CALIFORNIA (Reuters) - One of the smallest organisms on the planet could soon be used to combat a looming global food crisis.

Scientists in California hope genetically engineered micro-algae could be the food of the future, and they've taken a step closer to that reality with an outdoor field trial approved by the US Environmental Protection Agency.

The scientists inserted two genes into the algae - one a fluorescent protein to make the tiny organisms visible and a second to change their fatty acid profile.

"The world, in fact, is not short of calories. What they're short of is proteins and essential fatty acids. And that's the thing that algae naturally accumulate," said Stephen Mayfield, professor of biology and algae geneticist at the University of California San Diego.

The field trial showed that the genetically modified algae can be successfully cultivated outdoors without damaging the native algae populations that produce much of the oxygen on earth.

According to a recent report by the Food Security Information Network, global food crises are worsening, with conditions likely to deteriorate further this year in some areas.

The researchers hope algae, which can be grown on non-arable land with nothing but sunlight, air and water, can help meet the ever-increasing demand for food and alleviate the risk of famine.

"For us, you know, the world's a pretty good place. I can go and I can buy a hamburger, I can go and buy fish, I can go and buy anything I want. It's getting more expensive every year but, by and large, it hasn't really impacted us yet. But for the bottom three billion people on the planet that's not really an option. So, algae gives us an opportunity to produce protein and greatly reduce costs with a much smaller environmental footprint," said Prof Mayfield.

And that, say the researchers, could help feed a growing population while protecting the planet at the same time.