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Planet Earth

The Gene-Rich, Sex-Poor Rowboat Called Paramecium

By Mara GrunbaumJuly 4, 2011 5:00 AM

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Few organisms rank lower in life than the gelatinous, pond-dwelling paramecium. It consists of one cell, two orifices, and thousands of hairy feet that project from its surface like beard stubble. Yet this seemingly primitive organism is capable of some surprisingly complex behaviors. It can swim 10 times the length of its body in one second, reproduce with and without the help of a partner, and cunningly hunt for food, all of which allow it to thrive in unsalted waters worldwide.

The myth of the simple paramecium was shattered in 2006 when scientists sequenced its genome. They discovered almost 40,000 genes—about twice as many as in a human cell. They also found evidence of epigenetics, a process by which environmental factors can influence gene expression without changing the genes themselves. In mice, for example, researchers have found that a mother’s diet can make her offspring more vulnerable to illness later in life. “Paramecia have the same molecular tools as other organisms,” says Purdue University biochemist James Forney. “Yet their cellular processes are so unusual and eccentric that it forces you to step back and reconsider what is normal.”

paramecium.jpg
Courtesy Nikon Small World/Metropolitan Museum, Rotterdam | NULL

CENTRAL COMMANDScientists believe that sometime in the past 10 million years, paramecia abruptly spliced together two copies of their genome, doubling the number of genes. The boost in genetic information may have given the paramecium a survival advantage by allowing for more beneficial mutations, which drive evolution.

SEXUAL OFFERINGParamecia reproduce asexually, splitting into two identical daughter cells. Yet they still need sex to survive. Asexual division gradually damages DNA, so periodically paramecia dock together, exchange small capsules that hold DNA, and within six hours are reinvigorated with fresh genetic material.

ROWERSThousands of tiny hairs, or cilia, line a paramecium’s outer edge and work like oars to propel it through the water. External electric stimulation can force these oars to change direction. Last year bioengineers at Stanford University exploited this feature with an arcade-style game called PAC-mecium that uses electrical pulses to steer live paramecia through a maze and collect dots.

A HELPING HANDSome paramecia develop mutually beneficial relationships with other organisms. Paramecium bursaria appears green under a microscope because each cell hosts hundreds of chlorella algae that supply the paramecium with sugar and oxygen in exchange for nitrogen and phosphorus. Austrian ecologists recently found that the algae also protect against damaging ultraviolet radiation.

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