Cyanobacteria have played a critical role in creating the world as we know it. Around 2.5 billion years ago, the earth’s atmosphere contained almost no oxygen. The oxygen we breathe was derived from water via photosynthesis, which uses sunlight to extract energy-rich electrons from water and in turn uses those energy-rich electrons to turn carbon dioxide and other mineral nutrients into sugars, amino acids, and other organic building blocks of life via autotrophic metabolism.
Our lab studies several of the molecular machines involved in this process of photosynthesis and autotrophic metabolism. We study the assembly of photosystem II (PSII), the pigment-protein complex that splits water into hydrogen and oxygen. We use a range of techiques, including proteomics to develop a complete ‘parts list’ of the protein subunits of PSII, as well as cross-linking mass spectrometry to analyze how and when those parts interact with each other. These techniques from systems biology are leading to a more detailed and fundamental understanding of how the biosphere collects and uses sunlight.
At a broader level of organization, we have used small-angle neutron scattering (SANS) to study the arrangement of PSII within the membranes of both wild-type Synechocystis 6803 and several mutants having truncated light-collecting antennas. In dense wild-type cultures, cells near the surface often absorb more light energy than they can effectively use, while starving those deeper in the culture for light energy. These mutants could potentially lead to a more optimal distribution of light energy within a mass culture grown for biofuel or high-value chemical production.
In addition to basic scientific studies, our lab is interested in molecular machines that can transform sunlight into valuable products such as biofuels. We have a collection of Cyanothece strains that possess a unique type of metabolism that allows them to perform oxygen-producing photosynthesis during the day and oxygen-sensitive nitrogen fixation at night. As a natural byproduct of nitrogen fixation, these strains produce H2, a valuable biofuel. We have shown that one of these strains, Cyanothece 51142, produces the largest amount of H2 of any photosynthetic organism, and can use waste products like glycerol to enhance that production.