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Moselio Schaechter

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« Generation of Diversity, Phage Style | Main | Retrospective July, 2008 »

July 17, 2008

Comments

Stanley Maloy

Maybe the problem is simply a "numbers game". For example, based upon numbers from web sources, there are about 5 x 10^8 dogs and 6.4 x 10^7 house cats on earth. Even if the actual number of organisms within the genus Canis or Felis was off by 10-100x, this is so much lower than the number of bacteria on earth that the potential for kinky experiments which would confuse the species definition are much, much more limited.

elio

In regard to your story of the microbiologist and the genie, here's a little example of plus ca change...

I've been looking into the origins of Bergey's Manual, which include the descriptive chart the SAB prepared and sold for many years. This was a card which one could use to record all the salient characteristics of an unknown organism. Ideally, a value for each characteristic (1 or 0 for, say, Gram positive or negative) could be assigned a specific place to either side of a decimal point; once the full range of tests had been conducted, an 8 or 10-digit number would be generated, and could be handily compared to the number generated for previously described microorganisms.

Anyway, H. W. Conn (a founder of our Society) used the chart to describe a large number of dairy bacteria. In the introductory material to this report (Storrs Ag. Expt. Station for 1906) he says:

"The question of species -- The question of species among bacteria is at present an insoluble puzzle. It has become manifest that it is quite impossible to carry over to the classification of bacteria the conception of word species[*] which zoologists and botanists have developed in the last century. It has been recognized by the modern zoologist that the early conception of a species, as something sharp and distinct, is bound to be modified as variations are recognized. If this is true in animals and higher plants, it is more emphatically true of bacteria. Indeed, we must practically abandon any thought of using among bacteria the term species with a meaning which has any similarity to that which is used for the rest of the living world. The question as to whether physiological variations are sufficient to characterize a new species is one which we cannot now answer, but this would be involved in an attempt to determine species of bacteria."

The various bacteria described do get grouped according to some characteristics, but Conn reiterates his initial point regarding species:

"It should finally be stated that the forms which we recognize in the following pages which we name must be regarded as groups and not species. This is not at all material, inasmuch as we have no conception whether the term species has any meaning whatsoever among the bacteria."

Best

Jeff

* I'm not sure what Conn might specifically have meant by "word species," but to my mind it reflects a human desire (or need) to impose human-scale order; it is, after all, only humans who use words. The term Escherichia coli (which even includes the name of an actual human) is, of course, meaningless to the bacterium. Adam and Eve in the Garden, and all that.


Elio's note:
Jeff Karr is the Archivist of ASM. Visit the Archive website at
http://www.asm.org/Membership/index.asp?bid=15451

Mark O. Martin

My former thesis advisor, Sharon Long, told a great story about this kind of thing. She had been performing transposon mutagenesis (while she was a postdoc with Fred Ausubel at Harvard) on Rhizobium meliloti (now Sinorhizobium meliloti). Sharon isolated a transposon mutant incapable of forming root nodules on alfalfa.

A Harvard professor asked her how she knew that the mutant was Rhizobium. Sharon replied that it has the appropriate antibiotic resistance markers. The questioner pointed out that the *definition* of Rhizobium meliloti included the ability to nodulate alfalfa roots. The mutant did not. So was it still Rhizobium meliloti??!!

That story was the first time I became uneasy with the species concept among prokaryotes. It wasn't the last!

elio

Stan,

Had the genie asked me, I wouldn't have known what to tell him. But I am not as wise as you because I am so much younger: I went to graduate school much later than you ( 1950-1954).

It was a snap when I was grad student (1948-1952). Just ask Bergey's Manual.
But I admit, there sure were a lot of different Salmonellas!
-- stan zahler

Mark O. Martin

I have heard many versions of that joke, some of which are not family friendly. At last I have some koan like nerdish humor to share with my family! Many thanks.

By the way, I would love to see a post from Julian Davies from UBC over his idea (presented at ASM) that there exists a microverse of small molecules in nature which have profound effects on microbes in the natural world.

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