Cyanobacteria play a key role in primary production in both oceans and fresh waters
and hold great potential for sustainable production of a large number of commodities.
During their life, cyanobacteria cells need to acclimate to a multitude of challenges,
including shifts in intensity and quality of incident light. Despite our increasing
understanding of metabolic regulation under various light regimes, detailed insight
into fitness advantages and limitations under shifting light quality remains underexplored.
Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis
sp. PCC 6803 throughout the photosynthetically active radiation (PAR) range. Using
light emitting diodes (LEDs) with qualitatively different narrow spectra, we describe
wavelength dependence of light capture, electron transport and energy transduction
to main cellular pools. In addition, we describe processes that fine-tune light capture,
such as state transitions, or the efficiency of energy transfer from phycobilisomes
to photosystems (PS). We show that growth was the most limited under blue light due
to inefficient light harvesting, and that many cellular processes are tightly linked
to the redox state of the plastoquinone (PQ) pool, which was the most reduced under
red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the
main growth-limiting factor, since it was even more reduced under violet and near
far-red lights, where Synechocystis grew faster compared to blue light. Our results
provide insight into the spectral dependence of phototrophic growth and can provide
the foundation for future studies of molecular mechanisms underlying light acclimation
in cyanobacteria, leading to light optimization in controlled cultivations.
