A tiny form of bacteria that is likely the most abundant form of life in the ocean is giving up its secret for surviving without food — it can switch to using light much the way plants do to stay alive.

Oregon State University researchers have successfully cultured a laboratory microorganism with a gene for the alternate form of photochemistry exhibited by the bacteria known as SAR11, the smallest free-living cell known.

By studying the SAR11 “proteorhodopsin’’ gene, scientists will be able to better understand the ecology of the world’s oceans, researchers say.

The alternate form of photochemistry serves as a backup system to provide energy to the bacteria when they face starvation in the open ocean, which often has very limited nutrients.

It is similar to photosynthesis, the mechanism that plants use to turn sunlight into energy and food, but does not involve chlorophyll, a key ingredient produced only by plants.

“It’s exciting to learn more about another form of photochemistry that does not use chlorophyll,’’ said Stephen Giovannoni, an Oregon State microbiology professor.

The level of interest in SAR11 is high because it dominates microbial life in the oceans and survives where most other cells would die.

Although tiny, the huge numbers of SAR11 bacteria also give them a major role in the carbon cycle of the entire planet — carbon that is an essential ingredient of nearly all life on Earth.

Oxygen in the atmosphere was largely created and is maintained by photosynthesis. But in the oceans, SAR11 is a partner in this process, recycling carbon and producing the nutrients needed for the algae that produce about half of the oxygen that enters Earth’s atmosphere every day.

The bacteria may have been thriving for a billion years or more, but they have the smallest genetic structure of any independent cell and were first discovered by Oregon State scientists in 1990.

The research was published in this week’s edition of the journal Nature.