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Opening remarks
Microbial adaption to extreme environments
;As we have convened here, coming from laboratories with diverse structures and backgrounds, to discuss microbial adaptation during the following days, it is not surprising that the composition of this group is quite heterogeneous. I am sure there is also quite a diversity concerning the microorganisms we have chosen to work with, and the emphasis and goals of the rk that is done. But we certainly have one thing in common: We all find fascinating, for one reason or another, problems concerning life in the most diverse environments. Interest in the adaptation of lile to extreme conditions is obviously increasing, and that is quite understandable. If we just look back briefly over what has been the main concern in microbiology and related fields in the past, we can clearly distinguish a few shifting points. First there was the fierce fight concerning the principal question of whether those tiny microscopical objects called yeasts were at all able to initiate a process known as fermentation. The true believers of the mechanistic theory, of course, called the ideas of the “vitalists” sheer nonsense. With Buchner’s yeast extracts, and the separation of an apoferment and a coferment, the mechanistic school was shown to be on the wrong track. From then on it was established that microorganisms contain not only those enzymes needed to catalyze the glycolytic pathway, but many others as well. Next came the discussion whether one are the metabolic pr s with the metabo~
59
Kluyver and van Niel - people were, of course, concerned with just that: identity. Everything that would not fit was left aside for the time being. For several years then, almost everyone concentrated their research on Succharomyces, E. coli, B. subtilis, and other typical laboratory organisms, and even then, for reasons of reproducibility, only studied organisms that had been cultured at 3O”C, pH ‘7, and in a buffered salt solution of 0.01 or 0.1 M. But during this period more and more results emerged which made it clear that the range within which microorganisms could thrive was indeed very wide. Since that time we can recognize a growing interest in the “diversity of life”, s?imulated by discussions about the possibility of other forms of life, the origin of life and, last but not least, the concern about our environment. just mentioning these fields of interest, it omes clear that the study of adaptational processes can cover a wide r that many approaches to this possible. For the planning of this workshop we h of course, to make a choice out of these po ble approaches. I ceived many suggestions regarding the poss e of the meeting and the form it shou to all who offered suggestions. I hope that the choice that was finally made will serve the interests of all partici n setting up the w a certain line :
Mic~Jbialadaption to extreme env!ronments
60
will finish with the environmental extremes existing when life started to evolve and the cycle of trace elements and compounds in the
air. But we will start down to earth with a quite common environment , soil.
SOIL: A COMPLEX ENVIRONMENT
F.A. SKINNER
Many micro-organisms exist in soil, but they constitute only a very small part of the total soil volume. In non-rhizosphere soil, most bacteria occur as small cocci attached to particles and fungi as a sparse network of hyphae or as spores. In soil-agar films, as used for the direct counting of micro-organisins in soil, bacteria are distributed in aggregates or colonies according to the terms of a negative logarithmic series. The probability of finding colonies with 1, 2, 3 cells etc. is given by the successive terms x, x2/2, x3/3 etc, where x is less than 1 and frequently equals 0.7-0.8. Thus, though single celis and micro-colonies are abundant, there is little chance of finding a colony as large as, say, one with 100 cells. This distribution has been compared with that of colrpnies of soil bacteria growing in plates of a mineral salts agar with no added carbon source, in~~ulated with soil dilutions of 1O- 3 and 10 - Q. These nutrient conditions are poor compared with those normally obtaining in laboratory culture. After 7 days the agar was stained, examined microscopically and the volumes of colonies estimated. The most abundant of the microscopic colonies (ca 23%) were those of IO-20 ,prn diameter with, volumes of ca 500 and 4WQ (J,@~ respectively. As in soil-agar films, the frequency of occurrence of colonies decreased with increrqgingcolony size but t scale of dimension was quite ifferent.
Though bacterial growth was so poor in the agar plates it could still be considered as luxuriant compared with that of the bacteria in soil-agar films. This, and other evidence derived from soil sections and direct observations of soil particles, indicates that soil micro-organisms grow under severe constraint determined by lack of nutrients, presence of inhibitors, or by unfavourable physical conditions. Many soil microbes, especially species of Streptomyces, produce antibiotics in rich media but little is likely to be formed in unamended soils where nutrients, though varied, are scarce and subjects of competition. Moreover, many antibiotics are adsorbed by clays, especially montmorillonites, and by organic matter. Dramatic antibiotic effects are unlikely in soils but an accumulation of different inhibitors is probable. special case of microbial inhibition in soil is fungistasis which may be defined as the failure of fungal spores to germinate in contact with soil even when conditions of temperature and moisture favour germination. Fungistasis is widespread, tends to be stronger in warmer seasons and is more marked in surface than in deeper soil layers. It is probably microbial in origin because
;As we have convened here, coming from laboratories with diverse structures and backgrounds, to discuss microbial adaptation during the following days, it is not surprising that the composition of this group is quite heterogeneous. I am sure there is also quite a diversity concerning the microorganisms we have chosen to work with, and the emphasis and goals of the rk that is done. But we certainly have one thing in common: We all find fascinating, for one reason or another, problems concerning life in the most diverse environments. Interest in the adaptation of lile to extreme conditions is obviously increasing, and that is quite understandable. If we just look back briefly over what has been the main concern in microbiology and related fields in the past, we can clearly distinguish a few shifting points. First there was the fierce fight concerning the principal question of whether those tiny microscopical objects called yeasts were at all able to initiate a process known as fermentation. The true believers of the mechanistic theory, of course, called the ideas of the “vitalists” sheer nonsense. With Buchner’s yeast extracts, and the separation of an apoferment and a coferment, the mechanistic school was shown to be on the wrong track. From then on it was established that microorganisms contain not only those enzymes needed to catalyze the glycolytic pathway, but many others as well. Next came the discussion whether one are the metabolic pr s with the metabo~
59
Kluyver and van Niel - people were, of course, concerned with just that: identity. Everything that would not fit was left aside for the time being. For several years then, almost everyone concentrated their research on Succharomyces, E. coli, B. subtilis, and other typical laboratory organisms, and even then, for reasons of reproducibility, only studied organisms that had been cultured at 3O”C, pH ‘7, and in a buffered salt solution of 0.01 or 0.1 M. But during this period more and more results emerged which made it clear that the range within which microorganisms could thrive was indeed very wide. Since that time we can recognize a growing interest in the “diversity of life”, s?imulated by discussions about the possibility of other forms of life, the origin of life and, last but not least, the concern about our environment. just mentioning these fields of interest, it omes clear that the study of adaptational processes can cover a wide r that many approaches to this possible. For the planning of this workshop we h of course, to make a choice out of these po ble approaches. I ceived many suggestions regarding the poss e of the meeting and the form it shou to all who offered suggestions. I hope that the choice that was finally made will serve the interests of all partici n setting up the w a certain line :
Mic~Jbialadaption to extreme env!ronments
60
will finish with the environmental extremes existing when life started to evolve and the cycle of trace elements and compounds in the
air. But we will start down to earth with a quite common environment , soil.
SOIL: A COMPLEX ENVIRONMENT
F.A. SKINNER
Many micro-organisms exist in soil, but they constitute only a very small part of the total soil volume. In non-rhizosphere soil, most bacteria occur as small cocci attached to particles and fungi as a sparse network of hyphae or as spores. In soil-agar films, as used for the direct counting of micro-organisins in soil, bacteria are distributed in aggregates or colonies according to the terms of a negative logarithmic series. The probability of finding colonies with 1, 2, 3 cells etc. is given by the successive terms x, x2/2, x3/3 etc, where x is less than 1 and frequently equals 0.7-0.8. Thus, though single celis and micro-colonies are abundant, there is little chance of finding a colony as large as, say, one with 100 cells. This distribution has been compared with that of colrpnies of soil bacteria growing in plates of a mineral salts agar with no added carbon source, in~~ulated with soil dilutions of 1O- 3 and 10 - Q. These nutrient conditions are poor compared with those normally obtaining in laboratory culture. After 7 days the agar was stained, examined microscopically and the volumes of colonies estimated. The most abundant of the microscopic colonies (ca 23%) were those of IO-20 ,prn diameter with, volumes of ca 500 and 4WQ (J,@~ respectively. As in soil-agar films, the frequency of occurrence of colonies decreased with increrqgingcolony size but t scale of dimension was quite ifferent.
Though bacterial growth was so poor in the agar plates it could still be considered as luxuriant compared with that of the bacteria in soil-agar films. This, and other evidence derived from soil sections and direct observations of soil particles, indicates that soil micro-organisms grow under severe constraint determined by lack of nutrients, presence of inhibitors, or by unfavourable physical conditions. Many soil microbes, especially species of Streptomyces, produce antibiotics in rich media but little is likely to be formed in unamended soils where nutrients, though varied, are scarce and subjects of competition. Moreover, many antibiotics are adsorbed by clays, especially montmorillonites, and by organic matter. Dramatic antibiotic effects are unlikely in soils but an accumulation of different inhibitors is probable. special case of microbial inhibition in soil is fungistasis which may be defined as the failure of fungal spores to germinate in contact with soil even when conditions of temperature and moisture favour germination. Fungistasis is widespread, tends to be stronger in warmer seasons and is more marked in surface than in deeper soil layers. It is probably microbial in origin because