My mate Marc Buhler noticed this one:
This week's issue of Science magazine has an article that is the subject of a story (pasted below the fold) from the NY Times.
"From Scum, Perhaps the Tiniest Form of Life" by William J. Broad - Dec. 23, 2006The smallest form of life known to science just got smaller.
Four million of a newly discovered microbe - assuming the discovery, reported yesterday in the journal Science, is confirmed - could fit into the period at the end of this sentence.
Scientists found the microbes living in a remarkably inhospitable environment, drainage water as caustic as battery acid from a mine in Northern California. The microbes, members of an ancient family of organisms known as archaea, formed a pink scum on green pools of hot mine water laden with toxic metals, including arsenic.
"It was amazing," said Jillian F. Banfield of the University of California, Berkeley, a member of the discovery team. "These were totally new." In their paper, the scientists call the microbes "smaller than any other known cellular life form."
Scientists say the discovery could bear on estimates of the pervasiveness of exotic microbial life, which some experts suspect forms a hidden biosphere extending down miles whose total mass may exceed that of all surface life.
It may also influence the search for microscopic life forms elsewhere in the solar system, a discovery that would prove that life in the universe is not unique to Earth but an inherent property of matter.
The tiny microbes came from an abandoned mine at Iron Mountain in Shasta County, Calif., which produced gold, silver, iron and copper before closing in 1963.
Today, rain and surface water run over exposed minerals, producing sulfuric acid. The mine is one of the largest Superfund cleanup sites.
Starting in 2002, the scientists obtained drops of the acidic slime and searched for genetic signs of novel microbes. "We were essentially looking for new stuff," one of the scientists, Brett J. Baker, said in statement from Berkeley, "and we found it."
The microbes are about 200 nanometers wide - the size of large viruses, which scientists consider lifeless because they cannot reproduce on their own. Bacteria average about five times that size.
The scientists must do further tests to confirm that the organisms are the smallest ever found, and that they can reproduce. If those analyses hold up, they said in their Science paper, "it may be necessary to reconsider existing paradigms for the minimum requirements for life."
What's interesting about this is that it changes how we visualise metabolic processes in very small spaces. A while back, in 1998, Phillipa Uwins, then of the University of Queensland where I work, announced the existence of "nanobes", which were a little smaller than these beasties (20-150nm), and which were treated skeptically because they were too small for biological processes. I wonder, as a complete amateur, if there are chemical processes that are possible in small spaces that we have hitherto overlooked because we were focusing on the prototypical processes of much larger organisms. Carol Cleland, of the Center for Astrobiology at the University of Colorado,
has an argument that there may be kinds of life we do not know about because they fall through our assays, which were designed to deal with "ordinary" life. Watch this space.
These organisms are "pleomorphic", a lovely term that means they have no fixed morphology at the cell shape level. Folding their membranes gives them a lot more surface area to react upon.
Transmission electron microscope images of four cells inferred to belong to the ARMAN group. (A) A large area showing many cells of the ARMAN type, a subset of which are indicated by arrows. Also present are rounded objects, membrane debris, and a small number of Leptospirillum group II cells (LII). (B) Most cells exhibit one or two folded membrane-bounded protrusions.... (C) Most cells appear to be surrounded by an S-layer with periodicity in the cell surface. The dark internal contrast is consistent with densely packed ribosomes. (D) Some cells have very dark inclusions (arrow). [From the paper]
These cells are much smaller than the previously identified members of the Archae called Nanoarchaeota. They have been called "Archaeal Richmond Mine Acidophilic Nanoorganisms" (ARMAN).
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Let's Get Small (1977) was Steve Martin's first album.
"... I like to get small. It's very dangerous for kids, because they get realllly small."
"I know I shouldn't get small when I'm driving, but I was drivin' around the other day and a cop pulls me over ... says, 'Hey, are you small?' I say, 'No, I'm tall.' He says, 'I'm gonna have to measure you.' They give you a little test with a balloon. If you can get inside it, they know you're small ... and they can't put you in a regular cell either, because you walk right out...."
Got that? Steve Martin made an accurate microbiological prediction: "they can't put you in a regular cell either."
Well, he did, after all, major in philosophy at California State University at Long Beach, albeit he dropped out.
I was wondering if these small guys are as small as the small guys in the Martian meteorite that many said were too small to be alive?
Whew!
The Martian thingies were 20-100 nanometers, so on the same order of magnitude. That's also the same size as Uwins' nanobes. I suspect some organic chemistry does the latter that we don't yet know about.
The convoluted cell envelope is interesting because generally such a feature is of value as a way to increase surface area. The combination of small cell size and high surface area means that very few molecules are needed on one side of the membrane or the other in order to develop a gradient for energy generation but these cells are so small their surface area to volume ratio is already huge.
The authors do acknowledge that the irregular membrane prevent them from ruling out the possibility that there maybe connections between the individual objects they are calling cells in the EM image. So the actual size of the cells remains an open question. If these are protrusions from larger cells, then the pleomorphism is simply an adaptation to increase surface area for energy generation.
Another fact to take away from the paper is how much of the diversity in microbial communities we may be unaware of due to our dependence on PCR for identifying organisms from the environment. The authors make the point that these ARMANs were missed until now for at least two reasons. 1- They are not abundant relative to other members of the community and 2- Their 16s sequence do not match the commonly used archaeal and universal primers. The fact that these guys were missed until now is even more striking given that these acid environments are considered to be relatively low in total diversity and thus (in theory) easier to study than other more diverse communities.
Perhaps examination of these small, and presumably very simple life form would give some insights into the early evolution of life. Even if, for instance, Ms. Uwins' nanobes are not fully alive, they may reflect organic processes that are precursors to life. As a non-biologist, I am amazed that they did not generate more interest from the main-stream biological community, who seemed primarily interested in establishing that they were not alive (even if not, are they not of great interest?) These new small extremophiles seem more clearly to be cells... Just as an aside, I note that Ms. Uwins and her team seem to have disappeared, at least as far as Nanobes research.
Hi, first author of the paper here.
I just wanted to thanks Andrew (#4 above) for actually understanding the whole point of the study. The size, which is really somewhat of a mystery still (as well as ARMAN's lifestyle), was somewhat of a side discovery and surprise of course. As Andrew states the main movitation of the paper was the fact that we used community genomic analyses to find groups of life that we had not known to exist in these communities.
We are currently in the process of using several different microscopic techniques to identify the ARMAN groups in mixed communities to validate there apparent small size, or perhaps visualize their correlation with other cells.
To be honest, it's really nice to see that someone who read the paper (reading the Science paper, not just the Times article, is the key here) understood the findings. You made my day. Yes, I'm cross with how the media quoted us.