatty acid biosynthetic pathways were increased under this heterotrophic condition. These results indicated differential accumulation of AE and TFA, especially fatty acid compositions of TFA and AE in photoautotrophic and heterotrophic cells, suggesting a positive correlation between astaxanthin and fatty acid biosynthesis. [ABSTRACT FROM AUTHOR]

The carotenoid composition in cells of a ketocarotenoid-producing alga, Chlorococcum, was investigated by high-performance liquid chromatgraphy (HPLC). Astaxanthin (free and esters), adonixanthin (free and esters), canthaxanthin, β-carotene, lutein, and some cis-isomers of ketocarotenoids were found. The alga Chlorococcum cells could produce a large amount of ketocarotenoid esters, like the alga Haematococcus pluvialis. The esters of astaxanthin and adonixanthin, and free canthaxanthin were the major carotenoids in the alga Chlorococcum cells, while astaxanthin alone was the major carotenoid in the alga Haematococcus pluvialis. The alga Chlorococcum cells might synthesize astaxanthin from β-carotene via canthaxanthin and adonixanthin in parallel, respectively, which was controlled by the culture conditions. [Copyright &y& Elsevier]

Microalgae-based technology is an environmental-friendly and cost-effective method for treating antibiotics-contaminated wastewater. This work investigated the removal of levofloxacin (LEV) by an oleaginous microalgae Chromochloris zofingiensis under photoautotrophic and heterotrophic conditions. The results showed that the significantly higher biomass production, accumulation of extracellular polymeric substance and LEV removal efficiency were achieved in heterotrophic C. zofingiensis compared with the photoautotrophic ones. The removal efficiencies under the heterotrophic condition were 97%, 88% and 76% at 1, 10, and 100 mg/L LEV, respectively. HPLC-MS/MS and RNA-Seq analyses suggested that LEV could be bioaccumulated and biodegraded by heterotrophic C. zofingiensis through the reactions of defluorination, hydroxylation, demethylation, ring cleavage, oxidation, dehydrogenation, denitrification, and decarboxylation. The chemical composition of the algal biomass obtained after LEV treatment indicated the potential of this alga for removing LEV from wastewaters and simultaneously producing biodiesel, astaxanthin, and other products. Collectively, this research shows that the heterotrophic C. zofingiensis can be identified as a promising candidate for removing LEV in wastewater remediation. [Display omitted] • Chromochloris zofingiensis under heterotrophic condition can effectively biodegrade LEV (up to 97.1% of removal efficiency. • Seven LEV-degraded intermediates were identified and three potential biodegradation pathways were proposed. • The algal biomass obtained after LEV treatment in heterotrophic cultivation contained considerable value-added biomolecules. • C. zofingiensis can be identified as a promising candidate for LEV removal in wastewater remediation. [ABSTRACT FROM AUTHOR]