October 13, 2005

New Organism Caught in the Act of Kidnapping Plant

WASHINGTON -- A one-celled creature found on a sandy beach may be in the process of kidnapping and incorporating an even tinier plant to use as a living energy source, Japanese researchers reported on Thursday.

They said the newly discovered organism seems to be in the process of endosymbiosis -- in which one creature incorporates another, creating a new form of life.

Scientists believe this is how many modern plants and animals evolved. They believe the chloroplasts, the green solar power factories inside plants, were originally separate organisms.

Similarly, they believe components of the cells that make up all animals were originally captured microbes.

Writing in the journal Science, Noriko Okamoto and Isao Inouye of the University of Tsukuba said they may be seeing this process in action.

The new creature, which they have dubbed "Hatena" for "mysterious," is a flagellate -- a small organism with a tail that it uses to propel itself.

These creatures can resemble plants or animals, but during one phase of its life it resembles a predator. At another stage, Hatena carry a green, photosynthesizing alga inside. It divides during that phase, giving rise to two daughter cells -- one green and one colorless.

The colorless daughter develops a feeding tool and eventually engulfs another green alga, the scientists wrote.

The green cell, called the symbiont, belongs to a fairly well-known genus of algae called Nephroselmis, and is "abundant in the habitat," the researchers wrote.

It has a flagellum too, but loses this when it is engulfed, and also loses its outside structure, the exoskeleton.

"The symbiont cell retains its nucleus," as well as other key cell components such as mitochondria and the chloroplast, they added.

The green part then enlarges and seems to nourish the predator half, which loses its complex feeding apparatus, the researchers said.

They captured some of the clear, predator-like offspring and fed them other, related strains of Nephroselmis algae.

"Although the prey was engulfed and remained undigested, it did not undergo the modifications described above, suggesting a highly strain-specific interaction," they wrote.

Now they have to see if the two species have traded genes, considered an important step in the evolution of modern plants and algae.