Cyanobacteria were the first organisms to evolve oxygenic photosynthesis, and now comprise a vast number of species, adapted to almost all the Earth’s environments. Some cyanobacteria can do photosynthesis using far-red light, a portion of the solar spectrum that is unused by most other oxygenic photoautotrophs because of its low energy content. These species are of high interest, because they could inspire biotechnological applications aimed at expanding the light usage of crop plants and microalgae into the far-red. Nonetheless, it is still unclear how the low energy content of far-red light affects the photosynthetic efficiency of these cyanobacteria, and which consequences this could have on the production of biomass. In my previous postdoctoral research at IBPC in Paris, I adapted to cyanobacteria a spectroscopic method based on the ElectroChromic Shift (ECS) of photosynthetic pigments that is widely used in algae and plants to quantify the photosynthetic activity by measuring the trans-thylakoid electric field generated by electron transport. In the model species Synechocystis PCC6803 and Synechococcus elongatus PCC7942, I could show that ECS represents a new tool to measure the photosynthetic activity in vivo in cyanobacteria.
In the project funded by the IM2B, I adapted the ECS method to two far-red absorbing cyanobacteria species, Chroococcidiopsis thermalis PCC7203 and Acaryochloris marina. The funding IM2B was used to upgrade the spectroscopy instruments available in the P&E team at BIAM, and to build a dedicated incubator for the growth of the two far-red cyanobacteria species. Using the newly adapted ECS method, I could show that both Acaryochloris and Chroococcidiopsis use visible and far-red light with similar efficiency to sustain photosynthetic electron transport, despite the significant differences in their light absorption characteristics (https://doi.org/10.1016/j.bbabio.2024.149502 ). This is at variance with the majority of cyanobacteria, which cannot use the far-red portion of the light spectrum efficiently. ECS thus represents a new non-invasive tool to study the performance of naturally occurring far-red photosynthesis, potentially contributing to its future exploitation for sustainable biotechnological applications.