Much as an anthropologist can study populations of people to learn about their physical attributes, their environs and social structures, some marine microbiologists read the genome of microbes to glean information about the microbes themselves, their environments and lifestyles.
Using a relatively new methodology called comparative population genomics, these scientists compare the entire genomes of different populations of the same microbe to see which genes are “housekeeping” or core genes essential to all populations and which are population-specific. Scientists are able to read a genome and translate the genes into proteins that serve particular functions. Population-specific genes sometimes tell a very clear story about the environment, for instance temperature and the availability of light and particular elements, and over time, they can point to the microbes’ evolutionary adaptation to changes in the ecosystem. Occasionally, as was the case with recent research at MIT, the population-specific genes reveal this information with crystal clarity, even providing unmistakable clues about lifestyle.
Professor Sallie (Penny) W. Chisholm of MIT’s Department of Civil and Environmental Engineering (CEE) and former doctoral student Maureen Coleman compared the genetic makeup of two populations of the same oceanic photosynthetic bacterium, Prochlorococcus, one living in the Atlantic Ocean and one in the Pacific.
They found that although a continent separates the populations, they differ significantly in only one respect: those in the Atlantic have many more genes specifically related to the scavenging of phosphorus, an essential element for these microbes. And just as the variations in the beaks of Darwin’s finches were evolutionary adaptations related to food availability, so too are the variations in the Prochlorococcus genes related to phosphorous gathering. Both are examples of a powerful evolutionary force at work.