was a surprise to find hydrogen was the main energy source for microbes
in the hot springs," Pace said. "This project is also interesting in
the context of microbiology because it's one of the few times we've
been able to study microbes to get information on an entire ecosystem.
That's never before been possible."
The study was specifically designed to determine the main source of
metabolic energy that drives microbial communities in park features
with temperatures above 158 degrees Fahrenheit. Photosynthesis is not
known to occur above that temperature.
A combination of three different clues led researchers to conclude that
hydrogen was the main source of energy. Genetic analysis of the
varieties of microbes living in the hot springs communities revealed
that they all prefer hydrogen as an energy source. They also observed
ubiquitous H2 in all the hot springs at concentrations sufficient for
Thermodynamic models based on field data confirmed that hydrogen
metabolism was the most likely fuel source in these environments.
"This work presents some interesting associated questions," said John
Spear, lead author of the report. "Hydrogen is the most
element in the universe. If there is life elsewhere, it could be that
hydrogen is its fuel," Spear said. "We've seen evidence of water on
Mars, and we know that on Earth, hydrogen can be produced
biogenetically by photosynthesis and fermentation or non-biogenetically
by water reacting with iron-bearing rock. It's possible that
non-biogenic processes produce hydrogen on Mars and that some microbial
life form could be using that," he said.
There are many examples of bacteria living in extreme environments --
including the human body -- using hydrogen as fuel, according to Spear.
"Recent studies have shown that Helicobacter pylori bacteria, which
cause ulcers, live on hydrogen inside the stomach," said Spear.
"Salmonella metabolizes hydrogen in the gut. It makes me wonder how
many different kinds of microbes out there are metabolizing hydrogen in
Instead of relying on traditional techniques of microbiology that
utilize cultures grown in the lab, the CU-Boulder team used methodology
developed by Pace to genetically analyze the composition of the
microbial community as it appeared in the field. "We didn't look at
what grows in a culture dish, we looked at the RNA of samples directly
from the field," Spear said.
"We've never before known what microbes were living in Yellowstone hot
springs, and now we do," Pace said.
A novel suite of instruments was used to gather data, some of which had
never before been collected. "No one had measured the concentration of
hydrogen in the hot springs before because the technology didn't exist
until about seven years ago. Now we can detect very low-level
concentrations of hydrogen in water," Spear explained.
"We found lots of hydrogen in the hot springs -- an endless supply for
bacteria," he said. Measurements of the amount of H2 in water were
recorded in Yellowstone hot springs, streams and geothermal vents in
different parts of the park and during different seasons. All of the
environments had concentrat
ions appropriate for energy metabolism.
The team used computer-generated thermodynamic models to find out if
hydrogen was indeed the principle source of energy. "You can smell
sulfide in the air at Yellowstone, and the accepted idea was that
sulfur was the energy source for life in the hot springs," Spear said.
Not so, according to the team's computer models built on field
measurements of hydrogen, sulfide, dissolved oxygen concentration and
Spear said it was difficult to explore a microbial ecosystem. "We have
a hard enough time explaining what's going on in a forest, for example,
with all the interlacing systems. We can't even see a microbial
Sample extraction was a dangerous and delicate operation. In order to
accurately analyze a hot spring's entire microbial community, Spear
needed to collect only about as much material as a pencil eraser.
Sediment samples were scooped into special sample vials and immediately
frozen in liquid nitrogen canisters to preserve the microbial
In springs where there was no sediment, Spear collected samples of
planktonic organisms by hanging a glass slide in the water and allowing
the microbes to accumulate. "Bacteria are just like us. They like to be
together, they like to be attached to a surface and they like to have
their food - dissolved hydrogen, in this case -- brought to them."
Spear explained that the hot springs' colors are the result of
interactions between minerals and the microbes living in the pools.
Hotter water usually shows colors from minerals, and cooler water plays
host to photosynthetic pigments.
"Based on what I've seen in this analysis, I think hydrogen probably
drives a lot of life in a lot of environments," Spear said. "It's part
speculation, but given the number and kinds of bacteria that are
metabolizing hydrogen, it's probably a very old form of metabolism.
That's important because it tells us about the history of life on
Earth," he said. "And if it works this way on Earth
, it's likely to
happen elsewhere. When you look up at the stars, there is a lot of
hydrogen in the universe."
Source:University of Colorado at Boulder
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