Humble Bacteria Found to Possess Precision Clocks
Michael Schirber
July 01, 2004

It sounds like the beginning of a joke: "How do bacteria know what time it
is?" The surprising answer, reported today in Nature, is that some of these
single-celled entities actually have internal clocks.

In a living organism, changes in gene expression, physiology and behavior
that follow the cycle of day and night are called circadian rhythms. This
oscillation is well known to occur in various mammals, insects, plants and
fungi. But in recent years researchers have discovered that some
single-celled organisms, too, display circadian rhythms. Irina Mihalcescu of
the University Joseph Fourier in Saint Martin d'Heres, France, and her
colleagues studied cyanobacteria, or blue-green algae, that had been
engineered to light up when a particular regulatory gene turned on. By
observing the pattern of illumination under a microscope, the scientists
could measure the internal clockwork of individual bacteria.

Previous research had found that these photosynthetic bacteria keep a daily
schedule even without stimuli from the outside world. Mihalcescu and her
co-workers found that, under such constant conditions, the bacteria
maintained a specific rhythm even following cell division--that is, the
clock-setting was passed on to subsequent generations. To determine whether
intercellular interactions influence this synchronicity, the team grew two
cell colonies shifted in time by three hours--like New Yorkers and
Californians. When the scientists combined the bacteria, individuals
resisted changing their clocks even when butting up against those from a
different time zone.

Such resiliency in internal timing is not seen in more complex single-celled
organisms, nor in mammalian nerve cells. Instead, isolated cells of these
nonbacterial organisms tend to "have rather 'sloppy' daily oscillations,"
writes Carl Hirschie Johnson of Vanderbilt University in an accompanying
commentary. "Cyanobacterial clocks can dance alone with high precision."

>From NewScientist
Posted by
Robert Karl Stonjek.
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