Photosynthetic efficiency of Chlamydomonas reinhardtii in flashing light

Abstract

Efficient light to biomass conversion in photobioreactors is crucial for economically feasible microalgae production processes. It has been suggested that photosynthesis is enhanced in short light path photobioreactors by mixing-induced flashing light regimes. In this study, photosynthetic efficiency and growth of the green microalga Chlamydomonas reinhardtii were measured using LED light to simulate light/dark cycles ranging from 5 to 100 Hz at a light-dark ratio of 0.1 and a flash intensity of 1000 µmol m(-2) s(-1). Light flashing at 100 Hz yielded the same photosynthetic efficiency and specific growth rate as cultivation under continuous illumination with the same time-averaged light intensity (i.e., 100 µmol m(-2) s(-1)). The efficiency and growth rate decreased with decreasing flash frequency. Even at 5 Hz flashing, the rate of linear electron transport during the flash was still 2.5 times higher than during maximal growth under continuous light, suggesting storage of reducing equivalents during the flash which are available during the dark period. In this way the dark reaction of photosynthesis can continue during the dark time of a light/dark cycle. Understanding photosynthetic growth in dynamic light regimes is crucial for model development to predict microalgal photobioreactor productivities.

Microalgae production in a biofilm photobioreactor

“…Regarding the biomass yield on light (Y x/ph ), two values are depicted: 1.5 g-DW mol-ph -1 and a lesser value of 1.0 g-DW mol-ph -1 the first is the maximum biomass yield derived from our current comprehension of photosynthesis and the second is based on a range of dedicated studies. We believe 1.0 g-DW mol-ph -1 is a realistic aim for a large-scale microalgae production plant as this value is in the higher end of commonly measured biomass yields on light (Kliphuis et al 2010;Takache et al 2010;Vejrazka et al 2011;Zijffers et al 2010;Zittelli et al 2006). is selected as the maximum value in this graph.…”

“…The model was also validated for Chlamydomonas reinhardtii based on seven chemostat experiments (Kliphuis et al 2011a), 22 turbidostat experiments (de Mooij et al 2014;Kliphuis et al 2011c;Takache et al 2012;Vejrazka et al 2011;Vejrazka et al 2012) and three Batch experiments (Jacobi 2013;Takache et al 2012). All experiments utilized for validation were performed in flat plate photobioreactors or a similar design.…”

“…The primary outlier is from the dataset of Vejrazka et al (Vejrazka et al 2011) with experiments performed at low biomass concentrations and 500 µmol (m 2 s) -1 incident light. Under these light saturating conditions, the influence of the correction factor on the predicted growth rate is very low and result in a substantial correction factor.…”

“…Zijffers et al (Zijffers et al 2010), Mooij et al (de Mooij et al 2014), Takache et al (Takache et al 2012), and Vejrazka (Vejrazka et al 2011;Vejrazka et al 2012) measured the real specific absorption coefficients (Appendix 4.B). When evaluating the datasets separately, they all indicate photo acclimation, however, when combined, no trend was observed.…”

“…For the majority of datasets, only the average incident light intensity is reported, however, light intensities often vary over the illuminated surface (Bechet et al 2014a;de Mooij et al 2014;Vejrazka et al 2011). In the case of Vejrazka et al (Vejrazka et al 2011;Vejrazka et al 2012), the light intensity ranges from 30% of the average in the corners to 140% of the average in the center of the reactor (FMT150, PSI, Czech Republic).…”