But Johnson and Mukhopadhyay could not find any sign of such ability in the DNA sequence data for methanogens. "It was clear that either the ancient sulfite detoxification has been lost or it is not recognizable because it is unlike any known system," Mukhopadhyay said.
The challenge of the latter possibility attracted the group to the topic. They decided to see if methanogens that live in an environment where the early earth conditions are preserved ?deep-sea hydrothermal vents ?still have the ancient detoxification system.
Inside a hydrothermal vent, sulfide-containing superheated water at 350 C (662 F) mixes with cold oxygen-containing water, creating cooler environments -- 48 to 94 C (118 to 200 F) -- where M. jannaschii can thrive. "This sulfide-oxygen mixture can also generate sulfite. Therefore, M. jannaschii experiences conditions that existed on early earth," Mukhopadhyay said.
He knew that Lacy Daniels, his mentor at the University of Iowa, and Negash Belay, a colleague during his graduate studies, had found sulfite assimilation ability in an organism closely related to M. jannaschii, but had not investigated how that organism handled the sulfite toxicity. Putting all these pieces of information together, Johnson and Mukhopadhyay hypothesized that M. jannaschii has a sulfite-reducing enzyme and began to search for this system.
Protein analysis of M. jannaschii from sulfite-free and sulfite-enhanced environments revealed that M. jannaschii tolerates sulfite and even uses it as a sulfur source by expressing an enzyme not seen previously. The enzyme, which is located on the cell membrane, converts toxic sulfite into