Researchers have discovered a strange microbe that can use arsenic as a nutrient, a finding they say could change how scientists search for new life forms on Earth and elsewhere.

Until now, six major elements -- carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur -- were considered essential for life. The discovery of the new bacterium throws that assumption on its head.

"This organism has dual capability. It can grow with either phosphorous or arsenic. That makes it very peculiar, though it falls short of being some form of truly 'alien' life," said Paul C. W. Davies of Arizona State University, one of the co-authors of the report published in Thursday's online edition of the journal Science.

Researchers discovered the bacteria, dubbed GFAJ-1, in arsenic-heavy Mono Lake, Calif. They found it could substitute arsenic for phosphorous and continue to grow.

"It makes you wonder what else is possible," said Ariel D. Anbar of Arizona State University, another of the report's co-authors.

Anbar said the discovery could help scientists to recognize and identify new life forms both on Earth and on other planets.

In the study, researchers exposed the bacterium to higher and higher concentrations of arsenic, and found that it could adapt to the changing conditions and continue to grow.

The microbe grows more quickly using phosphorous, but the substitution with arsenic suggests that life forms that feed off arsenic could occur naturally.

Researchers held a news conference at 2 p.m., hours after NASA set the Internet abuzz by saying an announcement was imminent that would "impact the search for evidence of extraterrestrial life."

Jay Ingram, co-host of the science program "Daily Planet," said that while the discovery of bacteria that can grow using arsenic is significant, he said it wasn't entirely unexpected.

"In some ways it's not quite as dramatic maybe some people have been saying. Of course arsenic is poisonous to us, but the chemistry of arsenic isn't all that different… from that of phosphorous," he said.

"People have imagined for several years that, you know, in the right circumstances you might get forms of life that might substitute arsenic for phosphorous."

The research was funded by NASA, the Department of Energy and the National Institutes of Health.

If its findings are confirmed, it may prompt scientists to use chemical-detecting instruments that are "a little bit more ‘open-minded' about finding forms of life," Ingram said.

"Microbes on earth have proven themselves to be incredibly adaptable. You can only imagine that life on other planets where conditions are dramatically different, must be enormously adaptable as well," he said.

"I think it opens the door to possibilities that up till now we haven't considered."

With files from The Associated Press