`Twilight` microbes that capture carbon discovered

Mysterious organisms in the dark depths of the ocean are converting carbon dioxide into a form useful for life.

Washington: Scientists have identified some mysterious organisms in the dark depths of the ocean which they believe are converting carbon dioxide into a form useful for life.

The bugs, which the scientists call "twilight" microbes, could be the missing link of global carbon cycle as they are found turning inorganic carbon into useable food some 2,625 feet below the ocean surface, LiveScience reported.

The job of capturing carbon -- crucial to sustaining life on Earth -- is usually carried out by plants that use sunlight as energy. But light doesn`t penetrate below 656 feet of ocean, so plants can`t do this job.

To survive, living cells must convert carbon dioxide into molecules that can form cellular structures or be used in metabolic processes, the scientists said.

Simple, single-celled organisms called archaea that often live in extreme conditions were thought to be responsible for much of the dark ocean`s carbon fixation. But there was
evidence that archaea could not account for the total amount of carbon fixation going on there.

"Our study discovered specific types of bacteria, rather than archaea, and their likely energy sources that may be responsible for this major, unaccounted component of the dark ocean carbon cycle," said study author Ramunas Stepanauskas of the Bigelow Laboratory Single Cell Genomics Center in the Gulf of Maine in the US.

To get a glimpse of what was going on in the dark, the researchers looked at samples from two subtropical gyres, or systems of rotating ocean currents, in the South Atlantic and North Pacific.

The researchers isolated single cells from the samples and sequenced genomes (the complete set of inherited instructions for an organism) of 738. This allowed them to
identify a variety of strains of bacteria and verify the predominant lineages capable of fixing carbon.

To carry out this process, cells need a source of energy. While it is believed that archaea use ammonia, many of the bacteria the scientists sampled contained genes suggesting
they could use sulphur compounds as an energy source.

Others may also use single-carbon compounds, like methane, as energy sources, the researchers said.

These previously unrecognised types of dark ocean bacteria may play an important role in the natural cycling of nutrients from the environment to organisms and back, the
researchers wrote in the journal Science.


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