Toxicity response of Chlorella microalgae to glyphosate herbicide exposure based on biomass, pigment contents and photosynthetic efficiency

The extensive use of glyphosate (N-(phosphonomethyl) glycine) herbicide in agriculture is accompanied by the risk of environmental contamination of aquatic ecosystems. In this study, the effects of glyphosate at different concentrations (50–500 µg ml-1) on three Chlorella species including Chlorella ellipsoidea, Chlorella sorokiniana and Chlorella vulgaris especially in relation to the biomass, pigment contents and photosynthetic efficiency were assessed. After treatment for 24 hr, the acute toxicity results showed that C. vulgaris (IC50 = 449.34 ± 6.20 µg ml-1) was more tolerant to glyphosate than C. ellipsoidea (IC50 = 288.23 ± 23.53 µg ml-1) and C. sorokiniana (IC50 = 174.28 ± 0.50 µg ml-1). After a 72-hr chronic toxicity treatment with glyphosate, glyphosate concentrations decreased to 400–500 µg ml-1 in C. ellipsoidea, 200–300 µg ml-1 in C. sorokiniana and 200–500 µg ml-1 in C. vulgaris respectively. During 24-hr acute toxicity exposure to glyphosate, the pigment contents and maximum quantum efficiency of photosystem II (Fv/Fm) decreased as the concentration of glyphosate increased. Overall, the biomass, pigment contents and photosynthetic efficiency presented a high positive correlation. It is worthwhile to mention that our study provides detailed information on the toxicity and sensitivity of these Chlorella species to glyphosate.

Overexpression of the Transcription Factor AtLEC1 Significantly Improved the Lipid Content of Chlorella ellipsoidea

Microalgae are considered to be a highly promising source for the production of biodiesel. However, the regulatory mechanism governing lipid biosynthesis has not been fully elucidated to date, and the improvement of lipid accumulation in microalgae is essential for the effective production of biodiesel. In this study,LEAFY COTYLEDON1 (LEC1)fromArabidopsis thaliana, a transcription factor (TF) that affects lipid content, was transferred intoChlorella ellipsoidea. Compared with wild-type (WT) strains, the total fatty acid content and total lipid content ofAtLEC1transgenic strains were significantly increased by 24.20–32.65 and 22.14–29.91%, respectively, under mixotrophic culture conditions and increased by 24.4–28.87 and 21.69–30.45%, respectively, under autotrophic conditions, while the protein content of the transgenic strains was significantly decreased by 18.23–21.44 and 12.28–18.66%, respectively, under mixotrophic and autotrophic conditions. Fortunately, the lipid and protein content variation did not affect the growth rate and biomass of transgenic strains under the two culture conditions. According to the transcriptomic data, the expression of 924 genes was significantly changed in the transgenic strain (LEC1-1). Of the 924 genes, 360 were upregulated, and 564 were downregulated. Based on qRT-PCR results, the expression profiles of key genes in the lipid synthesis pathway, such asACCase,GPDH,PDAT1, andDGAT1, were significantly changed. By comparing the differentially expressed genes (DEGs) regulated byAtLEC1inC. ellipsoideaandArabidopsis, we observed that approximately 59% (95/160) of the genes related to lipid metabolism were upregulated inAtLEC1transgenicChlorella. Our research provides a means of increasing lipid content by introducing exogenous TF and presents a possible mechanism ofAtLEC1regulation of lipid accumulation inC. ellipsoidea.

EXPERIMENTAL DISPOSAL STUDIES MICROWEEDS OF WASTE WATER AND WATER PHASE AFTER THEIR HYDROTHERMAL LIQUIDATION

Микроводоросли (МКВ) рассматриваются как нетрадиционное возобновляемое сырье, трансформируемое в удобные виды биотоплива (биодизель, биоэтанол, биобутанол, бионефть и др.). Представленная работа посвящена утилизации микроводорослями питательных веществ из сточных вод и из побочного водного раствора, образующегося после гидротермального сжижения (HTL) биомассы МКВ. Выращивание МКВ на сточных водах и на побочном водном растворе от HTL обеспечивает: 1) минимизацию использования пресной воды; 2) снижение затрат на питательные вещества для получения биомассы; 3) очистку сточных вод и водного раствора после HTL от соединений азота и фосфора, легкорастворимой органики и других биогенных элементов и тяжелых металлов; 4) получение более дешевой водорослевой биомассы в качестве сырья для биотоплива. Проведен скрининг микроводорослей из коллекции НИЛ ВИЭ МГУ, способных эффективно расти на сточных водах (Arthrospira platensis rsemsu Р (Bios), Chlorella ellipsoidea rsemsu Chlel), и в разбавленной водной фазе после HTL (Arthrospira platensis rsemsu Р (Bios), Galdieria sulphuraria rsemsu G-1, Chlorella vulgaris rsemsu Chv-20/11-Ps). В статье показана экспериментально достигнутая степень использования питательных веществ микроводорослями из сточных вод и HTL-водной фазы. Из биомассы артроспиры, выращенной на сточных водах, была получена совместно с сотрудниками ОИВТ РАН технологией HTL бионефть Выход бионефти составил 34-46% от сухого веса биомассы, а величина теплоты сгорания - 33,4 МДж/кг. Был изучен фракционный и химический состав бионефти. Бионефть из МКВ с большим содержанием липидов и углеводов была близка к традиционной ископаемой нефти.