We all saw the hype. So, now, what’s actually going on? In a nutshell, there are certain chemicals that are—based on everything we know about life on Earth—assumed to be necessary for the development of life anywhere. When scientists talk about which planets could harbor life, part of what they’re basing that speculation on is the presence of these chemicals. At the same time, though, scientists do have active imaginations, and have long cherished the possibility that Earth life (as we know it) isn’t necessarily the same thing as life, itself.

This new paper, set to be published in Science, might be the first evidence of weird life in action. (Quick clarification, though. This is not evidence of a shadow biosphere or Second Genesis on Earth. More on that below.)

A couple of years ago, scientists found bacteria in California’s Mono Lake that used arsenic compounds, rather than water, as an ingredient of photosynthesis. In fact, there’s been a lot of weird life research centered around Mono Lake. Hot, salty, low in oxygen, and high in lots of other useful chemicals, the Lake has been described as a here-and-now model of the old primordial soup. (It also tastes terrible, as you can see around 4:00 minutes into the video I linked above.)

This new study is different, in that it is trying to show that certain bacteria can not only eat arsenic, they can use it in their DNA—completely replacing phosphate, which is one of those chemicals we thought was necessary for life to happen.

Wolfe-Simon and her
colleagues collected mud from the lake and added the samples to
an artificial salt medium lacking phosphate but high in
arsenate. They then performed a series of dilutions intended to
wash out any phosphate remaining in the solution and replace it
with arsenate. They found that one type of microbe in the mix
seemed to grow faster than others.

The
researchers isolated the organism and found that when cultured
in arsenate solution it grew 60% as fast as it did in phosphate
solution — not as well, but still robustly. The culture did
not grow at all when deprived of both arsenate and
phosphate.

When the researchers added
radio-labelled arsenate to the solution to track its
distribution, they found that arsenic was present in the
bacterium’s proteins, lipids and metabolites such as ATP and
glucose, as well as in the nucleic acids that made up its DNA
and RNA. The amounts of arsenate detected were similar to those
expected of phosphate in normal cell biochemistry, suggesting
that the compound was being used in the same way by the
cell.

The team used two different
mass-spectrometry techniques to confirm that the bacterium’s
DNA contained arsenic, implying — although not directly
proving –that the element had taken on phosphate’s role in
holding together the DNA backbone. Analysis with laser-like
X-rays from a synchrotron particle accelerator indicated that
this arsenic took the form of arsenate, and made bonds with
carbon and oxygen in much the same way as phosphate.

Not everybody agrees
that this research proves the bacteria are capable of replacing
phosphate with arsenic. You
can read more about that debate in the really nicely
done article at Nature News that I’m
quoting above.

Also, even if this is proof
that phosphate isn’t necessary for life, we still don’t know
whether the bacteria in question actually replace their
phosphate in the wild. Right now, this is something humans are
convincing it to do in a petri dish. That’s why it’s not
entirely fair to say that weird life has been
discovered—all this paper does (if it stands up to
the coming onslaught of scrutiny) is show that weird life is,
in fact, possible.

But
that’s still a pretty big deal. However you slice it, this is
an extremely interesting little bacterium. It isn’t alien. It
still has the same basic DNA structure we all know and love. It
just might be able to use different chemicals to build that
old, familiar structure. And that’s pretty cool on its own.

There are some implications when you start
thinking about how said bacterium might expand the list of
planets that could potentially harbor life. That, I can only
assume, is what got NASA’s press release writers so excited to
begin with. However, as far as astrobiology goes, what we have
here isn’t an answer, so much as it is a prompt for a lot of
other really interesting questions.

Nature
News:
Arsenic-eating microbe may redefine chemistry of
life

A
Bacterium That Can Grow by Using Arsenic Instead of
Phosphorous in the journal Science (Not available
yet, but should be later this afternoon, they tell
me.)

(Thanks to David
Dobbs, Lee
Billings and Adam
Rutherford for their help putting this together.
Rutherford, by the way, is the guy drinking Lake Mono water in
the video. He says, “I had to drink about 18 cups of Mono Lake.
I can exclusively reveal it tastes bloody
awful.”)