Laboratory of Cell Cycles of Algae
Basic research
Temperature shifts
Cell cycle progression in green algae dividing by multiple fission is influenced by growth rate under otherwise unrestricted conditions, which is determined by a combination of light intensity and temperature. Light intensity has a trophic effect on cells, such that more daughter cells are produced at higher (non-harmful) light intensity or longer light duration. In contrast, the effect of temperature is more far-reaching, as shown in Desmodesmus quadricauda cultures grown at 20 °C or 30 °C and shifts between the two temperatures. The duration of the cell cycle in cells grown under continuous illumination was more than twice as long at 20 °C as at 30 °C, suggesting that it was directly determined by the growth rate without temperature compensating for the cell cycle. For shift experiments, cells grown at either temperature were transferred to darkness to prevent further growth and cultured at the same or the other temperature. When transferred to the lower temperature, fewer nuclei and daughter cells were produced and not all cells were able to complete the cell cycle by division and remained multinucleate. Accordingly, cells transferred to the dark at the higher temperature divided into more daughter cells more rapidly than control cells. These differences correlated with shifts in preceding CDK activity, suggesting that cell cycle progression correlates with CDK activity rather than growth rate or cell biomass. Surprisingly, this suggests that there is no direct link between growth and cell cycle progression and that the two processes correlate only under stable conditions.
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Supra-optimal temperature
Temperature is one of the most important factors affecting the growth and division of algal cells. High temperatures inhibit the cell cycle in Chlamydomonas reinhardtii and in Parachlorella kessleri. At 39 °C, nuclear and cell divisions are completely blocked in synchronized cultures, while DNA replication is partially impaired. In contrast, growth (cell volume, dry matter, total protein, and RNA) is unaffected, and starch accumulates at very high levels. Cell cycle arrest is accompanied by high mitotic cyclin-dependent kinase activity, which decreased after completion of nuclear and cell division following transfer to 30 °C. Thus, cell cycle arrest was not caused by a lack of cyclin-dependent kinase activity but by a blockade of downstream processes. This process can be used for targeted starch accumulation in both Chlamydomonas reinhardtii and Parachlorella kessleri.
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Effect of deuterium
Extensive in vivo replacement of hydrogen by deuterium, a stable hydrogen isotope, elicits a pronounced stress response in various organisms, reduces cell growth, and impairs cell division. Microalgae, including Chlamydomonas reinhardtii and Parachlorella kessleri, are no exception. These algae divide by multiple fission, grow autotrophically, and can be synchronized by alternating light/dark regimes; making them a first choice model to study the effect of deuterium on growth and/or division. Synchronous cultures cultivated in a growth medium containing 70 or 90% D2O show specific deuterium-induced shifts in the attainment of commitment points during growth and/or division, contradicting the role of the “sizer” in regulating the cell cycle. Consequently, impaired cell cycle progression in deuterated cultures leads to (over)accumulation of starch and lipids, suggesting a promising potential for microalgae to produce deuterated organic compounds.
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Applied research
Rare earth elements
Rare earth elements (REEs) are metals that occur only on a small scale and are difficult to obtain. Their widespread use in modern technologies, especially in the electronics industry, also confirms their enormous economic importance. The main producer of REEs is China with more than 90% of world reserves. At present China has secured almost a monopoly in mining and trade in these metals. Import of REEs is thus associated with high risk and their possible recycling from industrial waste is at the center of interest. One of the possibilities of recycling REEs is through microorganisms. In collaboration with Austrian partners, we are developing new technology for the recovery of REEs (e.g. from electronic waste or water) by microorganisms (bacteria, algae, and cyanobacteria) in a sustainable and environmentally friendly manner. The research is funded by project REEGAIN.
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MULTI-STR3AM
MULTI-STR3AM will respond to the growing interest in and demand for sustainable products from microalgae by providing Europe with the first dedicated multi-strain, multi-process, and multi-product biorefinery (‘MULTIbiorefinery’), which will refine the biomass from A4F and PHY into high-quality, in-demand products: lipids including omega-3 and omega-6 fatty acids for feed and food applications; protein for feed and fragrance (microencapsulation) applications; pigments such as carotenoids and phycocyanin for food and feed applications; and low molecular weight (MW) organic compounds for fragrance applications. More information can be found directly on the project website
Methods
Commitment point attainment assay