Light respiration in Chlorella sorokiniana

Abstract

Respiration and photosynthesis are two important processes in microalgal growth that occur simultaneously in the light. To know the rates of both processes, at least one of them has to be measured. To be able to measure the rate of light respiration of Chlorella sorokiniana, the measurement of oxygen uptake must be fast, preferably in the order of minutes. We measured the immediate post-illumination respiratory O2 uptake rate (OUR) in situ, using fiber-optic oxygen microsensors, and a small and simple extension of the cultivation system. This method enables rapid and frequent measurements without disturbing the cultivation and growth of the microalgae. Two batch experiments were performed with C. sorokiniana in a short light-path photobioreactor, and the OUR was measured at different time points. The net oxygen production rate (net OPR) was measured online. Adding the OUR and net OPR gives the gross oxygen production rate (gross OPR), which is a measure for the oxygen evolution by photosynthesis. The gross OPR was 35–40% higher than the net OPR for both experiments. The respiration rate is known to be related to the growth rate, and it is suggested that faster algal growth leads to a higher energy (ATP) requirement, and as such, respiratory activity increases. This hypothesis is supported by our results, as the specific OUR is highest in the beginning of the batch culture when the specific growth rate is highest. In addition, the specific OUR decreases toward the end of the experiments until it reaches a stable value of around 0.3 mmol O2 h−1 g−1. This value for the specific OUR is equal to the maintenance requirement of C. sorokiniana as determined in an independent study of (Zijffers et al. 2010 (in press)). This suggests that respiration could fulfill the maintenance requirements of the microalgal cells.

Microalgae production in a biofilm photobioreactor

“…In accordance with Figure 4.1, the local light intensity (I ph (z)) is used to calculate the local specific photon absorption rate (q ph (z)) which is subsequently coupled to the sugar production and integrated over the reactor to acquire the average specific sugar production rate (Equation 4.11). The partitioning of the produced sugar between functional biomass (anabolism), growthrelated respiration (catabolism), and maintenance-related respiration is described by The light limited microalgae growth model was validated for Chlorella sorokiniana based on 17 chemostat experiments performed over a wide range of dilution ranges (Cuaresma Franco et al 2012;Cuaresma et al 2009;Tuantet et al 2014), 2 D-stat experiments including 32 data points (Zijffers et al 2010) and three batch experiments (Kliphuis et al 2011b;Kliphuis et al 2010;Van Wagenen et al 2015).…”

“…Typically microalgae concentrations are in the range of 0.05% to 0.5% dry solids (Acien et al 2012;Pahl et al 2013), and could be further increased to above 1% by choosing a short light path photobioreactor design (Kliphuis et al 2011b). Because of the low microalgae concentration large liquid volumes have to be handled during microalgae cultivation.…”

“…For C. sorokiniana the model was validated with batch data from three studies (Kliphuis et al 2011b;Kliphuis et al 2010;Van Wagenen et al 2015). The study of Kliphuis et al (Kliphuis et al 2011b) was also used to obtain a value for the maintenance sugar consumption.…”

Biological system development for GraviSat: A new platform for studying photosynthesis and microalgae in space

“…We focused on common and well-studied strains of green algae and cyanobacteria representative of the metabolic and physiological diversity within the microalgae. Cyanobacteria and algae differ metabolically in that algae, unlike cyanobacteria, are capable of performing oxygenic photosynthesis and respiration simultaneously (Kliphuis et al, 2011). Consequently, many algal strains are able to up or down-regulate photosynthesis and respiration activity depending on CO 2 and O 2 concentrations (Hoch et al, 1963;Foyer and Noctor, 2000).…”

Antenna size reduction in microalgae mass culture

“…The oxygen consumption rate (OCR) was measured under darkness in a three minute period after exposure to 1600 μmol photons m −2 s −1 . This OCR is considered to reflect respiratory oxygen consumption in the light (Kliphuis et al 2011) The fact that the biomass specific OCR for mass culture cells and high light acclimated cells were similar would normally indicate that the cells have the same metabolic activity as the respiration rate can be directly related to the growth rate (Falkowski et al 1985). At higher growth rates, more metabolic energy is required in the form ATP which leads to an increased respiration and thus increased consumption of oxygen (Kliphuis et al 2012).…”