Marine microbes called Prochlorococcus are the main basis for most ocean food webs, yet before this week not much was known about single-cell creatures.

Researchers detailed hundreds of subpopulations of the essential marine bacteria in a study released this week.

A team of researchers were able to identify the altered subgroups through genomic analysis of microbes in just a milliliter of ocean water, according to an MIT press release.

"The sheer enormity of diversity that must be in the octillion Prochlorococcus cells living in the seas is daunting to consider," said study author Sallie Chisholm, a professor of environmental studies at MIT, according the release. "It creates a robust and stable population in the face of environmental instability."

The researchers determined that the Prochlorococcus subpopulations all shared the same "genomic backbone," according to the study.

This includes a primary set of alleles connected to a couple flexible genes.

"This is perhaps the most sophisticated and thorough study yet to be published on the fine-scale genetic diversification of an environmental microbial species, and it correctly, I think, predicts that amazingly diverse populations may be maintained over astonishingly long times," said Ford Doolittle, a molecular biologist at Dalhousie University in Canada who was not involved in the research. "If microbiologists persist in believing in 'species,' they will likely have to drastically revise upward their estimates of how many such things there are."

Various subpopulations separated over the course of a couple of million years ago, and the "genomic backbone" is now a slower, older, changing component of the genome.

Flexible genes inhabit parts of the genome where swapping occurs quite often, which creates a quicker evolution process, according to the release.

The study area was found in the waters around Bermuda, but the team said that ocean currents can quickly separate daughter cells after cell division, according to the release. The currents are then capable of sending them hundreds of miles away in just a couple of days.

 "What we will probably be arguing about for a long time is what processes or forces other than selection might be responsible for such stable diversity, and, unless we find such processes, how something so seemingly well mixed as the ocean can offer up so many different tiny selective regimes," Doolittle said.

Research was published in the journal Science this week.

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