Seabed as a global "seed bank

Deep marine sediments contain quadrillions of long-lived bacterial endospores

Deep below the ocean floor, quadrillions of bacteria survive as endospores, recognizable by their bright fluorescence. © Fumio Inagaki / Jamstek
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Hidden Reservoir: Deep in the ocean floor, there are sixty-four million of endospores - forms of survival of bacteria that can survive enormous periods of time. This reservoir of dormant germs could account for up to six percent of total terrestrial biomass, new research suggests. The marine sediment endospores could act as a long-lasting seed bank for marine microbes, according to researchers in Science Advances.

For a long time, the sediments were considered deeply in the seabed as largely inanimate. But in the meantime, drilling has revealed that there is a whole lifeworld hundreds of feet deep underground - the deep biosphere. Even 2, 500 meters below the seabed researchers have discovered living bacteria. And in the "cellar" of the continents, according to a current estimate, a similarly high biodiversity could prevail.

Outlasting millions of years

But how the creatures of the deep biosphere manage to survive under high pressure, high heat and extreme lack of energy sources has only been partially clarified so far. However, it is obvious that at least some bacteria are not active at depth, but remain in a state of persistence - among others as so-called endospores.

"Bacterial endospores can withstand the most extreme conditions, including intense heat and drought, " explain Lars Wörmer from the MARUM Center for Marine Environmental Sciences in Bremen and his team. "It is believed that in certain circumstances, they can remain viable for millions of years." When environmental conditions change, the endospores "wake up" again and become actively replicating cells.

From 25 meters depth begins the realm of spores

How many endospores there are deep in the seabed of the oceans and how high their share of the entire deep biosphere could be, has now been determined by Wörmer and his team. For their study, they evaluated more than 300 marine sediment samples collected from a total of 15 ship expeditions worldwide. These samples were analyzed for their level of dipicolinic acid (DPA), a biomolecule found only in endospores that can therefore display their presence and abundance as biomarkers. display

The result: In fact, a large part of the marine deep biosphere is in the form of spores. Starting at a depth of 25 meters below the seafloor, the endospores begin to dominate over the active cells, the researchers noted. They identified two subsets of spores: a younger, shorter-lived endosporus species and a long-lived, abundant even in deep old sediments.

"An enormous biomass reservoir"

Impressive, however, is the enormous number of endospores: According to the researchers' calculations, there could be between 10 high 28 and 10 high 29 endospores in the upper one thousand meters of sea sediment alone. Expressed in words, this would be between 10, 000 and 100, 000 quadrillion spores an unimaginably large number. The spores are particularly abundant in the seabed of the coastal areas and marginal seas.

"Our data thus identifies the bacterial endospores as an enormous biomass reservoir that has been largely overlooked so far, " say W rmer and his colleagues. According to their estimates, the marine endospores could account for between 0.8 and 6 percent of the total terrestrial biomass.

Seed bank in the underground

Which Rollecological role endospores play in their habitat is not yet clear. However, the researchers speculate that the older, more endosporous endospores could act as a sort of seedbank at depth. "The genomic and functional diversity of these organisms is maintained over long periods of time and can then serve to spread, germinate and colonize new habitats, " say the scientists. (Science Advances, 2019; doi: 10.1126 / sciadv.aav1024)

Source: MARUM - Center for Marine Environmental Sciences at the University of Bremen

- Nadja Podbregar