The announcement that NASA experimenters had found a bacterium that seems to be able to subsist on arsenic in place of phosphorus — an element until now deemed essential for life — set off a cascading storm of criticism on the Internet, first about alleged errors and sloppiness in the paper published in Science by Felisa Wolfe-Simon and her colleagues, and then about their and NASA’s refusal to address the criticisms.

The result has been a stormy brew of debate about the role of peer review, bloggers and the reliability of NASA, at least as it pertains to microbiological issues, almost as toxic as the salty and arsenic waters of Mono Lake in California, from which Dr. Wolfe-Simon of the U.S. Geological Survey scooped up some bacteria last year.

Seeking evidence that life could follow a different biochemical path than what is normally assumed, Dr. Wolfe-Simon grew them in an arsenic-rich and phosphorus-free environment, reporting in the paper and a NASA news conference on Dec. 2 that the bacterium, strain GFAJ-1 of the Halomonadaceae family of Gammaproteobacteria, had substituted arsenic for phosphorus in many important molecules in its body, including DNA.

But the ink had hardly dried on headlines around the world when microbiologists, who have been suspicious of NASA ever since the agency announced that it had found fossils of microbes in a meteorite from Mars in 1996, began shooting back, saying the experimenters had failed to provide any solid evidence that arsenic had actually been incorporated into the bacterium’s DNA.