"Sex Cells"

December 17, 2004

"Sex Cells"

by Kristen Loyst

	Dr. Thane Papke (right) looks on as Jeremy Koenig prepares cell samples.

Birds do it. Bees do it. And now, even microscopic Archaea do it.

A trio of Dalhousie researchers has discovered that Halorubrum, a group of bacteria-like organisms that thrive in extremely salty environments, are a promiscuous lot. They've shown that, in nature, these organisms have "sex" and they do it all the time, even between species.

Senior researcher Dr. Thane Papke, graduate student Jeremy Koenig and Dr. W. Ford Doolittle, Canada Research Chair in Evolutionary Biology, all of the Biochemistry and Molecular Biology, have revealed the "sexual habits" of these frisky and mysterious creatures in a paper titled "Frequent Recombination in a Saltern Population of Halorubrum." The paper appears in the 10 December, 2004 issue of the leading American journal Science.

Halorubrum is one genus of Archaea, a category of single-celled organisms similar to Bacteria, although they aren't thought to cause infection.  The name "Archaea" comes from the fact that many of these organisms live in extremely hot or salty environments, much like the conditions on Earth billions of years ago.

	Dr. Thane Papke holds a cell culture teeming with frisky Halorubrum

Before this discovery, Archaean reproduction was believed to be much less titillating. "Normally, we think of Bacteria or Archaea as being asexual- a cell copies its DNA, and then splits in two," says Papke, lead author of the paper. Through this method, occasional gene mutations would be the source of genetic diversity.

However, the researchers have discovered that fragments of genetic material are transferred from cell to cell in a process called recombination-the Archaean equivalent to sex. Not only are Archaea having sex, but they do it quite frequently, resulting in much more genetic diversity than dividing alone. "We basically studied their sexual habits by analyzing their DNA," says Papke. "We've been able to show that Halorubrum use this recombination process frequently, and it generates 43 times more diversity in their DNA than mutation."

There's also evidence that this DNA might be transferred between different species. Papke explains, "We're not certain how they're doing it, but the 36 different organisms we identified as Halorubrum are mixing it up so much that we can't even map out the genes that we've analyzed." Although Doolittle's lab had previously studied Archaeal sex under laboratory conditions, this is the first time researchers have been able to show that it happens in nature, too. Very little is known about Archaea, making this a particularly significant discovery. The researchers hope this will provide a better foundation to understand prokaryotes (Bacteria and Archaea), and how they reproduce and evolve.

This knowledge is also on the cutting edge of biogeography, an emerging field in microbiology. It will be used to compare populations of Archaea found in similar environments throughout the world, to determine if genes are shared between them, or if different populations are evolving separately.

The paper was developed in collaboration with researcher Francisco Rodriguez-Valera at the Universidad Miguel Hernandez in Spain, and with support from Genome Atlantic and the Canadian Institutes for Health Research.