Starter Grant: Whole Genome Profiling of the Numerically-Dominant Ecotype of the Marine Cyanobacterium, Prochlorococcus, Grown Under a Simulated Daily Light/Dark Cycle

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The cyanobacterium Prochlorococcus is believed to be the most abundant photosynthetic organism in the oceans, and as such contributes significantly to global carbon cycling. The change in solar energy availability over the course of the 24 hour day has profound implications for the physiology of Prochlorococcus. Photosynthesis occurs during the day, while at night they must survive on energy reserves. Prochlorococcus is also unusual in that its cell division cycle is linked to the light - dark cycle: they replicate their chromosome in the afternoon and divide in the early evening. Gene expression also varies over the course of a light - dark cycle, as recent whole-genome profiling of strain MED4 has demonstrated. Most genes peaked either at the end of the night or end of the day, to prepare the cell for photosynthesis (in the day), respiration (in the night), cell division (in the night), or other cellular activities. This project is aimed at characterizing the whole-genome expression profile of a second strain of Prochlorococcus, MIT 9312, grown under the same conditions used for MED4. Strain MIT 9312 is in a different evolutionary lineage than MED4 (i.e. different species), and they have dramatically different distributions in the oceans. Given the central importance of the light - dark cycle to Prochlorococcus photophysiology and cell division, the different ecological distributions observed for the two lineages could be due (in part) to differences in the way that their cellular processes are coordinated with the light - dark cycle. A major focus of this project will therefore be the comparison of the gene expression profiles of the two strains. This project will involve the training of undergraduate and graduate students, and the results of this work will be presented at national and international conferences.