Abstract
BackgroundDay/night cycles regulate the circadian clock of organisms to program daily activities. Many species of microalgae have a synchronized cell division when grown under a day/night cycle, and synchronization might influence biomass yield and composition. Therefore, the aim of this study was to study the influence of day/night cycle on biomass yield and composition of the green microalgae Neochloris oleoabundans. Hence, we compared continuous turbidostat cultures grown under continuous light with cultures grown under simulated day/night cycles.ResultsUnder day/night cycles, cultures were synchronized as cell division was scheduled in the night, whereas under continuous light cell division occurred randomly synchronized cultures were able to use the light 10–15% more efficiently than non-synchronized cultures. Our results indicate that the efficiency of light use varies over the cell cycle and that synchronized cell division provides a fitness benefit to microalgae. Biomass composition under day/night cycles was similar to continuous light, with the exception of starch content. The starch content was higher in cultures under continuous light, most likely because the cells never had to respire starch to cover for maintenance during dark periods. Day/night cycles were provided in a ‘block’ (continuous light intensity during the light period) and in a ‘sine’ (using a sine function to simulate light intensities from sunrise to sunset). There were no differences in biomass yield or composition between these two ways of providing light (in a ‘block’ or in a ‘sine’).ConclusionsThe biomass yield and composition of N. oleoabundans were influenced by day/night cycles. These results are important to better understand the relations between research done under continuous light conditions and with day/night cycle conditions. Our findings also imply that more research should be done under day/night cycles.
Highlights
Day/night cycles regulate the circadian clock of organisms to program daily activities
As in turbidostat cultures, the light absorbed is kept constant, slight changes in biomass concentration are possible during the light period due to changes in biomass composition (Eq 2)
Dilution rate does not translate into growth rate in the cultures under 16:8 day/ night cycles (16D8N cycles), where oscillations in biomass composition occur that are not observed under continuous light
Summary
Day/night cycles regulate the circadian clock of organisms to program daily activities. It has been shown that during cell division of synchronous cultures, the biomass yield on light energy was lower than during de Winter et al Biotechnol Biofuels (2017) 10:104 the rest of the 24-h period [6]. Synchronization under day/night cycles would allow cells to grow in size during the day, when light is available, and undergo DNA replication and cell division in the dark, making optimal use of the available light energy [8]. This implies that the circadian clock, that schedules cell division in the night, may provide a fitness benefit to microalgae by increasing the photosynthetic efficiency
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