The rhythm of bacteria

Everybody has got rhythm, that is. From the most multicellular of creatures (humans included) to single-cell bacteria, many organisms display activities and behavior that oscillate precisely with daily cycles of light and dark. Almost nobody has perfect rhythm. In a multicellular organism, the clocks of individual cells may be slightly out of time. Communication among cells, however, allows them to synchronise so that the organism’s precise rhythm is maintained.

But what about bacteria? Colonies have been shown to have precise cycles by which genes express certain compounds. But is that because communication adjusts the variations among individual organisms? Or are the individual clocks more accurate?
Dr. Irina Mihalescu of Joseph Fourier University in France has answered that question, at least for a certain kind of bacteria – cyanobacteria, or blue-green algae. These organisms, she and colleagues report in the journal Nature, are like Swiss watches. Their rhythms are extremely precise. 

Dr. Mihalescu used cyanobacteria that had been altered to glow when certain genes expressed enzymatic compounds. Since this activity was related to rhythm, measuring the luminescence would show how precise the overall cycle was. The problem was detecting the glow from just one cell, something that had never been done. “I didn’t know it was impossible”, she said.

Dr. Mihalescu, a physicist by training, used a highly sensitive digital camera. Each cell produces so few photons that a special low-noise image-sensing chip, called a charge-coupled device, had to be used. An ordinary chip would have had too much background noise, corrupting the signal from the cell. Her results showed a stable rhythm that didn’t vary from cell to cell, or, for that matter, from parent cell to offspring as the bacteria reproduced.
“We didn’t expect the level of a single cell to be so stable”, she said. Her next goal, she added, “is to try to determine what gives the clock this stability”.

The New YorkTimes, 6 July 2004


1. Single-cell bacteria
A. have no rhythm.
B. exhibit activities that are linked to the daily cycle of light and dark.
C. have mechanical clocks inside them.
D. are largely inactive.

2. According to Dr Irina Mihailescu and her colleagues, blue-green algae
A. have very precise rhythms.
B. have irregular rhythms.
C. are not worth studying.
D. inhabit enzymatic compounds.

3. To study cells, Dr Mihailescu made use of
A. a digital watch.
B. a low-noise camera
C. a charge-sensing device.
D. a digital camera.

4. Dr. Mihailescu has shown that the rhythm of cyanobacteria
A. tends to vary from parent cell to offspring.
B. never varies from parent cell to offspring.
C. is altered by reproduction.
D. none of the above.

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