Wetenschap - 2 december 2010

Extra-terrestrial life more likely? Rubbish

NASA has discovered micro-organisms in a lake full of toxic arsenic. The space agency claims that this increases the likelihood that there is life on another planet. But the chances of that were already very big, says professor of Microbiology John van der Oost.

Has new life really been discovered?
‘I don’t think they have discovered a new species. It seems to me that this is an adaptation of an existing form of life, a known micro-organism that has adapted itself to extreme conditions.’

Why is arsenic toxic?
‘Arsenate, a form of arsenic, shows a strong resemblance to phosphate in chemistry and structure. Phosphate is the backbone of RNA and DNA. You can see it as the link between DNA building blocks.
If a ‘normal’ organism comes in contact with arsenic, arsenate in the DNA gets into that backbone. But it cannot be converted by enzymes, so the system eventually comes to a standstill and the organism dies.’

What has been discovered now?
Apparently, in the ‘new’ species, under circumstantial pressure, mutants came into being which can convert that arsenate using enzymes. What this suggests is that these organisms are more flexible than we thought. I see that as evidence that we should keep an open mind about the possibilities.’

NASA says it has become more likely that there is extra-terrestrial life.
‘That’s rubbish, if you ask me. The chances of that were already big. More and more planets are being discovered with similar conditions to those on earth. Life on earth is based on carbon. Just as with arsenate and phosphate, it seems more likely now that there are places where life is based on silicon.’

Van der Oost worked earlier on an edition of VPRO’s programme Labyrinth. After it was broadcast, he twittered about microbes under extreme conditions.