Extremophile genomes yielding clues to earliest life

[编者的话]

一种极其古老的生活在极端环境中的生物的基因组现在正在被测定，这项研究成果将提供大量信息，在比较基因组学和进化分析研究中都具有重大意义。

by Larry O扝anlon

Bacterial ecologists are closing in on some of the oldest genes in the world. A full genome of one extremophile is soon to be published, and it is already yielding information about "fossil genes," a microbial ecologist announced today in Edinburgh, Scotland.

After recently overcoming the odds and growing a pure culture of the hydrothermal vent bacteria Persephonella marina, researchers are now mapping its genome, announced microbe ecologist Anna-Louise Reysenbach of Portland State University in Oregon. "This could lead to the discovery of some genes left over from Earth first living things," she says.

"kind of like finding some new genus and species that has never been described before," Reysenbach told BioMedNet News in an interview. "It means a lot of new genetic information.

The isolates of Persephonella marina were obtained from hydrothermal vents in the Azores. After arduously separating the bacteria from others and growing a pure culture, the Oregon team recently sent it off to Integrated Genomics in Chicago for sequencing. "The complete sequence is due in a few months," Reysenbach said, during the joint meeting of the Geological Society of America and the Geological Society of London.

Although biotechnology companies are actively culling useful enzymes from such bacteria, they mostly do so with just snippets of genetic information. Few of these organisms have been completely sequenced."Most of the microbes [that are] present in any environment we just don抰 know how to grow," says deep-sea bacterial geneticist Doug Bartlett of the University of California-San Diego抯 Scripps Institution of Oceanography. "In this sense alone the Reysenbach work is already a big accomplishment," he says. "Mapping bacterial lineages is possible only by comparing entire genomes," he notes.

The specific deep-rooted phylogenetic lineage which most interests Reysenbach falls within a small rRNA subunit found in all thermophilic bacteria. That rRNA has been one of the few markers with which researchers can identify these bacteria in the mixed samples that are typically all they have to work with. "The rRNA can also serve as a molecular clock for the age of the genome," says Bartlett.

Persephonella marina belongs to lineage of bacteria known as Aquificales, which occur widely in hydrothermal vents and hot springs. They抮e noted for their flexible metabolisms: they are able to give and take electrons from a range of inorganic compounds. "It抯 this trait, and their ability to withstand extreme physical conditions that makes them good analogs for possible life on other planets ?on Mars or Jupiter抯 moon Europa, for instance," says Reysenbach.

If the genomes of Persephonella marina and other Aquificales species reveal a truly ancient lineage, the modern bacteria may also provide some clues to Earth抯 early carbon budget. Thermophile bacteria today are just as productive as algal mats, which are currently the earliest life known to have left fossil evidence behind.