CM \ r I i; i{ 



Physiology 



An 3" consideration of the physiology of 

 aetinomyeetes invoK-es a study of tlieir 

 growth and nutrition, tlieir nietaboHc proc- 

 esses, and their reacti(Mi to environmental 

 conditions. Such important phenomena as 

 saprophytism versus parasitism, aerobiosis 

 versus anaerobiosis, thermophilic rcrsus me- 

 sophilic growth, decomposition of organic 

 residues and nitrogen transformation, as 

 well as lytic phenomena and death rate may 

 also be considered here. Some of these proc- 

 esses are sufficiently important to warrant 

 more detailed treatment elsewhere in this 

 volume. 



The activites of a microbial cell consist of 

 a multiplicity of chemical reactions, which 

 are interlinked in a most amazing and be- 

 wildering fashion. Numerous attempts have 

 been made to base an understanding of the 

 metabolism of the various organisms upon 

 the transformations brought about by rest- 

 ing microbial cells. The capacity of such cells 

 to catalyze the transformation of specific 

 chemical substances has frequently yielded 

 information of considerable biochemical sig- 

 nificance. However, the results obtained 

 from such studies have not always been so 

 fruitful in unraveling the complex reactions 

 of microbial cells. 



Although our understanding of the phys- 

 iology of the microbial cell is limited chiefly 

 to a knowledge of the beha\ior of pure cul- 

 tures, it is not to be forgotten that, in nature, 

 microbes, especially' the actinomycetes, live 

 in constant association with other organisms 



and are subject to continuous influences of 

 these associated organisms. In the soil and 

 in water basins, each of these microbes lives 

 in association with thousands of others, as 

 well as with the root systems of higher plants 

 and with tissues of higher animals. Some in- 

 \-(»stigators have even asserted that actino- 

 mycetes lead only a limited vegetative exist- 

 ence in the soil and occur there largely in 

 the form of spores. The question has, there- 

 fore, frequently been raised: How significant 

 are laboratory studies in interpreting the ac- 

 tivitives of these microbes in nature? Path- 

 ogenic microbes, whether they attack plants 

 or animals, are influenced in their growth 

 and nutrition by the hosts which they in- 

 habit and the tissues which they attack. 

 Physiological reactions based upon pure cul- 

 ture studies and upon the growth of organ- 

 isms in artificial media may thus be (juite 

 distinct from corresponding reactions 

 })rought about by the same organisms in ;i 

 natural environment. 



The actinomycetes represent a fairl3^ 

 large group of microorganisms widely dis- 

 tributed in all natural substrates. They rep- 

 resent fairly heterogeneous systems differing 

 greatly in their mode of nutrition, metabolic 

 processes, storage and waste products. Since 

 literally hundreds of antibiotics have been 

 isolated as metabolic products of actinomy- 

 cetes, one can only surmise the variety of 

 metabolic reactions that led to their forma- 

 tion. 



Whenever the chemical composition of a 



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