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Living off Toxic Waste—Bacteria Swap Out Phosphorus for Arsenic

A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus

Researchers have discovered a bacterium that can live and grow off arsenic, a new study reports. 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.

The study is being published online 2 December at the ScienceExpress Web site.

Arsenic is normally highly toxic to living organisms because it disrupts metabolic pathways, but chemically it behaves in a similar way to phosphate. 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 of the NASA Astrobiology Institute and the U.S. Geological Survey and colleagues 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 of the 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.

These findings are of interest to NASA's astrobiology program, because they suggest that the requirements for life’s basic building blocks may be more flexible than previously thought. Earlier this week, a related announcement from NASA referencing the search for extraterrestrial life sparked a round of Internet speculation about whether such life had been discovered. Though these rumors were erroneous, the new bacteria are nonetheless exciting for their significance to biology.

Nadia Ramlagan and Kathy Wren

2 December 2010 AAAS News Release

Science Magazine Science DOI: 10.1126/science.1197258

Felisa Wolfe-Simon1,2,*, Jodi Switzer Blum2, Thomas R. Kulp2, Gwyneth W. Gordon3, Shelley E. Hoeft2, Jennifer Pett-Ridge4, John F. Stolz5, Samuel M. Webb6, Peter K. Weber4, Paul C. W. Davies1,7, Ariel D. Anbar1,3,8 and Ronald S. Oremland2

ABSTRACT: Life is mostly composed of the elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. Although these six elements make up nucleic acids, proteins, and lipids and thus the bulk of living matter, it is theoretically possible that some other elements in the periodic table could serve the same functions. Here, we describe a bacterium, strain GFAJ-1 of the Halomonadaceae, isolated from Mono Lake, California, which substitutes arsenic for phosphorus to sustain its growth. Our data show evidence for arsenate in macromolecules that normally contain phosphate, most notably nucleic acids and proteins. Exchange of one of the major bioelements may have profound evolutionary and geochemical significance.

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Comment by Dr. Aamir Mustafa on December 14, 2010 at 10:31pm

you are welcome.

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