The structural challenges faced by eukaryotic cells through the cell cycle are key for understanding cell viability and proliferation. We tested the hypothesis that the biosynthesis of structural lipids is linked to the cell cycle. If true, this would suggest that the cell's structure is important for progress through and perhaps even control of the cell cycle. Lipidomics (31P NMR and MS), proteomics (Western immunoblotting) and transcriptomics (RT-qPCR) techniques were used to profile the lipid fraction and characterise aspects of its metabolism at seven stages of the cell cycle of the model eukaryote, Desmodesmus quadricauda. We found considerable, transient increases in the abundance of phosphatidylethanolamine during the G1 phase (+35%, ethanolamine phosphate cytidylyltransferase increased 2·5×) and phosphatidylglycerol (+100%, phosphatidylglycerol synthase increased 22×) over the G1/pre-replication phase boundary. The relative abundance of phosphatidylcholine fell by ~35% during the G1. N-Methyl transferases for the conversion of phosphatidylethanolamine into phosphatidylcholine were not found in the de novo transcriptome profile, though a choline phosphate transferase was found, suggesting that the Kennedy pathway is the principal route for the synthesis of PC. The fatty acid profiles of the four most abundant lipids suggested that these lipids were not generally converted between one another. This study shows for the first time that there are considerable changes in the biosynthesis of the three most abundant phospholipid classes in the normal cell cycle of D. quadricauda, by margins large enough to elicit changes to the physical properties of membranes.

• Keywords
• Cell cycle, Cell division, Cell structure, Desmodesmus quadricauda, Green algae, Lipid composition, Lipid metabolism,
• MeSH
• Cell Cycle * MeSH
• Phosphatidylcholines metabolism   biosynthesis   MeSH
• Phosphatidylethanolamines metabolism   biosynthesis   MeSH
• Phospholipids * metabolism   biosynthesis   MeSH
• Lipidomics methods   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Phosphatidylcholines MeSH
• Phosphatidylethanolamines MeSH
• Phospholipids * MeSH
• phosphatidylethanolamine MeSH Browser

Red mud is a by-product of alumina production containing lanthanides. Growth of green microalgae on red mud and the intracellular accumulation of lanthanides was tested. The best growing species was Desmodesmus quadricauda (2.71 cell number doublings/day), which accumulated lanthanides to the highest level (27.3 mg/kg/day), if compared with Chlamydomonas reinhardtii and Parachlorella kessleri (2.50, 2.37 cell number doublings and 24.5, 12.5 mg/kg per day, respectively). With increasing concentrations of red mud, the growth rate decreased (2.71, 2.62, 2.43 cell number doublings/day) due to increased shadowing of cells by undissolved red mud particles. The accumulated lanthanide content, however, increased in the most efficient alga Desmodesmus quadricauda within 2 days from zero in red-mud free culture to 12.4, 39.0, 54.5 mg/kg of dry mass at red mud concentrations of 0.03, 0.05 and 0.1%, respectively. Red mud alleviated the metal starvation caused by cultivation in incomplete nutrient medium without added microelements. Moreover, the proportion of lanthanides in algae grown in red mud were about 250, 138, 117% higher than in culture grown in complete nutrient medium at red mud concentrations of 0.03, 0.05, 0.1%. Thus, green algae are prospective vehicles for bio-mining or bio-leaching of lanthanides from red mud.

• Keywords
• bio-mining, lanthanides, microalgae, recovery, red mud, toxicity,
• MeSH
• Bioreactors MeSH
• Chlamydomonas reinhardtii MeSH
• Lanthanoid Series Elements * chemistry   MeSH
• Microbiological Techniques MeSH
• Microalgae * MeSH
• Soil Microbiology * MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Lanthanoid Series Elements * MeSH

Selenium (Se) is a natural trace element, which shifts its action in a relatively narrow concentration range from nutritional role to toxicity. Although it has been well established that in plants chloroplasts are among the primary targets, the mechanism of toxicity on photosynthesis is not well understood. Here, we compared selenate and red-allotrope elemental selenium nanoparticles (red nanoSe) in in vitro tobacco cultures to investigate their effects on the structure and functions of the photosynthetic machinery. Selenate at 10 mg/L concentration retarded plant growth; it also led to a decreased chlorophyll content, accompanied with an increase in the carotenoid-to-chlorophyll ratio. Structural examinations of the photosynthetic machinery, using electron microscopy, small-angle neutron scattering and circular dichroism spectroscopy, revealed significant perturbation in the macro-organization of the pigment-protein complexes and sizeable shrinkage in the repeat distance of granum thylakoid membranes. As shown by chlorophyll a fluorescence transient measurements, these changes in the ultrastructure were associated with a significantly diminished photosystem II activity and a reduced performance of the photosynthetic electron transport, and an enhanced capability of non-photochemical quenching. These changes in the structure and function of the photosynthetic apparatus explain, at least in part, the retarded growth of plantlets in the presence of 10 mg/L selenate. In contrast, red nanoSe, even at 100 mg/L and selenate at 1 mg/L, exerted no negative effect on the growth of plantlets and affected only marginally the thylakoid membrane ultrastructure and the photosynthetic functions.

• Keywords
• Chlorophyll fluorescence transients, Chloroplast thylakoid membranes, Circular dichroism, Electron microscopy, Nicotiana tabacum, Selenate and Se-nanoparticles, Small-angle neutron scattering,
• MeSH
• Chlorophyll metabolism   MeSH
• Chloroplasts metabolism   MeSH
• Circular Dichroism MeSH
• Photosynthesis physiology   MeSH
• Selenic Acid metabolism   MeSH
• Nanoparticles chemistry   MeSH
• Nicotiana metabolism   MeSH
• Thylakoids metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll MeSH
• Selenic Acid MeSH

Microalgae are able to metabolize inorganic selenium (Se) to organic forms (e.g. Se-proteins); nevertheless at certain Se concentration culture growth is inhibited. The aim of this work was to confirm the hypothesis that the limit of Se tolerance in Chlorella cultures is related to photosynthetic performance, i.e. depends on light intensity. We studied the relation between the dose and irradiance to find the range of Se tolerance in laboratory and outdoor cultures. At low irradiance (250 µmol photons m-2 s-1), the daily dose of Se below 8.5 mg per g of biomass (<20 µM) partially stimulated the photosynthetic activity (relative electron transport rate) and growth of Chlorella cultures (biomass density of ~1.5 g DW L-1) compared to the control (no Se added). It was accompanied by substantial Se incorporation to microalgae biomass (~0.5 mg Se g-1 DW). When the Se daily dose and level of irradiance were doubled (16 mg Se g-1 DW; 500 µmol photons m-2 s-1), the photosynthetic activity and growth were stimulated for several days and ample incorporation of Se to biomass (7.1 mg g-1 DW) was observed. Yet, the same Se daily dose under increased irradiance (750 µmol photons m-2 s-1) caused the synergistic effect manifested by significant inhibition of photosynthesis, growth and lowered Se incorporation to biomass. In the present experiments Chl fluorescence techniques were used to monitor photosynthetic activity for determination of optimal Se doses in order to achieve efficient incorporation without substantial inhibition of microalgae growth when producing Se-enriched biomass.

• Keywords
• Chlorella, Chlorophyll fluorescence, Growth, Irradiance intensity, Photosynthesis, Selenium incorporation,
• Publication type
• Journal Article MeSH

Lanthanides are biologically non-essential elements with wide applications in technology and industry. Their concentration as environmental contaminants is, therefore, increasing. Although non-essential, lanthanides have been proposed (and even used) to produce beneficial effects in plants, even though their mechanisms of action are unclear. Recently, it was suggested that they may replace essential elements. We tested the effect of low concentrations of lanthanides on the common freshwater microalga Desmodesmus quadricauda, grown under conditions of metal ion-deficiency (lower calcium or manganese concentrations). Our goal was to test if lanthanides can replace essential metals in their functions. Physiological stress was recorded by studying growth and photosynthetic activity using a pulse amplitude modulation (PAM) fluorimeter. We found that nutrient stress reduced parameters of growth and photosynthesis, such as maximal quantum yield, relative electron transport rate, photon capturing efficiency and light saturation irradiance. After adding low concentrations of five lanthanides, we confirmed that they can produce a stimulatory effect on microalgae, depending on the nutrient (metal) deprivation. In the case of a calcium deficit, the addition of lanthanides partly alleviated the adverse effects, probably by a partial substitution of the element. In contrast, with manganese deprivation (and at even lower concentrations), lanthanides enhanced the deleterious effect on cellular growth and photosynthetic competence. These results show that lanthanides can replace essential elements, but their effects on microalgae depend on stress and the nutritional state of the microalgae, raising the possibility of environmental impacts at even low concentrations.

• Keywords
• algae, calcium, manganese, metal requirements, rare earth elements, toxicity,
• Publication type
• Journal Article MeSH

The aim of this work was to study the effect of Se(+VI) on viability, cell morphology, and selenomethionine accumulation of the green alga Chlorella sorokiniana grown in batch cultures. Culture exposed to sublethal Se concentrations of 40 mg · L(-1) (212 μM) decreased growth rates for about 25% compared to control. A selenate EC50 value of 45 mg · L(-1) (238.2 μM) was determined. Results showed that chlorophyll and carotenoids contents were not affected by Se exposure, while oxygen evolution decreased by half. Ultrastructural studies revealed granular stroma, fingerprint-like appearance of thylakoids which did not compromise cell activity. Unlike control cultures, SDS PAGE electrophoresis of crude extracts from selenate-exposed cell cultures revealed appearance of a protein band identified as 53 kDa Rubisco large subunit of Chlorella sorokiniana, suggesting that selenate affects expression of the corresponding chloroplast gene as this subunit is encoded in the chloroplast DNA. Results revealed that the microalga was able to accumulate up to 140 mg · kg(-1) of SeMet in 120 h of cultivation. This paper shows that Chlorella sorokiniana biomass can be enriched in the high value aminoacid SeMet in batch cultures, while keeping photochemical viability and carbon dioxide fixation activity intact, if exposed to suitable sublethal concentrations of Se.

• MeSH
• Bioreactors microbiology   MeSH
• Chlorella cytology   drug effects   physiology   MeSH
• Selenic Acid administration & dosage   MeSH
• Cell Proliferation drug effects   physiology   MeSH
• Selenomethionine isolation & purification   metabolism   MeSH
• Batch Cell Culture Techniques methods   MeSH
• Cell Size drug effects   MeSH
• Cell Survival drug effects   physiology   MeSH
• Dose-Response Relationship, Drug MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Selenic Acid MeSH
• Selenomethionine MeSH