By Bob Grant
This teeming earth
|
|
|
Jeremy Burgess / Photo Researchers, Inc
|
The paper:
J. Gans et al., "Computational improvements reveal great bacterial diversity and high metal toxicity in soil," Science, 309:1387-90, 2005. (Cited in 72 papers)
The finding:
John Dunbar and colleagues at Los Alamos National Laboratory developed a statistical technique to more accurately estimate the diversity of bacteria found in soil. Their reanalysis of historical data extended the upper limit of bacterial diversity from 10,000 (the established benchmark) to upwards of 8,000,000 species per gram of soil.
The significance:
The findings were a drastic shift from the benchmark (Appl Environ Microbiol, 56:782-7, 1990), but Dunbar's team provided only a statistical model for soil bacteria diversity, not a direct measurement. His findings sparked debate among soil biologists about how complex soil bacterial communities really are, says Noah Fierer, microbial ecologist at the University of Colorado.
The controversy:
Recently, Eric Triplett at the University of Florida and collaborators used high throughput pyrosequencing and found a maximum of about 53,000 distinct bacterial sequences in soils (ISME J, 1:283-90, 2007). Triplett admits the techniques are imperfect, but says that "if Gans et al. were correct, it means we'd have to be missing 99% of what's out there. I don't think our methodology is that flawed."
The future:
"It's only a matter of time before the right experiment gets done," says Dunbar, conceding that researchers should pursue experimental work that confirms or refutes his team's analysis. "But it's too early to believe that Triplett's experiment is the right one."
The numbers:
| Bacteria species per gram of typical soil |
| 10,000 |
The old benchmark for soil bacteria diversity |
| 25,000 - 50,000 |
From pyrosquencing |
| 1,000,000 - 8,000,000 |
From Gans et al. estimates |
Advertisement
Rate this article
Rating: 3.20/5 (5 votes )
Soil Biodiversity by Larry Woods
[Comment posted 2007-11-14 15:57:09]
I am astonished that this finding is presented as a "NEW" finding -- Soil Microbiologists have known about the enormous number of bacterial (and fungal and protozoan, etc.) species for decades. There is substantial Agronomic literature on the incredible biodiversity of soil populations.
Yes, every new way of looking at soil populations confirms this biodiversity
Teeming Earth by Richard Bentley
[Comment posted 2007-11-14 15:28:04]
Not only have we missed 99% of the
organisms, we refuse (in general) to
consider the strong possibility that
they not only do not live independently,
as a whole they are in effect a quasi
macro-organism. Until we consider the
interactions between these organisms
in much greater detail, we will not
understand them as we should.
Other estimates of diversity by Aaron Mills
[Comment posted 2007-11-14 14:05:53]
Although it is not clear that taxonomic diversity (as measured by, say 16S Ribosomal RNA approaches) has a great deal of relevance to ecosystem function, it is surprizing that in this brief article no mention was made of the elegant estimates of prokaryotic diversity reported by Curtis et al. (Proc. Nat. Acad. Sci. 99:10494 (2002)). In that paper, a global estimate of prokaryotic diversity in soil was reported, with plenty of caveats for the assumptions required to obtain the values. That number was around 4 x 10^6 taxa. Curtis et al. also lent support for Dykhuizen's reinterpration of the data of Torsvik et al. that suggested a range of between 40,000 and over 500,000 taxa per gram of soil. That range includes Triplett's value, and recognizing that all current techniques provide an underestimate reinforces the match between the work of Curtis et al., Dykhuizen, and Triplett. Triplett's experiment may not be the right one, but it produces data consistent with reasonable estimates determined with reasonable methods. Until an experiment is done that invalidates the estimates of Curtis et al. and Dykhuizen, those numbers must be accepted as the "best" estimates available.
|
Register for FREE Online Access
Subscribe to the Magazine