Текст 7 bugs shed light on the ozone

Meriel Jones examines the use of bacteria to measure UV rays hitting the planet's surface

ONE vital aspect of depletion of the ozone layer is its effect on the planet's surface. Concern is now focusing on the increased levels of ul­traviolet light, but there are difficulties in measuring it. The key thing is to be able to assess its biological activity, not just the amount in cold physi­cal terms.

Ultraviolet is the technical term for light in quite a wide band at the blue end of the spectrum, and it is not all the same when it comes to liv­ing creatures. Some regions produce suntans, while other parts cause serious damage to tissues.

In hospitals, operating theatres can be bathed with lethal wave­lengths of this light to kill germs floating around before an operation.

Researchers know they need a system based on some living or­ganism to measure what type of UV is reaching the ground and have experimented with several systems. A group of Germans, working at the Institute for Aerospace Medicine in Cologne, has come up with a system that worked well in the laboratory and which the scientists are now test­ing in Antarctica.

Lothar Quintem and his colleagues are exploiting a group of bacte­ria which have the unique ability to change into a dormant form called a spore if the cell starts to run out of food. It is a protective mechanism and the resting spores can withstand more extreme conditions than the growing cells while waiting for the cue to switch back to normal growth. UV light of the right wavelengths will still kill them.

The scientists stuck a thin layer of millions of these tiny spores on to a polyester film to use as a living UV monitor. To find out the effects of light all they had to do was see how well the spores responded to their usual growth triggers. This involved soaking the film in a solution of nu­trients for a few hours to give the spores the opportunity to resume growth.

After this, the film could be developed with a blue dye where its in­tensity was related to the number of growing cells. If the spores no longer grew, researchers assumed the light had done something nasty to them.

Their laboratory experiments, using beams of pure UV light, gave them confidence that the spores were responding in a predictable way. Shorter wavelength UV light put the spores out of action faster, but even the milder regions did harm.

In fact, the pattern of damage resembled the way DNA absorbs light, which scientists know is one reason why UV light can be so lethal. DNA absorbs this energetic short wavelength light, causing chemical reactions that can irreversibly damage it. Once its DNA is changed, the cell is mutated and will probably die. The Germans' biofilm may help them monitor the effects of the "ozone hole" as well as giving a deeper insight into why it should be taken so seriously.

Meriel Jones, Photochemistry and Photobiology

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