Supra-Optimal Temperature: An Efficient Approach for Overaccumulation of Starch in the Green Alga Parachlorella kessleri

Green algae are fast-growing microorganisms that are considered promising for the production of starch and neutral lipids, and the chlorococcal green alga Parachlorella kessleri is a favorable model, as it can produce both starch and neutral lipids. P. kessleri commonly divides into more than two daughter cells by a specific mechanism—multiple fission. Here, we used synchronized cultures of the alga to study the effects of supra-optimal temperature. Synchronized cultures were grown at optimal (30 °C) and supra-optimal (40 °C) temperatures and incident light intensities of 110 and 500 μmol photons m−2 s−1. The time course of cell reproduction (DNA replication, cellular division), growth (total RNA, protein, cell dry matter, cell size), and synthesis of energy reserves (net starch, neutral lipid) was studied. At 40 °C, cell reproduction was arrested, but growth and accumulation of energy reserves continued; this led to the production of giant cells enriched in protein, starch, and neutral lipids. Furthermore, we examined whether the increased temperature could alleviate the effects of deuterated water on Parachlorella kessleri growth and division; results show that supra-optimal temperature can be used in algal biotechnology for the production of protein, (deuterated) starch, and neutral lipids.

Targeting of proteins to the cell wall of the diatom Thalassiosira pseudonana

Diatoms are unicellular phototrophic organisms with huge ecological impact. Characteristic for these organisms is their peculiar cell wall, which is composed of inorganic and organic components. Cell wall formation is a highly complex and orchestrated process, and in the last years has been studied intensively, also on the molecular level. Here, we review on the cell wall proteins of diatoms, with a focus on the species Thalassiosira pseudonana. We report on the expression patterns of these proteins in synchronized cultures, as well as their modifications and intracellular targeting.

Comparing Biochemical and Raman Microscopy Analyses of Starch, Lipids, Polyphosphate, and Guanine Pools during the Cell Cycle of Desmodesmus quadricauda

Photosynthetic energy conversion and the resulting photoautotrophic growth of green algae can only occur in daylight, but DNA replication, nuclear and cellular divisions occur often during the night. With such a light/dark regime, an algal culture becomes synchronized. In this study, using synchronized cultures of the green alga Desmodesmus quadricauda, the dynamics of starch, lipid, polyphosphate, and guanine pools were investigated during the cell cycle by two independent methodologies; conventional biochemical analyzes of cell suspensions and confocal Raman microscopy of single algal cells. Raman microscopy reports not only on mean concentrations, but also on the distribution of pools within cells. This is more sensitive in detecting lipids than biochemical analysis, but both methods—as well as conventional fluorescence microscopy—were comparable in detecting polyphosphates. Discrepancies in the detection of starch by Raman microscopy are discussed. The power of Raman microscopy was proven to be particularly valuable in the detection of guanine, which was traceable by its unique vibrational signature. Guanine microcrystals occurred specifically at around the time of DNA replication and prior to nuclear division. Interestingly, guanine crystals co-localized with polyphosphates in the vicinity of nuclei around the time of nuclear division.

PROCYCLIC Trypanosoma brucei CELL CYCLE is IMPAIRED at the G1 STAGE by the PRESENCE of POLY (ADP-RIBOSE) in the NUCLEUS

Previously we demonstrated that an excess of poly (ADP-ribose) in the nucleus makes procyclic parasites more sensitive to hydrogen peroxide. However, the effect of an altered-PAR metabolism under standard conditions has not been addressed yet. Here we have analyzed the behavior of the growth curve of transgenic parasites that present this phenotype and studied cell cycle progression in synchronized cultures by flow cytometry and immunofluorescence. We have demonstrated that an excess of nuclear poly (ADP-ribose) produces a delay in the G1 phase of the cell cycle. Moreover, for the first time we have shown that poly (ADP-ribose) occurs at specific points very close to the mature basal body, suggesting there could be a link between the kinetoplast and poly (ADP-ribose) metabolism.

Extensive Regulation of Metabolism and Growth during the Cell Division Cycle

Yeast cells grown in culture can spontaneously synchronize their respiration, metabolism, gene expression and cell division. Such metabolic oscillations in synchronized cultures reflect single-cell oscillations, but the relationship between the oscillations in single cells and synchronized cultures is poorly understood. To understand this relationship and the coordination between metabolism and cell division, we collected and analyzed DNA-content, gene-expression and physiological data, at hundreds of time-points, from cultures metabolically-synchronized at different growth rates, carbon sources and biomass densities. The data enabled us to extend and generalize our mechanistic model, based on ensemble average over phases (EAP), connecting the population-average gene-expression of asynchronous cultures to the gene-expression dynamics in the single-cells comprising the cultures. The extended model explains the carbon-source specific growth-rate responses of hundreds of genes. Our physiological data demonstrate that the frequency of metabolic cycling in synchronized cultures increases with the biomass density, suggesting that this cycling is an emergent behavior, resulting from the entraining of the single-cell metabolic cycle by a quorum-sensing mechanism, and thus underscoring the difference between metabolic cycling in single cells and in synchronized cultures. Measurements of constant levels of residual glucose across metabolically synchronized cultures indicate that storage carbohydrates are required to fuel not only the G1/S transition of the division cycle but also the metabolic cycle. Despite the large variation in profiled conditions and in the scale of their dynamics, most genes preserve invariant dynamics of coordination with each other and with the rate of oxygen consumption. Similarly, the G1/S transition always occurs at the beginning, middle or end of the high oxygen consumption phases, analogous to observations in human and drosophila cells. These results highlight evolutionary conserved coordination among metabolism, cell growth and division.