Effect of oxygen at low and high light intensities on the growth of Neochloris oleoabundans

The effect of partial oxygen pressure on growth of Neochloris oleoabundans was studied at near-saturating light intensity in a fully-controlled photobioreactor. At the partial oxygen pressures tested (PO2=0.24; 0.42; 0.63; 0.84 bar), the specific growth rate was 1.36; 1.16; 0.93 and 0.68 day-1, respectively. An increase of the PCO2 from 0.007 to 0.02 bar at PO2 of 0.84 bar did not show any positive effect on the overall growth of the algae, contrary to what happens at sub-saturating light intensities. These results indicate that at near-saturating light intensity the inhibitory effect of oxygen by photorespiration cannot be overcome. The chlorophyll content of N. oleoabundans grown at 200 µmol m-2 s-1 is about 1.9 times higher than when cultivated at 500 µmol m-2 s-1, whereas the carotenoid contentwas about 1.5 lower, both demonstrating photoacclimation effects. The elevated oxygen concentration in the growth mediumdoes not affect the pigment content both at sub- and near-saturating light conditions. This indicates that elevated oxygen concentrations in the medium do not contribute to photooxidative damage at the light conditions that are predominantly experienced by algae in closed photobioreactors, but only inhibit the growth via photorespiration effects