Humans and other mammals are remarkably sensitive to acute doses of ionizing radiation
(IR) (eg, x and γ rays, neutrons, and α and β particles) [
], in that a whole-body exposure of just 5 Gy is lethal; the gray (Gy) is the amount
of energy absorbed by a tissue or substance and applies to all types of radiation.
Low-dose chronic IR is a well-established human carcinogen and is omnipresent on Earth.
Background sources of terrestrial IR include radioisotopes present in essentially
all materials in the environment and cosmic sources, including the sun and extremely
distant galactic events, such as supernovae. Collectively, these natural sources of
IR deliver only about 0.0024 Gy/y [
[2]
]. In this context, the evolution of bacteria that are able to grow under high-dose
chronic IR (60 Gy/h) [
[3]
] or survive acute irradiation exposures [
[4]
] of 15,000 Gy is truly extraordinary given the apparent absence of highly radioactive
habitats on Earth over geologic times. Human-made sources of IR, developed over the
last 60 years, have contributed significantly to low-dose radiation, including occupational
exposures associated with developing and maintaining nuclear weaponry and power sources;
environmental release of radionuclides, such as occurred during atomic bomb tests
during the Cold War (1945–1986); and nuclear power plant accidents, such as in Chernobyl,
Ukraine (1986) [
[5]
]. A recent National Research Council report [
[6]
] concluded that whereas risks of low-dose IR are small, there is no safe level. This
finding has grown stronger over the last 15 years, dismissing the notion that there
is a threshold of exposure to IR below which there is no health threat. Currently,
the most significant, widespread human-made sources of IR are medical devices and
procedures, including diagnostic radiographs and therapeutic radiation. Natural background
IR remains the most significant source of exposure for humans, however, representing
more than 80% of the total dose of a typical resident of the United States [
[6]
]. Although the biological hazards of IR have been evident for a century [
], a clear understanding of the molecular mechanisms underlying IR toxicity and resistance
remains controversial despite decades of molecular research dedicated to this field.
Perhaps paramount, the catastrophic terrorist events of September 11, 2001 underscore
the possibility of radiological terrorism and the pressing need to understand further
how to prevent radiation injury. This article presents a new view of IR-resistance
mechanisms in extremely radiation-resistant bacteria and questions some longstanding
assumptions regarding the causes of IR toxicity. The extrapolation of recent experimental
findings [
[7]
] to the potential development of approaches to modulate radiation resistance is intentionally
speculative, aimed at contributing to the groundwork of new ideas needed to address
the emerging threat of nuclear terrorism.To read this article in full you will need to make a payment
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Article info
Footnotes
“The Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the Department of Defense (U.S. Army, U.S. Navy, U.S. Air Force), the Department of Homeland Security, or other Federal Agencies.”
This work was supported by grant DE-FG02-04ER63918 from The United States Department of Energy under the Environmental Remediation Sciences Program of the Office of Biological and Environmental Research.
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