Prochlorococcus is a type of a cyanobacterium, a microbe that meets its energy needs through photosynthesis. It is estimated to be responsible for 5% of all photosynthesis occurring around the world, making it the most plentiful and the smallest photosynthesizing cell in the ocean. There are different strains of this bacterium living under many conditions in the ocean, from sunlit surfaces to darkened depths.
This organism carries an estimated 80,000 genes. That's a lot more than humans have, roughly 4 times as many. "It's a beautiful little life machine and like a superorganism," commented Penny Chisholm, an Institute Professor at the Massachusetts Institute of Technology. "It's got a story to tell us." She suggested that such a huge number of genes has allowed this microbe to thrive under many conditions and have a huge influence on the chemistry of the ocean.