LOS ANGELES - US researchers have successfully used certain microbes to produce biofuels, opening a door to developing cheaper "green" energy.

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The discovery was made by researchers at the University of California, Los Angeles. The findings were published on Sunday's issue of the journal "Nature Biotechnology."

The work concentrated on tricking microbes into eating protein and using the resulting energy to generate specific proteins that can be refined into fuel, the researchers explained.

This is different from the current biofuel production which is based on plants or microbes that generate fats, oils or carbohydrates that can be refined into biofuel, said Dr. James C. Liao, who took part in the study.

"This research is the first attempt to utilize protein as a carbon source for energy production and biorefining," Liao said. " Complex cellular regulation in nitrogen metabolization had to be rewired."

The researchers said they are now working to take ammonia out of individual cells, allowing the cells to keep their nitrogen.

"Our strategy effectively recycles nitrogen back into the biofuel production process, thus approaching nitrogen neutrality," Liao said.

"Growing algae to produce protein is like putting the interest back to the principal," he said.

The challenge was to trick microbes into using protein for creating fats or other substances that can be refined into fuel, rather than simply producing more protein -- also known as growing, explained Yi-xin Huo, a UCLA postdoctoral student and lead researcher.

"We have to completely redirect the protein utilization system, which is one of the most highly-regulated systems in the cell," Huo said.

This process has a side benefit - developing a new type of fertilizer that would use less nitrogen, dramatically reducing harmful greenhouse emissions generated by the production of fertilizer, the researchers said.

They said this discovery could unleash a new universe of fuel- producing microbes that eat naturally-occurring proteins that are otherwise unfit for animal consumption.