Exobiology and Evolutionary Biology

PI: Robert Blankenship

The early Earth was an anaerobic world, with only trace amounts of free oxygen present in the atmosphere and dissolved in the oceans. Life began in this anaerobic world and developed to a considerable level of sophistication utilizing a metabolism that did not involve molecular oxygen as either a terminal electron acceptor or as a waste product. The rules of the game changed forever when oxygenic photosynthesis was invented and started polluting the environment with large amounts of free oxygen. This event, perhaps the single most important metabolic innovation on Earth after the DNA/protein world was established, set the stage for the development of a metabolism based on oxygen as the terminal electron acceptor and also required the development of a suite of protective and repair systems to ameliorate the destructive effects of reactive oxygen species.

This proposal employs a multidisciplinary approach to explore the evolutionary transition from anoxygenic to oxygenic photosynthesis, which was the key innovation that induced the switch from an anaerobic to an aerobic world. Techniques that will be utilized include molecular evolution analysis, comparative biochemistry and genomics. We focus on two
broad areas or research, each of which is subdivided into two more specific sections. The first broad area relates to the origin and development of Photosystem II and the ability to evolve oxygen. The two specific aspects of this area concern elucidation of the mechanism of chlorophyll d biosynthesis in the cyanobacterium Acaryochloris marina and molecular evolutionary analysis of the proteins involved in Photosystem II. The second broad area is concerned with the earlier evolution of photosynthetic reaction centers and electron transport systems. The specific areas here concern the analysis of the electron transfer properties of the reaction center in and isolation and characterization of the cytochrome bc complex in the heliobacteria. The heliobacteria are unique phototrophs with the simplest known photosystem, which some evidence suggests has properties intermediate between Photosystem I and Photosystem II. These experiments may give critical clues to the development of the balance between noncyclic and cyclic electron transfer that is essential in modern oxygenic photosynthesis. This proposal relates to the Early Evolution of Life and the Biosphere research emphasis; sections iv) (key biological processes), and vi) (evolution of genes, pathways and species).