Optimisation of T-ISO biomass production rich in essential fatty acids: 1. Effect of different light regimes on growth and biomass production

T-ISO is a microalgal strain widely used in aquaculture for its favourable lipid composition. In this study, we report on the results of an optimisation scheme for maximal biomass production under three different photoperiods (24:0, 16:08 and 12:12-h L/D) combined with three photon flux densities (PFD, 120, 220 and 460 µmol photons m-2 s-1) at 25 °C. Sampling for growth took place in both the exponential and post-exponential (light-limited only) phase. Results showed that specific growth rate of T-ISO maximised with an increase of the total PFD supplied per day. Under continuous light, cell size of T-ISO (both cell dry weight (CDW) and cell volume) correlated positively to PFD with a further increase when the cells were transiently light-limited in the post-exponential phase. In contrast, cell dry weight under discontinuous light increased only at subsaturating PFD with a significant decrease in the post-exponential phase. Cell size, as volume, did not correlate to CDW under discontinuous light, revealing an intracellular density change particularly for the 16:08-h L/D regimes. As a result, biomass yield and productivity had different patterns for continuous and discontinuous light whereas cell yield and productivity were simply a function of total PFD per day. Biomass productivity under continuous light was inferior than under discontinuous light, although the final yield was maximal compared to those under discontinuous light