EDGE FGT: Genetic Tools for Picocyanobacteria that Dominate the Oceans

As the most abundant photosynthetic organism on the planet, the marine cyanobacterium Prochlorococcus plays a central role in providing energy and nutrients to ocean food webs. This species alone fixes approximately as much carbon dioxide annually as global croplands. Understanding the link between the diverse genes of Prochlorococcus and its central role in ocean metabolism is hindered by our inability to modify its genes to test various hypotheses.

Building on recent progress, this project aims to develop two distinct but parallel approaches to the challenge. In the first, barriers to the introduction of foreign DNA to Prochlorococcus will be bypassed by exploiting a system of newly discovered genetic elements that are found in some Prochlorococcus strains. In the second, approaches to trigger mechanisms that allow cells to take up and integrate new genes into their cellular machinery will be developed.

Once developed, these approaches would allow better understanding of the link between Prochlorococcus genes and the ocean environment, which is critical for characterizing the role ocean processes play in regulating the global carbon cycle. These advances will also provide a blueprint for the development of similar methodologies for studying other microbial organisms.

Finally, developing these technologies is a critical first step in enabling Prochlorococcus as a potential chassis for artificial photosynthesis. Since it has the smallest genome of any photosynthetic cell, Prochlorococcus is already the most basic photosynthetic machine occurring in nature, making it the ideal candidate for developing the tools that would enable bioengineering.

The tools this project aims to develop would provide immense potential for new inquiry and biotechnology applications. This project provides support for graduate students, a postdoctoral research associate, and two technicians.

Over the past three decades, the cyanobacterium Prochlorococcus, notable for its numerical dominance of the oceans and enormous genetic diversity, has been developed as a model organism for cross-scale systems biology. While each cell has around 2000 genes, the total unique gene content of the global Prochlorococcus ‘collective’ likely exceeds 80,000 genes, most of which have unknown function.

Thus, despite their central role in ocean metabolism, the relationship between Prochlorococcus’ diverse genetic content, and the selective pressures that have shaped it, is only beginning to be understood. Progress on this challenge has been stalled by the lack of a genetic system. In previous work supported by the EDGE program, the researchers developed a method of introducing exogenous DNA into Prochlorococcus cells, which represented a significant step forward in genomic manipulation.

In the process, a system of mobile genetic elements was discovered, which represent a promising new tool for integration of exogenous DNA into the Prochlorococcus, electroporation delivered tycheposons that are constructed with native genetic elements. A second approach to be developed utilizes a novel transposon-based screen to identify conditions for triggering natural competence activity among Prochlorococcus and will result in a genome-wide map of promising integration sites.

Both approaches have the advantage of utilizing DNA from Prochlorococcus itself, which should more effectively bypass cell defenses against exogenous DNA.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.