Photodamage and recovery of cyanobacteria

Cyanobacteria use light energy to perform oxygenic photosynthesis, converting CO2 and H2O into biomass. This process is driven by the photosynthetic reaction centers, photosystem I (PSI) and photosystem II (PSII), within the cyanobacterial internal thylakoid membrane system. Previous studies have shown that PSII becomes damaged due to its normal activities and upon acute exposure to excess light. In response to this photodamage, PSII must be constantly repaired by the cells.

Understanding how this photosynthetic processes work has been difficult using traditional ensemble approaches due to cell-cell heterogeneity. For example, in bulk culture, cells are exposed to a dynamic light environment that is a function of mixing, cell density, and cell state. To overcome this limitation, we have developed an automated imaging approach to film the growth of cyanobacterial cells using long-term, time-lapse, fluorescence microscopy, as well as software to analyze the resulting images.

I recently expanded the capabilities of the platform to enable multiple bacterial strains to be filmed simultaneously under highly repeatable growth conditions. In short, cyanobacteria cells are irradiated using UV light. I then film the cells for 20 hours after irradiation to see if cells recover. Preliminary results have revealed the evidence of asymmetric survival; Some cells recover and continue to grow after irradiation, while their genetically identical siblings do not. This evidence suggests that photoprotection could depend on not just on genetic traits but also the physical state of the cell.

Gif showing fluorescence movie of cyanobacteria

Plots showing lineage tree of cells which were irradiated

I am currently analyzing the collected data using machine learning algorithms to determine if physical factors, such as cell size or the state of the cell within its growth cycle, plays a determining role in avoiding irreversible damage.