NASA scientists have found a new form of bacteria that they say has changed their notion of life as we've known it.

Researchers said during a press conference Thursday that they found a strange microbe in Mono Lake, California. Unlike every other known micro-organism, this bacteria is able to survive and reproduce using arsenic, a toxic chemical.

It's a matter of substitution, according to Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow. The microbe, dubbed strain GFAJ-1, is able to substitute arsenic for phosphorus, a more standard element of living biology, in its cell structure.

"It's a microbe doing something different than life as we've known it," said Wolfe-Simon. "We've cracked open the door for what could be different life elsewhere. What else might we find? What else might we want to look for?"

Today's news will push back most of the speculation that has been rampant on the Internet since NASA announced several days ago that it would have an astrobiology announcement Thursday. Online stories and blogs overflowed with rumours of NASA finding alien life and real life extra terrestrials.

The announcement wasn't about alien life but, instead, focused on a different form of life right here on Earth.

The scientists were quick to note that this discovery of an alternative biochemistry makeup will force changes to be made to biology textbooks. It also will expand the scope of the search for life beyond Earth.

"The definition of life has just expanded," said Ed Weiler, NASA's associate administrator for the Science Mission Directorate. "As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely and consider life as we do not know it."

Building blocks of life

The issue here focuses on the fact that until now, life as it is known requires particular chemical elements and excludes others.

The six basic building blocks of all previously known life forms are carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. And phosphorus is a piece of the chemical backbone of DNA and RNA, which are the structures that carry genetic instructions for life.

Phosphorus, which aids in carrying energy in all cells, is considered an essential element for all living cells.

However, arsenic, which is chemically similar to phosphorus but disrupts natural chemical reactions inside cells, is poisonous for most life on Earth.

"We know that some microbes can breathe arsenic, but what we've found is a microbe doing something new, building parts of itself out of arsenic," said Wolfe-Simon. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?"

Scientists noted that the discovery will lead to further research into the organic chemistry, the Earth's evolution and disease mitigation.