Light respiration in <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> |
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Authors: | Anna M J Kliphuis Marcel Janssen Evert J van den End Dirk E Martens René H Wijffels |
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Institution: | (1) Bioprocess Engineering, Wageningen University, Wageningen, The Netherlands;(2) Bioprocess Engineering, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands |
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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. |
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