NASA-funded researchers announced today that they've found bacteria from Mono Lake that can maintain life without the presence of phosphorus. Let me count the number of ways that this could be confusing without some context.
First, Mono Lake. One of the oldest lakes in North America, the lake was pretty standard until Los Angeles started draining it for water back in the 40s. The surface of the lake dropped over 40 feet between then and 1995 and the result is a very salty, high pH body of water. If you recall a bit of high school biology, regular drinkable water has a pH of 7 which is considered neutral. As the pH is closer to zero, a substance is more basic and a pH closer to ~13/14 is more alkaline. Both of these conditions make it hard for normal life to thrive.
Despite being a particularly difficult place to live, it's not an impossible place to live and there are plenty of flies and shrimp that make Mono Lake their home. Bacteria are present as well, but nothing that was, until recently, noticed as out of the ordinary.
Because of Mono's interesting chemistry, researchers figured that bacteria there would be hardier under certain stressful conditions so they collected a random sampling of Mono Lake bacteria and did some testing. One test was designed to strip all the phosphorus out of the environment and replace it with arsenic.
Arsenic, as you may know, is toxic to most living organisms specifically because it acts quite a bit like phosphorus. Chemically, arsenic has a very similar structure to phosphorus and so if you get some arsenic in your system, your cellular functions that expect phosphorus are getting arsenic and that's where things go south.
Back to the bacteria. Despite the phosphorus-poor and arsenic-rich environment, a certain bacteria did pretty well living there - about 60% as well as they do in an environment with normal levels of phosphorus. For something that you expect to survive at a rate of 0%, 60% is pretty damn good.
The interesting part here is the absence of phosphorus. Phosphorus is one of a select few elements that biologists believed was crucial to life as we know it - every living thing was supposed to require all of these elements. To have bacteria that can use arsenic instead of phosphorus to survive is quite a revelation to astrobiologists, i.e. people who look for life elsewhere in the universe.
This may not be the most radical change of how we define life but it does change our expectations. If life can survive by replacing phosphorus with arsenic, what about replacing carbon with silicon? Life elsewhere in the universe is bound to be weird and different, this may be a glimpse in just how weird and different.