The strains' productivity as a significant source of marine food and their ability to capture carbon means the algae can influence the carbon flux and have an impact on climate change, according to the study published in Friday's edition of the journal Science.

An international team of researchers sampled two isolates of Microminas, one of the smallest known eukaryotic algae -- complex cellular structures containing a nucleus and enclosed within a membrane.

One sample was taken from the South Pacific and the other from the English Channel.

The algae's apparently broad physiological range may indicate more resilience to environmental change compared to other closely related species spread across a smaller geographical expanse, said Alexandra Worden of the California-based Monterey Bay Aquarium Research Institute (MBARI), the study's lead researcher.

Less than two microns in diameter, or about a 50th the width of a human hair, Microminas are among a few marine algal species present throughout the world's oceans.

The analysis identified about 10,000 genes in each Microminas strain that were compressed into genomes totaling about 22 million nucleotides.

"Yet, surprisingly, they are far more diverse than we originally thought," said Worden.

She added that these two picoeukaryotes -- photosynthetic eukaryotes thriving in salt water and freshwater -- are often considered to belong to the same species but only share 90 percent of their genes.

In comparison, humans and some primates share about 98 percent of their genes.

Microminas capture carbon dioxide, sunlight, water and nutrients while also producing oxygen and carbohydrates, explained the study.

The genetic code of Microminas indicates how photosynthesis transformed the Earth from barren land to one colonized by plants, noted the study, also led by the Joint Genome Institute of the US Department of Energy.

"The Microminas genomes encapsulate features that now appear to have been common to the ancestral algae that initiated the billion-year trajectory that led to the 'greening' -- the rise of land plants -- of the planet," said Worden.

Algae were leading the way to photosynthesis long before plants appeared on the planet.

The study complemented earlier scientific research seeking to identify actors playing a key role in regulating carbon dioxide, the principal source of greenhouse gas emissions.

"By understanding which genes a specific strain employs under certain conditions, we gain a view into the factors that influence the success of one group over another," Worden said.

"We may then be able to develop models that could more effectively predict a range of possible future scenarios, that will result from current climate change."

Such measures are urgent, the researchers said, due to the acceleration of carbon emissions in the atmosphere.

The flagellated Microminas are also particularly speedy. Unlike other algae sequenced thus far, Microminas can swim toward sunlight, their principal source of energy, at a speed of 50 body lengths per second.

Microminas and other picoeukaryotes account for only a quarter of picophytoplankton cells -- plankton performing photosynthesis -- but were responsible for three-quarters of net carbon production in a Pacific Ocean sampling, Worden and her fellow researchers showed in previous studies.

They also found that because Microminas lack a cell wall, they are more digestible as prey.

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