Nasa’s recent ‘arsenic life’ storm in a tea-cup controversy has been reheated to some extent by a new paper that undermines key claims controversially made at the end of last year.
The space agency’s announcement that its researchers had an amazing finding with implications for the search for extraterrestrial life quickly turned sour. Although the discovery of a strain of bacteria called Halomonadacea GFAJ-1 that can apparently use arsenic in place of phosphorous in its DNA was exciting, some complained that it had been hugely overhyped while others questioned the result itself (see: Microbe gets toxic response).
Even at the time it was pointed out that the arsenate ion that was being proposed as a phosphate substitute would be somewhat unstable. The authors of the original work – published in Nature’s rival Science – counter that the bonds in question could be reinforced.
Now a paper in ACS Chemical Biology looks at how stable – or unstable – arsenic DNA would actually be. (The paper came out on the 18th of this month, and has just been highlighted on the In The Pipeline blog.)
Kent Gates, of Cairo University, and his colleagues point out that arsenate and phosphate are in some chemical ways very similar. For example, they form bonds of (roughly) similar strength with oxygen. However, they point out that the phosphate diesters found in normal DNA have a “vastly different” stability in water than their arsenate equivalents.
Although there is little in the way of published data on the matter, they suggest that if exposed to water half the arsenic-based links in the genome of the bacteria in question would be cleaved in less than 0.1 seconds.
“The anticipated instability of the genetic material in an arsenate-utilizing organism would present a serious challenge to cellular operations,” they under-state. “…While some bacteria have evolved mechanisms for protecting their DNA under conditions of stress, overcoming such dramatic kinetic instability in its genetic material would be a significant feat for Halomonadacea GFAJ-1.”