Figure 1.

Experimental design for high-throughput light simulations of cells cycling in outdoor microalgae mass cultures. (A) Depicts the 3 factors that affect the light regime experienced by cells cycling in mass cultures: I_max, D_f and t_c, and the levels used for the full factorial experimental design which are based on ‘typical’ outdoor conditions. (B) Each combination of light factors was programmed by changing the light intensity of the LEDs over the cycle time, assuming cell cycling occurs in a sinusoidal trajectory. Here, I_max, is the amplitude of the sine, simulating the maximum irradiance that a cell would receive when at the ‘surface’ of a mass culture, D_f, is the proportion of time that PAR is below 5 µmol m⁻² s⁻¹ in one period; this simulates the fraction of time that a cell spends in the dark, depending on the culture density, and t_c is the period of one sine wave, that simulates the time required for a cell to cycle through the reactor. I_avg is the integration of light received, simulating the average irradiance or light dose received the by cell. Here t_light and t_dark are the time cells receive PAR (>5 µmol m⁻² s⁻¹) and no PAR (<5 µmol m⁻² s⁻¹) respectively. (C) The programmed LEDs form part of an 18-plate microwell robotic system. Chlamydomonas and Chlorella were incubated in 96-well plates placed on LED arrays with one LED per microwell and one unique light regime per plate. All light regimes occurred over a photoperiod of 16 h day⁻¹ and a dark period of 8 h day⁻¹.