Scientists have grown algae that was collected from the bottom of the Baltic Sea, and which probably sank about 7,000 years ago. Although it was without light or oxygen for thousands of years, it remained dormant until it could be fully revived. The work, which has been reported in The ISME Journal, was part of a larger effort to learn more about the history of the Baltic Sea, and what that might tell us about its future; this project is called PHYTOARK.
It's not unusual for a cell to transition to another state for protection under stress, such as when fungi form spores, or dormant cells are made by algae. In dormant cells, metabolic processes slow down, so that energy and resources and conserved, and various protective structures can form.
Phytoplankton are minuscule aquatic plants that can perform photosynthesis. When they become dormant in the bodies of water where they live, they sink to the floor and are eventually covered by sediment, and no oxygen can reach these buried, dormant cells.
In this work, the investigators collected sediment cores that were taken at a depth of 240 meters in a part of the Baltic Sea called the Eastern Gotland Deep in 2021.
"Such deposits are like a time capsule containing valuable information about past ecosystems and the inhabiting biological communities, their population development and genetic changes," explained first study author Sarah Bolius of the Leibniz Institute for Baltic Sea Research Warnemünde (IOW).
In an approach with "the rather unusual name of resurrection ecology," cells go into dormant stages. "And these stages can be assigned to specific periods of Baltic Sea history due to the clear stratification of the Baltic Sea sediment are to be brought back to life under favorable conditions, then they are genetically and physiologically characterized and compared with present-day phytoplankton populations," explained Bolius.
As the sediments that are collected are compared to other sediment components, which can act as a kind of proxy, the researchers can extrapolate information about the oxygen, salinity, and temperature conditions that once existed.
The scientists are aiming to learn more about how and why the genetic and functional characteristics of Baltic Sea phytoplankton have changed in response to changes in the environment, noted Bolius.
The scientists isolated strains of phytoplankton from nine sediment samples. They determined that the sediment laters themselves were about 7,000 years old, and in a primary phase of the Baltic Sea's climactic history.
A diatom known as Skeletonema marinoi was found in every sample. This phytoplankton usually grows during spring, and is very common in the Baltic Sea. The cells were estimated to be about 6,800 years old.
"It is remarkable that the resurrected algae have not only survived just so, but apparently have not lost any of their fitness...They grow, divide and photosynthesize like their modern descendants," added Bolius.
The investigators also ruled out cross-contamination, and used a genetic analysis to confirm that the sediment layers had not mixed. The genetic characteristics of the cells also showed that distinct groups had formed over time.
Sources: Leibniz-Institut für Ostseeforschung Warnemünde, ISME Journal
