The Fluctuating Cell-Specific Light Environment and Its Effects on Cyanobacterial Physiology

Area of Science:

• Photosynthesis
• Photobioreactor technology
• Cyanobacterial physiology

Background:

• Industrial photobioreactors (PBRs) deliver light irregularly to cells, unlike stable lab conditions.
• This irregular light reduces cyanobacterial and algal growth rates significantly.

Purpose of the Study:

• To investigate the photophysiology of *Synechocystis* sp. PCC 6803 under simulated industrial PBR light conditions.
• To identify strategies for enhancing cyanobacterial productivity in dynamic light environments.

Main Methods:

• Culturing *Synechocystis* in a bench-top PBR under a sinusoidal light regime.
• Developing a computational fluid dynamics model to simulate light fluctuations experienced by cells.
• Conducting physiological measurements and ex situ electron transport experiments.

Main Results:

• Cells experienced rapid light fluctuations (∼6 s) between 2,000 and <1 µmol photons m^-2 s^-1 due to mixing and self-shading.
• No significant nonphotochemical quenching or photoinhibition was observed in situ.
• Up to 50% of electrons from Photosystem II were diverted to alternative electron transport.

Conclusions:

• Nonphotochemical quenching modification is unlikely to boost cyanobacterial productivity in PBRs with fluctuating light.
• Enhancing alternative electron transport and downstream processing of electrons from Photosystem I are promising strategies.
• The methodology can be adapted for studying other aquatic photoautotrophs in various mixing regimes.