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Posts Tagged ‘Carl Woese

“Life’s a little weird”…

Needs must…

You may have ridden out the pandemic in compact living quarters without, say, much natural light or air conditioning. Perhaps you lived with roommates or family in an atmosphere that, as time wore on, grew increasingly toxic. 

Things could be worse! You could be a member of the Alviniconcha species—specifically, a small, spike-studded snail who thrives in an environment inhospitable to most aquatic life; mere meters from deep-sea hydrothermal vents that constantly spew toxic chemicals into the water. Think you have limited natural light? Try living nearly 10,000 feet below the surface of the ocean, where complete darkness envelops you 24 hours a day, under pressure so intense all the air pockets in your body would instantly collapse. 

And forget Seamless. Forget food—at least the kind you ingest with your mouth. Your survival hinges on bacteria living in your gills (you have gills!) in a symbiotic relationship that provides you with energy, via a process called chemosynthesis. It’s like photosynthesis, but chemosynthesis is driven by chemical reactions instead of light. As there’s no sunlight and minimal oxygen present, the bacteria that dwell within Alviniconcha use hydrogen and sulfur molecules to produce sugars and other macronutrients that the animals then use as food. “There’s very little food so deep in the ocean,” says Dr. Corinna Breusing, postdoctoral researcher at the University of Rhode Island and co-author of a recent paper on the snails and their symbionts. “Having your own food-producing machine is much better than waiting for it to fall to you.” While chemosynthesis is common around hydrothermal vents, it can occur in places outside of vents, such as in cold seeps and whale falls and even salt marshes: anyplace the proper mélange of inorganic compounds is brewing. 

The researchers studied Alviniconcha living at the bottom of the Lau Basin, in the southwestern Pacific Ocean, and found that the type of bacterial symbiont determined where their particular host species could live. “The symbionts have different metabolic capacities and adaptations, so we think that the symbionts influence the distribution of the animal,” Breusing says, adding that snails with Campylobacteria dominated at vents with higher concentrations of sulfide and hydrogen, while those with Gammaproteobacteria were able to thrive at sites with lower concentrations of sulfide and hydrogen. Meaning: your chef-roommate, who happens to live in your respiratory system, also decides where you hang your hat (so to speak).

Most hydrothermal vent-dwelling animals, such the aforementioned snails and deep-sea anemones, as well as some species of mussels and tube worms, depend on bacteria that they pick up from the environment, but there is a species of deep-sea clam that passes their symbiont down from mother to offspring, like a fancy set of dinner plates. (This is rare in the marine world, Breusing says.) In the case of the deep-sea clams, where the symbiont is inherited, the symbiont cannot thrive outside the host and dies with it. But if a symbiont is taken up from the environment, it can be released back into the environment after its host dies, ready to help feed a brand-new host.

Alviniconcha might not pack the same visual punch as much marine life does much closer to the surface, but their very existence points to the origins of life on Earth. Before oxygen was free and plentiful, microbial life had to work with inorganic compounds like methane and ammonia, which over millennia dissolved into the seas. Much is still murky about how these little snails co-evolved with the bacteria that enable them to survive, but these fascinating ecosystems indicate that our education about life at the margins is just getting started…

Life at the Edge of Impossible“: ten thousand feet under the sea, these snails thrive with a little help from their friends; from Adrienne Day (@adrienneday).

* Dr. Seuss

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As we examine extremes, we might send redefining birthday greetings to Carl Woese; he was born on this date in 1928. A microbiologist and biophysicist, he made many contributions to biology; but he is best remembered for defining the Archaea (a new domain of life).

For much of the 20th century, prokaryotes were regarded as a single group of organisms and classified based on their biochemistry, morphology and metabolism. In a highly influential 1962 paper, Roger Stanier and C. B. van Niel first established the division of cellular organization into prokaryotes and eukaryotes, defining prokaryotes as those organisms lacking a cell nucleus. It became generally assumed that all life shared a common prokaryotic (implied by the Greek root πρό [pro-], before, in front of) ancestor.

But in 1977 Woese (and his colleague George E. Fox) experimentally disproved this universally held hypothesis. They discovered a kind of microbial life which they called the “archaebacteria” (Archaea), “a third kingdom” of life as distinct from bacteria as plants are from animals, Having defined Archaea as a new “urkingdom” (later domain) which were neither bacteria nor eukaryotes, Woese redrew the taxonomic tree. His three-domain system, based on phylogenetic relationships rather than obvious morphological similarities, divided life into 23 main divisions, incorporated within three domains: BacteriaArchaea, and Eucarya.

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Well that changes everything…

source: Imperial College, London

As all of one’s assumptions about the future (and thus the past) seem to be weakening, two dispatches from the world of science are genuinely foundation-shaking…

First, from New Scientist (and though NS doesn’t mention it, earlier from Freeman Dyson in NYRB):

Just suppose that Darwin’s ideas were only a part of the story of evolution. Suppose that a process he never wrote about, and never even imagined, has been controlling the evolution of life throughout most of the Earth’s history. It may sound preposterous, but this is exactly what microbiologist Carl Woese and physicist Nigel Goldenfeld, both at the University of Illinois at Urbana-Champaign, believe. Darwin’s explanation of evolution, they argue, even in its sophisticated modern form, applies only to a recent phase of life on Earth.

At the root of this idea is overwhelming recent evidence for horizontal gene transfer – in which organisms acquire genetic material “horizontally” from other organisms around them, rather than vertically from their parents or ancestors. The donor organisms may not even be the same species. This mechanism is already known to play a huge role in the evolution of microbial genomes, but its consequences have hardly been explored. According to Woese and Goldenfeld, they are profound, and horizontal gene transfer alters the evolutionary process itself. Since micro-organisms represented most of life on Earth for most of the time that life has existed – billions of years, in fact – the most ancient and prevalent form of evolution probably wasn’t Darwinian at all, Woese and Goldenfeld say…

Woese can’t put a date on when the transition to Darwinian evolution happened, but he suspects it occurred at different times in each of the three main branches of the tree of life, with bacteria likely to have changed first…

As we remember that what has changed can change again, we can read the whole story here.

Second, from ArXiv and ITWire, a suggestion that we might not have as long to figure this out as we have been thinking:  entropy in the universe is much higher than previously expected; thus the “heat death” of existence as we’ve known it, much closer. As Tapecutter observes in Slashdot,

In a paper soon to be published in the Astrophysical Journal [ArXiv link, above], Australian researchers have estimated the entropy of the universe is about 30 times higher than previous estimates. According to their research, super-massive black holes “are the largest contributor to the entropy of the observable universe, contributing at least an order of magnitude more entropy than previously estimated.” For those of us who like their science in the form of a car analogy, Dr. Lineweaver compared their results to a car’s gas tank. He states, ‘It’s a bit like looking at your gas gauge and saying “I thought I had half a gas tank, but I only have a quarter of a tank.”

Happily a quarter of a tank should be good for hundreds of thousands (if not millions) of years.

As we regain our bearings, we might note that this was a bad day for revolutionaries of another stripe:  it was on this date in 1606 that Guy Fawkes was executed for his role in the Catholic Restorationist “Gunpowder Plot.”

Guy Fawkes

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