Most students taking an introductory biology class learn that there are five or six kingdoms of living things: animals, plants, fungi, protozoans, and either one or two kingdoms of bacteria.
But biotechnology is providing the weapons to overthrow the simplistic view of the tree of life. A new study of molecular variation in the single-celled organisms of the deep-sea hydrothermal vents has found previously unknown creatures, and their identy is a mystery.
A team of researchers from the Université Pierre et Marie Curie in Paris sampled microbial communities from hydrothermal vents 2,000 meters deep at two locations in the Mid-Atlantic Ridge near the Azores. They extracted DNA, the molecule on which genes are located, from the samples and looked at variation in the genetic coding for a subunit of ribosomes an organelle required by organisms for the manufacture of proteins without which life cannot survive. They focused on eukaryotic organisms those whose cells have DNA enclosed within a membrane-bound nucleus rather than floating freely in the cytoplasm.
The researchers found that some of the eukaryotic organisms consisted of two groups: alveolates, the group that includes formanifera and dinoflagellates; and kinetoplastids, flagellated protozoans that feed on bacteria. In addition they found unknown clusters of organisms that might correspond with new kingdoms. The study was published online in the Proceedings of the National Academy of Sciences.
"We are just beginning to discover a huge diversity of eukaryotes that has remained hidden . . . until now," says Purificación López-Garcia, lead author on the paper. "Therefore, we are just realizing that deep-sea ecosystems are far more complex than what we thought, and this may have consequences in global cycling of matter in oceans, which in turn is important for the whole terrestrial ecosystem." Another significant finding, she says, was that these organisms were found in extremely high temperatures, and were exposed to gases and concentrations of metals thought toxic to most eukaryotes.
"What these guys have done is to use a perspective that hasn't been around for very long to identify microbial organisms without having to culture them," says Norman Pace, a researcher at the University of Colorado and a pioneer in using ribosomal gene sequences to determine the relationships among groups of species.
Pace says that most of what we know about microbial organisms comes from species that can be cultured in the laboratory but that only a small fraction of microbes can be successfully cultured. He likened our current understanding of the microbial biology to what one might learn from a visit to the zoo.
"If our entire understanding of biology was based on a visit to the zoo, we wouldn't know much about biology," he says. But advances in biotechnological techniques are reducing the level of ignorance. "For the first time ever, we have access to the natural history of the microbial world."
López-Garcia believes the research sheds light on another important
question: the origins of eukaryotes. "Marine hydrothermal systems were
much more widespread in the early Earth," she says. "So we also think
that the study of eukaryotes living in these environments could lead to the
discovery of primitive eukaryotes or 'living eukaryotic fossils.'"
Geotimes contributing writer
Proceedings of the National Academy of Sciences