The most common bacteria in the oceans turned out to be a reservoir of viruses

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(ORDO NEWS) — Candidatus Pelagibacter ubique, aka SAR11, is arguably the most common living organism on Earth: in the oceans it is for sure. This is an alpha proteobacterium with a cell diameter of about 0.1-0.2 micrometers, one of the smallest self-replicating creatures on our planet.

These protobacteria have achieved incredible success in the struggle for a place in the sun. The total mass of SAR11 exceeds the total mass of all fish that live in the oceans and seas of the planet, and you can find them literally everywhere. Scientists suggest that the main guarantee of the prosperity of these organisms is in their simplicity. A new study published in the journal Nature Microbiology offers yet another possible success factor for Candidatus Pelagibacter ubique – viruses.

The study of the bacterial genome showed that it contains viral DNA, which most of the time is in a resting state. “Many bacteria have viruses that exist in their genomes. But so far, they have not found anything like this in the most common ocean organisms, says lead author of the study, Robert Morris. “We suspect that this is <…> more common than we thought – just never noticed.”

The survival strategy of the virus living in SAR11 cells is different from the strategies of other similar “organisms”. It settles in the host’s DNA and multiplies along with bacteria, but sometimes it can also be released, destroying the cell: the reasons for this are not yet clear to scientists.

A new study shows that as much as 3% of the SAR11 population can have a virus in their DNA that is prone to lysis of the host cell. This is a higher percentage than for most viruses living in the bacterial genome. Due to this, the pathogen releases a relatively large number of virions, which contributes to its survival.

Experiments on the study of sulfur utilization by bacteria showed an interesting feature: when Candidatus Pelagibacter ubique cells are in a condition of lack of nutrients, viruses begin to leave cells much more actively, lysing up to 30% of bacteria.

According to scientists, this helps not only viruses: due to the fact that bacterial genes also enter the virions, various strains of bacteria can exchange genetic material, improving their diversity. Such an approach could help SAR11 gain a competitive advantage over other microorganisms and become the most common ocean bacteria.


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