美国国家公共电台 NPR--Think all bacteria are microscopic? Tell that to these centimeter-long monsters（在线收听）

Think all bacteria are microscopic? Tell that to these centimeter-long monsters

Transcript

Bacteria typically live out their teeny-tiny lives in the microscopic realm, but now scientists have found a gargantuan one the size and shape of a human eyelash.

The new find is "by far the largest bacteria known to date," says Jean-Marie Volland of Lawrence Berkeley National Laboratory and the Laboratory for Research in Complex Systems. "These bacteria are about 5,000 times larger than most bacteria."

"To put things into perspective," he added, "it is the equivalent for us humans to encounter another human who would be as tall as Mount Everest."

The roughly 1 centimeter behemoth somehow attaches itself to sunken leaves in Caribbean mangrove swamps, according to a report in the journal Science.

The scientist who initially collected the thin white filaments had no idea that he'd discovered a new kind of bacteria visible to the naked eye.

But a lab examination showed that they didn't have key features of plant or animal cells, and a genetic analysis soon revealed their true nature. They're related to other bacteria that also make a living off of sulfur and grow large — but not this large.

Now called Thiomargarita magnifica, these bacteria haven't yet been grown in the lab, so much about their lifestyle remains mysterious — including what advantage they get in their underwater environment by growing to such a stupendous size.

In addition to challenging old ideas about the maximum possible size, each of these bacteria organizes its innards in an unusually advanced way.

Instead of allowing genetic material to float around freely, like other bacteria do, these beings wrap it up and contain it within a kind of package. This is similar to what's done in more complex kinds of cells, like those that make up plants and animals.

Volland cautions that this doesn't mean these bacteria are some kind of "missing link" between simple forms of life and more complex ones, saying it's just a "fascinating example of a bacterium that has evolved a higher level of complexity."

Still, finding this inside bacteria, along with their amazing size, makes this "a truly magnificent find," according to Thijs Ettema, a microbiologist at Wageningen University & Research who was not part of this research team.

"The researchers have identified a real 'microbial monster,'" Ettema said in an email. "Their work underlines that the microbial world continues to amaze us!"

These bacteria can't even rightly be called microbes, because microbes are by definition microscopic, points out Petra Anne Levin of Washington University in St Louis, who wrote a commentary accompanying the new report.

What's more, while most bacteria reproduce by dividing into two identical cells, these long, filament-like creatures seem to reproduce by budding off one small piece at the tip that can then float away and go on to create a whole new being.

And even though these organisms are so big that hundreds of thousands of smaller bacteria could fit on their outside surfaces, researchers found that these surfaces look pristine, suggesting that these bacteria might secrete some kind of antibiotic to ward off smaller relatives.

Finding this bacterium "has really opened our eyes to the unexplored microbial diversity that exists," says Shailesh Date of the University of California, San Francisco, and the Laboratory for Research in Complex Systems. "Really we are just scratching the surface, and who knows what interesting things we have yet to discover."