Thought for the day: More bacteria are alive in your mouth right now than the number of people who have ever lived on Earth. And if you’re swimming in the ocean and take an accidental gulp of seawater, some of those bacteria in your mouth are the very ones that may control global warming.
Consider an unusually tiny, hard-to-grow bacteria called SAR11, first identified in the Sargasso Sea by Prof. Stephen Giovannoni of Oregon State University when he hunted for genes in water samples more than a decade ago. “SAR11 was the first major group of uncultured bacteria to be discovered by gene cloning and sequencing techniques” he notes. A few weeks ago, a new analysis based on samples taken from across the planet revealed that Prof Giovannoni might have stumbled upon the most common creature on planet Earth. SAR11 may make up more than one third of all bacterial cells in the ocean surface waters, and almost one fifth of cells in deeper water. “They are possibly the smallest cells known, and all together they weigh about as much as all of the fish in the oceans,” says Giovannoni. SAR11 microbes have only 1% of the volume of common E. coli gut bacteria; so small that billions will fit into a teaspoon, so abundant that at 200 million metric tons of total biomass, they may influence the climate. “Vast populations of SAR11 increase during the summer and decrease during the winter, in a cycle that correlates with the build-up and decline of dissolved organic carbon in the ocean surface,” said Dr. Robert Morris, lead author of the recent SAR11 study. This suggests that SAR11 has an active role in the oceanic carbon cycle, which affects the concentrations of carbon dioxide in the Earth’s atmosphere that contribute to global warming.
In an impressive example of think globally, act locally, other researchers in Dr. Giovannoni’s lab have also recently made a different bacterial discovery not in the oceans, but beneath them. In the 3.5 million-year-old crust almost 1,000 feet beneath the bottom of the ocean off the coast of Oregon, Prof Giovannoni and colleagues found moderately hot water moving through heavily fractured basalt that was depleted in sulphate and enriched with ammonium. The discovery suggests biological activity in a high-pressure, undersea location far from the types of carbon or energy sources upon which most life on Earth is based. Instead of digesting organic molecules, as most life does, the novel bugs appear to dine on inorganic molecules such as sulphide or hydrogen, and carbon dioxide. The level of biological activity of these bacteria was sufficiently high that ammonia levels in the subsurface samples were 142 times higher than those in nearby sea water. Says co-author Dr. Michael Rappe, “We knew practically nothing about the biology of areas such as this, but we found about the same amount of bacteria in that water as you might find in surrounding sea water in the ocean. It was abundant. As more research such as this is done, we’ll probably continue to be surprised at just how far down we can find life within the Earth, and the many different environments under which it’s able to exist.” Thus the deep ocean crust can now be viewed as an immense “biosphere” of life in its own right that covers most of the Earth.