World's Largest Bacteria Invaded by Parasitic Ocean Dwellers

One of the world's largest bacteria is also one of the most susceptible to parasites. Now, scientists are learning a little bit more about the relationships that these massive, deep sea bacteria share with microorganisms, which may reveal a little bit more about ocean productivity.

At the bottom of the eastern Pacific off of the coast of Mexico lives a series of soft, noodle-like white strings. Known as Thioploca, this bacteria is one of the largest in the world and can be seen with the naked eye. Feeding on nitrate that it absorbs from the water, Thioploca can withdraw under the seabed through a tube that can measure up to 20 cm.

Yet Thioploca isn't the only nitrate harvester in the deep. Surprised by exactly how much nitrate was disappearing in these waters, the researchers investigated the bacteria a bit further. It turns out that in its tube-like sheath are smaller cells, called anammox bacteria. These smaller bacteria steal nitrate from Thioploca when it retires through the sheath with its harvest.

"The newly discovered symbiotic relationship increases nitrogen metabolism in the sea," said Bo Thamdrup, one of the researchers, in a news release. "This leads to fewer algae in the water and thus less food for marine organisms. The consequence is that there is less food for the fish."

Scientists usually worry about an excess of nutrients in the ocean. For example, the Gulf of Mexico dead zone that occurs each year is sparked by an algal bloom caused by large amounts of nutrients being dumped into the water. Yet in the case of these ocean waters, it's a lack of nutrients that's making researchers concerned.

"We have previously believed that nitrogen removal occurred mainly in the open ocean and in the water column rather than at the bottom," said Thamdrup in a news release. "However, if oxygen-depleted regions and Thioploca and anammox-bacteria spread over the seabed near the coasts, it could have implications for fish life and fisheries."

The findings are important for understanding the nutrient cycles of the ocean. In addition, they reveal a little bit more about these strange and large bacteria.

The study is published in the journal Nature.