Light attenuation changes with photo-acclimation in a culture of Synechocystis sp. PCC 6803

An inherent complication in the relationship between light intensity (LI) and microalgae growth rate is that light attenuates through a culture due to its absorption by biomass. While a biomass's specific extinction coefficient (ε describing how rapidly light attenuates) often is assumed to be a constant for a species for mathematical modeling, it is well documented that pigmentation and light absorption depend on growth conditions, particularly light intensity itself. In this study using Synechocystis sp. PCC 6803, we investigated the effect of LI on ε. Using cultures fully acclimated to the LI at which they were grown, we found that biomass grown at higher LI absorbed less light than biomass grown at lower LI; thus, ε was larger for lower LI. We quantify the relationship between ε and the acclimated LI and suggest that ε would be an appropriate metric for describing photo-acclimation.