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More on Mono Lake bacteria

Following up on Friday’s post on the arsenic-eating bacteria of Mono Lake, John Roth weighed in with some sceptical comments. Roth is Distinguished Professor of Microbiology at UC Davis, and one of the nation’s leading experts on bacterial genetics. The data presented just don’t support the claim that GFAJ-1 bacteria are not only tolerating arsenic but using it instead of phosphorous in their metabolism, he says.

“The main problem is that arsenate is so similar to phosphate that you can’t buy it without contaminating phosphate — enough phosphate to permit slow growth,” Roth said in an email.

The mass spectroscopy data in the Science paper shows just 3 percent arsenate and 97 percent phosphate in the bacteria grown supposedly without phosphate, Roth notes.

“I’d say all of the reported data are consistent with cells that tolerate but do not incorporate any arsenate. When these cells grow slowly on limiting amounts of contaminating phosphate and they derepress their phosphate transporters and mistakenly pump in lots of arsenate. The whole-cell composition would reflect these internal pools of free arsenate, even with no arsenate involved in metabolites.”

Roth is also sceptical of claims that GFAJ-1 is an obscure survivor of a primitive group of bacteria dating back to the first appearance of life on Earth.

“The cells tree out as recently diverged from standard lineages (including E. coli). Thus this is not some ancient life form and it is living in direct contact and competition with standard forms, rather than derived from some cryptic refugium where arsenate is critical. It’s living in an environment that has plenty of phosphate.”

The story could turn out to be a major embarrassment for the journal and for NASA, Roth predicted.

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