Researchers have discovered oases on the seabed where microbes from the genus Scalindua can accumulate energy over time. An international group of scientists in a new study found out what conditions are needed for this.
Researchers studied microbes from the genus Scalindua in the Norwegian Sea in Greenland. Microbes of this species were able to reactivate and increase their population by 4 orders of magnitude long after burial.
Millions of microbial cells fill every millimeter of 360,000,000 km2 of the Earth’s seabed. Over time, they sink deep into the sediment due to the continuous flow of particles from above to become part of the deep sedimentary biosphere. When the supply of food from the surface world is cut off, microbial populations gradually decrease. Metabolic activity slows down to an absolute minimum, providing barely enough energy for basic cell maintenance. Microbes’ survival on the seabed for millennia is a matter of tenacity and perseverance, not growth. In the new study, however, the research team describes how a small group of organisms that obtain their energy through anaerobic oxidation of ammonium (anammox) are an exception to this general rule and can reproduce after long periods of time under adverse conditions.
“It’s amazing what these cells can handle,” said senior study author Steffen L. Jorgensen of the Deep Sea Research Center at the University of Bergen, Norway. – From the moment Scalindua cells are deposited on the ocean floor, they find themselves in a hostile environment. Their food source (ammonium and nitrite) is very scarce. Once deposited on the ocean floor, they must survive burial for 80,000 years in places without any sources of energy or food. When cells are deep enough in sediment where ammonium and nitrate flow meet, they can receive energy. Here, the few cells that reach this depth begin to grow, and the population size increases. However, their time in this zone is limited since the zone itself remains at a fixed depth, while the microbes go deeper and deeper due to the incessant burial process. Basically, these cells spent 80,000 years going through hell to finally get to a place where they could get normal food, only to be expelled after a snack.”
One of the obvious questions for researchers was what traits allow these microbes to survive for so long in extremely hostile conditions. To investigate this, they sequenced the entire genome of these organisms and compared it to the content of the genome of their relatives on the surface. They found that organisms have specific genes that allow them to use different nitrogen-containing compounds to obtain the necessary ammonium. Besides, they can likely use reactions other than anammox for energy.