August 15, 2008
Scientists Find Bacteria That Thrives Off Arsenic
Scientists have isolated a bacterium that fuels itself on arsenic in the warm, bubbling pools of Mono Lake in California.
These bacteria combine light and arsenic to make their food and multiply using a chemical that is toxic to most other life forms.
Using arsenic as an energy source was a process used by ancient bacteria, researchers have speculated.
These bacteria are photosynthetic, using sunlight - like plants - to turn carbon dioxide into food, explained Ronald Oremland of the US Geological Survey.
What is different about them is that instead of using water in this process, they use arsenic.
The US-based researchers isolated the bacterium from the lake, which lies at the foot of the Sierra Nevada.
"These lakes are fed by hydrothermal waters that leach out arsenic-containing minerals from the surrounding rocks," said Dr. Oremland.
The researchers noticed that the bacteria had colonized small, hot pools, forming colorful "biofilms".
"We suspected that these bacteria were using arsenic to make a living, so we scraped the biofilms off the rock and studied them under laboratory conditions."
The team showed that the bacteria required both light and arsenic to grow.
Dr. Oremland believes this the first time an organism has been found that can use arsenic to photosynthesize under anaerobic conditions.
Oremland believes it might be an ancient ability in bacteria.
"We think that bacteria were photosynthesizing before oxygen was present in the atmosphere," he said.
A thorough understanding of how bacteria metabolize arsenic could help scientists comprehend its damaging affects inside human cells.
Around 144 million people worldwide are exposed to toxic levels of arsenic in their drinking water.
Arsenic enters the body's cells by diffusion; and once inside, it disrupts how they function by binding to their machinery, inactivating it, and disrupting the way energy is transported.
Exposure over a long period of time can lead to skin disease and kidney and bladder cancer, and it is thought to stunt the intellectual development of children.
The most arsenic-contaminated regions are in India, Pakistan, and China, where soluble arsenic in ground waters is above the World Health Organization's (WHO) suggested maximum safe level of 10 parts per billion.
Dr. Oremland's findings are reported in the journal Science.
Image Caption: South Tufa Area, Mono Lake. Courtesy Wikipedia
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