Aliens? Brand New Lifeform? Scientists Debate Odd Finding

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A scientific tiff went public Friday as the journal Science took the unusual step of publishing challenges to a report about a strange, arsenic-eating bacteria.

The authors of the study stood their ground, saying they still consider their interpretation of the research viable.

In the report published in Science last year, researchers led by Felisa Wolfe-Simon of NASA's Astrobiology Institute said they discovered bacteria that can substitute arsenic for some of the phosphorous in its diet. While the discovery was made on Earth, they said it shows that life has possibilities beyond the major elements that have been considered essential.

Six major elements have long been considered essential for life: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Arsenic is toxic mainly because its chemical behavior is so similar to that of phosphorus and some organisms have a hard time telling these elements apart. But once ingested, arsenic is different enough that it can disrupt the body's chemistry.

The bacteria were discovered in a California lake where there is a high concentration of arsenic and the researchers concluded that while it grows better with phosphorous it was able to substitute some arsenic successfully.

In one challenge, Patricia Foster of Indiana University pointed out that bacteria have two systems for assimilating phosphorous. Foster said the researchers inadvertently shut off one system when they grew bacteria in high-arsenic concentrations, increasing the capacity of the other.

Wolfe-Simon and colleagues responded that, in that case, a modified form of arsenic would appear and that did not happen.

In another challenge, James B. Cotner of the University of Minnesota and Edward K. Hall of the University of Vienna, Austria, argued that the microbes might simply have been able to live on very low levels of phosphorous. But Wolfe-Simon responded that the particular cells Cotner and Hall referred to actually had relatively high phosphorous levels.

Overall, Wolfe-Simon and colleagues said they "welcome the opportunity to better explain our methods and results and to consider alternative explanations."

Other newly published challenges came from Steven A. Benner of the Westheimer Institute for Science and Technology in Gainesville, Florida; Istvan Casbai of Johns Hopkins University and Eors Szathmary of the University of Budapest, Hungary; Rosemary Redfield of the University of British Columbia; David w. Borhani of Hartsdale, NewYork; Barbara Schoepp-Cothenet of the National Center for Scientific Research in Marseille, France; and Stefan Oehler of the Biomedical Sciences Research Center in Vari, Greece.