Photosynthetic parameters:
The oxygen PI (O2 production vs irradiance) curves were
determined in Algenol’s custom-designed system. The system is comprised
of a white light LED source, photosynthetically active radiation (PAR)
light sensor, and an O2 sensor, all in a
temperature-controlled cassette (Legere, 2017). The optical path length,
d, is 1 cm. For measurement of O2, needle-type oxygen
sensors (OXR50, Pyroscience) composed of fiber-optical cable connected
to FireSting O2 sensors were used. The temperature is
controlled to ±1 °C over the range from 10 °C to 50 °C. The culture
samples were taken from the PBR and incubated at 30 °C for 1.5 hr for
dark acclimation, and then diluted to an absorptivity of exp(-kd)=0.1
(concentration~ 1 mg Chl.a L-1) using
fresh Zarrrouk’s media, where k is the absorption coefficient for the
whole cell Arthrospira over the PAR range (400-750 nm). In
determining k, spectra are first corrected for scattering
(approximately) by subtracting at all wavelengths the absorbance at 750
nm (OD750). The first 10 min of oxygen uptake data in
the dark is used to calculate the dark respiration rate
(Rd). The light is then ramped up to 1000 µE
m-2 s-1 stepwise with 3 min at each
step (typically 15 steps). The oxygen evolution rate is fitted with a
Monod model form to report photosynthetic parameters: α,
Ek, and Pmax (limited quantum yield in
low light limit, photosaturation parameter, and max photosynthetic rate
in high light limit). The Monod model is used to be consistent with the
approach taken for the Algenol Productivity Model. All measurements are
carried out in duplicate.