Photosynthetic parameters
The oxygen PE (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. The cell contains 4 ml of fluid stirred at 400rpm with no
head space. For measurement of O2, needle-type oxygen
sensors (OXR50, Pyroscience) composed of fiber-optical cable connected
to FireSting O2 sensors were used. Response times to
changing conditions were rapid with no indication of mass transfer
limitations. 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 Arthrospiraaveraged 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. 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 (Bechet 2013) 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 mathematical model is used in order to
be consistent with the approach taken for the Algenol Productivity Model
(see Supplementary Material). All measurements are carried out in
duplicate.