Image: Loreto De Brabrandere, UC Davis
Symbiotic relationships between species are a popular evolutionary strategy, a reality anyone with a dog can verify. But the bacterial strains Thioploca and Anammox are taking it to a whole other level: in exchange for being Thioploca's toilet, Anammox gets to ride its elevator-like “sulfer braids” for free. It's among the more ingeniuos quid-pro-quos in the world, and it's necessitated by the tough conditions both bacteria have to confront in their habitat.
These are strains that live in the anoxic seabeds off the west coast of California and South America. Without the option of oxygen as a metabolic aid, Thioploca relies on less conventional sources—nitrate and sulfide—to fuel itself. It also had to evolve a way to be mobile so that it could scavenge those rare resources from the muddy sediment.
A snot-tunnel is the obvious answer. By secreting mucus into hollow chains, which can grow up to 7 centimeters, the Thioploca filament creates both a protective bunker and an elevator through the mud. It collects nitrate towards the top of the chain, where the seabed is, and encounters the sulfide on the way down. Reacting the two chemicals together is its specialty, and it can power itself off this process alone.
Image: Carola Espinoza, Flickr
Anammox cells, meanwhile, hitch a ride on the Thioploca filaments as they travel through the tube. When the Thioploca mixes nitrate and sulfide, it creates waste in the form of nitrite and ammonium. Luckily for both bacteria, Anammox cells can devour these byproducts, which are likely toxic to Thioploca. In this way, it acts as a one-stop waste treatment plant for their shared mucus elevator.
The finding, published in Nature this month, has a few unique applications. Astrobiologists interested in extremophile behavior have yet another example of how, as Ian Malcolm of Jurassic Park would put it, “life finds a way.” If there is energy to be scrounged, even in the most unpromising habitats, bacteria will exploit it. That bodes well for those of us who hope to find life on other planets, even if it does live in its own snot-hole.
The symbiotic relationship also has implications for climate change research. Global warming has the potential to severely deoxygenate the oceans. The vast majority of marine life will be affected by dropping oxygen levels, but not the Thioploca-Anammox partnership. Indeed, according to the study's lead author, Dr. Maria Prokopenko, the “Thioploca/Anammox consortium ultimately helps the ocean to stay more oxygenated” by impeding algae growth.
Turns out life on the edge doesn't have to be lonely after all.