Archaea
The following passage is taken from an article about tiny organisms called archaea (© 2009 Science Daily)
- It’s not every day you find
- clues to the planet’s inner
- workings in aquarium scum.
- But that’s what happened a
- few years ago when
- University of Washington
- (UW) researchers cultured
- a tiny organism from the
- bottom of a Seattle Aquarium
- tank and found it can digest
- ammonia, a key environmental
- function. New results show
- this minute organism and its
- brethren play a more central
- role in the planet’s ecology
- than previously suspected.
- The findings show that these
- microorganisms, members of
- ancient lineage called archaea,
- beat out all other marine life
- in the race for ammonia.
- Ecologists now assume that
- ammonia in the upper ocean
- will first be gobbled up by
- phytoplankton to make new
- cells, leaving very little
- ammonia for microbes to turn
- into nitrate.
- Ammonia is a waste product
- that can be toxic to animals.
- But plants, including
- phytoplankton, prize ammonia
- as the most energy-efficient
- way to build new cells. Archaea
- can scavenge nitrogen-
- containing ammonia in the
- most barren environments of
- the deep sea, solving a long-
- running mystery of how the
- microorganisms can survive
- in that environment. Archaea
- therefore not only play a role,
- but are central to the planetary
- nitrogen cycles on which all
- life depends.
- In the tree of life, archaea
- occupy their own branch.
- Archaea were discovered only
- about 30 years ago and were
- first thought to exist only in
- extreme environments, such
- as hot springs or hydrothermal
- vents. They are now known to
- be more widespread. In the
- early 1990s scientists
- collecting seawater found
- strands of genetic material
- that suggested at least 20
- percent of the ocean’s
- microbes are archaea, and
- circumstantial evidence
- suggested they might live off
- ammonia.
- The microbe is likely
- ubiquitous on land and in the
- seas, and new experiments
- show that the organism can
- survive on a mere whiff of
- ammonia – 10 nanomolar
- concentration, equivalent to
- a teaspoon of ammonia salt
- in 10 million gallons of water.
- In the deep ocean there is no
- light and little carbon, so this
- trace amount of ammonia is
- the organism’s only source of
- energy.
- These archaea can grow at the
- vanishingly low concentrations
- of ammonia found in the
- ocean,” says David Stahl, a
- UW professor and member
- of the research team. “Until
- we made the measurements,
- no one thought it would be
- possible that an organism
- could live on these trace
- amounts of ammonia as a
- primary energy source.”
- That finding has important
- implications for ocean
- ecosystems. Scientists knew
- that something was turning
- ammonia into nitrate in the
- deep ocean, but could not
- fathom what organism
- might be responsible. Now it
- appears archaea are those
- mysterious organisms.
- And in the upper ocean
- waters, it appears that archaea
- can out-compete
- phytoplankton for ammonia.
- The same may be true in soil
- environments. The archaea
- in question are small even by
- the standards of single-celled
- organisms. At 0.2
- micrometers across, about 8
- millionths of an inch, the only
- life forms smaller are viruses.
- Researchers speculate that
- archaea’s size could explain
- how they are able to survive
- on such a scant energy supply.
- A better understanding of
- archaea’s lifestyle and role in
- nitrogen cycles not only would
- rewrite ecology textbooks. It
- could also have practical
- applications, such as devising
- natural ways to boost a soil’s
- nitrogen content without
- needing to use chemical
- fertilizers, or designing sewage
- treatment plants that employ
- microbes to remove
- nitrogenous waste more
- efficiently, or understanding
- which microbes produce
- global-warming gases such
- as nitrous oxide.
- The new findings will also
- affect the equations used in
- global climate models.
- Computer models use global
- cycles of nitrogen and other
- chemicals to estimate how
- much carbon dioxide the
- oceans will absorb and
- ultimately sink to the
- bottom of the sea. The
- findings also suggest that
- most of the nitrate in the
- surface water comes from
- recycling of biomass, and
- not from the deep water as
- currently assumed. The new
- data suggests, however, that
- the carbon pump is weaker
- than currently assumed, so
- current climate models may
- overestimate how much
- carbon can be absorbed
- by the oceans.