On November 13 2020, Veerle Luimstra will defend her PhD thesis
The bluest blues: why cyanobacteria grow poorly in blue light
Cyanobacteria (blue-green algae) play a key role in aquatic ecosystems, the global carbon cycle, and the accumulation of oxygenation in the Earth’s atmosphere. These microorganisms are of great interest in the pursuit of a sustainable, biobased economy. However, in contrast to green algae and plants, cyanobacteria grow much slower in blue light than in other light colors. The work described in this thesis aims to elucidate the underlying mechanisms of this intriguing phenomenon.
Therefore, the model cyanobacterium Synechocystis was studied extensively. The performed experiments have lead to the hypothesis that the light-harvesting antennae of cyanobacteria are unable to distribute blue light between the two photosystems, while the different antenna composition of green algae allows them to balance blue light between the photosystems. This hypothesis was confirmed in several experiments, including a comparison with a mutant lacking light-harvesting antennae and analyses of gene expression in different light colors. The competition model that was developed in this research, and competition experiments between cyanobacteria and green algae, showed that the color-dependence of photosynthetic efficiency strongly influences the ecological distribution of phytoplankton and competition with other species.
The research described in this thesis guides the selection of suitable light colors to culture cyanobacteria in a variety of biotechnological applications. Furthermore, the findings complement knowledge of the evolution of phytoplankton species and their photosynthetic pigments. Finally, the results lead to improved prediction of how human-induced changes in underwater light color will affect the species composition of natural phytoplankton at the base of the food web.