CORNELL—Listed in the Guinness Book of World Records as “the world’s toughest bacterium,” Deinococcus radiodurans can withstand harsh conditions, lack of nutrients, and a thousand times more radiation than a human being. Now researchers think they’ve identified the ace up its sleeve.
A new study by Cornell University researchers reveals that nitric oxide—a gas molecule used in many metabolic processes in animals and a pollutant in the atmosphere that leads to smog—plays a key role in D. radiodurans’ recovery when exposed to ultraviolet radiation (UV).
The study, published in the Proceedings of the National Academy of Sciences, may have implications for why and how nitric oxides act as signals in mammals for cell-to-cell communication, dilation of the vascular system and activating the immune system; in bacterial responses to antibiotic treatments; and in food safety efforts as D. radiodurans appears in some canned foods. The organism is also studied for use in environmental cleanup of sites contaminated with radiation and toxic chemicals.
Brian Crane, an associate professor of chemistry and chemical biology, and colleagues at Cornell discovered a gene in D. radiodurans that, when exposed to UV radiation, increases production of an enzyme responsible for creating nitric oxide. They then engineered bacteria without this gene. When zapped by radiation, the engineered bacteria repaired themselves but failed to grow and proliferate.
“Bacteria are much more sensitive to radiation damage when nitric oxide is not there,” says Crane, the paper’s senior author. “If you block the nitric oxide signal, the cell will repair but [will] not divide,” Crane adds.
In addition, the researchers were surprised to find that removing nitric oxide increased sensitivity to radiation but had no effect on the bacteria’s ability to withstand other stressors, including exposure to oxidative damage that leads to toxic free radicals.
They also found that under normal circumstances there is a time lag in the process, where radiation exposure induces the cell to repair itself, but it takes a few hours for these bacteria to produce nitric oxide, which then activates a gene involved in cell proliferation and stress responses.
“Nitric oxide seems to coordinate this growth response, but it’s curious that the bacteria will wait to grow until they have repaired themselves,” says Crane. “We don’t know why it works this way, but there are analogies in human cells [for other processes]. There may be related pathways for controlling cell growth in animal cells.”
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