EAGER: Collaborative Research: Manganese Phototrophy in Cyanobacteria

Csu Fullerton Auxiliary Services Corporation, Fullerton CA

Investigators

Abstract

The rise of oxygen approximately 2.3 billion years ago was arguably the most significant event in Earth's history. The rise of atmospheric oxygen led to life as we know it today, including organisms that breath oxygen and multicellular life such as plants and animals. This event is principally related to the evolution of oxygen (O2) producing photosynthesis by Cyanobacteria. Photosystem II (PSII) is the catalyst that uses light energy to remove electrons from water and produce O2. The evolutionary route of PSII to produce O2 is uncertain. One hypothesis, based on both the geological record and biochemical studies of PSII, is a precursor photosystem was able to obtain electrons from the transition metal manganese, instead of water. The proposed work tests this hypothesis using modern Cyanobacteria and PSII, which may still be able to perform this reaction. The work will help scientists understand the evolution of this important process: the production of O2. It will also impact understanding of modern manganese cycling on our planet, which affects the fate of many pollutants in the environment. Students trained in this interdisciplinary research project from both a geobiology program at a research intensive university and a biological science program at a diverse regional Hispanic-serving primarily undergraduate institution will attend common group and professional meetings and develop mentor-mentee relationships across disciplines. Findings will also be integrated into presentations and coursework at K-12 and the two universities. This project concerns the hypothesis that the "missing link" in the evolution of photosynthetic water-oxidation by Photosystem II (PSII) was phototrophic Mn(II) oxidation, and examines Mn phototrophy in Cyanobacteria to test this hypothesis. High-valent manganese species comprise a critical pool of strong oxidants in the environment, involved in the cycling of both carbon and metals. This work will add to the understanding of modern biological Mn oxidation and the potential sources of high-valent Mn in nature by examining bacterial Mn oxidation in Mn phototrophy. Phototrophic Mn oxidation will be evaluated and linked to growth using whole cells of the genetically tractable Cyanobacterium, Synechocystis sp. PCC 6803, and a mutant of this organism impaired in photosynthesis. The stoichiometry and mechanism of Mn-oxidizing phototrophy will be determined using purified PSIIs from these strains. These studies have the potential to provide new insight into our understanding of the evolution of oxygenic photosynthesis. The broader impacts concern a research collaboration between a research intensive and primarily undergraduate institution that is also minority serving. Students from the two institutions will interact with each other and the research results will be incorporated into presentations and courses at the undergraduate and K-12 level. 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.