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Why are there so many species of microbes on earth?
Posted on August 25, 2011 at 10:00 AM in Talmudic Questions, Teachers Corner | Permalink
A Talmudic question requires an answer in the approximate form of a Talmudic answer. The first part of this process is the examination of the question itself. In the tradition of the Talmudic pilpul, the examination of the question as well of the answers occur in multiples. (Note: I am not a Talmudic scholar. Looked up Talmud on Wikipedia.)
The first issue is the concept of many. How many is many? What is the universe to be quantified so that we can tell if it is expanding or shrinking. On a local micro level the microbiota clearly are numerically and selectively oscillating wildly as conditions change. As Richard Castenholz pointed out while taking some of us on a tour of his research sites in Yellowstone, the composition of the microbial populations change with the temperature of the water as it flows out of a hot spring. The changes are quite visible to the eye due to the change in pigments produced by the various microorganisms. Are new species evolving and disappearing as the flow proceeds? Are the populations at each point in the water’s temperature gradient in steady state?
The second issue is the concept of species. If we want to quantify and explain the occurrence of many species, we need an objective definition of species. Such a definition eludes us and will always be beyond the horizon. See: Krichevsky, M.I. 2011 What is a bacterial species? I will know it when I see it. The Bulletin of BISMiS, Volume 2, part 1, pp. 17–23. “The English philosopher John Locke (August 29, 1632 - October 28, 1704), argued that nature does not make species. People do, as a mechanism to facilitate communication of a collection of similar ideas under one general term. In addition, Locke stated that the boundaries of species are opinions rather than natural borders.” The problem is even more difficult with the concept of strain (in preparation).
In theory, a definitive species description is constructed from a collection of laboratory and other direct observations. Thus, it is an interpretation of the observations not a an objective fact. This bears directly on one aspect of the question. To understand the mechanisms of species formation, we need a proximate agreed criterion of where does one species end and another begin.
In the bacteria, we have the Approved List of species names. The exponential growth of this list is one mechanism for the proliferation of species names. Clearly, this is an artificial measure but has a utility for inspecting the question. One measure of how many species occur is to look at the sources of isolation described in the published descriptions of the validly published names. This has two aspects, subjective and objective. The subjective aspect is the opinion of the discoverer as to what time and place should be investigated and by what methods. The objective aspect is the differences among the various times and places investigated.
In theory, any new species is an unique entity that may be found in any appropriate habitat. As new habitats are explored and we assume that the discoverer and designator of a new species name has adequately determined that the new species is in fact unique. The operational measure of expansion of knowledge about new species is a result of further investigation and characterization of isolates from a new habitat or more intense study of a previous one. This tells us nothing about how so many species develop.
One can surmise that changing the micro habitat will result in either the demise of at least some of the existing population or even micro genocide. In either case, the micro habitat is available for external colonization or adjustment to the new conditions. For example, in the making of saurkraut, there is a well known progression of types of bacteria as the fermentation occurs. Do we know if any members of the changing population represent new “species”? The opportunity exists for trading of genes among the population that exists on the cabbage. Such exchange may well confer survival benefit as the fermentation proceeds.
Such questions arise in the case of antibiotic resistance. Depending on the definition used, MRSA bacteria could be considered a new species as they are managed in quite a different way from the non-resistant staph. Other example come to mind such as botulism and diphtheria toxin producing organisms. Again we run into Locke’s boundary problem.
The pilpul technique leads to my conclusion that answering the question successfully requires a level of Talmudic expertise well beyond my capabilities.
Micah Krichevsky |
July 24, 2012 at 09:50 AM
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