25 Jun The upper 10 cm of sediment in the open ocean is included
Question
Please read the following article:
Whitman, W.B., Coleman, D.C., and Wiebe, W.J. (1998). Prokaryotes: The unseen majority. Proceedings of the National Academy of Sciences 95(2): 6578-6583.
Note: You can find the above article in your iBoard course under Homework Assignment Instructions.
Write a three to five page paper in which you summarize and reflect on this very important article that was one of the first to point out the magnitude of nutrients stored in microorganisms.
The paper must be in proper APA format, have a references section, and site at least 2 peer reviewed articles. Please use AAU’s LIRN Library to search for these articles. You may utilize the Academic Resource Center (ARC) for a concise guide on how to use LIRN and for APA formatting guidelines.
Proc. Natl. Acad. Sci. USA
Vol. 95, pp. 6578–6583, June 1998
Perspective
Prokaryotes: The unseen majority
William B. Whitman*†, David C. Coleman‡, and William J. Wiebe§
Departments of *Microbiology, ‡Ecology, and §Marine Sciences, University of Georgia, Athens GA 30602
portion of these cells are the autotrophic marine cyanobacteria
and Prochlorococcus spp., which have an average cellular
density of 4 ϫ 104 cells͞ml (6). The deep (Ͼ200 m) oceanic
water contains 5 ϫ 104 cells͞ml on average. From global
estimates of volume, the upper 200 m of the ocean contains a
total of 3.6 ϫ 1028 cells, of which 2.9 ϫ 1027 cells are
autotrophs, whereas ocean water below 200 m contains 6.5 ϫ
1028 cells (Table 1).
The upper 10 cm of sediment in the open ocean is included
in the oceanic habitat because, as a result of animal mixing and
precipitation, it is essentially contiguous with the overlying
water column. Most of the marine sediment is found in the
continental rise and abyssal plain, so the numbers of prokaryotes were calculated from an arithmetic average of the
cellular densities in the studies cited by Deming and Baross
(ref. 9; Table 1). The Nova Scotian continental rise was
excluded from this calculation because of its unusual hydrology
(10).
There are fewer estimates of the number of prokaryotes in
freshwaters and saline lakes (5). Given an average density of
106 cells͞ml, the total number of cells in freshwaters and saline
lakes is 2.3 ϫ 1026. This value is three orders of magnitude
below the numbers of prokaryotes in seawater.
In the polar regions, a relatively dense community of algae
and prokaryotes forms at the water–ice interface in annual sea
ice (11). In Antarctic sea ice, the estimated number of prokaryotes (2.2 ϫ 1024 cells) was based on the mean cell numbers
of Delille and Rosiers (12) and the mean areal extent of
seasonal ice (13). If the population size in the Arctic is similar
(14), the global estimate for both polar regions is 4 ϫ 1024 cells,
only a fraction of the total number of prokaryotes.
Soil. Soil is a major reservoir of organic carbon on earth and
an important habitat for prokaryotes. Prokaryotes are an
essential component of the soil decomposition subsystem, in
which plant and animal residues are degraded into organic
matter and nutrients are released into food webs (15). Many
studies indicate that the number of prokaryotes in forest soils
is much less than the number in other soils. The total number
of prokaryotes in forest soil was estimated from detailed direct
counts from a coniferous forest ultisol (16), which were
considered representative of forest soils in general (Table 2).
For other soils, including grasslands and cultivated soils, the
numbers of prokaryotes appear about the same, e.g., the
number of prokaryotes in Negev desert soil is comparable to
the number in cultivated soil (19). Therefore, the numbers of
prokaryotes in all other soils were estimated from the unpublished field studies of E. A. Paul for cultivated soils (cited in ref.
18).
Subsurface. The subsurface is defined here as terrestrial
habitats below 8 m and marine sediments below 10 cm. Few
direct enumerations of subsurface prokaryotes have been
made, largely because of the difficulty in obtaining uncontaminated samples. Nevertheless, circumstantial evidence suggests
that the subsurface biomass of prokaryotes is enormous (20).
For instance, groundwater from deep aquifers and formation
ABSTRACT
The number of prokaryotes and the total
amount of their cellular carbon on earth are estimated to be
4–6 ؋ 1030 cells and 350–550 Pg of C (1 Pg 5101 ؍g),
respectively. Thus, the total amount of prokaryotic carbon is
60–100% of the estimated total carbon in plants, and inclusion
of prokaryotic carbon in global models will almost double
estimates of the amount of carbon stored in living organisms.
In addition, the earth’s prokaryotes contain 85–130 Pg of N
and 9–14 Pg of P, or about 10-fold more of these nutrients than
do plants, and represent the largest pool of these nutrients in
living organisms. Most of the earth’s prokaryotes occur in the
open ocean, in soil, and in oceanic and terrestrial subsurfaces,
where the numbers of cells are 1.2 ؋ 1029, 2.6 ؋ 1029, 3.5 ؋
1030, and 0.25–2.5 ؋ 1030, respectively. The numbers of heterotrophic prokaryotes in the upper 200 m of the open ocean,
the ocean below 200 m, and soil are consistent with average
turnover times of 6–25 days, 0.8 yr, and 2.5 yr, respectively.
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