The arsenic is important because it takes the place of phosphorus, one of the six elements considered essential for life.
(The others: carbon, oxygen, nitrogen, hydrogen and sulfur.)
The big picture: the discovery means organisms can exist in the universe -- or even here on Earth -- using biochemical processes beyond the scope of currently accepted science.
In other words, it's as if we suddenly realized there were 27, not 26, letters of the English alphabet: all sorts of possibilities exist that didn't before.
The bacteria, taken from the bottom of Mono Lake in California, was grown in the lab using a mixture containing arsenic. A research team led by NASA astrobiology fellow Felisa Wolfe-Simon observed the bacteria slowly swap atoms of phosphorus for those of arsenic.
To date, no bacterium has been observed without the six basic elements.
From a chemical standpoint, arsenic is related to phosphorous, which plays a key role in how organisms store energy. It's directly beneath phosphorus on the periodic table of elements, sharing several properties.
The discovery resonates with NASA's space missions seeking extraterrestrial life, which until now filtered out information about chemical reactions that didn't adhere to commonly-accepted expectations about what defines life.
In effect, it means we may have to revisit previous searches for life and broaden the scope.
The researchers will publish their findings Friday in Science.
This post was originally published on Smartplanet.com