5. ANTIBIOSIS AND ANTIBIOTICS
333
questions: What is the significance—if any—of antibiotics in nature? In
particular, what function do they play in the producing organism?
What is their role in the physiology of complex ecosystems? Are there
significant correlations between antibiotic production, or antibiotic sensitivity, and taxonomy? Finally, apart from obvious utilitarian reasons, is
there any sound biological justification for grouping together certain
natural compounds under the common and particular name antibiotics?
Antibiotics were initially, and a priori, considered to be the main
agents responsible for microbial antagonism, an evident natural phenomenon. They were therefore regarded as important factors of evolution by virtue of the natural selection which they were supposed to exert
in nature. Experiments on heterogeneous microbial populations in vitro,
as well as the current selection of resistant species, naturally resistant
races, and resistant mutants, as a consequence of chemotherapy and
chemoprophylaxis (326), have clearly shown that under suitable conditions antibiotics do act in the postulated way. However, the question
whether they do or do not act effectively so in nature, apart from their
artificial introduction in ecosystems through human agency, remains
open.
Against their role in nature, it has been argued that the production
of antibiotics often requires very special conditions of environment (44)
that are not likely to be met in natural surroundings and, further, that
attempts to demonstrate their presence in natural habitats have most
often given negative results, either because they are not actually produced or because they are rapidly inactivated by destruction or adsorption. Finally, it has been remarked that producers of antibiotics do not
appear to have a selective advantage over other microorganisms, since
species without any known antibiotic activity are often much more
abundant in a given substrate than the former.
This argumentation, however, appears insufficient to rule out the
possibility of a selective action of antibiotics under natural conditions.
There certainly would be little justification in the inference that an
organism producing an antibiotic in a suitably prepared and maintained
artificial culture medium would behave similarly when growing, for
instance, in the soil. But the converse is also true. If a microorganism
does not produce any detectable antibiotic when artificially cultured, it
does not follow that it is necessarily equally inactive when developing in
its natural habitat. The fact that no antibiotic can be extracted from its
natural surroundings is devoid of any absolute significance, since the
important consideration here is the "microenvironment" (327), practically inaccessible to our means of investigation. It is also well known
that some of the antibiotics are reasonably stable in soil and other natural
333
questions: What is the significance—if any—of antibiotics in nature? In
particular, what function do they play in the producing organism?
What is their role in the physiology of complex ecosystems? Are there
significant correlations between antibiotic production, or antibiotic sensitivity, and taxonomy? Finally, apart from obvious utilitarian reasons, is
there any sound biological justification for grouping together certain
natural compounds under the common and particular name antibiotics?
Antibiotics were initially, and a priori, considered to be the main
agents responsible for microbial antagonism, an evident natural phenomenon. They were therefore regarded as important factors of evolution by virtue of the natural selection which they were supposed to exert
in nature. Experiments on heterogeneous microbial populations in vitro,
as well as the current selection of resistant species, naturally resistant
races, and resistant mutants, as a consequence of chemotherapy and
chemoprophylaxis (326), have clearly shown that under suitable conditions antibiotics do act in the postulated way. However, the question
whether they do or do not act effectively so in nature, apart from their
artificial introduction in ecosystems through human agency, remains
open.
Against their role in nature, it has been argued that the production
of antibiotics often requires very special conditions of environment (44)
that are not likely to be met in natural surroundings and, further, that
attempts to demonstrate their presence in natural habitats have most
often given negative results, either because they are not actually produced or because they are rapidly inactivated by destruction or adsorption. Finally, it has been remarked that producers of antibiotics do not
appear to have a selective advantage over other microorganisms, since
species without any known antibiotic activity are often much more
abundant in a given substrate than the former.
This argumentation, however, appears insufficient to rule out the
possibility of a selective action of antibiotics under natural conditions.
There certainly would be little justification in the inference that an
organism producing an antibiotic in a suitably prepared and maintained
artificial culture medium would behave similarly when growing, for
instance, in the soil. But the converse is also true. If a microorganism
does not produce any detectable antibiotic when artificially cultured, it
does not follow that it is necessarily equally inactive when developing in
its natural habitat. The fact that no antibiotic can be extracted from its
natural surroundings is devoid of any absolute significance, since the
important consideration here is the "microenvironment" (327), practically inaccessible to our means of investigation. It is also well known
that some of the antibiotics are reasonably stable in soil and other natural