From the great outdoors to our internal organs, the world is awash in unseen bacteria. Most people assume that these germs are all dangerous but biologists know better. Studying these poorly understood microbes could better reveal how they function as the “invisible backbone of life.”  Victoria Orphan of San Diego, California and now a geobiologist at Caltech, has loved the ocean for as long as she can remember. She now spends her days exploring the hidden single-celled world found in ocean water. She studies how bacteria and other microscopic life shape the deep sea.  Bacteria play central roles in many ecosystems. These include the oceans, soil and atmosphere. They’re also a big part of the global food web. Bacteria make it possible for all other life on Earth to exist. That’s why scientists say these single-celled organisms are the invisible backbone of all life — at least on Earth.  Yet there’s plenty we don’t know about them. Scientists think they’ve identified fewer than one percent of all bacterial species. That’s been driving Orphan and others to explore the mysteries of their one-celled world. They suspect bacteria will prove key to understanding — and protecting — Earth’s most important natural resources.  Specifically, Orphan studies a type of bacteria that live on the sea floor and gobble up methane.  Methane can seep out of the Earth on the sea floor. Some scientists say that even more methane would escape into the atmosphere if it wasn’t for marine bacteria. Certain of those bacteria dine on methane. That allows the oceans to trap a huge amount of the gas. “These microorganisms are the gatekeepers. They prevent ocean methane from getting into the atmosphere where it can change greenhouse-gas levels,” Orphan explains.

Finding single-celled organisms on the vast sea floor can be a challenge. Through the window of a submarine, she looks for clusters of clams and giant tube worms. These organisms signal that invisible marine bacteria live there, too. Wherever those methane-eaters live, they create new molecules as they dine. Other organisms use those new molecules as food. An entire food web springs up on the ocean floor.  Orphan and her team have found methane-eating bacteria along cracks on the sea floor, where this gas is seeping out. These cracks often happen where two tectonic plates bump into each other and create enormous canyons. Some bacteria, they learned, can eat methane only by partnering with other single-celled organisms called archaea. That important detail could help scientists better predict how much methane is escaping into the air, says Orphan.

More than 1,000 scientists around the world are helping collect samples. They’re looking in a host of different environments, then testing them for bacterial DNA.  So far the researchers have collected 100,000 samples. They’ve catalogued bacteria from the deepest ocean. They’ve found bacteria on the International Space Station, some 350 kilometers (220 miles) above Earth. They’ve discovered bacteria in exotic locations like the Amazon rainforest and ordinary places like public toilets.

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