News & Views item - December 2010

 

 

 Update on the Bacterium That May Be Able to Use Interchangeably Phosphorus and Arsenic. (December 8, 2010)

On December 3 TFW reported on the work of Felisa Wolfe-Simon and her colleagues who reported they have found a bacterium growing in California's Mono Lake able to subsist on the heavy metal arsenic and that the organism can use arsenic to build the backbone of its genetic material, DNA. While there has been considerable hype regarding the discovery and its effect on considering the means of extraterrestrial life forms, the authors, in their  paper are conservative in describing their findings, though rather less so in their fronting of the popular media.

 

Now NatureNews' Alla Katsnelson reports on some of the sober assessments of the findings: "Many readily agree that the bacterium, described last week in Science and dubbed GFAJ-1, performs a remarkable feat by surviving high concentrations of arsenic in California's Mono Lake and in the laboratory. But data in the paper, they argue, suggest that it is just as likely that the microbe isn't using the arsenic, but instead is scavenging every possible phosphate molecule while fighting off arsenic toxicity."

 

Then to some of the expert comments:

 

"It's a great story about adaptation, but it's not ET," says Gerald Joyce, a biochemist at the Scripps Research Institute in La Jolla, California.

 

Steven Benner, a chemist at the Foundation for Applied Molecular Evolution in Gainesville, Florida, notes that the arsenate ion said to replace phosphate in the bacterium's DNA forms bonds that are orders of magnitude less stable.

 

Roger Summons, a biogeochemist at the Massachusetts Institute of Technology: "[The authors] haven't unambiguously identified any arsenic-containing organic compounds, and it's not difficult to do," e.g. the team could have directly confirmed or disproved the presence of arsenic in the DNA or RNA using targeted mass spectrometry.

 

 

Dr Joyce also told  NatureNews that the paper shows that the organisms appear bloated, and contain large, vacuole-like structures — often a sign of sequestered toxic material, and the arsenate-grown cells were analysed in their resting phase, which requires less phosphate for survival than does active growth. In addition cells grown in high concentrations of arsenate did not seem to contain any RNA — possibly because RNA production had shut down to conserve phosphate. One calculation in the paper showed that the DNA in arsenate-grown cells actually contained 26 times more phosphorus than arsenic.

 

Rosemary Redfield, a microbiologist at the University of British Columbia in Vancouver, Canada said, "I fault the authors for not noticing these things and sorting them out; we shouldn't have to do the thinking for them."

 

In rebuttal Felisa Wolfe-Simon has said: "We are not going to engage in this sort of discussion. Any discourse will have to be peer-reviewed in the same manner as our paper was, and go through a vetting process so that all discussion is properly moderated."

 

But this didn't sit well with Jonathan Eisen, a microbiologist at the University of California, Davis, who called the repost "ludicrous", after a NASA press release drew media attention with claims of an "astrobiology finding that will impact the search for evidence of extraterrestrial life", a theme that Dr Wolfe-Simon echoed at the briefing. "It is absurd," Professor Eisen said, "for them to say that they are only going have the discussion in the scientific literature, when they started it."