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

蓝藻原绿球藻被认为是海洋中最丰富的光合生物，因此对全球碳循环做出了重大贡献。在一天24小时的过程中，太阳能可用性的变化对原绿球藻的生理有深远的影响。光合作用发生在白天，而在晚上，它们必须依靠能量储备生存。原绿球藻的不同寻常之处在于，它的细胞分裂周期与昼夜周期有关：它们在下午复制染色体，在傍晚分裂。正如最近菌株MED4的全基因组图谱所证明的那样，基因表达也会在光-暗循环过程中发生变化。大多数基因在晚上或白天结束时达到顶峰，为细胞进行光合作用（白天）、呼吸作用（晚上）、细胞分裂（晚上）或其他细胞活动做准备。该项目旨在表征第二株原绿球藻MIT 9312的全基因组表达谱，该菌株在与MED4相同的条件下生长。菌株MIT 9312与MED4在不同的进化谱系中（即不同的物种），它们在海洋中的分布也截然不同。考虑到光-暗循环对原绿球藻光生理和细胞分裂的中心重要性，在两个谱系中观察到的不同生态分布可能（部分）归因于它们的细胞过程与光-暗循环协调方式的差异。因此，这个项目的一个主要焦点将是两个菌株的基因表达谱的比较。这个项目将包括对本科生和研究生的培训，这项工作的结果将在国内和国际会议上发表。

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.