Biographical Statement: Penny Chisholm holds a joint faculty appointment in the Department of Biology and Civil and Environmental Engineering. She recently served as Director of the MIT Earth System Initiative, and was formerly Director of the MIT/Woods Hole Joint Program in Oceanography and Oceanographic Engineering. She is a key participant of The Darwin Project. The general goal of Professor Chisholm's research is to advance our understanding of microbial ecology and evolution in the oceans. In recent years her lab group has focused attention on a single group, the cyanobacterium Prochlorococcus, which is the smallest and most abundant microbe in ocean ecosystems — sometimes accounting for half of the total chlorophyll. They investigate this creature, which can convert CO2, sunlight, and inorganic nutrients into a living cell with as few as 1700 genes, as a model system to study marine microbial ecology at all levels of organization — from the genome level to the whole ocean. Prof. Chisholm's approach to this problem involves both laboratory and field studies, as well as modeling, and the use of tools of genomics and systems biology.