In this project, the genome of Prochloron didemni, a photosynthetic bacteria that lives in a symbiosis with a primitive animal found in coral reefs, will be sequenced, annotated and used for comparative genomic studies. This symbiosis is important for many reasons including (1) that the host (the coral reef ascidian Lissoclinum patella) is a primitive representative of the chordate animals - thus this study may help understand symbioses between bacteria and other chordates such as humans; (2) that the symbiont is a cyanobacterial prochlorophyte and thus is a close relative of the photosynthetic organelles of plants (chloroplasts); and (3) there are no genomes currently available from cyanobacteria symbionts. Analysis of the genome will be used to elucidate genes responsible for symbioses between chordates and bacteria, to further define the unique photosynthetic characteristics of prochlorophytes and to determine which factors are important in the conversion of free-living cyanobacteria into obligate symbionts. In addition, this project should help in understanding the broader context of symbiosis such as the distinction between mutualistic and pathogenic associations, the profound role of microbial symbionts in marine invertebrate ecology, and the mechanisms of innovation through symbiosis, a major process in the history of life. This project will be a collaborative effort between The Institute for Genomic Research (TIGR), the University of Utah and the University of California San Diego and will involve graduate and undergraduate students from these institutes and from the Republic of Palau where the symbiosis occurs. Perhaps most importantly, photosynthesis represents the primary pathway for fixation of carbon from the atmosphere. Thus a better understanding of the diversity of carbon fixation pathways, especially in the organisms related to plant and algal chloroplasts, will potentially help in efforts to understand global carbon cycles and eventually to mitigate the effects of carbon being released into the atmosphere by human activity.
