Respect the microbes, says Prof. Martin Polz. “They’ve been on Earth longest, and they run the show.” He notes that there are some one million bacteria per milliliter of seawater — or about 237 million per cup. Further, if you put all the microbes in the oceans on a scale, they would outweigh all marine animals, including the whales.

Yet while the seas are almost entirely microbial, Polz says, scientists know very little about these organisms, which include bacteria, microscopic algae, and protozoa. “It wasn’t until the 1980s and 1990s, with the application of genetic techniques, that we began to learn how very diverse they are,” says this professor of civil and environmental engineering. “So we’re really looking at a timeframe of 20 years when we’ve had access to understanding this whole hidden world.”

Polz is part of a team of MIT faculty considered to be national leaders in the relatively new field of environmental microbiology. He is principally involved in very basic research toward understanding such things as the population dynamics of microbes, and how they develop certain traits through natural selection. The work could have many important applications, such as better ways to predict — and prevent — outbreaks of pathogenic microbes. Two of the bacteria he studies are responsible for 95 percent of deaths related to the consumption of contaminated seafood. He also studies the bacterium responsible for cholera, a disease that still affects millions of people around the world. And, says Polz, who is part of the Woods Hole Center for Oceans and Human Health, these and other pathogens could become more prevalent with climate change since they thrive in warm waters.

“In an uncontaminated ecosystem, pathogenic microbes are actually extremely rare,” he says. “Consider that you’re constantly eating and drinking microbes, and that you have 10 times more bacterial cells in your body than you have of your own body cells. They play very important roles in digesting food, feeding you, and keeping you healthy in general.”

Studying marine microbes is a challenge, Polz says. “They are hard to tell apart even with a microscope,” and less than one percent can be isolated and grown in a laboratory for study. So Polz is using a variety of other techniques involving, for example, genetic characterization of the organisms and computer modeling of the resulting data. Using these techniques, Polz led a group that showed, for the first time, that marine microbes organize into different “professions,” or lifestyle groups, within the water column.

Polz notes that what he learns about marine microbes should also aid our understanding of their cousins in the soil, in our bodies, and in other ecosystems. “These are organisms that we have to study intensely, because they really do drive the health of the planet.”