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Living off toxic waste: Bacteria that munch on arsenic

Clarification: This paper describes a bacterium that substitutes arsenic for a small percentage of its phosphorus, rather than living entirely off arsenic

Here, Dr. Felisa Wolfe-Simon is taking samples from a sediment core she pulled up from the remote shores of 10 Mile Beach at Mono Lake in California. She uses these samples as starters for cultures to select for interesting microbes that can survive and flourish with high arsenic and no added phosphorus. (Sept 2010)
[Image 2010 Henry Bortman]

Can you imagine eating toxic waste for breakfast? Researchers have discovered a bacterium that can live and grow entirely off arsenic, reports a new study appearing in the December 2 issue of the journal Science Express.

The findings point for the first time to a microorganism that is able to use a toxic chemical (rather than the usual phosphate) to sustain growth and life.

Arsenic is normally highly toxic to living organisms because it disrupts metabolic pathways, but chemically it behaves in a similar way to phosphate.

Mono Lake, located in eastern California, is boarded to the west by the Sierra Nevada Mountains. This old alkaline lake is known for unusual tufa formations rising from the water's surface (shown here) as well as its hypersalinity and high concentrations of arsenic. (Sept 2010)
[Image 2010 Henry Bortman]

Scientists have previously found organisms that can chemically alter arsenic; and these organisms have been implicated in ground water poisoning events in Bangladesh and other places in Asia when people have shifted to using borehole or well water to avoid cholera.

Now, Felisa Wolfe-Simon and colleagues at the NASA Astrobiology Institute have found a bacterium able to completely swap arsenic for phosphorus to the extent that it can even incorporate arsenic into its DNA.

The salt-loving bacteria, a member Halomonadaceae family of proteobacteria, came from the toxic and briny Mono Lake in California.

In the lab, the researchers grew the bacteria in Petri dishes in which phosphate salt was gradually replaced by arsenic, until the bacteria could grow without needing phosphate, an essential building block for various macromolecules present in all cells, including nucleic acids, lipids and proteins.

Using radio-tracers, the team closely followed the path of arsenic in the bacteria; from the chemical's uptake to its incorporation into various cellular components. Arsenic had completely replaced phosphate in the molecules of the bacteria, right down its DNA.