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Archaea

The following passage is taken from an article about tiny organisms called archaea (© 2009 Science Daily)

1. It’s not every day you find
2. clues to the planet’s inner
3. workings in aquarium scum.
4. But that’s what happened a
5. few years ago when
6. University of Washington
7. (UW) researchers cultured
8. a tiny organism from the
9. bottom of a Seattle Aquarium
10. tank and found it can digest
11. ammonia, a key environmental
12. function. New results show
13. this minute organism and its
14. brethren play a more central
15. role in the planet’s ecology
16. than previously suspected.
17. The findings show that these
18. microorganisms, members of
19. ancient lineage called archaea,
20. beat out all other marine life
21. in the race for ammonia.
22. Ecologists now assume that
23. ammonia in the upper ocean
24. will first be gobbled up by
25. phytoplankton to make new
26. cells, leaving very little
27. ammonia for microbes to turn
28. into nitrate.
29. Ammonia is a waste product
30. that can be toxic to animals.
31. But plants, including
32. phytoplankton, prize ammonia
33. as the most energy-efficient
34. way to build new cells. Archaea
35. can scavenge nitrogen-
36. containing ammonia in the
37. most barren environments of
38. the deep sea, solving a long-
39. running mystery of how the
40. microorganisms can survive
41. in that environment. Archaea
42. therefore not only play a role,
43. but are central to the planetary
44. nitrogen cycles on which all
45. life depends.
46. In the tree of life, archaea
47. occupy their own branch.
48. Archaea were discovered only
49. about 30 years ago and were
50. first thought to exist only in
51. extreme environments, such
52. as hot springs or hydrothermal
53. vents. They are now known to
54. be more widespread. In the
55. early 1990s scientists
56. collecting seawater found
57. strands of genetic material
58. that suggested at least 20
59. percent of the ocean’s
60. microbes are archaea, and
61. circumstantial evidence
62. suggested they might live off
63. ammonia.
64. The microbe is likely
65. ubiquitous on land and in the
66. seas, and new experiments
67. show that the organism can
68. survive on a mere whiff of
69. ammonia – 10 nanomolar
70. concentration, equivalent to
71. a teaspoon of ammonia salt
72. in 10 million gallons of water.
73. In the deep ocean there is no
74. light and little carbon, so this
75. trace amount of ammonia is
76. the organism’s only source of
77. energy.
78. These archaea can grow at the
79. vanishingly low concentrations
80. of ammonia found in the
81. ocean,” says David Stahl, a
82. UW professor and member
83. of the research team. “Until
84. we made the measurements,
85. no one thought it would be
86. possible that an organism
87. could live on these trace
88. amounts of ammonia as a
89. primary energy source.”
90. That finding has important
91. implications for ocean
92. ecosystems. Scientists knew
93. that something was turning
94. ammonia into nitrate in the
95. deep ocean, but could not
96. fathom what organism
97. might be responsible. Now it
98. appears archaea are those
99. mysterious organisms.
100. And in the upper ocean
101. waters, it appears that archaea
102. can out-compete
103. phytoplankton for ammonia.
104. The same may be true in soil
105. environments. The archaea
106. in question are small even by
107. the standards of single-celled
108. organisms. At 0.2
109. micrometers across, about 8
110. millionths of an inch, the only
111. life forms smaller are viruses.
112. Researchers speculate that
113. archaea’s size could explain
114. how they are able to survive
115. on such a scant energy supply.
116. A better understanding of
117. archaea’s lifestyle and role in
118. nitrogen cycles not only would
119. rewrite ecology textbooks. It
120. could also have practical
121. applications, such as devising
122. natural ways to boost a soil’s
123. nitrogen content without
124. needing to use chemical
125. fertilizers, or designing sewage
126. treatment plants that employ
127. microbes to remove
128. nitrogenous waste more
129. efficiently, or understanding
130. which microbes produce
131. global-warming gases such
132. as nitrous oxide.
133. The new findings will also
134. affect the equations used in
135. global climate models.
136. Computer models use global
137. cycles of nitrogen and other
138. chemicals to estimate how
139. much carbon dioxide the
140. oceans will absorb and
141. ultimately sink to the
142. bottom of the sea. The
143. findings also suggest that
144. most of the nitrate in the
145. surface water comes from
146. recycling of biomass, and
147. not from the deep water as
148. currently assumed. The new
149. data suggests, however, that
150. the carbon pump is weaker
151. than currently assumed, so
152. current climate models may
153. overestimate how much
154. carbon can be absorbed
155. by the oceans.