Type IV pili-mediated metal acquisition in cyanobacteria

Abstract

Cyanobacteria can perform photosynthesis, but for doing so they require high amounts of metals such as iron and manganese. Therefore, cyanobacteria had to developed effective metal acquisition strategies. Not much is known about how cyanobacteria access metal oxides that have a low bioavailability. In recent years, it has been suggested that type IV pili, thin protein structures on the outside of non-photosynthetic bacteria, can facilitate electron donation to metal oxides, thereby making them bioavailable. Cyanobacteria also possess type IV pili, and this thesis focuses on elucidating the possible role of type IV pili in metal acquisition.

In the freshwater cyanobacterium Synechocystis sp. PCC 6803, we deleted the PilA protein that is responsible for the formation of type IV pili and investigated changes in global gene expression patterns when the deletion mutant is exposed to manganese limitation. Our results not only suggest a role of type IV pili in manganese acquisition, but also that PilA1 might be involved in the assembly of Photosystem II.

We developed a new cost-efficient and time-reducing transformation technique first to generate a deletion strain of PilA1 in the coastal cyanobacterium Synechococcus sp. PCC 7002. We then investigated this deletion strain under iron limitation using a suite of physiological and genetic techniques. Our results support a role of type IV pili in iron acquisition.

Finally, we developed new protocols to work in both an iron-defined and sterile environment with Synechococcus in collaboration with the Department of Chemistry at NTNU to follow the fate of iron more accurately in future experiments.

Taken together, our results indicate a novel function of type IV pili in metal acquisition in cyanobacteria.