PS Seminar Series: Identification and characterization of ion channels in the photosynthetic bacterium Synechocystis PCC 6803

ABSTRACT

The photosynthetic bacterium Synechocystis PCC6803 is a widely used model organism for studying bacterial photosynthesis and has considerable biotechnological potential. In plants, many ion channels involved in the regulation of photosynthesis are known and characterized. In cyanobacteria on the other hand, only one K⁺ channel, SynK, has been shown to be expressed on the thylakoid membrane and its knockout mutant showed a small photosynthetic phenotype. Here, we identified putative K⁺ and Cl^- ion channels in the Synechocystis genome. First, we determined their localization in a GFP-fusion overexpression system. To increase the effective resolution of imaging, we applied expansion microscopy (ExM), a technique in which a sample is physically expanded. In cyanobacteria, the gain in resolution and decrease of autofluorescence is essential to localize the proteins to either the thylakoid membrane, plasma membrane or periplasm.

Then, we determined the photosynthetic phenotype of the knockouts of the putative ion channels. Photosynthetic yield of the two photosystems was hardly altered in the knockouts, but the proton motive force buildup and thylakoid conductivity, as measured by electrochromic shift, was lowered in a putative Cl^-/H⁺ antiporter KO. Next, a putative mechanosensitive ion channel showed an altered response to high external NO₃^- concentrations and fluctuating light. Together, our results show a large impact of ion concentrations on photosynthetic efficiency. In summary, by identifying novel ion transporters in cyanobacteria and creating knockouts and overexpressions, we have been able to shine light on the complicated flows of ions during photosynthesis.

BIOGRAPHY

Peter is a postdoc at Turku University, Finland, in the group of Dr. Lauri Nikkanen, where he studies photosynthesis in cyanobacteria, with a focus on ion channels. He is currently on a research visit at ANU at the Byrt lab to characterize the ion transport capabilities of several putative ion channels. Peter did his PhD at Wageningen University & Research at the Laboratory of Biophysics under supervision of Dr. Emilie Wientjes and Prof. Dr. Herbert van Amerongen. There, he studied the thylakoid organization and its adaptation responses to short term light changes with expansion microscopy. Moreover, he used time-resolved fluorescence to study the evolutionary adaptations of photosystem I to shade light environments.