Effects of oxygen concentration on the growth of Nannochloropsis sp.
Raso, S. - \ 2013
Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marian Vermue. - S.l. : s.n. - ISBN 9789461737472 - 157
algen - voer - aquacultuur - visvoeding - fotobioreactoren - eicosapentaeenzuur - zuurstof - algae - feeds - aquaculture - fish feeding - photobioreactors - eicosapentaenoic acid - oxygen
ANannochloropsissp. is a promising microalgal resource for production of food, feed and bio-based commodities, as it can grow relatively fast and combines high lipid content with high content of poly-unsaturated fatty acids. High productivity with constant product quality can be achieved in fully controlled closed photobioreactors. In these closed photobioreactors, however, oxygen accumulation occurs and causes inhibition of the growth by photorespiration combined with photoinhibition.
The inhibitory effects of photorespiration and photoinhibition can be partly dealt with via the carbon concentration mechanism of the cells and by activation of the water-water cycle. At constant high oxygen concentration and high light intensity, however, the growth of the cells ceases. To our surprise, the accumulating oxygen did not affect the growth rate of the algae if the oxygen was removed regularly. In large scale production in closed photobioreactors, it is thus crucial apply degassing to achieve high algal productivity.
Effect of oxygen concentration on the growth of Nannochloropsis sp. at low light intensity
Raso, S. ; Genugten, B. van; Vermuë, M.H. ; Wijffels, R.H. - \ 2012
Journal of Applied Phycology 24 (2012)4. - ISSN 0921-8971 - p. 863 - 871.
eicosapentaenoic acid - inorganic carbon - reactors - mass - photobioreactors - optimization - temperature - metabolism - microalgae - outdoors
In large-scale microalgal production in tubular photobioreactors, the build-up of O2 along the tubes is one of the major bottlenecks to obtain high productivities. Oxygen inhibits the growth, since it competes with carbon dioxide for the Rubisco enzyme involved in the CO2 fixation to generate biomass. The effect of oxygen on growth of Nannochloropsis sp. was experimentally determined in a fully controlled flat-panel photobioreactor operated in turbidostat mode using an incident photon flux density of 100 µmol photons m-2 s-1 and with only the oxygen concentration as variable parameter. The dissolved oxygen concentration was varied from 20 to 250% air saturation. Results showed that there was no clear effect of oxygen concentration on specific growth rate (mean of 0.48¿±¿0.40 day-1) upon increasing the oxygen concentration from 20% to 75% air saturation. Upon further increasing the oxygen concentration, however, a linear decrease in specific growth rate was observed, ranging from 0.48¿±¿0.40 day-1 at a dissolved oxygen concentration of 75% air saturation to 0.18¿±¿0.01 day-1 at 250% air saturation. In vitro data on isolated Rubisco were used to predict the quantum yield at different oxygen concentrations in the medium. The predicted decrease in quantum yield matches well with the observed decrease that was measured in vivo. These results indicate that the effect of oxygen on growth of Nannochloropsis sp. at low light intensity is only due to competitive inhibition of the Rubisco enzyme. At these sub-saturating light conditions, the presence of high concentrations of oxygen in the medium induced slightly higher carotenoid content, but the increased levels of this protective antioxidant did not diminish the growth-inhibiting effects of oxygen on the Rubisco.